WO2001035825A1

WO2001035825A1 - Magnetic resonance monitoring of thermal therapy

Info

Publication number: WO2001035825A1
Application number: PCT/IL1999/000618
Authority: WO
Inventors: Harvey Cline; Christopher J. Hardy
Original assignee: Insightec-Txsonics Ltd.
Priority date: 1999-11-17
Filing date: 1999-11-17
Publication date: 2001-05-25
Also published as: AU1176100A; EP1233699A1; EP1233699A4

Abstract

This invention is a system for selectively applying heat (30) to destroy tumorous tissue (66) while using a double echo line scan sequence (50, 51, 52, 53, 54, 56, 60, 61, 62, 63, 64) generating two parallel scrolling displays during the heat therapy. One of the displays provides a temperature map, and the other display provides images of tissue damage by showing tissue intensity values.

Description

MAGNETIC RESONANCE MONITORING OF THERMAL THERAPY

FIELD OF THE INVENTION This invention is concerned with noninvasive or minimally invasive surgical procedures, and more particularly, to minimally invasive surgery using locally generated heat that is monitored and positioned by magnetic resonance imaging methods.

BACKGROUND OF THE INVENTION The present invention relates to surgery by necrosis caused by heat focused on tumorous tissue and guided by magnetic resonance (MR) imaging (MRI) methods. Such surgery, performed with pulsed radiant heat means, is now well known and in use. The pulsed heat means presently in use includes, among other things, coherent optical heat sources guided by laser fiber to the tissue to be destroyed. Another often used heat source for such surgical use utilizes pulsed heat means that is generated by a focused ultrasound transducer dissipating ultrasonic energy at a focal point within a region of tissue to be destroyed.

In the past, ultrasound imaging has been used for both generating and positioning focused ultrasound waves on tissue to be destroyed. It was soon found that the MR images were much better suited for such guidance, since MR provides excellent images of tissue, and is not limited to "windows" that excludes bones, for example. Further, MRI system images are useful not only for guiding the actual surgical procedures, but also for planning the surgical procedures. In fact, a tumor is much more visible in an MR image than as seen in actual surgery. In actual surgery, the tumor and normal tissues often look similar. In addition, during the surgery, the tumor can be obscured by blood. Presently, patients are first scanned in an

MRI system to locate the tumor and plan a safe trajectory between the entry of the ultrasound radiation and the target points. Planning can be accomplished as described in U.S. Patent No.

4,961,054 or U.S. Patent No. 5,017,871, the disclosures of both are hereby incorporated herein by reference and made a part hereof.

It is now well-known that heating a zone of tissue above a critical temperature destroys the tissue in that zone. It has further been discovered that the control of heat was improved by using short pulses such that the effect of blood profusion is made negligible. The state of the art has advanced to the point where the MRI is used not only for planning the surgery, but also during the actual destruction of the cancerous tissue. The MRI using separate scanning sequences provides temperature information and, in addition, also provides tissue information. Thus, the actual temperature of the tissue can be ascertained using magnetic resonance imaging methods, and in addition the ablation of the tissue can be observed using MRI. The observation of the tissue temperature is used to accurately position either the laser beams or the focal spot ofthe ultrasound waves. This is described, for example, in U.S. Patent 5,291,890 and U.S. Patent 5,368,031. The disclosures of both patents are hereby incorporated herein by reference. The observation of the ablation in a separate scanning sequence enables more precisely limiting the treatment time to prevent damage to healthy tissue.

Thus, the prior art performs thermal surgery guided by MRI procedures and systems to selectively destroy tumorous tissue in the patient with localized heating, without adversely affecting healthy tissue. The heat is applied to the tumor tissue in a pulsed or oscillating fashion. The pulsed energy creates a heat focus that heats either at the tip of the optical fiber, or at the focal point of the transducer, depending on the heat source. The heated tumorous region may be imaged with the use of the MRI systems, employing a temperature sensitive MR pulse sequence to acquire a temperature "map" that is used basically to assure that the heat is being applied to the tumorous tissue and not to the surrounding healthy tissue. This is done by applying a quantity of heat that is insufficient to cause necrosis but is sufficient to raise the temperature of the heated tissue. The MRI temperature map shows whether or not the heat is applied to the previously located tumorous tissue. The imaging system is also used in a separate scan sequence to create an image of the tissue intended to be destroyed. Using the imaging system in the prior art, the operator of the apparatus adjusts the placement of the radiation on the site of the tissue to be destroyed. The MR image of the tumor acquired in the separate scan determines in real time if necrosis is occurring and effectively ablating the tumorous tissue. However, the monitoring and guiding are provided using separate two- dimensional scan sequences.

When laser beams are used as the heat source, then mechanical means are used to position the optical fiber carrying the laser beam to the diseased tissue to accurately position it within the diseased tissue. When ultrasound beams are used as the heat source, then the focus of the ultrasound beams can be positioned either by mechanically moving the ultrasound generator to move its focal point, or a phased array ultrasound system can be used to manipulate the position of the focal point so that it is within the diseased tissue that is to be destroyed by heating. Systems for properly positioning the heat focus within the tumorous tissue are now well known in the art and are taught for example in an article entitled "Optimization of Spoiled Gradient Echo Phase Imaging for in Vivo Localization of Focused Ultrasound Beam", by Andrew H. Chung et al, published in the Journal of Magnetic Resonance Med.; vol. 36; pp. 745-752; 1996. Accordingly, in the prior art, MRI is used to image the tumorous tissue during the planning stage of the treatment and for the post-treatment lesion evaluation. Further, the MRI monitor in the prior art is known to display both the temperature elevation and tissues during the treatment, but the prior art uses separate two-dimensional scan sequences. This non-invasive temperature monitoring is important for two reasons. First, the detection ofthe transient low-temperature elevation is crucial for localization ofthe low-power focused ultrasound beams and tissues, before the high-powered thermal therapy exposure, to accurately position the heat focus. Second, the measurement of the degree of temperature elevation is important to accurately quantify the thermal dose induced by the heat source. The measured temperature is used to verify whether enough thermal dose is delivered to necrose the targeted tissues. So, in the prior art both a temperature measuring image and a separate tissue-image acquired during different scan sequences are used.

There are several MRI methods that have been used in the past for measuring temperatures using well-known MRI parameters, such as the spin-lattice relaxation time Tl, the time to repeat (TR), the time to echo TE, and the flip angle. For example, temperature maps are generated based on such procedures that provide Tl derived images i.e., proton resonance frequency shift (PRFS) sequences, evaluated with fast spoiled gradient echo sequences applied during the actual thermal therapy exposure. The parameters used are to some degree based on the tissue type and the precise evaluation of the behavior due to physiological or metabolic changes in the tissue during thermal therapy exposure. For example, TE, TR and the flip angle of the spoiled gradient echo have been used for localizing the low-temperature elevation induced by a focused ultrasound beam during both the planning and treatment.

The MRI equipment in the prior art is also used for viewing the volume of ablated tissue with T2 weighted fast spin echo images. Thus, in the prior art, a plurality of images using MRI are required to properly monitor the thermal therapy. First, a two-dimensional scan is made to locate the tumorous tissue, then another multi-dimensional scan is made to acquire an image to assure that the heat is being applied to the tumorous tissue. This is done with the temperature imaging, while the power used on the heat source is such that the temperature is kept below the necrosis value; i.e., the temperature needed for ablation or coagulation.

Accordingly, in the past, the MRI locating and monitoring of the applied heat has been accomplished using two images, each acquired with a two-dimensional scan. The necessity of requiring two separate scans reduces the efficiency of the thermal therapy. It precludes monitoring both temperature and ablation simultaneously.

SUMMARY OF THE INVENTION An aspect of a preferred embodiment of the present invention is to most efficiently ablate tumorous tissue while non-invasively simultaneously, continuously monitoring and controlling the ablation with MRI systems. The necrosis is caused by applied heat. The heat source may be generated by focused ultrasound, by microwave radiation, or by laser beams directed through laser fiber optics. The heat source is preferably a pulsed source used to selectively destroy tumorous tissue of the patient with the minimum amount of surgery and without damage to suπounding healthy tissue.

According to an aspect of the present invention, a system is provided for selectively applying heat to destroy tumorous tissue while using a one-dimensional (line scan) imaging sequence to simultaneously, continuously monitor both the temperature of the tumorous tissue and the tumorous tissue itself in a time frame that is presently used to generate either the temperature or the tissue display. Thus, among other things, in some preferred embodiments, the inventive method and apparatus significantly increases throughput of patients. Line scans are accomplished using intersecting slices or cylindrical excitation regions such as disclosed in U.S. Patents 4,995,394, 5,307,812 and 5,327,884, the disclosures of which are hereby incorporated herein by reference. The line is not rastered through space, but is instead repeatedly excited and read out from a single location to provide a time-dependent scrolling display of intensities along the line.

In addition, according to a prefeπed aspect of the present invention improved feedback of the condition of treated tissue is provided, which enables improved control of the thermal therapy. An aspect ofthe invention contemplates using a double-echo MR line scan sequence to generate two parallel scrolling displays during the heat therapy. The two displays are generated in the same time period that one display is normally generated. One of the displays provides a temperature map; the second display provides images of tissue damage by showing tissue intensity values. More particularly, the system guides or monitors thermal therapy using MRI apparatus, whereby heat is selectively applied for destroying tumorous tissue while two MRI displays are simultaneously generated. One ofthe two displays may be a Tl derived temperature map used to monitor the temperature at the tumorous tissue, and the other display may be a T2 weighted display that images edematious regions for evaluating the necrosed image volume. "Simultaneously" as used herein means during the same scan sequence, such as for example a double echo MR line scan sequence.

The two displays are acquired at a rate of 20 frames per second in the time presently required to generate one display (approximately 30 seconds). In addition, to the time savings obtained by acquiring the two images in the time frame of one image, time is also saved because instead of a 2-D image, line or 1-D images are used for monitoring both the temperature at the tumorous tissue, and the necrosis of the tissue itself. Such time savings, of course, result in a greater throughput, and therefore more efficient use of the MRI and heat generating equipment. The two simultaneous images also enable the user to view the two images simultaneously, thus improving the ability ofthe user to properly control the system.

A prefeπed aspect of the present invention is a method for performing thermal therapy on tumorous tissue using MRI apparatus and a source of radiant heat, selectively applying heat to the tumorous tissue using a 1-D scanning sequence to simultaneously monitor both the temperature ofthe tumorous tissue and the heat caused tissue damage in the tumorous tissue.

A related aspect of the invention is the use of a scan sequence that simultaneously provides a temperature image and a tissue image ofthe tumorous tissue in the time used by the prior art in obtaining either the temperature image or the tissue image.

There is thus provided, in accordance with a prefeπed embodiment of the invention, apparatus for guiding and monitoring thermal therapy, comprising a heat source for selectively applying heat for destroying tumorous tissue, and magnetic resonance imaging (MRI) apparatus for performing a line scanning sequence to generate and monitor two displays in the same scan, one display being of temperature responsive data and the other display being an image of selected tissue. Preferably, a control processor for doing a double echo scan to acquire the two displays in a single scan is provided. In a prefeπed embodiment, both displays are displays of the same selected tissue. In one prefeπed embodiment, the display of the temperature responsive data encompasses a larger region than the display that is an image of selected tissue. In another prefeπed embodiment of the invention, the MRI apparatus for performing the line scanning sequence includes a pencil beam generator for generating a pencil beam, and a read-out gradient for reading out MR signals along the pencil beam. Preferably, the cross-section of the pencil beam is cylindrical. Alternatively, preferably the cross-section of the pencil beam is non-cylindrical. In yet another prefeπed alternative embodiment, the

MRI apparatus for performing the line scanning sequence includes an intersecting plane generator for generating intersecting planes to provide lines at the intersections of the planes, and a read-out gradient generator for reading out MR signals along the lines. Preferably, the pencil beam generator includes a first gradient generator for applying a first-time varying magnetic field gradient in a first direction and a second gradient generator for applying a second time varying magnetic field gradient in a second direction orthogonal to the first direction, and a synchronizer for applying both said first gradient and said second gradient substantially simultaneously with an RF excitation pulse so as to provide an elongated excitation region in said patient. In still another prefeπed embodiment, the apparatus includes a control processor for applying a first read-out gradient in a manner that provides a Tl weighted display; and for applying a second read-out gradient in a manner that provides a T2 weighted display. Preferably, the heat source for selectively applying heat for destroying tumorous tissue comprises laser means for selectively applying a laser light beam to said tumorous tissue. Alternatively, preferably the heat source for selectively applying heat for destroying tumorous tissue comprises means for selectively applying ultrasound energy to said tumorous tissue.

There is further provided apparatus for performing and monitoring thermal surgery on a patient comprising a magnetic resonance imaging (MRI) system for creating an internal image of tissues of said patient, the system including magnetic gradient generators for transmitting magnetic field gradients for determining the position of a specified tissue in the patient, a heat source for applying heat to the specified tissue to create a heated region within the specified tissue, means for monitoring the heated region with the MRI system, including: an RF generator for transmitting an RF excitation pulse into said patient; magnetic field gradient generators for applying a time varying magnetic field gradient in a first direction, and a time varying magnetic field gradient in a second direction, the second direction being orthogonal to the first direction, both gradients applied substantially simultaneously with the RF excitation pulse so as to excite longitudinal magnetization of an elongated excitation region in said patient; said magnetic field gradient generators applying a first read-out gradient to produce a first echo; and a second read-out gradient to produce a second echo; and an image processor using the first echo to acquire a first display and the second echo to acquire a second display. In a prefeπed embodiment ofthe invention, the apparatus includes a control processor for temperature encoding said first echo with a Tl weighted read-out gradient and for tissue intensity encoding said second echo with a T2 weighted read-out gradient. Alternatively, the control processor temperature encodes said first echo with diffusion of magnetic gradient fields. In a preferred embodiment of the invention, the apparatus includes an image processor for reconstructing said first and second echoes to generate magnetization profiles, the profile of the first echo indicating the temperature of tissue along the length of the excitation region and the profile of the second echo showing tissue intensity values along the length of the excitation region, said heat source applying pulsed heat at a predetermined pulse frequency, and heat source controls for controlling the heat source to adjust the frequency and position of the heated region so as to heat the specified tissue without substantial damage to adjacent tissue. Preferably, said image processor reconstructs using one-dimensional Fourier Transformations. Preferably, the heat source for applying heat comprises a focused ultrasonic heat source for focusing ultrasonic waves on an application point, and a position controller for positioning the application point at a predetermined location within the specified tissue. Alternatively, preferably the heat source is a phased aπay ultrasonic transducer. In a prefeπed embodiment of the invention, the heat source for applying pulsed heat comprises a generator for generating optical energy, and an optical fiber for transferring the optical energy to a predetermined application point positioned at a predetermined location within the specified tissue. There is further provided a magnetic resonance (MR) monitored heat system for allowing an operator to selectively heat tissue within a patient, comprising a heat producing source adopted for concentrating energy at an application point in a patient; a heat source positioner for positioning the application point of the heat producing source in a specified tissue within the patient so as to create a heated region within the specified tissue; a controller for enabling said operator to control the positioner; MR apparatus comprising: a radio- frequency (RF) transmitter for transmitting an RF excitation pulse into said patient; gradient generators for producing a time-varying magnetic field gradient in a first direction and a time- varying magnetic field gradient in a second direction orthogonal to the first direction, both gradients applied substantially simultaneously with the RF excitation pulse for exciting longitudinal magnetization of an elongated excitation region in said patient; a control processor for applying first and second read-out gradients to the elongated excitation region; an RF receiver for receiving first and second echo signals from the elongated excitation region responsive to the application of said first and second read-out gradients; an image processor for producing a temperature versus position profile to provide a display of temperature versus position data responsive to the first echo signal from the receiver and for producing an intensity versus position profile responsive to the second echo signal from the receiver to provide a display of intensity versus position data; and a display monitor for displaying an image of both the temperature data and the intensity data. In a prefeπed embodiment of the invention, the heat source comprises: a source of pulsed optical energy; an invasive device adapted for insertion into the patient to reach the specified tissue of the patient; and an optical fiber having a first end and a second end, said first end adapted to be fitted into the invasive device, within the specified tissue, when said second end is proximate to the pulsed heat producing source, the fiber being adapted to pass the optical energy from the pulsed heat- producing source into the specified tissue. Preferably, the heat-producing source comprises a laser. Alternatively, the heat-producing source comprises: an ultrasonic transducer adapted for generating pulsed ultrasonic energy concentrated at a focal point, the focal point being the application point.

There is further provided magnetic resonance (MR) monitored heat system for enabling an operator to selectively heat tissue within a patient comprising: a heat source adapted for concentrating heat at an application point; a positioner for positioning the application point of the heat in a specified tissue within the patient so as to create a heated region within the specified tissue; an operator responsive control for enabling said operator to control the positioning means; an MR imaging means comprising: a homogenous magnetic field applied to said patent to align spins in the patient; a radio frequency (RF) transmitter for applying an RF pulse for tipping said spins into a transverse plane; first and second gradient generators for transmitting a first and a second time-varying gradient during the application of the RF pulse, said first and second gradients being orthogonal to each other, said RF pulse being the two- dimensional Fourier transform of a desired excitation profile; and a third gradient generator for transmitting first and second read-out gradients to provide a first echo signal and a second echo signal, said first echo signal providing a temperature profile at the specified tissue and said second echo signal providing an intensity profile at the specified tissue. There is still further provided a method for guiding and monitoring thermal therapy using magnetic resonance imaging (MRI) apparatus, comprising selectively applying heat for destroying tumorous tissue and performing a line scanning sequence to generate and monitor two types of information in the same scan, one type being temperature responsive data and the other type being intensity responsive data. In a prefeπed embodiment ofthe invention, the line scanning is performed in real time. Preferably, double echo scanning is used to acquire the two types of information in a single scan. Preferably, said line scanning sequence is accomplished by: generating a pencil beam; and reading out MR signals along the pencil beam. Alternatively, preferably said line scanning sequence is accomplished by generating intersecting planes to provide lines at the intersection of the planes. In a prefeπed embodiment of the invention, the pencil beam is generated by applying a time varying magnetic field gradient in a first direction and a time varying magnetic field gradient in a second direction orthogonal to the first direction; and applying both gradients simultaneously with an RF excitation pulse so as to excite longitudinal magnetization of an elongated excitation region in said patient. Preferably, a first read-out gradient is supplied in a manner that provides a Tl weighted display; and a second read-out gradient is supplied in a manner that provides a T2 weighted display. In a prefeπed embodiment of the invention, selectively applying heat for destroying tumorous tissue comprises selectively applying a laser light beam to said tumorous tissue. Alternatively, preferably selectively applying heat for destroying tumorous tissue comprises applying ultrasound energy to said tumorous tissue.

There is further provided a method of performing thermal surgery on a patient guided by MRI, comprising: creating an internal image of tissues of said patient; determining the position of a specified tissue in the patient; applying pulsed heat at a predetermined pulse frequency to the specified tissue to create a heated region within the specified tissue; monitoring the heated region with MRI by: transmitting an RF excitation pulse into said patient; applying a time varying magnetic field gradient in a first direction, and a time varying magnetic field gradient in a second direction, , both gradients applied during the RF excitation pulse so as to excite longitudinal magnetization of an elongated excitation region in said patient; applying a first read-out gradient designed to produce a first echo; applying a second read-out gradient designed to produce a second echo; and using the first echo to acquire a first display and the second echo to acquire a second display. In a prefeπed embodiment of the invention, the method includes temperature encoding said first echo with a Tl weighted readout gradient and tissue intensity encoding said second echo with a T2 weighted read-out gradient. In a prefeπed alternative embodiment of the invention, temperature encoding includes temperature encoding said first echo with diffusion of magnetic gradient fields. Preferably, the method includes applying one-dimensional Fourier transformations to the echo signals to generate magnetization profiles, the profile of the first echo indicating the temperature of tissue along the length of the excitation region and the profile of the second echo showing tissue intensity values along the length of the excitation region and adjusting the frequency and position of the pulsed heat so as to heat the specified tissue without substantial damage to adjacent tissue. In a prefeπed embodiment of the invention, applying pulsed heat comprises: focusing ultrasonic waves on an application point and positioning the application point at a predetermined location within the specified tissue. In a prefeπed alternative embodiment of the invention, applying pulsed heat comprises: creating optical energy; transferring the optical energy through an optical fiber to a predetermined application point; and positioning the application point at a predetermined location within the specified tissue.

A BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, together with further objects and advantages thereof may best be understood by reference of the following description taken in conjunction with the accompanying drawings, in which :

Fig. 1 is a schematic block diagram of an embodiment ofthe present invention; Fig. 2 is a cross sectional view of a patient positioned for thermal surgery within the bore of the magnet of one embodiment of the present invention, employing a focused ultrasound heat source;

Fig. 3 is a partial perspective cutaway view of a patient positioned for thermal surgery within the bore of the magnet of another embodiment of the present invention employing a laser heat source and a fiber optics heat delivery system;

Fig. 4 is a double echo scan sequence used to simultaneously perform line scanning and temperature mapping of the tumorous and/or immediately surrounding tissue, in accordance with a preferred embodiment ofthe invention;

Fig. 5 is a 2-D image generated during the planning stage or the post-heating stage of the present invention; and

Fig. 6 is a showing of pencil beam line scanning ofthe present invention. DETAILED DESCRIPTION

Fig. 1 shows a typical MRI system 11 comprising a magnet 12 for receiving a patient therein. In a prefeπed embodiment the magnet is a super-conducting magnet, but within the scope of this invention other types of magnets can be used.

A large static, relatively homogeneous magnetic field Bo is generated by field generator Ho indicated at 13. The large static field causes certain nuclei ("spins") to align with the static field. Gradient fields are generated by gradient field generators Gx indicated at 14,

Gy indicated at 16 and Gz indicated at 17. The gradient fields are used to vary the large magnetic field in a known manner. According to convention, the gradient fields are aπanged orthogonally in X, Y and Z directions, as shown by the orthogonally directed arrows at 20. The field Bo is conventionally in the Z direction.

Means are provided for generating radio-frequency (RF) pulses for "flipping" the aligned spins into a transverse plane such as the XY plane or to have a component in the XY plane. The means for flipping the spins comprises RF coils (not shown) in the magnet and a pulse transmitter 18. The pulse transmitter frequency may be supplied by synthesizer 19 and controlled by control processor or controller 21. The controller 21 controls, among other things, the time and amplitude of the outputs of the various component parts making up the MRI system. The transmitted pulse goes from the transmitter 18 through a transmitter-receiver selection switch 22 to an RF coil (not shown) in the magnet. The synthesizer signal is coupled to the transmitter 18 when the system is in the transmitting mode through a second transmitter- receiver selection switch 23.

In the receiving mode, the RF coil in the magnet senses free induction decay (FID) signals, including echo signals. The signals received at the RF coil go through switch 22 when it is switched by controller 21 into the receiving mode to connect the RF coil to the receiver. Separate RF coils can be used for receiving and transmitting within the scope ofthe invention. The received signal then passes through an analog-to-digital converter 25. The digital output of the converter 25 is applied to an image processor 26 having an associated memory 27 to provide an image in display unit 28 using reconstruction methods such as fast Fourier Transforms. The control processor 21, as shown, is connected to a surgical control unit 29 which controls a heat source 30 that generates the heat used to destroy the tumorous tissue.

According to some prefeπed embodiments of the invention, the magnetic resonance system is used both for monitoring the temperature at the focal point of the heat, that is at the tumorous tissue, and for monitoring the necrosis at the tumorous tissue. As shown in Fig. 2, patient 31 is located on a bed or table 32, designed to accommodate a heat source such as an ultrasound transducer 33 in a water bath 34. A focused ultrasound transducer is shown, however, a phased aπay ultrasound transducer having controllable focal points can be used. In any case, the focal point ofthe transducer is shown at 36. The patient-table ultrasound unit and water bath are all shown mounted within the bore 38 of the magnet 12. An alternative embodiment, not shown, may utilize an ultrasound transducer that creates heat over a line segment instead of a point. The ultrasound transducer 33 can alternatively be moved inside the bore ofthe magnet to different locations so as to focus on different locations within the patient. Alternatively, the ultrasound unit itself can be a phased aπay ultrasound transducer, enabling electronically moving the focal point.

As shown in Fig. 3, a patient 41 lies on a table 42 that moves into the bore 43 of the magnet 12. A laser fiber 44 is inserted into the patient with a hollow needle 46, guided by a mechanical positioning device indicated at 47. The positioning device, preferably is a hydraulic positioner. While a closed type magnet 12 is shown, the magnet can also be an open type magnet such as shown, for example, in U.S. Patent 5,119,372, the disclosure of which is hereby incorporated herein by reference. A safe trajectory from the entry point to the target that does not intersect critical anatomy, such as large blood vessels is determined during the preplanning stage of the operation. Heat is applied to the tumorous tissue 48 by periodically pulsing the laser through a fiber-optic material 44 and needle 46 to destroy the tumor 48, while the operator views the temperature-sensitive magnetic resonance images. While one needle 46 is shown, more than one needle may be required to remove an iπegularly shaped tumor. Here again, while a heat source that creates heat at a point as shown, a heat source that creates heat over a line segment instead of a point may be utilized.

During the pre-surgical planning stage, images are acquired to locate the tumorous tissue. During the actual surgical procedure, images are acquired, according to prefeπed aspects of the invention for example, temperature elevation during heat exposure is monitored by using scans that provide Tl weighted images such as through the diffusion of magnetic field gradients or by using proton resonance frequency shift images or with fast gradient echo sequence images. In the same scan sequence, tissue is imaged with T2 weighted fast spin echo images. Both images are acquired using cylindrical excitation beams, also known as pencil beams for performing line scanning, rather than 2-D scanning or volume scanning. By using pencil beams, the line scanning can be readily oriented in real time along non-orthogonal lines aligned with the tumorous tissue, wherever that may be. Thus, the line scanning is not necessarily limited to orthogonal axes, but can be used at any line location following the tumorous tissue. The pencil beams can be individually shaped. For example, a rectangular cross-section pencil beam is acquired using crossed selective 80 and 90 degree pulses with spin echo imaging. Circular cross-sections are acquired with selective 90 degree pulses in a selective spiral acquisition scan. Alternatively, line scanning could be accomplished using intersecting slices.

Initially, during the surgical procedure, heat is applied to the tumorous tissue that is sufficient to raise the temperature of the tumorous tissue without necrosing the tumorous tissue. This is done to determine in real time that the focal point of the heat being applied is being applied directly to the tumorous tissue and not to suπounding healthy tissue. After the determination that the focal point coincides with the tumorous tissue, the temperature is raised, and at the same time real time temperature imaging and real time tissue imaging are accomplished in a single scan, as is shown in Fig. 4.

A double echo sequence is used that involves an RF selective pulse 51 , followed by two readout gradient echo signals directed along the axis of the beam. The first echo signal is used to measure the temperature, for example using the proton resonance frequency shift method. The second echo measures the tissue T2 property, which images the heat treatment of the tumorous anatomy. This provides an image of the tissue when using an imaging pencil beam probe such as beam 68 of Fig. 6.

For example, as shown in Fig. 4, an RF pulse 51 is applied during the application ofthe heat pulses. Pulse 51 has an amplitude modulated envelope, which may be symmetrical or asymmetrical. Simultaneously with the RF pulse 51, a two-dimensional magnetic field gradient is applied with the gradient magnetic fields, such as magnetic gradient Gz and magnetic gradient Gy shown at 52 and 53. These pulses generate a "k" space spiral that reorients itself in a manner that generates a desired cylindrical or pencil probe beam such as beam 68 of Fig. 6. The gradient pulses 52 and 53 have amplitudes decreasing with time and have a plurality of periods within the excitation time. It should be understood that while pulses with six periods are shown, the number of periods could be more or less within the scope of the invention. These pulses are inherently refocused, and do not need extra gradient refocusing lobes.

It has been found that these excitation pulses can be utilized even where the probe beam is tipped at large angles, as much as 90° or more from, in this case, the X-axis of the imaging volume. Probe beams can be produced which excite volumes which are the Fourier Transform of the weighted trajectory through k space, with the gradient wave forms 52 and 53 following a spiral which efficiently samples k space. The RF pulse 51 which can be normalized to the k space velocity serves as a weighting function for the k space trajectory so that the method can be used to produce a cylindrical excitation beam with a Gaussian profile cross-section, for example. The bandwidth of the pulse is maximized by varying the rate of traversal of k space, subject to the constraint of the particular maximum gradient slew rate available in a particular MRI system. In accordance with the invention, two separate echoes are provided in a single scan. One echo 50 is Tl weighted and is used to monitor the temperature of the tumorous tissue subjected to the heat treatment. The other echo 60 is T2 weighted to enable viewing the tissue damage. The T2 weighted gradient echo is provided by applying Gx gradient echo read-out pulses 63 and 64 in a well-known manner. The display of the tissue based on the T2 weighted echo highlights the edematous regions to effectively monitor the heat initiated surgery.

More particularly, as shown in Fig. 4 a gradient echo 50 is acquired by the application of the Gx read-out gradient pulses 54 and 56. The gradient pulses 61 and 62 are well-known spoiler lobes. These de-phase the total magnetization and eliminate coherence prior to commencement ofthe next profile imaging sequence.

Fig. 5 shows the two-dimensional scan used in the planning phase which is used to locate diseased tissue such as tumorous tissue 66 located in the image of the patient's body part 67. This is shown to be in the X,Y plane.

The probe "pencil-like" beam is shown in Fig. 6 at 68 for accomplishing the line scans. Beam 68 is shown intercepting the tumorous tissue so as to provide temperature readings of the tumorous tissue during the surgical procedure. The beam 68 also intercepts the tumorous tissue during the same scan, to enable monitoring tissue by highlighting the edematous tissue.

In summary, focused or directed heat is used to selectively destroy tumor tissue of a patient in a minimum invasive procedure. MRI is employed to monitor the location of the heating and the tissue destruction caused by the heating during the surgical procedure. The use of line scanning, while generating both a temperature map and a tissue image during single scans efficiently monitors the thermal therapy in real time. The efficiency is further increased when pencil beams are generated during single scans to monitor the temperature map and to highlight edematous regions, and therefore tissue damage. The utilization of the pencil beams to provide line data during a single scan provides a more precise guide for the surgeon during the surgery.

The foregoing description of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously many modifications and variations are possible in the light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application to thereby enable others skilled in the and to best utilize the invention and various embodiments with various modifications as suited for the particular use contemplated. It is intended that the scope of the invention be defined by claims appended hereto and their equivalents.

The terms "comprise", "include" or "have", or their conjugates as used herein mean "including but not necessarily limited to".

Claims

1. Apparatus for guiding and monitoring thermal therapy, said apparatus comprising: a heat source for selectively applying heat for destroying tumorous tissue; and magnetic resonance imaging (MRI) apparatus for performing a line scanning sequence to generate and monitor two displays in the same scan, one display being of temperature responsive data and the other display being an image of selected tissue.

2. The apparatus of claim 1, including a control processor for doing a double echo scan to acquire the two displays in a single scan.

3. The apparatus of claims 1 or 2 wherein both displays are displays of the same selected tissue.

4. The apparatus of claim 1 or 2 wherein the display of the temperature responsive data encompasses a larger region than the display that is an image of selected tissue.

5. The apparatus of claims 1-4 wherein said MRI apparatus for performing the line scanning sequence includes: a pencil beam generator for generating a pencil beam; and a read-out gradient for reading out MR signals along the pencil beam.

6. The apparatus of claim 5 wherein the cross-section ofthe pencil beam is cylindrical.

7. The apparatus of claim 5 wherein the cross-section of the pencil beam is non- cylindrical.

8. The apparatus of any of claims 1-7 wherein said MRI apparatus for performing the line scanning sequence includes an intersecting plane generator for generating intersecting planes to provide lines at the intersections ofthe planes, and a read-out gradient generator for reading out MR signals along the lines.

9. The apparatus of claims 5-7, wherein: said pencil beam generator includes a first gradient generator for applying a first-time varying magnetic field gradient in a first direction and a second gradient generator for applying a second time varying magnetic field gradient in a second direction orthogonal to the first direction; and a synchronizer for applying both said first gradient and said second gradient substantially simultaneously with an RF excitation pulse so as to provide an elongated excitation region in said patient.

10. The apparatus of claim 9 including a control processor for applying a first read-out gradient in a manner that provides a Tl weighted display; and for applying a second read-out gradient in a manner that provides a T2 weighted display.

11. The apparatus of claim 10 wherein said heat source for selectively applying heat for destroying tumorous tissue comprises laser means for selectively applying a laser light beam to said tumorous tissue.

12. The apparatus of claim 10, wherein said heat source for selectively applying heat for destroying tumorous tissue comprises means for selectively applying ultrasound energy to said tumorous tissue.

13. Apparatus for performing and monitoring thermal surgery on a patient, said apparatus comprising: a magnetic resonance imaging (MRI) system for creating an internal image of tissues of said patient; said system including magnetic gradient generators for transmitting magnetic field gradients for determining the position of a specified tissue in the patient; a heat source for applying heat to the specified tissue to create a heated region within the specified tissue; means for monitoring the heated region with the MRI system, including: an RF generator for transmitting an RF excitation pulse into said patient; magnetic field gradient generators for applying a time varying magnetic field gradient in a first direction, and a time varying magnetic field gradient in a second direction, the second direction being orthogonal to the first direction, both gradients applied substantially simultaneously with the RF excitation pulse so as to excite longitudinal magnetization of an elongated excitation region in said patient; said magnetic field gradient generators applying a first read-out gradient to produce a first echo, and a second read-out gradient to produce a second echo; and an image processor using the first echo to acquire a first display and the second echo to acquire a second display.

14. The apparatus of claim 13, including: a control processor for temperature encoding said first echo with a Tl weighted read- out gradient and for tissue intensity encoding said second echo with a T2 weighted read-out gradient.

15. The apparatus of claims 13 or 14 wherein said control processor temperature encodes said first echo with diffusion of magnetic gradient fields.

16. The apparatus of claim 14 or 15, including: an image processor for reconstructing said first and second echoes to generate magnetization profiles, the profile of the first echo indicating the temperature of tissue along the length of the excitation region and the profile of the second echo showing tissue intensity values along the length ofthe excitation region; said heat source applying pulsed heat at a predetermined pulse frequency; and heat source controls for controlling the heat source to adjust the frequency and position of the heated region so as to heat the specified tissue without substantial damage to adjacent tissue.

17. The apparatus of claim 16 wherein said image processor reconstructs using one- dimensional Fourier Transformations.

18. The apparatus for performing thermal surgery on a patient of claims 16 or 17, wherein the heat source for applying heat comprises: a focused ultrasonic heat source for focusing ultrasonic waves on an application point; and a position controller for positioning the application point at a predetermined location within the specified tissue.

19. The apparatus of claim 18 wherein the heat source is a phased aπay ultrasonic transducer.

20. The apparatus for performing thermal surgery of claim 16 or 17 wherein the heat source for applying pulsed heat comprises: a generator for generating optical energy; an optical fiber for transferring the optical energy to a predetermined application point positioned at a predetermined location within the specified tissue.

21. A magnetic resonance (MR) monitored heat system for allowing an operator to selectively heat tissue within a patient, comprising: a heat producing source adopted for concentrating energy at an application point in a patient; a heat source positioner for positioning the application point of the heat producing source in a specified tissue within the patient so as to create a heated region within the specified tissue; a controller for enabling said operator to control the positioner;

MR apparatus comprising: a radio-frequency (RF) transmitter for transmitting an RF excitation pulse into said patient; gradient generators for producing a time-varying magnetic field gradient in a first direction and a time-varying magnetic field gradient in a second direction orthogonal to the first direction, both gradients applied substantially simultaneously with the RF excitation pulse for exciting longitudinal magnetization of an elongated excitation region in said patient; a control processor for applying first and second read-out gradients to the elongated excitation region; an RF receiver for receiving first and second echo signals from the elongated excitation region responsive to the application of said first and second read-out gradients; an image processor for producing a temperature versus position profile to provide a display of temperature versus position data responsive to the first echo signal from the receiver and for producing an intensity versus position profile responsive to the second echo signal from the receiver to provide a display of intensity versus position data; and a display monitor for displaying an image of both the temperature data and the intensity data.

22. The MR monitored pulsed-heat system of claim 21 , where the heat source comprises: a source of pulsed optical energy; an invasive device adapted for insertion into the patient to reach the specified tissue of the patient; and an optical fiber having a first end and a second end, said first end adapted to be fitted into the invasive device, within the specified tissue, when said second end is proximate to the pulsed heat producing source, the fiber being adapted to pass the optical energy from the pulsed heat-producing source into the specified tissue.

23. The MR monitored pulsed heat system of claims 21 or 22 wherein the heat-producing source comprises a laser.

24. The MR monitored pulsed heat system of claim 21, wherein the heat-producing source comprises: an ultrasonic transducer adapted for generating pulsed ultrasonic energy concentrated at a focal point, the focal point being the application point.

25. A magnetic resonance (MR) monitored heat system for enabling an operator to selectively heat tissue within a patient comprising: a heat source adapted for concentrating heat at an application point; a positioner for positioning the application point of the heat in a specified tissue within the patient so as to create a heated region within the specified tissue; an operator responsive control for enabling said operator to control the positioning means; an MR imaging means comprising: a homogenous magnetic field applied to said patent to align spins in the patient; a radio frequency (RF) transmitter for applying an RF pulse for tipping said spins into a transverse plane; first and second gradient generators for transmitting a first and a second time-varying gradient during the application of the RF pulse, said first and second gradients being orthogonal to each other, said RF pulse being the two-dimensional Fourier transform of a desired excitation profile; and a third gradient generator for transmitting first and second read-out gradients to provide a first echo signal and a second echo signal, said first echo signal providing a temperature profile at the specified tissue and said second echo signal providing an intensity profile at the specified tissue.

26. A method for guiding and monitoring thermal therapy in a patient using magnetic resonance imaging (MRI) apparatus, said method comprising; selectively applying heat for destroying tumorous tissue; and performing a line scanning sequence to generate and monitor two types of information in the same scan, one type being temperature responsive data and the other type being intensity responsive data.

27. The method of claim 26 wherein the line scanning is performed in real time.

28. The method of claim 26 or 27, including using a double echo scan to acquire the two types of information in a single scan.

29. The method of claims 26-28 wherein said line scanning sequence is accomplished by: generating a pencil beam; and reading out MR signals along the pencil beam.

30. The method of claims 26-28 wherein said line scanning sequence is accomplished by generating intersecting planes to provide lines at the intersection ofthe planes.

31. The method of claim 29, wherein: the pencil beam is generated by applying a time varying magnetic field gradient in a first direction and a time varying magnetic field gradient in a second direction orthogonal to the first direction; and applying both gradients simultaneously with an RF excitation pulse so as to excite longitudinal magnetization of an elongated excitation region in said patient.

32. The method of claim 31 wherein a first read-out gradient is supplied in a manner that provides a Tl weighted display; and wherein a second read-out gradient is supplied in a manner that provides a T2 weighted display.

33. The method of claims 26-32 wherein selectively applying heat for destroying tumorous tissue comprises selectively applying a laser light beam to said tumorous tissue.

34. The method of claim 26-32, wherein selectively applying heat for destroying tumorous tissue comprises applying ultrasound energy to said tumorous tissue.

35. A method of performing thermal surgery on a patient guided by MRI, said method comprising: creating an internal image of tissues of said patient; determining the position of a specified tissue in the patient; applying pulsed heat at a predetermined pulse frequency to the specified tissue to create a heated region within the specified tissue; monitoring the heated region with MRI by: transmitting an RF excitation pulse into said patient; applying a time varying magnetic field gradient in a first direction, and a time varying magnetic field gradient in a second direction, , both gradients applied during the RF excitation pulse so as to excite longitudinal magnetization of an elongated excitation region in said patient; applying a first read-out gradient designed to produce a first echo; applying a second read-out gradient designed to produce a second echo; and using the first echo to acquire a first display and the second echo to acquire a second display.

36. The method of claim 35, including: temperature encoding said first echo with a Tl weighted read-out gradient; and tissue intensity encoding said second echo with a T2 weighted read-out gradient.

37. The methods of claims 35 and 36, including: temperature encoding said first echo with diffusion of magnetic gradient fields.

38. The method of claims 35-37, including: applying one-dimensional Fourier transformations to the echo signals to generate magnetization profiles, the profile of the first echo indicating the temperature of tissue along the length of the excitation region and the profile of the second echo showing tissue intensity values along the length ofthe excitation region; and adjusting the frequency and position of the pulsed heat so as to heat the specified tissue without substantial damage to adjacent tissue.

39. The method of performing thermal surgery on a patient of claim 38, wherein applying pulsed heat comprises: focusing ultrasonic waves on an application point; and positioning the application point at a predetermined location within the specified tissue.

40. The method of performing thermal surgery of claim 39 wherein applying pulsed heat comprises: creating optical energy; transferring the optical energy through an optical fiber to a predetermined application point; and positioning the application point at a predetermined location within the specified tissue.