Mathematics and Physics of Emerging Biomedical Imaging (1996) / Chapter Skim
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12 IMAGE-GUIDED MINIMALLY INVASIVE DIAGNOSTIC AND THERAPEUTIC INTERVENTIONAL..
12 IMAGE-GUIDED MINIMALLY INVASIVE DIAGNOSTIC AND THERAPEUTIC INTERVENTIONAL..
Pages 167-186
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From page 167... ...
Although static images are sufficient for planning radiation therapy or providing some anatomical information for surgery, real-time image guidance has been funclamental to the evolution of interventional radiological procedures. More recently, the emergence of minimally invasive therapeutic procedures has encouraged the tendency for surgical procedures to shift from 1NOTE: This chapter is adapted in large part from Jolesz and Blumenfeld, 1994; see suggested reading list at end.
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From page 168... ...
It is expected that allowing medical imaging systems to play a more direct role in interventional and therapeutic procedures thus enabling greater precision, increasing foreknowledge, and facilitating even less invasive surgical access will reduce the cost of patient management and improve the quality of patient outcomes. rmage-guided therapy is a new, emerging field that has close relationships to interventional radiology, minimally invasive surgery, computer-assisted visualization, and robot-assisted surgery.
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From page 169... ...
CT has much better geometric accuracy than does MRT, because of the intrinsic curved nature of the magnetic fleld. Thus CT may be preferred in applications for which geometric accuracy is important, such as surgical procedures that rely on prospectively derived images for navigational guidance.
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From page 170... ...
has specific advantages, over and above its lack of ionizing radiation, for guiding, monitoring, and controlling minimally invasive diagnostic and therapeutic interventions, including the following: . Superb tissue discrimination, enabling excellent discrimination between various organs, including blood vessels, nerves.
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From page 171... ...
, fast spin echo imaging, anal gradient echo imaging, and various hybrid pulse sequences, enabling a close-to-real-time or real-time viewing of physiological motions and the changes induced by the interventional procedures; and · Ability to characterize functional and physiological parameters of the treated tissues, such as (Effusion, perfusion, flow, and temperature. As a result of these characteristics, MRI can depict the tissue damage induced by various tissue ablative methods4 and therefore has the unparalleled potential to not only monitor but also control interventional or minimally invasive surgical procedures.
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From page 172... ...
At this point appropriate analytic and synthetic operations of trajectory simulation or planning, of probe guidance, and of surgical planning are carried out on the three-dimensional images thus created. Images from various sources, particularly MRI or CT volume rendered images, can
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From page 173... ...
"Dead-reckoning" navigational methods are more feasible for precise biopsies and for minimally invasive surgical procedures. The stereotactic tech 5That is, those regarded as or employed as a standard of reference, as in surveying.
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From page 174... ...
Frameless stereotaxy, a proprietary method of registration without frames, permits registration of the patient coordinate system with the three-dimensional patient model or the surgical planning model. This method utilizes a video image or a laser-scanner defined surface area of the patient made during the procedure with the three-dimensional mode!
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From page 175... ...
This system consists basically of light-emitting diodes mounted on instruments whose positions can be determined accurately by triangulation via a number of line scan video cameras mounted in the room. 12.2.3 Monitoring and Localization On-line, real-time imaging of the delivery of therapy or of an interventional procedure allows the physician to watch his or her progress.
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From page 176... ...
Dissection exposes surfaces only, and so the surgeon cannot see effects below the surface and has to approach the target, (lissecting carefully layer by layer. This limitation of direct visual control confined the use of surgical lasers to relatively Tow penetration an(1 doomed the use of interstitial laser therapy, cryosurgery, and focused ultrasound surgery until appropriate imaging methods, combined with the capability to control energy deposition, were developed.
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From page 177... ...
12.3 Thermal Surgery O O 177 Tma~-~uided interstitial thermal therapy or surgery is the process of optimally defining a target volume using diagnostic imaging techniques and then destroying all the tissue cells within the target volume by inducing a localized temperature change in the target volume only. Thermal therapeutic techniques use heat or freezing (cryosurgery)
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From page 178... ...
Computerized control of this procedure has been suggested but has not yet been implemented because significant progress must be made in understanding the structure and biology of the target tissues, as well as their optical and thermal properties and how they change during irradiation, before laser-induced thermal surgery can be fully automated. 12.3.2 Cryotherapy Freezing causes cell destruction through the development of ice crystals, which gives cryotherapy some advantages over heat surgery because the collagen structure of the tissues is not destroyed, vessel walls are preserved, and reinnervation is possible.
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From page 179... ...
Highaperture ultrasound transducers can create a converging beam focused to a high-intensity zone. Within this focal volume various quantities of thermal energy can be deposited without any obvious damage to the surrounding tissue.
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From page 180... ...
Because ultrasound beams are blocked by air and bone, treatment of (different anatomic locations will likely require different transducer shapes and application methods to optimize the treatment. Ultrasound transducers for neurosurgical procedures or for use with the thyroid will differ from those for the breast or lower abdomen.
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From page 181... ...
Requirements Should destroy target and nothing but the target No entry track of destruction or injury Resultant lesions reproducible and predictable Size, shape, and position of resultant lesions are finely controllable Resultant lesions should be nonhemorrhagic Resultant lesions should be sharply demarcated from unaffected surrounding tissue Resultant lesions should be instantaneous in clevelopment No delayed effects such as those produced by radiation therapy Should allow creation of transient alterations of function sublethally to assist in target localization Should enable process to be repeatable without additional risk to the patient ShouIcl not require creep anesthesia Should be able to reach any part of the body MRI-GuidedFocused Ultrasound Can destroy preselected targets located deep within tissue without clamage to surrounding tissue Tissue in the entry path is not irreversibly heated Lesion size and shape can be accurately predicted and monitored in real time Size, shape, and position of lesions in target organ are controllable with MR] guidance Nonhemorrhagic lesions produced, because cavitation easier to avoid Margins of the necrotized tissue are sharply (lemarcated from the surroun(ling normal tissue and visible in MR images Lesions develop within fractions of a second No delayed effects Reversible heat pulse visible on MR image to enable locating the subsequent irreversible pulses Repeatable without a dose limit (unlike radiosurgery)
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From page 182... ...
· Research in the area of surgical planning and simulation, particularly trajectory planning for needle biopsy, its basic surgical application today. · Improvement, via more complex automated technologies, of current registration or image fusion methods of different medical imaging modaTities and more particularly of video-based and laser-scanning techniques with prospectively created models.
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From page 183... ...
. · Development of methods to update prospectively created models using real-time imaging information acquired during the interventional procedure and reflecting changes effected by the intervention.
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From page 184... ...
with histological and physiological changes in the tissue and resulting image changes, for the purpose of determining mechanisms of thermal damage and the biophysical changes that take place during various thermal surgical procedures such as interstitial laser therapy, cryoablation, and high-intensity focused ultrasound treatment. Such investigations need to be done for various anatomic regions and medical conditions for which such therapy might be appropriate.
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From page 185... ...
Cope, C., ea., Current Techniques in Interventional Radiology, 2nd Edition, Current Medicine, Philaclelphia, 1995.
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