Imaging Technology News - November/December 2008 - (Page 39)

> > special report PET/CT Targets MPI SPECT/CT dominates myocardial perfusion imaging, but new agents and techniques are driving the adoption of cardiac PET/CT. by Amy Ballard, MEd, director of research, Arkansas Urology Siemens Biograph PET/CT series consists of two-, six-, 16-, 40- and 64-slice configurations and provides high-imaging quality and clarity. M yocardial perfusion imaging (MPI) using single photon emission computed tomography/computed tomography (SPECT/CT) is an application that has been recently bolstered by the development of quantitative tools that enhance the system’s clinical capabilities in the nuclear cardiology community. Similarly, the use of positron emission tomography fused with computed tomography (PET/CT) is well established in oncology for diagnosis and staging, however, there is a trend among clinicians toward using PET/CT for cardiac imaging, levering its superior image quality, visualization and quantitative capabilities. Yet the adoption of PET/CT for MPI is notably slow due to several contributing factors. Pros, cons of cardiac PET/CT vs. SPECT/CT Over the last year, vendors have introduced a series of new hybrid SPECT/CT systems and software solutions, including GE Healthcare’s Volumetrix Suite with automatic registration and 3D image rendering, which expedites patient throughput and streamlines workflow. Another is Siemens’ SMARTZOOM collimator, which is referred to as a cardio-centric orbit that enables the heart to remain within the collimator’s magnification area throughout the entire study, enabling the study to be performed in less than one minute. Adding to the list is Philip’s Brightview XCT system, which offers the only scalable hybrid camera to fit into a 12-by15.5-foot room, thus requiring little to no room renovation and reducing the overall cost of ownership. Despite the growing number of SPECT/CT tools with enhanced capabilities dramatically improving image quality, the current generation of PET/CT systems still produces superior images, according to Partha Ghosh, M.D., clinical marketing manager, molecular imaging, Siemens Medical Solutions USA. “Cardiac PET/CT uses a short-acting isotope and higher doses can be injected. This, when combined with the higher sensitivity of PET, contributes to the overall improved image quality,” said Dr. Ghosh. “Thus, in obese patients or in patients who have thick chest walls or women with large breasts, we expect PET/CT to be definitely superior. Other advantages of PET/CT include the use of short-acting isotopes, which are true perfusion agents. Due to this, both stress and rest imaging can be performed in a relatively short time. This is a major advantage over SPECT/CT, requiring about two to three hours between stress and rest, which in turn, increasMyocardial perfusion PET es the total procedure time. We can perform blood flow quantifistudy following IV admincations much more effectively and reproducibly with PET/CT due istration of 60 mCi of Rubidium-82 at rest and to dynamic imaging capabilities. Thus with PET, we have better 60 mCi of Rubidium-82 image quality, better visualization in obese patients and better during peak quantitative capability.” Dypiridamole stress, PET/CT is also capable of absolute quantification of myocarrespectively. Gated dial blood flow and flow reserve estimation. This helps overall images were obtained at visual interpretation of myocardial perfusion by providing flow rest and during peak stress. Image courtesy of reserve estimations, which provide higher diagnostic confidence, GE Healthcare. particularly in situations where there are borderline changes and also in situations with balanced disease. In balanced disease, all four vessels are equally diseased, in which case there is a generalized decrease in myocardial blood flow. Due to the global reduction in blood flow, the perfusion images can artificially appear to be normal. PET/CT is able to accurately identify areas of abnormality in balanced disease, according to Dr. Ghosh. Despite the value of this capability, it is still not widespread and is used only in certain major research centers. “However, we are working to make this process user-friendly so that people can use it on a regular basis. Initial calculation methods require input from physicists, but we are trying to make it simple so that standard users can use it more effectively.” Dr. Ghosh said. New agent extends shelf life Another factor weighing in on the advantages of PET/CT over SPECT/CT is the development of new agents for cardiac PET/CT. Bracco Diagnostics recently introduced an agent for cardiac PET/CT perfusion imaging - CardioGen-82, a Rubidium Rb 82 generator, which is currently the only generator-based PET/CT agent reimbursed for the evaluation of coronary artery disease. The physical half-life for Rb-82 is 75 seconds, which allows for an efficient protocol. By the time the imaging is completed for the rest portion (approximately six minutes), stress can follow immediately and then the stress images can be acquired (approximately six minutes). The study can be completed in approximately 40-45 minutes. Key features of Rb-82 are that it has properties similar to Thallium-201 (Tl201), defects are visualized within two to seven minutes after injection, and due to its short half-life, both sets of images can be acquired using the same sized dose. PET/CT is able to accurately identify areas of abnormality in balanced disease. Slow to catch on With all of the advances in PET/CT perfusion imaging, why isn’t it more widely adopted for cardiac imaging? According to Dr. Ghosh, the main impairment to its widespread adoption is the limited availability and expense of Rubidium, which is the main isotope required for PET/CT perfusion imaging. Another factor is the limited expertise in cardiac PET/CT among nuclear medicine physicians. However, Dr. Ghosh noted, “We expect this to significantly improve in the next few years because we are expecting new radiopharmaceuticals — Fluorine-18 labeled myocardial perfusion agents — which will have a much better logistic advantage for cardiac PET. In the next two to three years, we hope to have this new radiopharmaceutical available, and we will be able to see much more utilization of PET/CT in cardiology. There is also a significant need for us to educate the general PET/CT users on the value of PET/CT in cardiac imaging, although I see more and more physicians are getting interested.” Others attribute PET/CT’s slow penetration in cardiac imaging to a lack of coverage for FDG-PET/CT in non-oncology applications. According to Frost and Sullivan research analyst, Travis Chong, this has placed a cap on near-term market growth and left it susceptible to disrupPET/CT continued on page 42 Nov/Dec 2008 > special report > 39 http://new.reillycomm.com/imaging/special-report-b.php

Table of Contents Feed for the Digital Edition of Image Technology News - November 2008

Image Technology News - November 2008 Contents RSNA CT Systems Imaging An Image is Worth a Thousand Words Ultrasound Systems MBI Takes on FFDM Trouble in Multi-PACS Paradise When is Appropriateness Criteria Appropriate? RIS/PACS in a Web 2.0 World Digital Mammography Helps Center Continue its Commitment to the Best in Patient-Focused Breast Cancer Cardiovascular Imaging Systems PARCA Extends Expertise to World PACS Market

Image Technology News - November 2008

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