Molecular Imaging Insight - September 2007 - (Page 7) B y L I S A F R AT T Read more on Siemens SPECT/CT ADDITIONAL RESOURCES: Molecular Imaging’s Next Horizon: Whole-Body SPECT/CT SPECT is far from the new kid on the molecular imaging block, but except for cardiac imaging, this nuclear medicine modality has not yet realized routine clinical utility as a replacement for conventional planar scanning. Recently developed reconstruction protocols and hybrid SPECT/CT scanners, however, could breathe new life into SPECT by opening the door to clinically feasible whole-body SPECT/CT. The University of Texas M.D. Anderson Cancer Center in Houston, is at the cutting edge of SPECT/CT research. This month, M.D. Anderson experts, Chair of Nuclear Medicine Homer Macapinlac, MD, Associate Professor Osama Mawlawi, PhD, and Senior Medical Physicist Bill Erwin from the department of Imaging Physics discuss the clinical path to and potential of whole-body SPECT/CT. The University of Texas M.D. Anderson Cancer Center Department of Imaging Physics Q Has nuclear medicine optimized SPECT/CT? MACAPINLAC: No, definitely not. If one uses PET/CT as a model, one can see the potential of SPECT/ CT. The combination of CT and PET data produces a more complete image set, providing the physician with the anatomical and functional views necessary to render a solid diagnosis. The goal of SPECT/CT is to utilize a system capable of multislice CT scanning to improve the interpretation of SPECT studies. Standard SPECT studies can lack specificity; the addition of CT seems to add data needed to boost specificity. Q Q What factors limit the utility of SPECT/CT? MACAPINLAC: Two challenges confront SPECT/ CT and limit its value in routine clinical use. For starters, the Centers for Medicare and Medicaid Services (CMS) has not approved reimbursement for the CT part of the study, which presents an economic challenge. On top of that, the time to acquire a SPECT study reduces its clinical value. It can take from 20 to 45 minutes to acquire a single-bed SPECT study, making multi-bed scans not tolerable for many patients. Consequently, SPECT/CT studies are typically limited to a single anatomical area such as the chest. In some cases, a second or third study of the abdomen or pelvis is performed later. Q How does whole-body SPECT/CT differ from localized studies? MAWLAWI: Whole-body SPECT/CT requires three to five bed positions to cover the entire body. Traditional step-and-shoot acquisition completes an image at one angle and then pauses acquisition counting before moving to the next position to acquire data. As a result, it might take anywhere from 60 minutes to two hours to acquire a whole-body SPECT/CT. Can you describe the whole-body SPECT/CT research program at M.D. Anderson? MACAPINLAC: We’d like to determine if we can complete a whole-body SPECT/CT study using multiple bed positions in a clinical environment. Our physics team is trying to determine if it can link together multiple bed studies to reconstruct the scans and transform SPECT/CT into a routine acquisition protocol. Our goal is simple; we want to mimic PET/CT with SPECT/CT. That is, we’d like to acquire the cross-sectional images in a single pass to make the entire whole body study tolerable for patients, which requires an acquisition time in the 25 to 30 minute range. MAWLAWI: Our vision is to transfer planar bone imaging to SPECT/CT. Currently, 40 percent of our patient load is bone imaging, which primarily consists of planar imaging. SPECT/CT can deliver several advantages including improved sensitivity and specificity. The hitch is completing the study in a time slot comparable to planar images, or about 25 minutes. The 25-minute goal is attainable with a six to eight minute acquisition time per bed position. Our team researched the potential by acquiring SPECT scans of different durations including four, six, eight and 10 minutes and asking multiple physicians to compare the image quality of the scans. We imaged 40 patients on Siemens Medical Solutions e.Cam SPECT and TruePoint Symbia SPECT/CT systems. The consensus seems to be that seven minutes per bed position will produce a scan with optimal image quality in the appropriate length of time. Homer Macapinlac, MD Chair of Nuclear Medicine Osama Mawlawi, PhD Associate Professor Bill Erwin Senior Medical Physicist Q Are other advances facilitating this approach? MACAPINLAC: New SPECT systems reduce the acquisition time, which makes it feasible to acquire the CT study. In addition, our physics research team MolecularImaging.net Molecular Imaging Insight 7 http://www.medical.siemens.com/siemens/en_INT/gg_nm_FBAs/files/multimedia/symbia/home.htm http://MolecularImaging.net
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