Molecular Imaging Insight - September 2007 - (Page 8) ADDITIONAL RESOURCES: View SPECT/CT clinical images Q Does the change in acquisition mode require a different approach to reconstruction? ERWIN: We looked at different iterations and subsets. Our reconstructions are full 3D iterative and take into account attenuation, scatter and system resolution. In this case, we opted for a reconstruction with eight iterations and 15 subsets with 8 mm Gaussian post-filtering. The reconstruction parameters can be further optimized, once an acquisition time is settled upon. Q A research team at M.D. Anderson is working to develop whole-body SPECT combined with CT to increase specificity and reduce overall scan time to less than 25 minutes. is working with Siemens to develop software to help improve the reconstruction process. Oncoflash 3D ordered-subset expectation-maximization (OSEM) iterative reconstruction software is an important development. First, reconstruction times are greatly reduced with Oncoflash [approximately four times faster than current options], allowing an entire whole-body SPECT scan to be reconstructed both with and without attenuation correction, as is done for PET, in under 10 minutes. Second, Oncoflash improves the reconstruction of slices along the top and bottom of the field-of-view for each bed position, which are known to be problematic for 3D reconstruction algorithms. This will improve the quality of the whole-body SPECT dataset when it is formed by combining the individual bed position reconstructions [so-called “stitching” operation]. MAWLAWI: Most new scanners can operate in the conventional step-and-shoot mode or in continuous acquisition mode. To complete the scan in a reasonable amount of time, the camera must operate in continuous acquisition mode, to eliminate the dead time between views that would occur in step-and-shoot mode and retain all counts, which is vital to maintain image quality when reducing acquisition time. Can you describe how this might impact patient care? MACAPINLAC: The potential is very intriguing. Whole-body SPECT/CT could improve the way we interpret bone scans. The current protocol is intense and time-consuming. If we see a suspicious finding, we order a SPECT scan and plain film. If those studies are negative, the next step is a CT or MRI. Whole-body SPECT/CT streamlines the protocol, limiting the studies to a plain film and SPECT/CT. With SPECT/CT, the physician can determine if a finding is benign or malignant in a single pass. In addition, it appears that the correlative images provide better specificity than conventional SPECT. (Large clinical trials demonstrating the improved specificity of SPECT/CT aren’t yet available.) The approach could better inform physicians and provide them with data needed to refine treatment for individual patients. For example, if a patient is scheduled for a mastectomy, the whole-body SPECT/CT could inform the surgeon and oncology team if the disease metastasized to the bone prior to surgery. MAWLAWI: Ultimately, whole-body SPECT/CT offers a means to increase physician confidence. They will have a clearer understanding of the extent of disease. Q It sounds like whole-body SPECT/CT could broaden the role of SPECT in oncology. MACAPINLAC: Absolutely. The promise of SPECT/CT exists not only on the diagnostic side, but also on the therapeutic side. Whole-body SPECT/CT could be used to quantify the distribution of an internal radionuclide therapy treatment dose, which represents a significant improvement over the conventional methods that rely on planar images and “guesstimates.” Q Where do you see SPECT/CT headed in the next few years? MACAPINLAC: Right now, whole-body SPECT/CT is not quite ready for prime time. I believe we will see multiple factors converge over the next few years to bring these scanners into routine clinical use. Medicare approval, welldesigned reconstruction software and properly developed and researched protocols can move SPECT/CT into the clinical environment. 8 Molecular Imaging Insight September 2007 http://www.medical.siemens.com/siemens/en_INT/gg_nm_FBAs/files/multimedia/symbia/images/index.htm
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