image coregistration of the abdomen or the thorax. In the future, however, this technology may play an important role in allowing correction of misregistration due to patient motion or breathing artifacts, which may also arise from integrated SPECT/CT. Besides anatomic referencing, the added value of CT coregistration is also based on the attenuation correction capabilities of CT. Cardiac imaging poses a particular problem in attenuation correction because of respiratory and cardiac motion in

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... e thorax. Individual CT-based attenuation correction of brain studies using SPECT may also lead to improved image quality and more accurate data evaluation. Furthermore, radionuclide treatment planning using attenuation correction of imaging data and assessment of organ or target volumes derived from simultaneously performed CT may be more accurate and potentially allows safe and effective therapy. A similar discussion on the need for integrated hybrid scanners has already been raised after the introduction of hybrid PET/CT systems to clinical medicine. As indicated for PET/CT, image fusion is faster, more reliable, and more accurate using an integrated scanner than using separately performed imaging modalities (4). In addition to these technical issues, hybrid image acquisition of both modalities in a single clinical visit (1stop) offers apparent logistic advantages and is obviously more comfortable for the patient. PET/CT scanners represent the imaging modality with the most rapid growth worldwide and play an increasing role in routine patient care, especially in oncologic applications. Yet, there is a lack of evidence that the same holds true for hybrid SPECT/CT systems. CT coregistration, however, has been recognized to result in higher specificity and sensitivity of scintigraphic imaging and to markedly reduce the number of indeterminate findings. The superiority of SPECT/CT over planar scintigrams or SPECT has been clearly demonstrated for imaging skeletal diseases, parathyroid adenomas, and neuroendocrine cancers and for mapping sentinel lymph nodes in various cancers (1). Studies demonstrating superiority in other clinical applications are lacking; however, pilot studies encourage the use of SPECT/CT in cardiac and neurologic imaging. Regarding the growing number of studies demonstrating an added value of hybrid SPECT/CT over separately performed imaging modalities (1), it appears likely that this promising technique will gain an important role in clinical routine practice. The broad spectrum of existing SPECT tracers and their widespread availability suggests SPECT/CT as a complementary imaging modality to PET/CT procedures. In summary, we agree with Knoll and colleagues that advanced software-based coregistration procedures do have a legitimate relevance for image fusion, particularly if no hybrid technology is available. However, we believe that hardware-based hybrid acquisition offers several apparent advantages regarding accuracy, reliability, logistics, and comfort for the patient, which cannot be easily outweighed by software-based image fusion approaches. F FDG PET 18 Tumor Metabolic Phenotypes on http://jnm.snmjournals.org/content/50/6/1010 This article and updated information are available at: http://jnm.snmjournals.org/site/subscriptions/online.xhtml Information about subscriptions to JNM can be found at: http://jnm.snmjournals.org/site/misc/permission.xhtml