Bohdan Bybel

SPECT/CT Imaging : Clinical Utility of an Emerging Technology

Single-photon emission computed tomography (SPECT) has been a mainstay of nuclear medicine practice for several decades. More recently, combining the functional imaging available with SPECT and the anatomic imaging of computed tomography (CT) has gained more acceptance and proved useful in many clinical situations. Most vendors now offer integrated SPECT/CT systems that can perform both functions on one gantry and provide fused functional and anatomic data in a single imaging session. In addition to allowing anatomic localization of nuclear imaging findings, SPECT/CT also enables accurate and rapid attenuation correction of SPECT studies. These attributes have proved useful in many cardiac, general nuclear medicine, oncologic, and neurologic applications in which the SPECT results alone were inconclusive. Optimal clinical use of this rapidly emerging imaging modality requires an understanding of the fundamental principles of SPECT/CT, including quality control issues as well as potential pitfalls and limitations. The long-term clinical and economic effects of this technology have yet to be established.

Vertebral hemangiomas on FDG PET scan.

A fluorodeoxyglucose (FDG) positron emission tomographic (PET) scan performed to stage a nasopharyngeal carcinoma revealed hypometabolic regions in multiple thoracic vertebrae. These corresponded to multiple hemangiomas seen on magnetic resonance images (MRI). The FDG findings are similar to the reduced uptake typically seen with bone scintigraphy and helps to differentiate metastatic disease from the more benign hemangioma.

Arterial injection artifact on F-18 FDG positron emission tomographic scan

Radiotracer mistakenly injected into the arterial system rather than the venous system will cause image artifacts. Most commonly, a glove phenomenon appearance, previously described in bone scintigraphy, is noted. The authors observed this finding in the right forearm of a patient after intra-arterial fluorodeoxyglucose injection into the right antecubital fossa. This artifact may lead to difficulty with visual interpretation and cause inaccuracy with standard uptake value calculations.

Scintigraphic and radiographic appearance of osteomas in Gardner's syndrome.

Increased uptake in the maxilla and mandible on bone scanning is not unusual and is most commonly attributed to periodontal disease. However, sometimes atypical findings suggest other diagnoses. A 22-year-old woman with Gardners syndrome had a bone scan to investigate a soft tissue mass in the shoulder. Intense uptake in the maxilla and mandibles was demonstrated, which was related to osteomas, a common finding of this syndrome.

Machine learning identified an Alzheimer’s disease-related FDG-PET pattern which is also expressed in Lewy body dementia and Parkinson’s disease dementia

Utilizing the publicly available neuroimaging database enabled by Alzheimer’s disease Neuroimaging Initiative (ADNI; http://adni.loni.usc.edu/), we have compared the performance of automated classification algorithms that differentiate AD vs. normal subjects using Positron Emission Tomography (PET) with fluorodeoxyglucose (FDG). General linear model, scaled subprofile modeling and support vector machines were examined. Among the tested classification methods, support vector machine with Iterative Single Data Algorithm produced the best performance, i.e., sensitivity (0.84) × specificity (0.95), by 10-fold cross-validation. We have applied the same classification algorithm to four different datasets from ADNI, Health Science Centre (Winnipeg, Canada), Dong-A University Hospital (Busan, S. Korea) and Asan Medical Centre (Seoul, S. Korea). Our data analyses confirmed that the support vector machine with Iterative Single Data Algorithm showed the best performance in prediction of future development of AD from the prodromal stage (mild cognitive impairment), and that it was also sensitive to other types of dementia such as Parkinson’s Disease Dementia and Dementia with Lewy Bodies, and that perfusion imaging using single photon emission computed tomography may achieve a similar accuracy to that of FDG-PET.