Objective: To review new incidental findings detected on low-resolution CT attenuation correction (CTAC) images acquired during single-photon emission CT (SPECT-CT) myocardial perfusion imaging (MPI) and to determine whether the CTAC images had diagnostic value and warrant reporting. Methods: A multicentre study was performed in four UK nuclear medicine departments. CTAC images acquired as part of MPI performed using SPECT were evaluated to identify incidental findings. New findings considered to be clinically significant were evaluated further. Positive predictive value (PPV) was determined at the time of definitive diagnosis. Results: Of 1819 patients studied, 497 (27.3%) had a positive CTAC finding. 51 (2.8%) patients had findings that were clinically significant at the time of the CTAC report and had not been previously diagnosed. Only four (0.2%) of these were potentially detrimental to patient outcome. Conclusion: One centre had a PPV of 0%, and the study suggests that these CTAC images should not be reported. Two centres with more modern equipment had low PPVs of 0% and 6%, respectively, and further research is suggested prior to drawing a conclusion. The centre with best quality CT had a PPV of 67%, and the study suggests that CTAC images from this equipment should be reported. Advances in knowledge:This study is unique compared with previous studies that have reported only the potential to identify incidental findings on low-resolution CT images. This study both identifies and evaluates new clinically significant incidental findings, and it demonstrates that the benefit of reporting the CTAC images depends on the type of equipment used.Myocardial perfusion imaging (MPI) performed using singlephoton emission CT (SPECT) is often subject to artefacts owing to the scatter and absorption of photons prior to detection. These artefacts can mimic myocardial perfusion defects leading to false-positive findings. It has been demonstrated that CT attenuation correction (CTAC) can compensate for these errors in SPECT MPI, resulting in image quality improvement and more accurate diagnosis. 1,2 The lowresolution/low-dose CT scan is performed through the area of the chest, which is aligned with the SPECT scan of the heart, so only a limited CT scan of the thorax is acquired. CT images are essentially a by-product of the attenuation correction (AC) process, the CT acquisition being primarily for AC purposes.Acquisition using a low tube current (mA) and large slice thickness results in images that have low signal-tonoise ratio, poor spatial resolution and an increased potential for partial volume artefacts compared with those of diagnostic CT studies. Motion artefacts may also be evident, as patients are not required to hold their breath during the CT acquisition. The resulting images are adequate for the purpose for which they have been acquired but are often not considered to be of diagnostic quality. The latest guidelines from the British Nuclear Cardiology Society suggest that if the CTAC images are of diagnostic qua...

CE credit: For CE credit, you can access the test for this article, as well as additional JNMT CE tests, online at https://www.snmmilearningcenter.org. Complete the test online no later than September 2019. Your online test will be scored immediately. You may make 3 attempts to pass the test and must answer 80% of the questions correctly to receive 1.0 CEH (Continuing Education Hour) credit. SNMMI members will have their CEH credit added to their VOICE transcript automatically; nonmembers will be able to print out a CE certificate upon successfully completing the test. The online test is free to SNMMI members; nonmembers must pay $15.00 by credit card when logging onto the website to take the test.Incidental findings are common in medical imaging. There is a particularly high prevalence of incidental findings within the thorax, the most frequent being pulmonary nodules. Although pulmonary nodules have the potential to be malignant, most are benign, resulting in a high number of false-positive findings. Low-resolution CT images produced for attenuation correction of SPECT images are essentially a by-product of the imaging process. The high number of false-positive incidental findings detected on these attenuation-correction images causes a reporting dilemma. Early detection of cancer can be beneficial, but falsepositive findings and overdiagnosis can be detrimental to the patient. Attenuation-correction CT images are not of diagnostic quality, and further diagnostic tests are usually necessary for a definitive diagnosis to be reached. Given the high number of falsepositive findings, the psychologic effect on the patient should be considered. This review recommends caution when the findings on attenuation-correction CT images are routinely reported. Medi cal imaging uses a range of modalities that yield both anatomic and functional information (1). Visual correlation of images acquired using separate modalities can provide more information than images from a single modality alone, though there is an inevitable risk of misregistration between images that have been acquired during different imaging sessions. The development of hybrid imaging has led to the integration of two modalities in one machine, allowing coregistration of images that have been acquired in a single session (1,2). This allows direct correlation of anatomic and functional information, increasing sensitivity and specificity while adding clarity to indeterminate cases (3). SPECT/CT offers an excellent example of hybrid imaging, combining the functional ability of SPECT with the anatomic ability of CT.The strength of SPECT lies in gaining pathophysiologic detail in a minimally invasive way (4). Pathologic processes can be identified by uptake of radiopharmaceuticals, but the precise location is often difficult to ascertain because of low image resolution and a lack of anatomic landmarks. Moreover, uptake on some scans is often nonspecific, revealing abnormalities but not their specific cause. CT can provide a useful means of localization, also enabl...

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Incidental findings on low-dose CT images obtained during hybrid imaging are an increasing phenomenon as CT technology advances. Understanding the diagnostic value of incidental findings along with the technical limitations is important when reporting image results and recommending follow-up, which may result in an additional radiation dose from further diagnostic imaging and an increase in patient anxiety. This study assessed lesions incidentally detected on CT images acquired for attenuation correction on two SPECT/CT systems. Methods: An anthropomorphic chest phantom containing simulated lesions of varying size and density was imaged on an Infinia Hawkeye 4 and a Symbia T6 using the low-dose CT settings applied for attenuation correction acquisitions in myocardial perfusion imaging. Twenty-two interpreters assessed 46 images from each SPECT/CT system (15 normal images and 31 abnormal images; 41 lesions). Data were evaluated using a jackknife alternative free-response receiver-operatingcharacteristic analysis (JAFROC). Results: JAFROC analysis showed a significant difference (P , 0.0001) in lesion detection, with the figures of merit being 0.599 (95% confidence interval, 0.568, 0.631) and 0.810 (95% confidence interval, 0.781, 0.839) for the Infinia Hawkeye 4 and Symbia T6, respectively. Lesion detection on the Infinia Hawkeye 4 was generally limited to larger, higher-density lesions. The Symbia T6 allowed improved detection rates for midsized lesions and some lower-density lesions. However, interpreters struggled to detect small (5 mm) lesions on both image sets, irrespective of density. Conclusion: Lesion detection is more reliable on low-dose CT images from the Symbia T6 than from the Infinia Hawkeye 4. This phantom-based study gives an indication of potential lesion detection in the clinical context as shown by two commonly used SPECT/CT systems, which may assist the clinician in determining whether further diagnostic imaging is justified.

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