Dextrocardia, although a rare cardiac abnormality, carries the same risk for cardiac events as other people. SPECT Myocardial perfusion imaging is a potentially helpful diagnostic tool in patients with dextrocardia. Due to swapping of lateral and septal walls on SPECT slices, although visual analysis is possible, quantitation is substantially limited. Here, we introduce a simple practical method to make quantitative analysis feasible and accurate. Case reportA 50-year-old male patient with known history of dextrocardia with situs inversus presented for cardiac evaluation. A dipyridamole gated SPECT myocardial perfusion imaging (G-SPECT MPI) was performed with same-day stress-rest protocol. As we knew that the patient had dextrocardia, we modified the acquisition protocol. The patient was positioned supine and imaging was acquired from left anterior oblique (LAO) to right posterior oblique (RPO) views. Other acquisition parameters were as routine (e.g., orientation: feet-in, number of projections: 32 and number of frames for gating: 8). First, Images were reconstructed and processed with routine protocol, then, with modified protocol (Figure 1). In modified protocol, we changed orientation of images from "Feet-in" to "Head-in". Analysis for gating was also performed with both protocols (Figure 2). DiscussionDextrocardia is a rare congenital abnormality of the heart with incidence of less than 0.01% [1]. The heart is positioned on the right side and the axis of left ventricle (LV) is directed toward the left side. In dextrocardia with situs inversus or mirror-image dextrocardia, the LV is positioned posterior and left to the right ventricle (RV). The position of other organs including visceral organs (e.g., liver, stomach and etc.) is also reversed [1].It has been shown that the risk of coronary artery disease in patients with dextrocardia is the same as that in general population [2,3]. SPECT MPI is a potentially helpful modality for cardiac assessment in these patients, although some modifications in acquisition protocol are required. Otherwise, perfusion abnormalities in LV myocardium will occur. The acquisition arc ranges from LAO to RPO. When images are reconstructed as routine, tomographic slices are visualized mirrored in a way that interventricular septum and lateral free wall are swapped and RV is located on the right side of image. Quantitative analysis usually reveals perfusion defect and motion abnormality in lateral segments of polar map, because septal wall of patients are compared to lateral wall in normal database. Therefore, quantitative analysis is not helpful in these situations and images are interpreted solely visually.
Objective:Evaluating the effects of heart cavity volume, presence and absence of perfusion defect, gender and type of study (stress and rest) on the difference of systolic parameters of myocardial perfusion scan in 16 and 8 framing gated SPECT imaging.Methods:Cardiac gated SPECT in both 16 and 8 framing simultaneously and both stress and rest phases at one-day protocol was performed for 50 patients. Data have been reconstructed by filter back projection (FBP) method and left ventricular (LV) systolic parameters were calculated by using QGS software. The effect of some factors such as LV cavity volume, presence and absence of perfusion defect, gender and type of study on data difference between 8 and 16 frames were evaluated.Results:The differences in ejection fraction (EF), end-diastolic volume (EDV) and end-systolic volume (ESV) in both stress and rest were statistically significant. Difference in both framing was more in stress for EF and ESV, and was more in rest for EDV. Study type had a significant effect on differences in systolic parameters while gender had a significant effect on differences in EF and ESV in rest between both framings.Conclusion:In conclusion, results of this study revealed that difference of both 16 and 8 frames data in systolic phase were statistically significant and it seems that because of better efficiency of 16 frames, it cannot be replaced by 8 frames. Further well-designed studies are required to verify these findings.
Dual-energy X-ray absorptiometry is currently the standard and validated tool for measurement of bone mineral density and for the evaluation of osteoporosis. Current densitometry scanners based on dual-energy X-ray absorptiometry method produce two X-ray beams with different energies to differentiate the overlapped soft tissue and bony structures, by creating two different attenuation profiles. Procedural guidelines are available to technicians and physicians to guarantee the best practice, including consistent positioning during scanning and standard reporting. However, similar to other imaging modalities, dual-energy X-ray absorptiometry may be influenced by technical errors, and thus, imaging artifacts may arise and accuracy and precision of the results may be influenced. This issue may, in turn, affect the final result and interpretation. Hence, the article is arranged with the intention of presenting some less common and rare technical and patient-related sources of error and resultant artifacts, from poor patient preparation to acquisition and data processing. Where appropriate, the corresponding tables of densitometric results (bone mineral density) and statistical parameters ( T - and Z -scores) are provided.
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