ABSTRACT
Background: Smoothing in 99mTc myocardial perfusion single-photon emission computed tomography (SPECT) often increases myocardial artifacts due to subdiaphragmatic activity near the heart. To reduce these artifacts, we developed a new process flow, masking on unsmoothed images (MUS), that includes the extraction of the myocardium by masking before smoothing. Methods: This study evaluated the relationships between matrix sizes and distances to the subdiaphragmatic activity using the MUS method compared to conventional methods using a combination of image reconstruction methods (filtered back-projection [FBP] and ordered subset expectation maximization [OSEM]) with or without corrections (attenuation [AC], scatter [SC], and resolution recovery [RR]) using a myocardial phantom. The results were compared for two matrix sizes (pixel sizes) (128×128 [3.3 mm] and 64×64 [6.6 mm]); four subdiaphragmatic activity distances (5, 10, 15, and 20 mm); and three reconstruction methods (FBP without correction; OSEM with RR; and OSEM with AC, SC, and RR). Results: In the conventional method, increasing distance resulted in interference with myocardial perfusion SPECT evaluation however, the artifacts were less apparent when the MUS method was applied. The images converted to 64×64 did not show the same effect as the 128×128 images, even when RR was used. The MUS method was useful for acquisition at 128×128, along with the use of RR in the reconstruction process. Conclusion: MUS mitigated the effects of subdiaphragmatic activity on myocardial perfusion SPECT, particularly combined with 128×128 acquisitions and iterative reconstruction with RR.
ABSTRACT
BACKGROUND: Reduced exercise capacity may be related to decreased redistribution of blood flow from the non-exercising tissues to the exercising skeletal muscle in patients with mild chronic heart failure (CHF). METHODS AND RESULTS: In the present study 14 patients with mild CHF and 10 healthy subjects (N) underwent symptom-limited multistage-ergometer exercise, during which forearm vascular resistance (FVR), cardiac index (CI), systemic vascular resistance index (SVRI), and oxygen uptake (VO(2)) were measured non-invasively using the plethysmograph, impedance, and respiratory gas analysis methods, respectively. The VO(2) and CI at peak exercise were lower (p<0.01 each), and SVRI and FVR at both rest and peak exercise were higher in the CHF group than in N. However, both the percent increase in FVR and percent decrease in SVRI from the resting state to peak exercise were lower in CHF than N, and both of them correlated with not only peak VO(2), but also the corresponding resting value of FVR and SVRI (p<0.01 each). CONCLUSIONS: Redistribution of blood flow from the non-exercising tissues to the working skeletal muscles, which may participate in exercise capacity, can be blunted in CHF. The decreased vasoconstrictive response in the non-exercising tissues is intimately related to the increased resting vascular tone in CHF.
