Comparison of calculation algorithms between arithmetic mean of washout rate and total-count-based washout rate in single-photon emission computed tomography

Abstract

Abstract Background Myocardial washout rate (WR) analysis of radiopharmaceuticals is utilized in nuclear cardiology to evaluate the clinical pathophysiology of the heart. WR is defined as the ratio of the difference between the count in the early image and the time-decay-corrected delayed image divided by the former. The arithmetic mean of washout rate (AMWR) of each segment is a commonly used algorithm for calculating WR from a polar map in single-photon emission computed tomography (SPECT). However, in this algorithm, uneven radiotracer uptake among segments affects WR calculation. Therefore, we newly formulated a modified algorithm for calculating WR based on the total count (TCWR). Purpose To clarify the usefulness of TCWR by comparing the calculation algorithms between TCWR and AMWR. Methods The WR of iodine-123-β-methyl-p-iodophenylpentadecanoic acid (BMIPP) was calculated using TCWR and AMWR, and WR values using TCWR and AMWR were compared by disease. We focused on the patients with specific conditions that decreased BMIPP uptake in the early image — CD36 deficiency is a human loss-of-function genetic mutation model for BMIPP uptake, and old myocardial infarction (OMI) may present such a clinical phenotype. Also, patients with triglyceride deposit cardiomyovasculopathy (TGCV) were enrolled since a markedly decreased BMIPP WR (<10%) is one of the essential criteria for its diagnosis. Consecutive patients who underwent BMIPP scintigraphy were reviewed, and the analysis included patients without detectable cardiovascular diseases (normal) (n = 11), those with CD36 deficiency (n = 6), TGCV (n = 14), TGCV with OMI (n = 17), and non-TGCV with OMI (n = 10). Results WR values using TCWR and AMWR did not differ significantly in the following groups: normal, 27.4 ± 8.5 and 27.3 ± 8.5% (p = 0.97); CD36 deficiency, -3.2 ± 6.5 and -4.1 ± 7.4% (p = 0.81); TGCV, 2.4 ± 6.3 and 2.2 ± 6.3% (p = 0.93); and TGCV with OMI, -0.9 ± 7.6 and -3.7 ± 8.4% (p = 0.32). However, AMWR showed a lower WR than TCWR in non-TGCV with OMI (4.8 ± 8.7 and 18.9 ± 6.7%, p = 0.0008). Conclusions TCWR is suitable for calculating WR using SPECT polar maps even in cases with heterogeneous radiotracer uptake, such as OMIs. TCWR may be applied to measuring the WR of radiopharmaceuticals other than BMIPP in investigating the pathophysiology of heart diseases.Definition of calculation algorithms.Comparison of TCWR and AMWR.