Effect of Severe Hypocellular Anemia on Image Quality in Equilibrium Radionuclide Angiocardiography

A 72-year-old female developed anasarca and suspected cardiac dysfunction post three cycles of ibrutinib + rituximab regimen as second-line treatment for refractory diffuse large B-cell lymphoma. Equilibrium radionuclide angiocardiography (ERNA) imaging was requested for the evaluation of ventricular function and to exclude treatment-induced cardiotoxicity. The images [Figure 1] were of poor quality, and the delineation of cardiac chambers was not possible. On review of other investigations, her hemoglobin level was found to be 6.5 g/dL and red blood cell (RBC) count was 1.9 million/μL on the day of imaging. Repeat ERNA imaging [Figure 2] of the same patient after two units of packed RBC transfusion resulting in a higher hemoglobin level of 8.5 g/dL and RBC count of 2.6 million/μL showed improvement in image quality with normal systolic ventricular function. Dynamic imaging (not shown here) revealed normal wall motion, and the size of the biventricular cavities was within normal limits.

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Figure 1 End-diastolic (a) and end-systolic (b) frames demonstrate suboptimal image quality with poor target-to-background ratio and increased technetium-99m uptake in the stomach (yellow arrows). Phase histogram (c) showed a relatively wider peak while the left ventricular volume curve (d) appeared flattened

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Figure 2 Improved quality of images in end-diastolic (a) and end-systolic (b) frames returned a normal left ventricular ejection fraction (LVEF) value of 56% with a narrow peak in the phase histogram (c) and normal U-shaped left-ventricular volume curve (d)

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Image quality in ERNA is vulnerable to compromise from numerous factors, including motion artifacts, obesity, large breast volume, intrathoracic tumors, and procedural variability linked to the use of intravenous cannula for injections, method of RBC labeling, or image-processing techniques.[123456] Among labeling methods, the in vivo technique, although yielding lower radiolabeling efficiency compared to in vitro methods, can achieve clinically acceptable imaging quality if proper injection timing protocols are strictly adhered to. The convenience of the simple kit-based in vivo method has rendered it a mainstay in routine clinical practice.[78] Drugs such as penicillin, propranolol, heparin, and prazosin, alongside other biological and chemical substances, can interfere with RBC labeling process and degrade imaging outcomes.[491011] Poor RBC labeling is immediately identifiable since free technetium-99m pertechnetate builds up in the thyroid gland and the stomach mucosa, as shown in Figure 1. With these images, we illustrate the impact of severe hypocellular anemia on ERNA imaging, a phenomenon that has not been previously reported in medical literature.

The mechanism of poor imaging in Figure 1 is explained by the low RBC count, which leads to a poor target-to-background ratio and thus produces low-contrast images, where the outlines of cardiac chambers cannot be delineated either manually or with the use of software-based automated processing, thus introducing errors in quantitative image parameters. Following partial correction of anemia, a marked improvement in imaging quality was observed, underscoring the critical dependence of radiolabeling process on adequate RBC counts.

Clinicians must recognize that a low RBC count presenting as severe anemia can degrade the diagnostic quality of ERNA scans. Prior correction of anemia is essential to ensure optimal imaging and accurate quantification of ventricular function.