Relationship between 99mTc-MAA Planar Image Accumulation Distribution in Pulmonary Hypertension and Indices Obtained by Right Heart Catheterization

Introduction: Pulmonary blood flow scintigraphy is useful to diagnose pulmonary hypertension because the distribution of ^99mTc-MAA in the lungs is proportional to pulmonary blood flow. Pulmonary blood flow distribution is affected by gravity, and the body position upon injection determines the distribution of ^99mTc-MAA. If injections are performed in the sitting position, in the normal lungs, the majority is distributed in the lower lungs. Conversely, in patients with pulmonary hypertension, the vessels on the basolateral side of the lungs are more prone to stenosis because of the pressure load caused by gravity, and pulmonary blood flow is believed to increase in the upper lungs. Additionally, pulmonary hypertension is diagnosed if the mean pulmonary artery pressure (mPAP) is ≥25 mmHg on right heart catheterization. However, right heart catheterization is highly invasive and is expected to be replaced by minimally invasive pulmonary blood flow scintigraphy. In this study, we investigated the relationship between the distribution of accumulation of ⁹⁹mTc-MAA scintigraphy planar images and indices obtained from right heart catheterization.

Methods: In this study, 35 patients with pulmonary hypertension who underwent ⁹⁹mTc-MAA testing and right heart catheterization at Nagoya University Hospital between April 2018 and April 2019 were included. First, the lungs on planar images were trisected from the apex to the base of the lungs into upper, middle, and lower lung fields, and regions of interest were established in each to obtain counts. Subsequently, the left-right average of the counts in the upper, middle, and lower lung fields was calculated. Finally, from the left and right averages, the percentages of the counts in the upper, middle, and lower lung fields to the total counts in all lung fields were calculated. The correlation between these values and three indices, mPAP, right atrium pressure (RAP), and pulmonary artery wedge pressure (PAWP), obtained from right heart catheterization was determined.

Results: The percentage of counts in the upper lungs showed a significant positive correlation with the value of PAWP, whereas the percentage of counts in the lower lungs showed a significant negative correlation with the value of PAWP. No significant correlation was found between indices, excluding PAWP and distribution of accumulation.

Conclusions: Higher PAWP increases the percentage of accumulation in the upper lung fields, and lower PAWP increases the percentage of accumulation in the lower lung fields.