New method for measuring right-left shunt fraction by quantitative analysis using SPECT/CT images

We devised a quantitative method for measuring the right-left shunt fraction using SPECT/CT images.

In this study, 43 patients at our hospital underwent pulmonary perfusion scintigraphy with ^99mTc-macroaggregated albumin. The lung radioactivity dose was calculated via quantitative analysis, and the lung uptake proportion (%) of the total dose was calculated. The right-left shunt fraction was calculated by subtracting the lung uptake proportion from the total dose (100 %), and the results was evaluated by comparing the right-left shunt fraction measured using the quantitative method with the results obtained using whole-body planar imaging (W.B.).

In cases without a shunt, no significant difference in measurement results was observed between the two methods (p = 0.55). Conversely, when a shunt was present, the shunt fraction was 19.0 % ± 6.0 % for the W.B. method and 29.1 % ± 10.2 % for the quantitative method, with the difference being statistically significant (p < 0.05). Moreover, the quantitative method demonstrated an area under the receiver operating characteristic curve of 0.948 and an accuracy of 93.0 % when employing a threshold of 19 %-22 %.

When shunts were present, the quantitative method showed a significantly higher shunt fraction than the W.B.

However, an accuracy of >90 % could be obtained by setting the threshold range to 19 %-22 %, indicating that the quantitative method is useful for diagnosis.

Improving the accuracy of shunt fraction measurement using quantitative methods, it will be possible to assess the severity of right-to-left shunts and evaluate treatment outcomes. In addition, this method can be used to evaluate a right-left shunt even when it is difficult to obtain a whole-body image and is expected to be applied clinically.