Purpose: Among nuclear medicine examination, lung right to left shunt whole body scan is excellent for confirming right to left shunt and has the advantage of enabling quantitative analysis. In previous overseas studies, the ROI was set according to the body contour, but radiopharmaceuticals remaining at the injection site included in the ROI result in shunt rate errors during quantitative analysis. Additionally, since there isn’t measurement or correction for background radioactivity, errors may occur during quantitative analysis due to sources invisible to the naked eye around the scan room and contamination of radiopharmaceuticals around the gamma camera. The purpose of this study is to compare the differences in shunt rate according to the method of setting the ROI and compare the presence or absence of background radiation correction when analyzing a lung right to left shunt whole body scan. Materials and Methods: The study subjects were 31 people who examined lung right to left shunt scan from February 2023 to March 2024, with images acquired from four gamma cameras. The original data of the lung right to left shunt whole body scan and blank scan were set at four locations on the anterior and posterior of the body and eight locations on both lungs. WB ROI was set as a rectangle for Model I from cranial to knees, excluding the upper extremity. Model II was set as a rectangle from cranial to foot, excluding the upper extremity, and Model III included the entire body contour. A paired t test was performed to compare the difference in shunt rate before and after background radiation correction for each model. To compare the difference in shunt rate according to the ROI setting method, one way analysis of variance and post-hoc test (Scheffe) were performed between the models before and after background radiation correction. Results: This is the result of analyzing the difference in shunt rate according to with and without background radiation correction for Models I, II, and III. In Model I, the average and standard deviation before background radiation correction were 4.6±1.3%, and after correction, it decreased by about 17% to 3.9±1.3%. In Model II, the average and standard deviation before background radiation correction were 5.0±1.4%, and after correction, they decreased by about 18% to 4.2±1.4%. For Model III, the average and standard deviation before background radiation correction were 5.9±1.5%, and after correction, they decreased by about 20% to 4.9±1.4%. A paired t test on the shunt rate before and after correction of background radiation for each model showed a statistically significant difference (P<0.05). The difference in shunt rate according to the ROI setting method showed a statistically significant difference between Model I and Model III, and Model II and Model III for the shunt rate before background radiation correction (P<0.05), and for the shunt rate after correction between Model I and Model III showed a statistically significant difference (P<0.05). Conclusion: There was a statistically significant difference in all three models before and after correction for background count, and there was a significant difference between models depending on the method of setting the ROI. If the test takes into account accurate dose administration and patient posture, it appears that sufficient guidelines can be provided when performing a whole-body examination of right-left lung shunt. Setting the ROI as a rectangle from cranial to knees (Model I) is believed to be greatly helpful in diagnosing and differentiating right to left shunt by measuring and correcting background radioactivity