Normal liver-to-heart transit time and shunt fraction after transplenic injection of 99MTC-pertechnetate in healthy cats

Portosystemic shunts (PSS) are rare vascular anomalies in cats. Transsplenic portal scintigraphy (TSPS) can aid in diagnosing PSS in cats. Although the actual performance of the scan remains the same between species, it is questionable whether the generally accepted transit time of seven seconds for small dogs can be applied to cats, thereby influencing shunt fraction (SF) calculation. In this study, normal mean transit time and SF were determined in a population of cats without PSS following two methods established in canine medicine. For both, the mean ± SD transit time was calculated as 6.75 ± 1.58 seconds and 7.40 ± 1.64 seconds respectively, without significant difference between both methods. The results confirmed the validity of the generally used transit time of seven seconds for SF calculation in cats. The average normal SF (± SD) for the cats in this study was 0.73 % (±0.74; range 0.11-2.48%).

198 Intrapulmonary shunt assessment in pulmonary arterial hypertension

Aims Pulmonary arterial hypertension (PAH) is a rare, progressive disease with a poor prognosis. It is characterized by the presence of mean pulmonary arterial pressure (mPAP) ≥25 mmHg along with a pulmonary arterial wedge pressure (PAWP) ≤15 mmHg and pulmonary vascular resistance (PVR) >3 Wood units at right heart catheterization, in the absence of other causes of pre-capillary PH such as PH due to lung diseases, chronic thromboembolic PH, or other rare diseases. Hypoxaemia is a frequent finding in patients with PAH and could be related to ventilation–perfusion mismatch, reduced diffusing capacity, decreased cardiac output, or the opening of intrapulmonary (IP) or intracardiac shunt. Purpose of the present study is to detect IP shunts in PAH patients and its determinants. Methods and results We retrospectively enrolled 29 PAH patients, collecting clinical parameters, haemodynamic and blood gas analysis at baseline and after specific therapies at follow-up. Shunt fraction was calculated by the formula (Cc—Ca)/(Cc—Cv) during oxygen supplementation (FiO2 100%). Intracardiac defects were excluded by echo contrast examination. As expected, after treatments our results showed a significant decrease of PAPm (−7.2 ± 11.6 mmHg) and a significant decrease of PVR (−2.1 ± 3.9 WU). However, it was reported a statistically significant decrease in Hb value (−1.2 ± 1.7 g/dl), in SpO2 (−2.1 ± 3.8%) and in the alveolar–arterial oxygen gradient (a-ADO2) (+54.5 ± 113.1 mmHg). 6MWT and NYHA decreased at follow-up but not statistically significance was detected. IP shunt increase was detected at follow-up after specific treatments (delta Shunt +6.9 ± 6.5%). At multivariate analysis delta PVR remains the only independent determinants of delta Shunts with a significative increment of shunts when PVR are reduced by more than three WU. Conclusions Specific PAH treatments determine a decrease of PVR, but a reverse correlation with IP shunt was noticed. Increase of IP shunt could be not a favourable clinical feature. In fact high IP shunt fraction could determine hypoxaemia and the need of a chronic oxygen supply therapy. Although a not statistically significant decrease of 6MWT and NYHA was found, it is reasonable that a long-standing hypoxaemia could reduce the aerobic function capacity. Ours results unfortunately were deeply influenced by the loss of a great part of elective patients during the pandemic, with the most part of data coming from patients needing hospitalization. This could explain why the delta shunt fraction is higher than expected.

Lung shunt fraction calculation using 99mTc-MAA SPECT/CT imaging for 90Y microsphere selective internal radiation therapy of liver tumors

Background 99mTc-macroaggregated albumin (99mTc-MAA) scintigraphy is utilized in treatment planning for Yttrium-90 (90Y) Selective Internal Radiation Therapy (SIRT) of liver tumors to evaluate hepatopulmonary shunting by calculating the lung shunt fraction (LSF). The purpose of this study was to evaluate if LSF calculation using SPECT/CT instead of planar gamma camera imaging is more accurate and if this can potentially lead to more effective treatment planning of hepatic lesions while avoiding excessive pulmonary irradiation. Results LSF calculation was obtained using two different methodologies in 85 cases from consecutive patients intended to receive 90Y SIRT. The first method was based on planar gamma camera imaging in the anterior and posterior views with geometric mean calculation of the LSF from regions of interest of the liver and lungs. The second method was based on segmentation of the liver and lungs from SPECT/CT images of the thorax and abdomen. The differences in planar imaging versus SPECT/CT derived LSF values along with the estimated absorbed lung mean dose (LMD) were evaluated. The LSF values were higher in planar imaging versus SPECT/CT in 81/85 cases, with a mean value of 8.5% vs. 4.6% respectively; the difference was statistically significant using a paired t-test (alpha = 0.05). In those patients who received SIRT, the estimated absorbed LMD calculated with planar imaging was significantly higher than with SPECT/CT (t-test, P < 0.005). Repeated phantom experiments using an anthropomorphic torso phantom with variable 99mTc activity concentrations for the liver and lungs were performed with the standard patient protocol, demonstrated improved accuracy of the LSF calculation based on SPECT/CT than planar imaging (mean overestimated value of 6% vs. 26%). Conclusions This study demonstrates that LSF calculation using planar imaging can be significantly overestimated while calculation using SPECT/CT imaging and appropriate segmentation tools can be more accurate. Minimizing the errors in obtaining the LSF can lead to more effective 90Y SIRT treatment planning for hepatic tumors while ensuring the lung dose will not exceed the standard acceptable safety thresholds.

Lung Shunt Fraction Calculation Using 99mTc-MAA SPECT/CT Imaging for 90Y Microsphere Selective Internal Radiation Therapy of Liver Tumors

Background99m Tc-macroaggregated albumin ( 99m Tc-MAA) scintigraphy is utilized in treatment planning for Yttrium-90 ( 90 Y) Selective Internal Radiation Therapy (SIRT) of liver tumors to evaluate hepatopulmonary shunting by calculating the lung shunt fraction (LSF). The purpose of this study was to evaluate if LSF calculation using SPECT/CT instead of planar gamma camera imaging is more accurate and if this can potentially lead to more effective treatment planning while avoiding excessive pulmonary irradiation. ResultsLSF calculation was obtained using two different methodologies in 85 cases from consecutive patients intended to receive 90Y SIRT. The first method was based on planar gamma camera imaging in the anterior and posterior views with geometric mean calculation of the LSF from regions of interest of the liver and lungs. The second method was based on segmentation of the liver and lungs from SPECT/CT images of the thorax and abdomen. The differences in planar imaging versus SPECT/CT derived LSF values along with the estimated absorbed lung mean dose (LMD) were evaluated. The LSF values were higher in planar imaging versus SPECT/CT in 81/85 cases, with a mean value of 8.5% vs. 4.6% respectively; the difference was statistically significant using a paired t-test (alpha = 0.05). In those patients who received SIRT, the estimated absorbed LMD calculated with planar imaging was significantly higher than with SPECT/CT (t-test, P<0.005). Repeated phantom experiments using an anthropomorphic torso phantom with variable 99m- Tc activity concentrations for the liver and lungs were performed with the standard patient protocol, demonstrated improved accuracy of the LSF calculation based on SPECT/CT than planar imaging (mean overestimated value of 6% vs. 26%).ConclusionsThis study demonstrates that LSF calculation using planar imaging can be significantly overestimated while calculation using SPECT/CT imaging and appropriate segmentation tools can be more accurate. A lower calculated LSF could allow for a higher dose prescription which can potentially lead to more effective treatments for hepatic tumors.