ABSTRACT
Aim/Introduction: Pulmonary emboli (PE) have conventionally been reported in a binary fashion without quantification. Following development and phantom validation of a Pulmonary Parenchymal Burden (PPB) quantification method to measure the percentage of lung parenchyma affected by PE, we wanted to explore whether the %PPB is clinically pertinent, specifically whether it correlates with the development of long term sequelae and so may be helpful in outcome prediction and triaging patients to different management pathways. Material(s) and Method(s): : A retrospective single centre study carried out on patients scanned before the COVID pandemic. Patients with pre-existing cardiorespiratory disease were excluded. 40 patients who had PE and had undergone V/Q SPECT between January 2018- May 2020 with documented clinical follow up of >20 months were included. All patients had undergone simultaneous V/Q SPECT with 81mKr, 99mTc-MAA according to the departmental clinical protocol. Images were reconstructed according to a prevalidated V/Q quantification optimised protocol and PEs were quantified using a SPECT viewing platform with volumetric quantification. %PPB was calculated as the total parenchymal PE volume divided by the total lung ventilation volume. Clinical outcome was assessed using NHS trust electronic clinical documentation. Note was made of presence or absence of 2 parameters: persistent dyspnoea/impaired exercise tolerance (DIETT) with 3 months of anti coagulation and presence or absence of chronic thromboembolic pulmonary hypertension (CTEPH). Statistical analysis was performed by Graphpad prism 9.3.1 version for windows. Result(s): :21 females and 19 males with a mean age of 45.2(range 19-72years). There was a statistically significant difference in %PPB with the presence or absence of DIETT (mean%PPB:34.5%, standard deviation (SD):18.92 vs mean%PPB:10.81%, SD:14.03%;t-test p=0.001). There was a statistically significant difference in %PPB with the presence or absence of CTEPH (mean%PPB:51%, SD= 10.12 vs mean PPB = 20.76, SD: 17.4% ;t-test p=0.0002). Conclusion(s): In patients with known persistent PE, %PPB can discriminate long term sequelae of DIETT and CTEPH following PE. A quantitative %PPB tool may therefore be a useful addition to standard imaging to help triage patients into different clinical management groups.