Comparison of planar and SPECT perfusion lung scintigraphy in the diagnosis of pulmonary embolism

Abstract

Pulmonary embolism (PE) is a severe and potentially fatal disease and therefore needs to be diagnosed as early as possible. PE is caused when an embolus travels to the lungs, and gets lodged within the arteries in the lungs, resulting in lack of blood supply to the area supplied by that blocked artery [2]. A lung scintigraphy scan is performed to diagnose PE. There are two parts to a lung scintigraphy scan: ventilation and perfusion. A ventilation scan is performed to assess the air distribution within the lung, after inhalation of a radioactive aerosol. The particles are suspended in air and remain within the lung. The clearance is then used for diagnostic purposes. A perfusion scan is performed to assess the blood flow within the lung, after the intravenous administration of technetium-99m macroaggregated human albumin (99mTc-MAA). The micorembolisation of radiolabelled particles of trapped 99mTc-MAA within the pulmonary capillaries defines regional lung perfusion. Planar two-dimensional (2-D) scintigraphy scans have the following limitations: images result in high levels of image nose, image registration difficulties due to superimposition of structures and poor contrast. Single photon emission computed tomography (SPECT) provides three-dimensional (3-D) images, with more accurate data. Therefore, SPECT has been shown to be more sensitive and specific than planar (2-D) scintigraphy in the clinical diagnosis of PE and this has been supported by many studies, which determine an increase in sensitivity and specificity to detect PE with the use of SPECT imaging. SPECT ventilation/perfusion (V/Q) imaging is considered a quick and easy scan to perform. Bailey et al., (2010), state that SPECT V/Q images have reduced inter-observer variability and improved the detection of small perfusion defects. Bajc et al., (2009), stated that SPECT V/Q imaging is preferred over planar (2-D) studies as it allows a more accurate diagnosis of PE, even when other diseases such as chronic obstructive pulmonary disease (COPD) and pneumonia are present. However, many centres still find it difficult to make the transition from planar imaging to SPECT imaging, the reason being the need to implement a new imaging protocol. The purpose of this study was to compare the clinical utility and work load efficacy between planar perfusion lung scintigraphy and SPECT perfusion lung imaging in the implementation of a SPECT imaging protocol within a nuclear medicine department in Malta.