Abstract
<h3>Summary</h3> Ventilation/perfusion single photon emission computed tomography (V/P SPECT), is the scintigraphic technique of choice for the diagnosis of pulmonary embolism (PE) and other conditions that affect lung function. In the study of ventilation, hydrophobic radioaerosol Technegas shows advantages over radiolabelled liquid aerosols because of its more even distribution and better peripheral penetration; this is very important in patients with COPD. Macro-aggregated human albumin is the imaging agent for perfusion scintigraphy. V/P SPECT is recommended as a one-day protocol and the whole study is conducted in 20 minutes under a gamma camera. An optimal combination of nuclide activities for ventilation and perfusion, general purpose collimators and a 64×64 imaging matrix yields an adequate sensitivity and ensures that radiation doses are kept very low. It is important that the patient remains in an unchanged supine position to allow reconstructed images of matching ventilation and perfusion slices in all projections as well as in rotating volume images. Probabilistic interpretation applied earlier for planar technique is replaced by a holistic interpretation strategy. This has resulted in a decrease in the number of nondiagnostic findings to less than 3%. To reduce costs and radiation exposure, pre-imaging assessment of clinical probability is recommended. PE is diagnosed when there is more than one subsegment showing a ventilation/perfusion mismatch conforming to an anatomic vascular lung unit. Apart from PE, other pathologies should be identified and reported, <i>e.g</i>. COPD, heart failure and pneumonia. Comparison of V/P SPECT with multidetector CT (MDCT) showed higher sensitivity for V/P SPECT, similar specificity and a similar number of nondiagnostic findings. The advantage of V/P SPECT is a 25-times lower absorbed radiation dose to the female breast and its applicability to all patients. The advantage of MDCT is its wider availability. Hybrid SPECT/CT imaging is a novel technique primarily developed to improve sensitivity and specificity of oncological diseases and it is not recommended as the primary tool for PE diagnosis in all patients with suspected PE. The application of SPECT/CT may be relevant in the case of COPD patients where small tumours may be identified as part of the diagnosis; in addition, it may help in the classification of COPD degree. <h3>Aims</h3> To increase awareness of the importance of optimal V/P SPECT and familiarity with the procedure. To explain the value of the new holistic, as opposed to probabilistic, interpretation in the diagnosis of PE. To show how the quantification of ventilation/perfusion defects can be used to define patient-specific treatments. To understand the role of V/P SPECT scintigraphy in other cardiopulmonary diseases, in addition to PE. To outline the pros and cons of angio-CT and V/P SPECT in the diagnosis of PE. To introduce the role of V/P SPECT and low-dose CT hybrid system in patients with suspected PE.
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