ulmonary embolism (PE) represents a prevalent acute cardiovascular condition that has considerable morbidity and mortality and requires prompt diagnosis and treatment (1). Since 2007, multidetector CT pulmonary angiography has been the standard technique used to detect PE (2), achieving sensitivity and specificity (3-5) higher than 90% with state-of-the-art equipment (6). A missed PE carries a high potential risk for a future venous thromboembolism. On the other hand, false-positive results and subsequent anticoagulation treatment can result in complications (7). The potential for overdiagnosis of PE is as harmful as underdiagnosis (8).Iodine maps depict abnormalities that correspond to loss of blood flow caused by an acute (or chronic) PE (9-12). Iodine maps improve sensitivity in the detection of emboli, especially small emboli at a subsegmental level or in more distal vessels (13,14) and support prognosis determination and monitoring of anticoagulation therapy effectiveness (15).The most common technique used to generate these maps is dual-energy CT (16,17). However, this requires dedicated hardware. On the other hand, subtraction CT requires motion correction software but no additional hardware, making it easier to adopt and less costly to
Subtraction computed tomography (SCT) is a technique that uses software-based motion correction between an unenhanced and an enhanced CT scan for obtaining the iodine distribution in the pulmonary parenchyma. This technique has been implemented in clinical practice for the evaluation of lung perfusion in CT pulmonary angiography (CTPA) in patients with suspicion of acute and chronic pulmonary embolism, with acceptable radiation dose. This paper discusses the technical principles, clinical interpretation, benefits and limitations of arterial subtraction CTPA.
Key Points
• SCT uses motion correction and image subtraction between an unenhanced and an enhanced CT scan to obtain iodine distribution in the pulmonary parenchyma.
• SCT could have an added value in detection of pulmonary embolism.
• SCT requires only software implementation, making it potentially more widely available for patient care than dual-energy CT.
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