MRA Pulmonary Arteries Without IV Contrast Noncontrast MRA sequences alone for PE have been reported but remain investigational [41,43,44]. There is limited relevant literature to support the use of noncontrast MRA for suspected PE, low or intermediate pretest probability with a positive D-dimer. US Duplex Doppler Lower Extremity Compression US with Doppler flow studies are used to evaluate for peripheral DVT [45,46] and may be useful for patients who do not have a high likelihood of PE, particularly if the patient has symptoms of extremity DVT. The presence of DVT does not indicate the presence of PE, but it increases the likelihood. A negative extremity US study does not exclude PE, although it significantly decreases its likelihood [47-49]. Suspected Pulmonary Embolism will undergo CTPA to identify a filling defect in the diagnosis of PE [51]. Risk stratification for right ventricular failure when there is a positive CTPA [52-57] is commonly used, but this clinical situation (after a diagnosis of PE) is not within the scope of this document. V/Q Scan Lung The use of V/Q scans has considerably diminished with the widespread use of CTPA. Imaging protocols have evolved [10,58,59], and in some cases, perfusion imaging alone can be performed. The high negative predictive value of a normal V/Q scan has been confirmed by several studies, including a large outcome study [60]. Among the weaknesses of V/Q scanning are the high proportion of nondiagnostic results and the inability to provide an alternative diagnosis [1,58]. Abnormal regional lung perfusion may suggest the diagnosis of PE, but it is not specific. Findings require correlation with ventilation studies or other imaging. Investigators have studied single- photon emission CT (SPECT) to improve the sensitivity and specificity of V/Q scintigraphy [61].
Suspected Pulmonary Embolism PCAs. MRA Pulmonary Arteries Without IV Contrast Noncontrast MRA sequences alone for PE have been reported but remain investigational [41,43,44]. There is limited relevant literature to support the use of noncontrast MRA for suspected PE, low or intermediate pretest probability with a positive D-dimer. US Duplex Doppler Lower Extremity Compression US with Doppler flow studies are used to evaluate for peripheral DVT [45,46] and may be useful for patients who do not have a high likelihood of PE, particularly if the patient has symptoms of extremity DVT. The presence of DVT does not indicate the presence of PE, but it increases the likelihood. A negative extremity US study does not exclude PE, although it significantly decreases its likelihood [47-49]. Suspected Pulmonary Embolism will undergo CTPA to identify a filling defect in the diagnosis of PE [51]. Risk stratification for right ventricular failure when there is a positive CTPA [52-57] is commonly used, but this clinical situation (after a diagnosis of PE) is not within the scope of this document. V/Q Scan Lung The use of V/Q scans has considerably diminished with the widespread use of CTPA. Imaging protocols have evolved [10,58,59], and in some cases, perfusion imaging alone can be performed. The high negative predictive value of a normal V/Q scan has been confirmed by several studies, including a large outcome study [60]. Among the weaknesses of V/Q scanning are the high proportion of nondiagnostic results and the inability to provide an alternative diagnosis [1,58]. Abnormal regional lung perfusion may suggest the diagnosis of PE, but it is not specific. Findings require correlation with ventilation studies or other imaging. Investigators have studied single- photon emission CT (SPECT) to improve the sensitivity and specificity of V/Q scintigraphy [61].