Prevalence and nature of excluded findings at reduced scan length CT angiography for pulmonary embolism

Background Scan length reduction effectively decreases radiation dose at CT pulmonary angiography (CTPA) for pulmonary embolism (PE) but may exclude important incidental scan findings. Objective We aimed to determine the prevalence and nature of excluded findings with the use of reduced scan length CTPA. Methods We reviewed 335 consecutive emergency department CTPA studies performed on 16- or 64-detector row scanners with the use of a standard scan range. A scan length of 14.2 cm that was centered 4.1 cm below the carina has been shown to be adequate for PE diagnosis. Boundary slices for this scan range were determined. All pertinent and incidental findings within and outside the reduced scan range were noted. To determine the significance of newly detected excluded findings, we reviewed medical records and all relevant imaging studies before and 9–11 months after the reference CTPA. Results We found 374 pertinent findings in 192 patients, including 28 (8%) cases of PE. All except 3 (0.8%) were adequately seen with the reduced scan range, among which only one finding altered clinical management. There were a total of 230 incidental findings in 165 patients, 60 (26%) of which were excluded; 23 (10%) of the 60 were newly detected, including 10 thyroid nodules, 6 liver lesions, and an 8-mm pulmonary nodule. The reduced scan length decreased z-axis coverage by 49% ± 6%. Conclusion Substantial scan length reduction at CTPA may not compromise the diagnostic yield for pertinent alternative diagnoses.