Diagnosis Pulmonary embolism detection: prospective evaluation of dual-section helical CT versus selective pulmonary arteriography in 157 patients
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Summary
Posted By:	Stephen Drage
E-Mail:	fiona_and_steve@bigpond.com
Posted Date:	24/06/2003
Title:	Pulmonary embolism detection: prospective evaluation of dual-section helical CT versus selective pulmonary arteriography in 157 patients
Authors:	Qanadii SD, Hajjam ME, Mesurolle B, Barre O, Bruckert F, Joseph T, et al.
Reference:	Radiology 2000; 217:447-55
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Abstract:	PURPOSE: To evaluate the accuracy of dual-section helical computed tomography (CT) in acute pulmonary embolism (PE) diagnosis. MATERIALS AND METHODS: Of 204 consecutive patients with clinically suspected acute PE (mean age, 58 years ± 14 [SD]), 158 were enrolled. All patients underwent dual-section helical CT (2.7-mm effective section thickness) and selective pulmonary arteriography within 12 hours of each other. Each image was analyzed independently by two observers, who determined image quality and presence of PE among arterial segments, including at the subsegmental level. The final diagnosis was made with consensus. RESULTS: Selective pulmonary arteriography was considered optimal in 147 (93%), suboptimal in 10 (6%), and inconclusive in one (0.6%) of 158 patients. Dual-section helical CT findings were considered technically optimal in 140 (89%), suboptimal in 11 (7%), and inconclusive in six (4%). Selective pulmonary arteriography demonstrated PE in 62 patients. Four (6%) of 62 patients had isolated subsegmental PE. The sensitivity of dual-section helical CT was 90%, and the specificity was 94%. The positive and negative predictive values were 90% and 94%, respectively. CONCLUSION: Dual-section helical CT is an improvement in helical CT that offers a high sensitivity and specificity for the depiction of PE, including at the subsegmental level. Dual-section helical CT can replace pulmonary arteriography for the direct demonstration of PE in a majority of patients.
Are the Results Valid?
1. Was there an independent, blind comparison with a reference standard?
	Yes, the radiologist assessing each CT scan was unaware of the results of the pulmonary angiogram and vice versa. Selective pulmonary arteriography is widely accepted as the reference standard in PE detection.
2. Did the patient sample include an appropriate spectrum of patients to whom the diagnostic test will be applied in clinical practice?
	Yes, patients with symptoms and signs of PE were enrolled. They were drawn from both inpatients and outpatients. Of 204 patients approached to participate, 158 provided consent. Only 2 of the 158 did not have CT and SPA within 12 hours of each other.
3. Did the results of the test being evaluated influence the decision to perform the reference standard?
	No, the results of the CT did not influence the performance of the SPA.
4. Were the methods for performing the test described in sufficient detail to permit replication?
	Yes, details of the technique for each scan was described in detail.
What are the Results?
1. Are likelihood ratios for the test results presented or data necessary for their calculation provided?
	Results were presented as sensitivity and specificity. 1)Inconclusive CT scans included: Sensitivity: 90% Specificity: 94% Likelihood Ratio+: 14.3 (as compared to 18.3 for a high probability V/Q scan, PIOPED study) Likelihood Ratio-: 0.103 (as compared to 0.100 for a normal V/Q scan, PIOPED study)
Will the Results Help Me In Caring For My Patients?
1. Will the reproducibility of the test result and its interpretation be satisfactory in my setting?
	Yes. Multislice CT scanning and radiologists experienced in its use are now widely available. There was some disagreement between radiologists on the diagnosis of PE both on CT and pulmonary arteriography (k=0.861 & 0.781 respectively). However, this did not appear to affect the overall accuracy of detecting PE on CT.
2. Are the results applicable to my patient?
	It was unclear how many were post surgical or critical care patients so it is not clear whether the results are applicable to ICU patients. Atelectasis, pleural effusions and low perfusion states resulted in suboptimal scans, which may limit there usefulness in ICU patients.
3. Will the results change my management?
	Multislice helical CT is currently the 'diagnostic test of choice' in the majority of ICU patients however, given the possibility of decreased performance in this patient population and the relatively small size of this study compared to PIOPED, a confirmatory study in an ICU population is still desirable. This study provides some good evidence that CT may significantly affect the post-test probability of the presence of PE.
4. Will patients be better off as a result of the test?
	Possibly. CT revealed more emboli in subsegmental vessels (5th order) than arteriography. There is debate over the clinical significance of such distal emboli. Thus, such a sensitive test may result in unnecessary treatment. However, CT is a less invasive procedure than selective pulmonary arteriography and requires less iodinated contrast however the relevent comparator is V/Q scans.
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