David D. Arrington MD, PhD, Presenter: Nothing to Disclose

Sameer Tipnis PhD, Abstract Co-Author: Nothing to Disclose

James G. Ravenel MD, Abstract Co-Author: Nothing to Disclose

Walter Huda PhD, Abstract Co-Author: Research support, Siemens AG Consultant, Hologic, Inc Speaker, Carestream Health, Inc Royalties, Lippincott Williams & Wilkins President, Huda's Physics in Medicine

Estimate effective doses to patients with suspected pulmonary embolism (PE) who undergo CT pulmonary angiography or NM ventilation/perfusion (V/Q) scans using published imaging protocols.

We identified 10 ventilation, 10 perfusion, and 18 CT protocols, that were published in the primary literature and which had satisfactory diagnostic performance. NM studies were included provided they include the administered (range) activity to permit nominal patient effective doses to be determined using published effective dose per unit administered activity (E/MBq) coefficients. Nuclear medicine V/Q study data were combined using a convolution of the individual ventilation and perfusion data sets. CT studies were included when the published techniques (kV, mAs, pitch, etc.) permitted the Dose Length Product to be determined using the ImPACT CT Patient Dosimetry Calculator. CT DLP data were converted into an effective dose using a k-factor of 17 μSv/mGy-cm to ensure that all effective doses used ICRP 60 tissue weighting factors.

For V/Q studies, the median effective dose was 1.7 mSv, with 10th and 90th percentile values of 0.7 and 3.1 mSv, respectively. For CT studies, the median effective dose was 10.5 mSv, with 10th and 90th percentile values of 3.9 and 17.4 mSv, respectively. Seven of the CT studies (39%) had effective doses of 2.5 mSv or less with no evidence of impaired diagnostic performance. Current CT PE studies have doses that are of the order of six times higher than the corresponding NM PE studies. Low dose CT pulmonary angiography protocols, however, do exist and which show no evidence of impaired diagnostic performance.

CT scanning in PE patients can be performed at doses that are comparable to those currently encountered in NM imaging.

CT pulmonary angiography can be performed at doses equivalent to those in ventilation/perfusion imaging without loss of diagnostic quality and is recommended for the evaluation of suspected PE.

Arrington, D, Tipnis, S, Ravenel, J, Huda, W, Effective Doses to PE Patients Undergoing V/Q and CT Examinations.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11015292.html