Comparison of Image Quality in High Pitch Free Breathing Versus Standard Pitch Breath-Holding Computed Tomographic Pulmonary Angiography.

Date of Award


Document Type


Degree Name

Master of Medicine (MMed)

First Supervisor/Advisor

Prof. Sudhir Vinayak

Second Supervisor/Advisor

Prof. Rodney Adam

Third Supervisor/Advisor

Dr. Kevin Were


Imaging and Diagnostic Radiology (East Africa)


Background: Pulmonary embolism (PE) is the third most common acute cardiovascular disease. Missed diagnosis is responsible for most preventable deaths associated with PE. Artefacts from cardiac and breathing motion are a main pitfall. Advances in Computed Tomographic imaging have enabled rapid imaging in an attempt to overcome these pitfalls.

Objective: To compare image quality when using high pitch free breathing versus standard pitch breath holding Computed Tomographic Pulmonary Angiography (CTPA) using a dual source scanner.

Methods: This was a randomised control trial whereby patients referred to the radiology department for CTPA examination for suspected pulmonary embolism were randomly selected into two arms: Arm A underwent the standard CTPA protocol using a pitch of 1.2 with breath-holding instructions while those in arm B underwent the examination using a pitch of 3.2 with quiet free breathing. Two blinded reviewers subjectively assessed the image quality while a single blinded reviewer recorded objective image parameters. The primary endpoint was to demonstrate non-inferiority of high pitch free breathing CTPA. Continuous variables were expressed as mean ± SD. Categorical variables were expressed as frequency (percentage). For calculation of statistically significant differences between both groups, Chi-square test was performed to assess categorical variables and t test for continuous variables. P-values of ≤0.05 were considered statistically significant. Cohen kappa testing was used to assess the degree of agreement between the 2 independent readings, with results expressed in terms of kappa statistics and proportional agreement.

Results: A total of 112 patients were randomly selected into the two arms of the study. The patients in the high pitch group received a lower mean radiation dose compared to those in the standard pitch group (P<0.001). There was no statistically significant difference in the mean main pulmonary artery attenuation between the two groups (P=0.215). There was no significant difference in the qualitative analysis of the images between the two groups. Inter reader agreement for the subjective measurements ranged from moderate to almost perfect agreement between the 2 independent readers.

Conclusion: Main pulmonary artery contrast opacification in high pitch CTPA is non-inferior to standard pitch CTPA using a dual source 256 slice scanner. High pitch dual source CTPA can be performed on all patients with no compromise on the image quality and with the added advantage of reduction in the radiation dose.

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