Iterative reconstructed ultra high pitch CT pulmonary angiography with cardiac bowtie-shaped filter in the acute setting: Effect on dose and image quality
To evaluate the effect of a cardiac bowtie-shaped filter in an ultra high pitch CTPA protocol at 100kV on image quality and radiation dose.
Materials and methods
Retrospective study of 100 patients referred for CTPA. 50 patients scanned with a standard 100kV protocol at pitch 2.8 (Protocol A) and 50 patients scanned with a 100kV protocol at pitch 3.2 with a cardiac bowtie-shaped filter (Protocol B). All other scanning parameters kept constant. Images from both groups reconstructed with filtered back projection and iterative reconstruction. Central pulmonary vessel attenuation and background noise were quantitatively measured and signal-to-noise (SNR) and contrast-to-noise (CNR) were calculated. Two radiologists performed qualitative assessment grading visualization of the pulmonary vasculature and noise level. CTDIvol and DLP were recorded and effective dose was calculated.
CTDIvol, DLP and effective dose were significantly (p<0.0001) lower in Protocol B (2.3±0.5mGy, 78.4±16.5mGycm, 1.4±0.3mSy, respectively) compared to Protocol A (4.3±0.5mGy, 152.0±19.6mGycm, 2.7±0.3mSy, respectively). Protocol B had significantly (p<0.0001) higher noise than Protocol A (23.8±6.9HU vs 36.8±7.3HU) and lower SNR (11.8±3.7HU vs 19.2±8.1HU) and CNR (10.3±3.7HU vs 24.9±13.4HU) but there was no significant difference in the subjective visualization of the pulmonary vasculature (p=0.63). Furthermore, iterative reconstruction significantly (p<0.0001) improves image noise (29.4±5.5HU from 36.8±7.3HU).
The addition of a cardiac bowtie-shaped filter with an ultra high pitch CTPA protocol at 100kV resulted in a 48% dose reduction without significantly affecting diagnostic image quality. In addition, the use of iterative reconstruction significantly improves image quality by reducing noise permitting the possibility for further dose reduction strategies.
Authors: Co SJ, Mayo J, Liang T, Krzymyk K, Yousefi M, Nicolaou S.
Full text available at: Eur J Radiol. 2013 Jun 15. pii: S0720-048X(13)00267-2.