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Lowering Radiation Dose While Still Maintaining Quality With Automatic Tube Current Modulation

October 9, 2009
Written by: , Filed in: Pediatric Radiology
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A recent study was conducted to assess the effect of weight-based automatic tube current modulation in children with congenital thoracic cardiovascular disease using conventional angiography, sonography, or surgery as reference standards.

The findings show that automatic tube current modulation combined with low tube voltage settings markedly reduces radiation exposure without significant reduction in image quality.

The Study
68 patients referred to the pediatric radiology department for known or suspected cardiovascular abnormalities over a 2-year period were identified.

Methodology

Overall, 38 patients underwent 64-MDCT and 30 underwent 16-MDCT.

Patients were divided into 3 groups based on tube voltages used corresponding to 80, 100, and 120 kVp. A normality distribution test was used based on age, height, and body weight.

Of those who underwent surgery, postoperative scanning was identified.

Tube voltage was individually adjusted to patient weight.

For those undergoing 64-MDCT, commercially available tube current modulation software was used which obtains monitoring of tissue attenuation and results in real-time adjustment of the base tube current.

Image evaluation was performed on a 3D-enabled workstation. Each data set was assessed for image noise and graded for quality.

To assess diagnostic quality, 2 readers were asked to independently assess the display of relevant vascular structures and to identify cardiovascular defects.

Image quality was graded using multiple previously published criteria, and structures were assessed on a 5-point scale, with 1 corresponding to qualitative unacceptability and 5 to excellent diagnostic quality.

All defects that had been documented on MDCT were correlated to cardiac sonography, conventional angiography, or surgery.

Radiation dose was calculated using CT dose calculation software with variables such as CT dose index (CTDI), dose-length product (DLP), and effective radiation dose equivalent being reported.

Pediatric Diagnostic Imaging

The Society for Pediatric Radiology
Pediatric Diagnostic Imaging program features the advances and diversity of pediatric imaging by reviewing state-of-the-art clinical material and advanced cutting-edge research presentations. This program presents a group of international experts who discuss state-of-the art diagnostic imaging and the outlook for the future direction of the specialty.
Read more or order:  Pediatric Diagnostic Imaging

Results
Compared with scanning without automated tube current modulation, the tube current-time product was statistically significantly reduced by 57.8%. CTDI was reduced by 56.3% and DLP by 54.9%. The radiation dose equivalent was reduced by 60.3%.

In comparison with 16-MDCT, 64-MDCT with tube current modulation resulted in a significant reduction in all these variables as well.

Image quality scores and image noise levels were comparable for both CT scanning techniques.

All cardiovascular defects documented on MDCT scans were correlated at cardiac sonography with agreement calculated to be 94.9% and 91.5% for the 2 reviewers.

Using catheter angiography and surgery, agreement was 100%.

Conclusions
Automated tube current modulation combined with low tube voltage resulted in significantly decreased radiation dose while maintaining image quality and diagnostic accuracy.

Reviewer’s Comments
When presented with data from studies such as this, it is surprising that the standard of practice has been to wantonly expose children to unnecessary ionizing radiation without establishing a threshold where study quality would not suffer.

For the time being, the data from a significant cohort such as this should be put into practice at any institution with the same scanning equipment.

Author: Basil Hubbi, MD

Reference:
Herzog C, Mulvihill DM, et al. Pediatric Cardiovascular CT Angiography: Radiation Dose Reduction Using Automatic Anatomic Tube Current Modulation. AJR; 2008; 190 (May): 1232-1240

Pediatric Diagnostic Imaging

The Society for Pediatric Radiology
Pediatric Diagnostic Imaging program features the advances and diversity of pediatric imaging by reviewing state-of-the-art clinical material and advanced cutting-edge research presentations. This program presents a group of international experts who discuss state-of-the art diagnostic imaging and the outlook for the future direction of the specialty.
Read more or order:  Pediatric Diagnostic Imaging
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