Bismuth Breast Shields Work

The objective of a recent study was to evaluate radiation dose savings by using a lower peak kilovoltage (kVp), automatic tube current modulation, and bismuth breast shields on a phantom using a 64-MDCT pulmonary embolism protocol, and how these changes affect image quality.

The study has shown that the use of bismuth breast shields and automatic tube current modulation significantly reduces the radiation dose absorbed by the breasts and lungs during a CT pulmonary angiogram without causing a qualitative decrease in image quality.

Methodology

Two female phantoms, a small phantom and a large phantom, were used to measure radiation dose. Phantoms were anthropomorphic, and the smaller phantom had a weight of 55 kg and the larger phantom had a weight of 73 kg.

Twenty detectors were placed within each phantom within the breasts, as well as various other parts of the phantom. Various 64-MDCT protocols were used on each phantom.

The first protocol used 140 kVp with and without breast shields. The second protocol used 120 kVp with and without breast shields. The last protocol used 140 kVp with breast shields and a foam pad. Automatic tube current modulation was used.

The breast shield was a bismuth breast shield. The foam pad was a 1-cm thick black foam placed between the shields and breasts. Image quality was ascertained quantitatively and qualitatively.

Regions of interest were placed in various locations within the phantoms to assess image noise. Qualitative image assessment was made by three chest radiologists independently who were blinded to CT protocol.

A scale of 1 to 5 was used to assess different areas, with 5 being excellent quality with no streak artifact or mottle, and 1 being poor image quality with >50% of area being not well assessed.

Results
A lower kVp (120 kVp instead of usual 140 kVp) led to 27% radiation dose savings to the breast and 47% radiation dose savings to the lungs. Use of a lower kVp and breast shields led to 55% radiation dose savings to the breast, and 45% radiation dose savings to the lungs.

Qualitatively, there was no change in image quality of the mediastinum and lungs with use of a lower kVp and/or breast shields. Breast shields caused a lower quality score for the anterior chest wall regardless of kVp. There was no significant streak artifact extending into the thorax with any protocol.

Conclusions
Use of bismuth breast shields, a lower kVp (120 kVp), and automatic tube current modulation significantly reduces the radiation dose absorbed by the breasts and lungs without causing a qualitative decrease in image quality.

Reviewer’s Comments
It would be interesting to see what percentage of radiology departments use breast shields for their CT pulmonary angiograms.

Author: Vineet R. Jain, MD

Reference:
Hurwitz LM, Yoshizumi TT, et al. Radiation Dose Savings for Adult Pulmonary Embolus 64-MDCT Using Bismuth Breast Shields, Lower Peak Kilovoltage, and Automatic Tube Current Modulation. AJR Am J Roentgenol; 2009;192 (January): 244-253: