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The effects of gantry tilt on breast dose and image noise in cardiac CT
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Image of FIG. 1.

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FIG. 1.

Lungman with RANDO phantom breast models and MOSFET dosimeters.

Image of FIG. 2.

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FIG. 2.

The GE CT750HD with its gantry tilted to perform a tilted acquisition.

Image of FIG. 3.

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FIG. 3.

Simulated lateral scout of one voxelized phantom, demonstrating the acquired volume thickness. The arrow represents the projection direction for a 30° gantry tilt.

Image of FIG. 4.

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FIG. 4.

Voxelized phantom including glandular breast tissue, bone, lung, and blood.

Image of FIG. 5.

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FIG. 5.

Average thickness of glandular breast tissue at each slice of the eight voxelized phantoms. Each marker corresponds to one voxelized phantom. Slice number zero corresponds to the most superior slice in the phantom.

Image of FIG. 6.

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FIG. 6.

Relative change in dose for the three breast dosimeters as measured experimentally and as estimated through Monte Carlo simulations.

Image of FIG. 7.

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FIG. 7.

Relative change in noise in the anthropomorphic phantom as measured experimentally and as estimated through ray-tracing simulations.

Image of FIG. 8.

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FIG. 8.

The percent change in glandular breast dose for the tilted acquisition relative to the 0° tilt for each voxelized phantom with respect to tilt angle. Each phantom is denoted by unique marker. The solid markers represent the change in dose in the experimental dosimeters.

Image of FIG. 9.

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FIG. 9.

Reconstructed images of a voxelized phantom at 0° tilt (left) and 30° tilt (right).

Image of FIG. 10.

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FIG. 10.

Percent change in noise standard deviation for the tilted acquisition relative to 0°. Each marker represents a specific phantom model.

Image of FIG. 11.

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FIG. 11.

The ratio of noise standard deviation for tilted acquisitions relative to 0° tilt is plotted against the breast dose ratios for tilt angles between 5° and 30° in 5° increments. Also plotted is the relationship that noise standard deviation is inversely proportional to the square root of dose. The region above the curve represents points where the tilted gantry has a net detriment to dose.

Image of FIG. 12.

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FIG. 12.

The estimated percent change in glandular breast dose when the reconstructed image noise standard deviation is equivalent to that of the nontilted scan. Each marker represents a unique simulated phantom.


Generic image for table

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Perimeter of the eight voxelized phantoms as estimated on the central axial slice of the cardiac volume.


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This study investigated the effects of tilted-gantry acquisition on image noise and glandular breast dose in females during cardiac computed tomography (CT) scans. Reducing the dose to glandular breast tissue is important due to its high radiosensitivity and limited diagnostic significance in cardiac CT scans.

Tilted-gantry acquisition was investigated through computer simulations and experimental measurements. Upon IRB approval, eight voxelized phantoms were constructed from previously acquired cardiac CT datasets. Monte Carlo simulations quantified the dose deposited in glandular breast tissue over a range of tilt angles. The effects of tilted-gantry acquisition on breast dose were measured on a clinical CT scanner (CT750HD, GE Healthcare) using an anthropomorphic phantom with MOSFET dosimeters in the breast regions. In both simulations and experiments, scans were performed at gantry tilt angles of 0°–30°, in 5° increments. The percent change in breast dose was calculated relative to the nontilted scan for all tilt angles. The percent change in noise standard deviation due to gantry tilt was calculated in all reconstructed simulated and experimental images.

Tilting the gantry reduced the breast dose in all simulated and experimental phantoms, with generally greater dose reduction at increased gantry tilts. For example, at 30° gantry tilt, the dosimeters located in the superior, middle, and inferior breast regions measured dose reductions of 74%, 61%, and 9%, respectively. The simulations estimated 0%–30% total breast dose reduction across the eight phantoms and range of tilt angles. However, tilted-gantry acquisition also increased the noise standard deviation in the simulated phantoms by 2%–50% due to increased pathlength through the iodine-filled heart. The experimental phantom, which did not contain iodine in the blood, demonstrated decreased breast dose and decreased noise at all gantry tilt angles.

Tilting the gantry reduced the dose to the breast, while also increasing noise standard deviation. Overall, the noise increase outweighed the dose reduction for the eight voxelized phantoms, suggesting that tilted gantry acquisition may not be beneficial for reducing breast dose while maintaining image quality.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: The effects of gantry tilt on breast dose and image noise in cardiac CT