Technical Note: Phantom study to evaluate the dose and image quality effects of a computed tomography organ‐based tube current modulation technique

Abstract

Purpose: This technical note quantifies the dose and image quality performance of a clinically available organ-dose-based tube current modulation (ODM) technique, using experimental and simulation phantom studies. The investigated ODM implementation reduces the tube current for the anterior source positions, without increasing current for posterior positions, although such an approach was also evaluated for comparison. Methods: Axial CT scans at 120 kV were performed on head and chest phantoms on an ODM-equipped scanner (Optima CT660, GE Healthcare, Chalfont St. Giles, England). Dosimeters quantified dose to breast, lung, heart, spine, eye lens, and brain regions for ODM and 3D-modulation (SmartmA) settings. Monte Carlo simulations, validated with experimental data, were performed on 28 voxelized head phantoms and 10 chest phantoms to quantify organ dose and noise standard deviation. The dose and noise effects of increasing the posterior tube current were also investigated. Results: ODM reduced the dose for all experimental dosimeters with respect to SmartmA, with average dose reductions across dosimeters of 31% (breast), 21% (lung), 24% (heart), 6% (spine), 19% (eye lens), and 11% (brain), with similar results for the simulation validation study. In the phantom library study, the average dose reduction across all phantoms was 34% (breast), 20% (lung), 8% (spine), 20% (eye lens), and 8% (brain). ODM increased the noise standard deviation in reconstructed images by 6%-20%, with generally greater noise increases in anterior regions. Increasing the posterior tube current provided similar dose reduction as ODM for breast and eye lens, increased dose to the spine, with noise effects ranging from 2% noise reduction to 16% noise increase. At noise equal to SmartmA, ODM increased the estimated effective dose by 4% and 8% for chest and head scans, respectively. Increasing the posterior tube current further increased the effective dose by 15% (chest) and 18% (head) relative to SmartmA. Conclusions: ODM reduced dose in all experimental and simulation studies over a range of phantoms, while increasing noise. The results suggest a net dose/noise benefit for breast and eye lens for all studied phantoms, negligible lung dose effects for two phantoms, increased lung dose and/or noise for eight phantoms, and increased dose and/or noise for brain and spine for all studied phantoms compared to the reference protocol.

Estimating the Patient-specific Dose to the Thyroid and Breasts and Overall Risk in Chest CT When Using Organ-based Tube Current Modulation

“…Herein, we gave an overview of the dose-reducing potential of OBTCM reported in the literature. All studies were performed with anthropomorphic phantoms in which the breasts were centered anteriorly and fully located in the reduced current zone (7,(9)(10)(11)(12). The real position of the breasts in women lying supine is more lateral, which explains the lower potential for breast dose reduction observed in our study.…”

“…Dose reduction to the female breast with use of OBTCM and the resulting effect on posterior organs have been investigated before with anthropomorphic phantoms (6,7,9,10,11). Duan et al (6) indicated an increase in posterior surface dose, suggesting a possible higher lung dose, whereas Wang et al (10) reported an elevated dose to the spine and lungs.…”

A fast, linear Boltzmann transport equation solver for computed tomography dose calculation (Acuros CTD)

“…Monte Carlo simulations, which stochastically model the transport of photons, are typically used to estimate the distribution of radiation dose deposited in an object. Dose deposition maps and organ doses estimated via Monte Carlo simulations have been widely used to quantify radiation dose, [13][14][15][16][17] evaluate CT dose reduction techniques, [18][19][20][21] and to optimize CT scan parameters. 22,23 Monte Carlo simulations are traditionally slow, though recent advancements in acceleration and GPU implementation have greatly reduced run times.…”

Evaluation of an organ-based tube current modulation tool in pediatric CT examinations

“…In a second approach, implemented by GE Medical Systems with ODM, mA is reduced when the x-ray tube rotates over the anterior part of the patient's body without increase over the remaining lateral and posterior parts. However, this approach has been documented to deliver images of increased noise [10,11]. Previous studies performed in adult patients have shown that OTCM may substantially reduce radiation dose to superficial radiosensitive organs [6,8,12,13].…”