The anatomic and radiation attenuation characteristics of cadavers are comparable to those of living human tissue. This methodology allows direct measurement of organ doses from clinical CT examinations.
The organ dose equations developed represent a method for organ dose estimation from direct organ dose measurements that can estimate organ doses more accurately than the calculated SSDE, which provides a less-specific patient dose estimate.
Purpose: In the field of Computed Tomography (CT) dosimetry, there remains a need to accurately measure organ doses. Such measurements are only meaningful if they are performed under actual clinical scanning conditions, for this purpose, a cadaver can serve as the measurement subject that most closely mimics a living patient. Organ doses were measured in 7 adult female cadaveric subjects with varying body mass indices (BMIs) and for various CT protocols. Methods: A tube placement system allowed external access to internal organs, in which optically‐stimulated luminescent dosimeters (OSLDs) were placed and used to measure dose. Dosimeter placement and location was based on organ size and distribution. In order to determine organ doses of real patients, a correlation between various patient size parameters and the measured organ doses was explored. Only measurements that could be performed on a CT image or subject‐specific parameters or data which could otherwise be obtained for an actual patient were considered for this correlation. The size parameters that were examined included: body mass index (BMI), the AP and lateral dimensions of the patient, and patient perimeter. Results: The BMIs for the 7 subjects ranged from 16.6–43.9, spanning from underweight to extreme obesity. Overall average organ doses from a CAP exam for all subjects ranged from 11.8–24.4 mGy. Generally, organ doses were shown to increase with all size parameters examined. Conclusion: For the purpose of accuracy, the estimation of patient dose in CT must be based on actual physical measurements. A complete set of direct organ dose measurements for 7 adult female cadavers has been accomplished for common CT exams with this research. It has been shown before that patient size parameters can be indicative of patient dose. This work has shown further validation of this concept.
Objective To compare organ specific radiation dose and image quality in kidney stone patients scanned with standard CT reconstructed with filtered back projection (FBP-CT) to those scanned with low dose CT reconstructed with iterative techniques (IR-CT). Materials and Methods Over a one-year study period, adult kidney stone patients were retrospectively netted to capture the use of noncontrasted, stone protocol CT in one of six institutional scanners (four FBP and two IR). To limit potential CT-unit use bias, scans were included only from days when all six scanners were functioning. Organ dose was calculated using volumetric CT dose index and patient effective body diameter through validated conversion equations derived from previous cadaveric, dosimetry studies. Board-certified radiologists, blinded to CT algorithm type, assessed stone characteristics, study noise, and image quality of both techniques. Results FBP-CT (n=250) and IR-CT (n=90) groups were similar in regard to gender, race, body mass index (mean BMI = 30.3), and stone burden detected (mean size 5.4 ± 1.2 mm). Mean organ-specific dose (OSD) was 54-62% lower across all organs for IR-CT compared to FBP-CT with particularly reduced doses (up to 4.6-fold) noted in patients with normal BMI range. No differences were noted in radiological assessment of image quality or noise between the cohorts, and intrarater agreement was highly correlated for noise (AC2=0.873) and quality (AC2=0.874) between blinded radiologists. Conclusions Image quality and stone burden assessment were maintained between standard FBP and low dose IR groups, but IR-CT decreased mean OSD by 50%. Both urologists and radiologists should advocate for low dose CT, utilizing reconstructive protocols like IR, to reduce radiation exposure in their stone formers who undergo multiple CTs.
Purpose: To introduce and investigate effective diameter ratios as a new patient metric for use in computed tomography protocol selection as a supplement to patient‐specific size parameter data. Methods: The metrics of outer effective diameter and inner effective diameter were measured for 7 post‐mortem subjects scanned with a standardized chest/abdomen/pelvis (CAP) protocol on a 320‐slice MDCT scanner. The outer effective diameter was calculated by obtaining the anterior/posterior and lateral dimensions of the imaged anatomy at the middle of the scan range using Effective Diameter= SQRT(AP height*Lat Width). The inner effective diameter was calculated with the same equation using the AP and Lat dimensions of the anatomy excluding the adipose tissue. The ratio of outer to inner effective diameter was calculated for each subject. A relationship to BMI, weight, and CTDI conversion coefficients was investigated. Results: For the largest subject with BMI of 43.85 kg/m2 and weight of 255 lbs the diameter ratio was calculated as 1.33. For the second largest subject with BMI of 33.5 kg/m2 and weight of 192.4 lbs the diameter ratio was measured as 1.43, indicating a larger percentage of adipose tissue in the second largest subject's anatomical composition. For the smallest subject at BMI of 17.4 kg/m2 and weight of 86 lbs a similar tissue composition was indicated as a subject with BMI of 24.2 kg/m2 and weight of 136 lbs as they had the same diameter ratios of 1.11. Conclusion: The diameter ratio proves to contain information about anatomical composition that the BMI and weight alone do not. The utility of this metric is still being examined but could prove useful for determining MDCT techniques and for giving a more in depth detail of the composition of a patient's body habitus.
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