Single versus multi-detector row CT: comparison of radiation doses and dose profiles

RATIONALE AND OBJECTIVES: The purpose of this study was twofold: (a) to compare the radiation dose profile between computed tomography (CT) with a single detector row (SD) and with a multi-detector row (MD) and (b) to compare specific organ doses between SD CT and MD CT. MATERIALS AND METHODS: Thermoluminescent dosimeters placed within a 32-cm-diameter cylindrical phantom were used to measure and compare dose profiles from one SD CT scanner and from one MD CT scanner. SD CT scanning parameters were 210 mA, 140 kVp, pitch of 1.0, 5-mm section thickness, and 0.8-second gantry rotation speed. MD CT scanning parameters were 130 mA, 140 kVp, pitch of 0.75, 4 x 5-mm section thickness, 15-mm table feed, and 0.8-second gantry rotation speed. To plot radiation dose profile, doses were measured both in the imaging plane and in the area adjacent to the imaging plane. The resultant data were normalized to achieve constant image noise between MD CT and SD CT. Direct doses to individual organs from primary and scattered radiation were measured with an anthropomorphic phantom containing thermoluminescent dosimeters and with a standard pelvic imaging protocol for both MD CT and SD CT. RESULTS: MD CT resulted in a dose profile approximately 27% higher than that from SD CT in the plane of imaging (8.0 vs 6.3 mGy) and 69% higher adjacent to the plane of imaging (6.8 vs 4.0 mGy). The individual doses to the kidneys, uterus, ovaries, and pelvic bone marrow were 92%-180% higher with MD CT than with SD CT. CONCLUSION: With image noise constant between SD CT and MD CT, the radiation dose profile both inside and outside the plane of imaging was higher with MD CT than with SD CT. Organ dose also was higher with MD CT than with SD CT. This difference should be accounted for in the design of MD CT protocols, especially as MD CT technology becomes more widely available for clinical use.     

Radiation dose to the fetus from body MDCT during early gestation

OBJECTIVE: The purpose of our study was to determine radiation dose to the fetus at early gestation when contemporary MDCT scanners are used for common clinical indications. MATERIALS AND METHODS: Anthropomorphic phantoms were constructed to reflect a pregnant woman. Thermoluminescence dosimeters (TLDs) and metal oxide semiconductor field effect transistor (MOSFET) detectors were placed in appropriate locations to determine real-time radiation exposure to the fetus at 0 and 3 months' gestation. Imaging was performed on a 16-MDCT scanner using current institutional CT protocols: renal stone (140 kVp, 160 mA, rotation time of 0.5 sec, 16 x 0.625 mm), appendix (140 kVp, 340 mA, rotation time of 0.5 sec, 16 x 0.625 mm), and pulmonary embolus (140 kVp, 380 mA, rotation time of 0.8 sec, 16 x 1.25 mm). RESULTS: The radiation dose to the fetus at 0 and 3 months, respectively, was as follows: renal stone protocol, 0.8-1.2 and 0.4-0.7 cGy; appendix protocol, 1.52-1.68 and 2-4 cGy; and pulmonary embolus protocol, 0.024-0.047 and 0.061-0.066 cGy. CONCLUSION: Radiation doses to the fetus from institutional MDCT protocols that may be used during pregnancy (for pulmonary embolus, appendicitis, and renal colic) are below the level thought to induce neurologic detriment to the fetus. Imaging the mother for appendicitis theoretically may double the fetal risk for developing a childhood cancer. Radiation doses to the fetus from pulmonary embolus chest CT angiography are of the same magnitude as ventilation-perfusion (V/Q) scanning.     

Differentiating normal from abnormal inferior thoracic paravertebral soft tissues on chest radiography in children

OBJECTIVE: The purposes of this investigation were to define the normal appearances, define factors that have the potential to influence appearance, and establish defined criteria to differentiate normal from abnormal appearances of posteroinferior paravertebral soft tissues on chest radiography in children. SUBJECTS AND METHODS: Paravertebral soft tissues were evaluated on frontal chest radiographs in 23 children with documented abnormalities and 275 children without abnormalities in the region. The frequency of visualization, course, width, and factors (patient positioning, age, and sex) potentially influencing the appearance of paravertebral soft tissues were determined. Inferolateral course and width greater than that of the adjacent pedicle were evaluated as criteria for abnormality. RESULTS: Only 28% of the children without abnormalities had paravertebral soft tissues visualized, and the frequency of visualization directly increased with age (p = 0.001). For identification of abnormal cases on the left side, width greater than the adjacent pedicle had a sensitivity of 100% and a specificity of 98%, and inferolateral course had a sensitivity of 86% and a specificity of 95%. Visualization on the right side (n = 5) was always abnormal. Six normal cases had a width greater than that of the adjacent pedicle on the left side on initial radiographs obtained with supine positioning and met normal criteria on repeated radiographs with upright positioning. CONCLUSION: Width greater than the adjacent pedicle is the best radiographic criterion for differentiation of abnormal from normal left-sided paravertebral soft tissues, particularly on radiographs obtained with upright positioning. Identifiable right-sided paravertebral soft tissue is always abnormal. These criteria are useful aids in determining the need for additional imaging, such as CT.     

Peer assessment of pediatric surgeons for potential risks of radiation exposure from computed tomography scans

Purpose

Radiology literature reports potential cancer risk from radiation exposure from computed tomography (CT). We hypothesized that pediatric surgeons' knowledge of potential risks of radiation exposure from CT scan is limited.

Methods

We used an anonymous, Internet-based peer assessment survey for members of the American Pediatric Surgical Association (APSA). The survey assessed surgeon's knowledge based on potential risks of radiation exposure from CT as well as current practice patterns for use of CT. The χ² test of significance was used to detect any differences in responses based on years in training.

Results

Twenty percent (147/753) of the American Pediatric Surgical Association members completed the survey. About one half (54%) of surgeons believe that the lifetime risk of cancer was increased because of radiation from one abdominal/pelvic CT scan, although more than 75% of respondents underestimated the radiation dose from a CT scan compared to a chest radiograph. Most surgeons generally did not discuss the potential risks of CT scan with their patients. Surgeons demonstrated a range of responses for use of CT for select clinical scenarios.

Conclusions

Pediatric surgeon's knowledge of potential risks of radiation exposure from CT scan is limited. As the radiology literature indicates an increasing awareness for potential cancer risks from radiation exposure from CT, there is also a need for education of subspecialties outside of radiology.