Radiation dose and image quality from a recently introduced mobile CT imaging system are presented. Radiation dose was measured using a conventional 100 mm pencil ionization chamber and CT polymethylmetacrylate (PMMA) body and head phantoms. Image quality was evaluated with a CATPHAN 500 phantom. Spatial resolution, low contrast resolution, Modulation Transfer Function (MTF), and Normalized Noise Power Spectrum (NNPS) were analyzed. Radiation dose and image quality were compared to those from a multi-detector CT scanner (Siemens Sensation 64). Under identical technique factors radiation dose (mGy/mAs) from the AIRO mobile CT system (AIRO) is higher than that from a 64 slice CT scanner. Based on MTF analysis, both Soft and Standard filters of the AIRO system lost resolution quickly compared to the Sensation 64 slice CT. The Siemens scanner had up to 7 lp/cm for the head FOV and H40 kernel and up to 5 lp/cm at body FOV for the B40f kernel. The Standard kernel in the AIRO system was evaluated to have 3 lp/cm and 4 lp/cm for the body and head FOVs respectively. NNPS of the AIRO shows low frequency noise due to ring-like artifacts which may be caused by detector calibration or lack of artifact reducing image post-processing. Due to a higher dose in terms of mGy/mAs at both head and body FOV, the contrast to noise ratio is higher in the AIRO system than in the Siemens scanner. However detectability of the low contrast objects is poorer in the AIRO due to the presence of ring artifacts in the location of the targets.

Relative mAs values required to generate a constant plate readout signal for the Kodak Ektascan general purpose (GP-25) and high resolution (HR) photostimulable phosphors were measured as a function of x-ray beam quality and for a range of representative x-ray examinations. The signal intensity was determined from the exposure index (EI) generated during the read out of uniformly exposed phosphor imaging plates. These data were compared to the corresponding relative mAs values required to produce a constant film density of Lanex screen-film combinations with nominal speeds of 40, 400, and 600. The relative detection performance of the photostimulable phosphors generally decreased with increasing kVp and beam filtration. The relative response of GP-25 phosphors was independent of examination type, and modified by approximately 10% when scattered radiation was present. The HR phosphor was more efficient than a Lanex Single Fine extremity screen used with an EM-1 film. These relative response data will be useful for selecting the x-ray technique factors which minimize patient dose in x-ray examinations performed with photostimulable phosphors.

During interventional procedures, the vast majority of scatter radiation originates from the patient and table and travels in all directions in straight lines. Because the operator's head is much higher than the patient and at an angle upward and to the side of the patient (not directly above), the scatter received by the operator's head is projected in an upward angle. Thus a face shield could potentially be lower than the object it is shielding, e.g., below the eyes. This principle may be used as an advantage to design the lowest shield that effectively protects the head while providing optimum vision, appearance, acoustics, low weight, and sense of openness. A flat acrylic plate shield, 0.5 mm Pb equivalence, was suspended vertically in front of a 451P dosimeter. A phantom patient created scatter in an interventional suite while the dosimeter was placed at the level of the crowns of different operators' heads. Many different configurations were tested to determine which ones would provide effective shielding. The results confirmed that the top of the shield may reside several centimeters below the vertical height of the dosimeter (operator's crown), allowing line of sight to monitor above the shield, and still provide effective shielding equivalent to when the dosimeter is positioned directly behind the center of the shield. The image receptor functioned as an effective shield against scatter. Factors increasing the minimum height of effective shielding included shorter operator, opposite oblique projection of image receptor, and shield closer to the face (in horizontal direction).

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PURPOSE: Patient radiation dose during Computed Tomography (CT) guided biopsy procedures is determined by both acquisition technical parameters and physician practice. The potential effect of the physician practice is of concern. This study is to investigate the effects of those intangibles on patient radiation dose. METHODS: Patient radiation dose from 252 patients who underwent CT guided biopsy from 2009 to 2010 were retrospectively studied. Ten physicians who used conventional intermittent shots, low mA dose saving feature, or both were included in the study. The patient dose reports were retrieved and the total dose length products (DLPs) were analyzed. Linear regression analysis performed between various variables and reported dose. Patient detriment index (PDI) was developed, which sets threshold (standard of practice) for comparing physician practice with their peers. Odds ratio was calculated to determine odds of a group of patients receiving dose above threshold when compared to another group. RESULTS: Median DLP among ten physicians was 1194 mGy-cm. There was a significant difference (p < 0.01) between reported DLPs doses when physicians used dose saving feature vs. when feature not used (539.8 ± 169.4 mGy-cm vs. 1269.7 ± 659.0 mGy-cm). In general, physicians who used dose saving feature had lower relative PDIs (< 1) compared to the PDIs (> 1) without the dose feature. Odds ratio estimate of 7.7 at 95% confidence level indicates that the odds of a group receiving a high dose depends on practitioner. CONCLUSION: Adjustments of practice habits, use of dose saving features or both may be needed to improve patient care for CT biopsy.

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Adjustments of practice habits, the use of CT dose saving features or both may be needed to improve patient care for CT fluoroscopy.