A review of dental cone-beam CT dose conversion coefficients.

OBJECTIVE: The purpose of this study was to review the literature to examine the usage and magnitude of effective dose conversion factors (DCE) for dental cone beam CT (CBCT) scanners. METHODS: A PubMed literature search for publications relating to radiation dosimetry in dental radiography was performed. Papers were included if they reported DCE, or reported ICRP 103 effective dose and dose-area product. 71 papers relating to dental CBCT dosimetry were found, of which eight reported effective dose conversion factors or provided enough information to calculate dose conversion factors. Scanner model, effective dose, dose-area product, tube voltage, field of view size and DCE were extracted from the papers for analysis. RESULTS: DCE values ranged from 0.035 to 0.31 µSv/mGy-cm2 with a mean of 0.129 µSv/mGy-cm2 (SD = 0.056). When categorized into small (<100 cm2), medium (100-225 cm2) and large (>225 cm2) fields of view (FOV), linear fits to the effective dose and dose-area product yielded slopes of 0.129, 0.111 and 0.074 µSv/mGy-cm2 for small, medium and large FOVs respectively. CONCLUSION: The range of reported DCE values and spread with respect to field of view category suggests that DCE values that depend on FOV would provide more accurate effective dose estimates. Tube voltage was found to be a smaller factor in determining DCE. Reasonable values for DCE taking into account FOV size were obtained. There is considerable room for more work to be done to examine the behaviour of DCE with changes to patient age and dental CBCT imaging parameters.

Hacking and Ransomware: Challenges for Institutions Both Large and Small.

OBJECTIVE. This commentary discusses the need for awareness of and action against hackers and ransomware to protect medical data. CONCLUSION. Efforts must be made by medical groups at all levels to reinforce security measures, maintain an upgraded computing infrastructure to combat new hacking techniques, and share knowledge obtained from hacking incidents.

Radiation exposure contribution of the scout abdomen radiograph in common pediatric fluoroscopic procedures.

BACKGROUND: Contrast enema, voiding cystourethrography and upper gastrointestinal studies are the most common fluoroscopic procedures in children. Scout abdomen radiographs have been routinely obtained prior to fluoroscopy and add to the radiation exposure from these procedures. Elimination of unnecessary routine scout radiographs in select studies might significantly reduce radiation exposure to children and improve the overall benefit-to-risk ratio of these fluoroscopic procedures. OBJECTIVE: To determine the radiation exposure contribution of the preliminary/scout abdomen radiographs with respect to the radiation exposure of the total procedure. MATERIALS AND METHODS: We retrospectively collected demographic information and radiation exposure values of dose area product (in Gy-cm(2)) and entrance air kerma (in mGy) - initially for the scout abdomen radiographs done prior to fluoroscopy and subsequently the total procedural radiation values (the combined values of the scout radiograph and fluoroscopic radiation exposure) - in children who underwent contrast enemas, voiding cystourethrograms and upper gastrointestinal studies in a 4-month period. The radiation parameters, including fluoroscopy time, dose area product and entrance air kerma, were available in the log book maintained in the fluoroscopy suite. Fluoroscopy procedures were performed on a single fluoroscopy machine using four frames per second pulse rate and other radiation-minimizing techniques. Usage of the grid to obtain scout radiographs was also recorded. The proportion of radiation exposure from the scout radiograph relative to that of the total procedure was calculated by dividing the individual parameters of the scout to the total procedural values and multiplied by 100 to express these values as a percentage. We calculated mean, median and range and performed statistical analysis of the data. RESULTS: A total of 151 procedures performed on 71 males and 80 females qualified for the study. The age range of the patients was 2 days to 18 years, with a mean of nearly 3.5 years (40 months) and median of 15 months. There were 63 upper gastrointestinal studies, 65 voiding cystourethrography studies and 23 contrast enema studies. The fluoroscopy time for all procedures combined ranged from 0.1 min (6 s) to 2 min, with mean and median values of 0.4 min and 0.3 min, respectively. The fractional radiation exposure contribution for the dose area product of scout abdomen radiograph to the total procedure ranged from 4% to 98%, with mean and median values of 51% and 49%, respectively. The fractional contribution of the scout radiograph to the total procedure for the entrance air kerma values ranged from 6% to 97%, with mean and median values of 29% and 26%, respectively. There was a significant negative correlation (P<0.001) between fluoroscopy radiation time and the proportion of radiation parameters of scout radiograph to total procedural values. CONCLUSION: Scout radiographs can contribute a significant proportion (median values of approximately 50% for the dose area product and 26% for the entrance air kerma) of radiation exposure in common fluoroscopy procedures in children.

Radiation dosimetry of intraoperative cone-beam compared with conventional CT for radiofrequency ablation of osteoid osteoma.

BACKGROUND: Radiofrequency (RF) ablation is the standard of care for the surgical treatment of non-spinal osteoid osteoma and has greatly reduced morbidity associated with surgical excision. Precise placement of the RF ablation probe is necessary to avoid incomplete ablation. Limiting radiation exposure is especially advantageous in the pediatric population in whom osteoid osteoma frequently occurs. The aim of this study was to compare the radiation dosimetry and clinical outcomes among patients treated with RF ablation using three different localization techniques. METHODS: Case-control methods were used to analyze sixty-six cases. Patients were categorized into three treatment groups: (1) intraoperative three-dimensional cone-beam CT (computed tomography) imaging (O-Arm) with surgical navigation (StealthStation S7), (2) intraoperative three-dimensional imaging (O-Arm) only, and (3) radiology suite-based diagnostic CT imaging. Radiation dosimetry and clinical outcome were analyzed with use of the dose-length product and local-relapse-free survival, respectively. RESULTS: Mean age was nineteen years for the twenty-three patients in group 1, twenty years for the seven patients in group 2, and nineteen years for the thirty-six patients in group 3. Mean follow-up was fifty-three months. The mean radiation dose for groups 1, 2, and 3 was 446.62, 379.78, and 1058.83 mGy-cm, respectively. Significant (p < 0.05) differences in the radiation dose existed between groups 1 and 3 and between groups 2 and 3, whereas no difference was found between groups 1 and 2. Local-remission-free survival at three years for groups 1, 2, and 3 was 84.7% (95% confidence interval [CI], 64.5% to 100%), 100% (95% CI, 100% to 100%), and 90.7% (95% CI, 80.7% to 100%), respectively. Fifty-eight (92%) of the sixty-three followed patients were asymptomatic at the latest follow-up visit. CONCLUSIONS: RF ablation using intraoperative cone-beam CT imaging, with or without surgical navigation, was associated with a significantly lower radiation dose compared with ablation using a radiology suite-based CT technique. Ablation using each of the three imaging techniques was equally effective in treating osteoid osteomas with a similar risk of relapse.

A real-time data acquisition and control of gradient coil noise for fMRI identification of hearing disorder in children with history of ear infection.

Early ear infection and trauma, from birth to age 12 are known to have a significant effect on sensory and cognitive development. This effect can be demonstrated through the fMRI study of children who have a history of ear infection compared to a control group. A second research question is the extent to which brain plasticity at an early age can reduce the impact of infection on hearing and cognitive development. Functional Magnetic Resonance Imaging (fMRI) provides a mapping of brain activity in cognitive and sensory regions by recording the oxygenation state of the local cerebral blood flow. The gradient coils of fMRI scanners generate intense acoustic noise (GCN) - to which the subject is in close proximity - in the range of 90 to 140 db SPL during the imaging process. Clearly this noise will impress its signature on low level brain response patterns. An Active Noise Canceller (ANC) system can suppress the effect of GCN on the subject's perception of a phonetic stimulus at the phoneme, word or phrase level. Due to a superimposition of the frequency and time domain components of the test signal and GCN for MR test, the ANC filtering system performs its function in real time - we must capture the brain's response to the test signal AFTER the noise has been removed. This goal is achieved through the application of field programmable gate array (FPGA) technology of NI LabVIEW. The presentation (in the noisy fMRI environment) of test words and phrases to hearing impaired children can identify sources of distortion to their perceptual processes associated with GCN. Once this distortion has been identified, learning strategies may be introduced to replace the hearing function distorted by early infection as well as the short term effect of GCN. The study of speech cognition without the confounding effect of GCN and with the varying level of GCN for a repeated test signal at later age can be allowed to a measure of recovery through brain plasticity.

Dosimetric characterization of a cone-beam O-arm imaging system.

This study compared patient dose and image quality of a mobile O-arm cone beam imaging system in the 3D scan acquisition mode to those of a 64 slice Computed Tomography (CT) imaging system. The investigation included patient dose, scattered radiation, and image quality measurements. The patient dose was measured using a 0.6 cc Farmer ion chamber and 30 cm long Computed Tomography (CT) head and body polymethylmethacrylate (PMMA) phantoms. The results show that under identical radiographic techniques (kVp, mAs, etc.) and with the same scan length, the O-arm in 3D scan acquisition mode delivers approximately half the radiation dose of a 64 slice CT scanner. Scattered radiation was measured at several locations around the O-arm, at 1 m, 2 m and 3 m distances in 3D CT scan acquisition mode with a RadCal 10 x 5-180 pancake ion chamber using a 30 cm long CT body phantom as the source of scatter. Similar measurements were made in a 64 slice CT scanner. The data demonstrate that scattered radiation from the O-arm to personnel involved in a clinical procedure is comparable to that from a 64 slice CT scanner. Image quality was compared by exposing a CATPHAN phantom to comparable doses in both the O-arm and the CT scanner. The resultant images were then evaluated for modulation transfer function (MTF), high-contrast spatial resolution, and low contrast sensitivity for clinical application purpose. The O-arm shows comparable high contrast to the CT (7 lp/cm vs. 8 lp/cm). The low contrast in the O-arm is not visible due to fixed pattern noise. For image guided surgery applications where the location of a structure is emphasized over a survey of all image details, the O-arm has some advantages due to wide radiation beam coverage and lower patient dose. The image quality of the O-arm needs significant improvement for other clinical applications where high image quality is desired.

Measurement of the presampled two-dimensional modulation transfer function of digital imaging systems.

The purpose of this work was to develop methods to measure the presampled two-dimensional modulation transfer function (2D MTF) of digital imaging systems. A custom x-ray "point source" phantom was created by machining 256 holes with diameter 0.107 mm through a 0.5-mm-thick copper plate. The phantom was imaged several times, resulting in many images of individual x-ray "spots." The center of each spot (with respect to the pixel matrix) was determined to subpixel accuracy by fitting each spot to a 2D Gaussian function. The subpixel spot center locations were used to create a 5 x oversampled system point spread function (PSF), which characterizes the optical and electrical properties of the system and is independent of the pixel sampling of the original image. The modulus of the Fourier transform of the PSF was calculated. Next, the Fourier function was normalized to the zero frequency value. Finally, the Fourier transform function was divided by the first-order Bessel function that defined the frequency content of the holes, resulting in the presampled 2D MTF. The presampled 2D MTF of a 0.1 mm pixel pitch computed radiography system and 0.2 mm pixel pitch flat panel digital imaging system that utilized a cesium iodide scintillator was measured. Comparison of the axial components of the 2D MTF to one-dimensional MTF measurements acquired using an edge device method demonstrated that the two methods produced consistent results.