Comparison of pediatric lens scattered dose measurements between axial 40-mm and helical 160-mm detector width computed tomography scan modes.

BACKGROUND: Reports comparing field lens doses between helical scans with a 40-mm detector width and axial scans with a 160-mm detector width using different computed tomography (CT) scanners are currently scarce. OBJECTIVE: To compare scatter doses for lenses between a helical scan with a 40-mm detector width and an axial scan with a 160-mm detector width when using different CT scanners in the context of pediatric chest examinations. MATERIALS AND METHODS: Two different CT machines were used: Revolution CT (GE Healthcare, Waukesha, WI) with a 256-row, 0.625-mm multidetector; and Aquilion ONE GENESIS Edition (Canon Medical Systems, Otawara, Japan) with a 320-row, 0.5-mm multidetector. Three pediatric anthropomorphic phantoms were used, with optically stimulated luminescence dosimeters (OSLDs) placed on the left and right lenses. The scatter dose values measured by the OSLDs were compared between a helical scan with a 40-mm detector width and an axial scan with a 160-mm detector width during pediatric chest CT examinations. RESULTS: Median equivalent doses for the helical and axial scans were 0.12 and 0.12 mSv/mGy for the newborn, 0.17 and 0.16 mSv/mGy for the 1-year-old, and 0.18 and 0.15 mSv/mGy for the 5-year-old, respectively, when using the Revolution CT. With the Revolution CT, no significant differences were observed in the scatter doses between helical and axial scans in the newborn and 1-year-old phantoms. However, the lens scatter dose for the helical scan was approximately 20-35% higher than that for the axial scan in the 5-year-old phantom (P<0.01). The median equivalent doses of eye lenses for the helical and axial scans were 0.12 and 0.07 mSv/mGy for the newborn, 0.07 and 0.05 mSv/mGy for the 1-year-old, and 0.14 and 0.12 mSv/mGy for the 5-year-old, respectively, when using the Aquilion ONE. With the Aquilion ONE, lens scatter doses for the helical scan were approximately 70%, 40%, and 30% higher in the newborn, 1-year-old, and 5-year-old phantoms, respectively, than those for the axial scan (P<0.01). CONCLUSIONS: When using the Aquilion ONE, lens scatter doses for the helical scan were significantly higher in all three phantoms than those for the axial scan. In contrast, when using the Revolution CT, the lens scatter dose for the helical scan was significantly higher in the 5-year-old phantom than that for the axial scan. These results suggest that although scattered doses may vary with respect to the CT scanner and body size, they are generally lower in the case of axial scans.

Impact of beam collimation of z-overscanning on dose to the lens and thyroid gland in paediatric thoracic computed tomography imaging.

BACKGROUND: Adaptive collimation reduces the dose deposited outside the imaged volume along the z-axis. An increase in the dose deposited outside the imaged volume (to the lens and thyroid) in the z-axis direction is a concern in paediatric computed tomography (CT). OBJECTIVE: To compare the dose deposited outside the imaged volume (to the lens and thyroid) between 40-mm and 80-mm collimation during thoracic paediatric helical CT. MATERIALS AND METHODS: We used anthropomorphic phantoms of newborns and 5-year-olds with 40-mm and 80-mm collimation during helical CT. We compared the measured dose deposited outside the imaged volume using optically stimulated luminescence dosimeters (OSLD) at the surfaces of the lens and thyroid and the image noise between the 40-mm and 80-mm collimations. RESULTS: There were significant differences in the dose deposited outside the imaged volume (to the lens and thyroid) between the 40-mm and 80-mm collimations for both phantoms (P < 0.01). CONCLUSION: Compared with that observed for 80-mm collimation in helical CT scans of the paediatric thorax, the dose deposited outside the imaged volume (to the lens and thyroid) was significantly lower in newborns and 5-year-olds with 40-mm collimation.

Radio Frequency Identification Gate System to Identify Misused Personal Dosimeters.

The use of two personal dosimeters, one worn over and one worn under a protective apron, provides the best estimate of effective dose. However, inappropriate positioning of dosimeters is a common occurrence, resulting in abnormally high or low radiation exposure records. Although such incorrect positioning can be identified by radiation exposure records, doing so is time-consuming and labor-intensive for administrators. Therefore, a system that can identify incorrect locations of dosimeters without burdening administrators must be developed. In this study, we developed a radio frequency identification (RFID) gate system that can differentiate between two RFID-tagged dosimeters placed over and under a metal apron and identify misused dosimeters. To simulate the position of the RFID-tagged dosimeters, we designed four dosimeter-wearing classes, including "proper use" and three types of "misuse" (i.e., "reversed," "both under," and "both over"). When the system predicts "misuse" based on the tag reading, the worker is alerted with lights and alarms. The system performance was evaluated using a confusion matrix, with an overall accuracy of 97.75%, demonstrating high classification performance. The safety of the system against life support devices was also investigated, demonstrating that they were not affected by the electric field at 0.3 m or more from the antenna of the system under any transmit powers tested. This RFID gate system is highly capable of identifying incorrectly positioned dosimeters, enabling real-time monitoring of dosimeters to manage their positioning.

Performance of Ultra-High-Resolution Computed Tomography in Super High-Resolution Mode at the Routine Radiation Dose: Phantom Study.

OBJECTIVE: Using a chest phantom, we compared the image quality of ultra-high-resolution computed tomography (U-HRCT) images acquired in super high-resolution (SHR) and normal resolution (NR) mode and at the routine radiation dose. The detector size was 0.25 and 0.5 mm, respectively. METHODS: A chest phantom was scanned on a U-HRCT scanner. The scan parameters were tube voltage 120 kV and volume CT dose index 13.0 mGy, the routine radiation dose for conventional scans. The rotation time was 0.5 s/rot, the number of matrices was 512 in NR and 1024 in SHR mode. For physical evaluation, the modulation transfer function was measured on the spherical simulated nodule, and the noise power spectrum on the cylindrical water phantom. A CT value profile curve was created using an in-house simulated bronchial phantom. For visual evaluation, 3 radiologists and 3 radiology technologists evaluated overall image quality using a 4-grade scale (grade 1, poor; and grade 4, excellent). RESULTS: The 10% of modulation transfer function was 13.5 lp/cm in NR and 14.9 lp/cm in SHR mode ( P <0.01). ƒ peak was 5.6 lp/cm in NR and 8.8 lp/cm in SHR mode ( P <0.01), and the peak of noise power spectrum shifted. On the profile curves, the CT value at the edge changed in NR but not in SHR mode. The overall image quality was grade 3.0 ± 0.7 in SHR and grade 2.0 ± 0.7 in NR mode ( P <0.01). CONCLUSIONS: The image quality of SHR mode with U-HRCT was superior to that of NR mode at the routine radiation dose.

[Organ-based Tube-current Modulation Applied on Different MDCT Scanners: Reduction in the Radiation Dose to the Eye Lens at Head CT].

PURPOSE: Organ-based tube current modulation (OB-TCM) techniques, which are provided by three vendors, reduces the radiation dose to the lens of the eyes by decreasing the tube current, when the X-ray tube passes over the anterior surface of critical organs. However, the characteristics of dose modulation of these techniques are different. The purpose of this study was to understand the performance characteristics of OB-TCM technique of each computed tomography (CT) vendor at head CT. METHODS: We used three CT scanners (SOMATOM Definition Flash; Siemens Healthcare, Revolution CT; GE Healthcare, and Aquilion ONE Genesis Edition; Canon Medical Systems). We measured the radiation dose to the lens surface as evaluation of radiation dose reduction and measured the image noise as index of image quality. We measured the radiation dose rate in the air for analysis of the characteristics of dose modulation in each OB-TCM. RESULTS: When applying OB-TCM, the radiation doses for the lens surface were decreased by 28%, 22%, and 25% for Siemens, GE, and Canon CT scanners, respectively, and the image noise level was increased by 5.6%, 8.5%, and 15.1% for Siemens, GE, and Canon CT scanners, respectively. The characteristics of dose modulation in each OB-TCM were also confirmed by measured the radiation dose rate. CONCLUSION: We confirmed that each OB-TCM has different influence on image quality and radiation doses for lens surface, due to the different characteristics of dose modulation for each CT vendor.

Radiation Dose Reduction With a Low-Tube Voltage Technique for Pediatric Chest Computed Tomographic Angiography Based on the Contrast-to-Noise Ratio Index.

INTRODUCTION: The aim of this study was to evaluate the radiation dose and image quality at low tube-voltage pediatric chest computed tomographic angiography (CTA) that applies the same contrast-to-noise ratio (CNR) index as the standard tube voltage technique. MATERIALS AND METHODS: Contrast-enhanced chest CTA scans of 100 infants were acquired on a 64-row multidetector computed tomography (MDCT) scanner. In the retrospective study, we evaluated 50 images acquired at 120 kVp; the image noise level was set at 25 Hounsfield units. In the prospective study, we used an 80-kVp protocol; the image noise level was 40 Hounsfield units because the iodine contrast was 1.6 times higher than on 120-kVp scans; the CNR was as in the 120-kVp protocol. We compared the CT number, image noise, CT dose index volume (CTDIvol), and the dose-length product on scans acquired with the 2 protocols. A diagnostic radiologist and a pediatric cardiologist visually evaluated all CTA images. RESULTS: The mean CTDIvol and the mean dose-length product were 0.5 mGy and 7.8 mGy-cm for 80- and 1.2 mGy and 20.8 mGy-cm for 120-kVp scans, respectively (P < .001). The mean CTDIvol was 42% lower at 80 kVp than at 120 kVp, and there was no significant difference in the visual scores assigned to the CTA images (P = .28). CONCLUSIONS: With the CNR index being the same at 80-kVp and 120-kVp imaging, the radiation dose delivered to infants subjected to chest CTA can be reduced without degradation of the image quality.

Aortic and Hepatic Contrast Enhancement During Hepatic-Arterial and Portal Venous Phase Computed Tomography Scanning: Multivariate Linear Regression Analysis Using Age, Sex, Total Body Weight, Height, and Cardiac Output.

OBJECTIVE: We evaluated the effect of the age, sex, total body weight (TBW), height (HT) and cardiac output (CO) of patients on aortic and hepatic contrast enhancement during hepatic-arterial phase (HAP) and portal venous phase (PVP) computed tomography (CT) scanning. METHODS: This prospective study received institutional review board approval; prior informed consent to participate was obtained from all 168 patients. All were examined using our routine protocol; the contrast material was 600 mg/kg iodine. Cardiac output was measured with a portable electrical velocimeter within 5 minutes of starting the CT scan. We calculated contrast enhancement (per gram of iodine: [INCREMENT]HU/gI) of the abdominal aorta during the HAP and of the liver parenchyma during the PVP. We performed univariate and multivariate linear regression analysis between all patient characteristics and the [INCREMENT]HU/gI of aortic- and liver parenchymal enhancement. RESULTS: Univariate linear regression analysis demonstrated statistically significant correlations between the [INCREMENT]HU/gI and the age, sex, TBW, HT, and CO (all P < 0.001). However, multivariate linear regression analysis showed that only the TBW and CO were of independent predictive value (P < 0.001). Also, only the CO was independently and negatively related to aortic enhancement during HAP and to liver parenchymal enhancement when the contrast material injection protocol was adjusted for the TBW (P < 0.001). CONCLUSION: By multivariate linear regression analysis only the TBW and CO were significantly correlated with aortic and liver parenchymal enhancement; the age, sex, and HT were not. The CO was the only independent factor affecting aortic and liver parenchymal enhancement at hepatic CT when the protocol was adjusted for the TBW.

Relationship between the radiation doses at nonenhanced CT studies using different tube voltages and automatic tube current modulation during anthropomorphic phantoms of young children.

To compare the radiation dose and image noise of nonenhanced CT scans performed at 80, 100, and 120 kVp with tube current modulation (TCM) we used anthropomorphic phantoms of newborn, 1-year-old, and 5-year-old children. The noise index was set at 12. The image noise in the center of the phantoms at the level of the chest and abdomen was measured within a circumscribed region of interest. We measured the doses in individual tissues or organs with radio-photoluminescence glass dosimeters for each phantom. Various tissues or organs were assigned and the radiation dose was calculated based on the international commission on radiological protection definition. With TCM the respective radiation dose at tube voltages of 80, 100, and 120 was 29.71, 31.60, and 33.79 mGy for the newborn, 32.00, 36.79, and 39.48 mGy for the 1-year-old, and 32.78, 38.11, and 40.85 mGy for the 5-year-old phantom. There were no significant differences in the radiation dose among the tube voltages and phantoms (P > 0.05). Our comparison of the radiation dose using anthropomorphic phantoms of young children showed that the radiation dose of nonenhanced CT performed at different tube voltages with TCM was not significantly different.

Effect of the Motion Correction Technique on Image Quality at 320-Detector Computed Tomography Coronary Angiography in Patients With Atrial Fibrillation.

OBJECTIVE: Adaptive motion correction (AMC) is a new technique that can suppress blurring of the coronary arteries. We evaluated its effect on the image quality of coronary computed tomography angiography in patients with atrial fibrillation (AF). METHODS: Twenty-five patients with persistent AF underwent coronary computed tomography angiography. Axial image data sets were reconstructed with and without AMC and the image noise in the perivascular tissue of the coronary arteries was measured. Two radiologists visually evaluated the overall image quality of the coronary artery segment using a 4-point scale (1, uninterpretable; 4, good). RESULTS: The mean image noise in the perivascular tissue of the right, but not the left coronary artery, was reduced by AMC (43.8 vs 52.5 Hounsfield units; P < 0.01) and the mean image quality score for the right, but not the left coronary artery, was improved by AMC (3.01 vs 2.74; P < 0.01). The image quality scores in patients with a heart rate of 75 to 114 beats per minute tended to be improved by AMC (75-94 beats per minute: P = 0.06; 95-114 beats per minute: P < 0.01); in patients with a heart rate up to 74 or above 115 beats per minute, they were not improved (P = 0.46 and P = 0.13, respectively). CONCLUSIONS: Adaptive motion correction reduced motion artifacts and improved image quality of the right coronary artery in some patients with AF.

A new technique for noise reduction at coronary CT angiography with multi-phase data-averaging and non-rigid image registration.

OBJECTIVES: To investigate the feasibility of a newly developed noise reduction technique at coronary CT angiography (CTA) that uses multi-phase data-averaging and non-rigid image registration. METHODS: Sixty-five patients underwent coronary CTA with prospective ECG-triggering. The range of the phase window was set at 70-80% of the R-R interval. First, three sets of consecutive volume data at 70%, 75% and 80% of the R-R interval were prepared. Second, we applied non-rigid registration to align the 70% and 80% images to the 75% image. Finally, we performed weighted averaging of the three images and generated a de-noised image. The image noise and contrast-to-noise ratio (CNR) in the proximal coronary arteries between the conventional 75% and the de-noised images were compared. Two radiologists evaluated the image quality using a 5-point scale (1, poor; 5, excellent). RESULTS: On de-noised images, mean image noise was significantly lower than on conventional 75% images (18.3 HU ± 2.6 vs. 23.0 HU ± 3.3, P < 0.01) and the CNR was significantly higher (P < 0.01). The mean image quality score for conventional 75% and de-noised images was 3.9 and 4.4, respectively (P < 0.01). CONCLUSIONS: Our method reduces image noise and improves image quality at coronary CTA. KEY POINTS: • We introduce a new method for image noise reduction at cardiac CT. • Multiple data acquisitions of an object and their averaging yield lower noise. • Our method uses multi-phase images reconstructed from unused redundant imaging data. • It reduces image noise by averaging multi-phase images transformed by non-rigid registration. • This method achieves a 20% image noise reduction at cardiac CT.

Measurement of electron density and effective atomic number by dual-energy scan using a 320-detector computed tomography scanner with raw data-based analysis: a phantom study.

We evaluated the accuracy of the electron densities and effective atomic numbers determined by raw data-based dual-energy analysis on a 320-detector computed tomography scanner. The mean (SD) errors between the measured and true electron densities and between the measured and true effective atomic numbers were 1.3% (1.5%) and 3.1% (3.2%), respectively. Electron densities and effective atomic numbers can be determined with high accuracy, which may help to improve accuracy in radiotherapy treatment planning.

[Effects of differences in head holder on image quality and radiation dose in head CT].

PURPOSE: For emergency or pediatric head CT scans, a simplified pillow made of hard sponge instead of a dedicated head holder may be used if it is difficult to immobilize the head. However, the radiation dose when using a simplified head holder may be increased due to radiation absorption by the patient couch if the automatic exposure control (AEC) system is used. In this phantom study, we compared the radiation dose delivered when using a dedicated and a simplified head holder. MATERIALS AND METHODS: We used a dedicated-type and a pillow-type head holder made of hard sponge (simplified head holder). We placed a 20 cm-diameter cylindrical phantom made of water-equivalent material and an anthropomorphic head phantom in the head holders and then scanned them five times with a 64-detector CT scanner (VCT, GE Healthcare). We performed step-and-shoot and helical scanning with AEC; the noise index was set to 2.8. We measured the radiation dose using fluorescent glass dosimeters in the head phantom and the image noise at five sites in the cylindrical phantom. All values were averaged. RESULTS: With step-and-shoot scans, the mean image noise with the dedicated and the simplified head holder was 3.30 ± 0.05 [SD] and 3.20 ± 0.05, respectively. With helical scans they were 3.00 ± 0.09 and 2.88 ± 0.03, respectively. There was no statistically significant difference (p = 0.02 and 0.04, Student's t-test). The radiation doses with the dedicated and the simplified head holder were 58.6 and 70.4 mGy, respectively, for step-and-shoot scanning and 41.8 and 49.0 mGy, respectively, for helical scanning. The doses were thus significantly higher with the simplified head holder for both step-and-shoot and helical scanning (p < 0.01 and < 0.01). CONCLUSION: We recommend the use of a dedicated head holder for head scanning with AEC since the radiation dose was lower than with the simplified head holder.

Task-based assessment of resolution properties of CT images with a new index using deep convolutional neural network.

In this study, we propose a method for obtaining a new index to evaluate the resolution properties of computed tomography (CT) images in a task-based manner. This method applies a deep convolutional neural network (DCNN) machine learning system trained on CT images with known modulation transfer function (MTF) values to output an index representing the resolution properties of the input CT image [i.e., the resolution property index (RPI)]. Sample CT images were obtained for training and testing of the DCNN by scanning the American Radiological Society phantom. Subsequently, the images were reconstructed using a filtered back projection algorithm with different reconstruction kernels. The circular edge method was used to measure the MTF values, which were used as teacher information for the DCNN. The resolution properties of the sample CT images used to train the DCNN were created by intentionally varying the field of view (FOV). Four FOV settings were considered. The results of adapting this method to the filtered back projection (FBP) and hybrid iterative reconstruction (h-IR) images indicated highly correlated values with the MTF10% in both cases. Furthermore, we demonstrated that the RPIs could be estimated in the same manner under the same imaging conditions and reconstruction kernels, even for other CT systems, where the DCNN was trained on CT systems produced by the same manufacturer. In conclusion, the RPI, which is a new index that represents the resolution property using the proposed method, can be used to evaluate the resolution of a CT system in a task-based manner.

Effectiveness of low tube voltage scan in the exposure dose for lenses during paediatric thoracic CT examination: anthropomorphic phantoms study.

To determine whether using lower-tube voltage reduces the scattered dose for the lens during paediatric thoracic computed tomography (CT). Two paediatric anthropomorphic phantoms (ATOM Phantom, CIRS, Norfolk, Virginia, USA) representing a newborn and 5-year-old were placed on the gantry of CT scanner, and optically stimulated luminescence dosemeters were placed on the left and right lenses, in front of the left and right thyroid glands, in front of the left and right mammary glands, and in front of and behind the mammary gland level and we measured scattered dose of the optically stimulated luminescence dosemeter was compared for each phantom between 80 and 120 kVp. Significant differences were observed in the scatter doses for the lens between 80 and 120 kVp (p < 0.01). Compared with the 120 kVp scan, the scatter doses for the lens were ~15-40% lower in newborn and 5-year-olds using the 80 kVp scan during paediatric CT.

Occupational radiation exposure among medical personnel in university and general hospitals in Japan.

OBJECTIVE: This study aimed to compare the occupational radiation exposure of medical workers between general hospitals and university hospitals. METHODS: Radiation exposure data from three hospitals in Hiroshima city, including one university hospital and two general hospitals, were collected using personal dosimeters. Monthly radiation doses were analyzed, and the annual sum of radiation exposure dose was calculated for 538 subjects in general hospitals and 1224 subjects in the university hospital. To assess the impact of locality, additional data from Nagasaki University Hospital and Fukushima Medical University Hospital were included for comparative analysis. Professional affiliations, such as doctors, nurses, and radiological technologists, were considered in the evaluation. RESULTS: The study revealed slight but significant differences in radiation doses between general and university hospitals. In general hospitals, except for radiological technologists, a slightly higher radiation dose was observed compared to university hospitals. Despite the annual increase in the use of medical radiation, the majority of hospital workers in both settings adhered to safety guidelines, with occupational radiation exposure remaining below the limit of detection (LOD). Workers who involved in fluoroscopic procedure, whether at university or general hospitals, had higher radiation doses than those who did not. CONCLUSION: The study's primary conclusion is that workers in general hospitals experience a slight but significantly higher radiation dose and a lower percentage below the LOD compared to university hospitals. The observed difference is attributed to the greater workload at general hospitals than at university hospitals, and also may be due to the different nature of university hospital and general hospital. University hospitals, characterized by greater academic orientation, tend to benefit from comprehensive support systems, specialized expertise, and advanced technology, leading to more structured and regulated radiation control. These findings provide a basis for targeted interventions, improved safety protocols.

Comparison of the equivalent doses of the eye lenses, thyroid, and mammary gland among three pediatric and one adult anthropomorphic phantom during the chest CT examinations using a 40 mm volume helical scan.

Equivalent doses for the eye lenses, thyroid, and mammary glands were measured and compared between one adult and three pediatric anthropomorphic phantoms during chest computed tomography (CT) using 40 mm volume helical scan on the Aquilion ONE GENESIS Edition CT equipment. Placing an optically stimulated luminescence dosemeter (OSLD) on the eye lenses, thyroid, and mammary gland, we measured and compared the equivalent dose of OSLD among different phantoms during chest CT using a helical scan. Compared with adults, the equivalent doses to the eye lens, thyroid, and mammary glands were ~81%, 77%, and 63% lower in newborns, 1-year-olds, and 5-year-olds using comparable image noise during chest CT.

[Validation of Optimal Imaging Conditions for Coronary Computed Tomography Angiography Using High-definition Mode and Deep Learning Image Reconstruction Algorithm].

PURPOSE: To verify the optimal imaging conditions for coronary computed tomography angiography (CCTA) examinations when using high-definition (HD) mode and deep learning image reconstruction (DLIR) in combination. METHOD: A chest phantom and an in-house phantom using 3D printer were scanned with a 256-row detector CT scanner. The scan parameters were as follows - acquisition mode: ON (HD mode) and OFF (normal resolution [NR] mode), rotation time: 0.28 s/rotation, beam coverage width: 160 mm, and the radiation dose was adjusted based on CT-AEC. Image reconstruction was performed using ASiR-V (Hybrid-IR), TrueFidelity Image (DLIR), and HD-Standard (HD mode) and Standard (NR mode) reconstruction kernels. The task-based transfer function (TTF) and noise power spectrum (NPS) were measured for image evaluation, and the detectability index (d') was calculated. Visual evaluation was also performed on an in-house coronary phantom. RESULT: The in-plane TTF was better for the HD mode than for the NR mode, while the z-axis TTF was lower for DLIR than for Hybrid-IR. The NPS values in the high-frequency region were higher for the HD mode compared to those for the NR mode, and the NPS was lower for DLIR than for Hybrid-IR. The combination of HD mode and DLIR showed the best value for in-plane d', whereas the combination of NR mode and DLIR showed the best value for z-axis d'. In the visual evaluation, the combination of NR mode and DLIR showed the best values from a noise index of 45 HU. CONCLUSION: The optimal combination of HD mode and DLIR depends on the image noise level, and the combination of NR mode and DLIR was the best imaging condition under noisy conditions.

Variable procedural strategies adapted to anatomical characteristics in catheter ablation of the cavotricuspid isthmus using a preoperative multidetector computed tomography analysis.

OBJECTIVES: This study aimed to investigate the anatomical characteristics complicating cavotricuspid isthmus (CTI) ablation and the effectiveness of various procedural strategies. METHODS AND RESULTS: This study included 446 consecutive patients (362 males; mean age 60.5 ± 10.4 years) in whom CTI ablation was performed. A total of 80 consecutive patients were evaluated in a preliminary study. The anatomy of the CTI was evaluated by multidetector row-computed tomography (MDCT) prior to the procedure. A multivariate logistic regression analysis revealed that the angle and mean wall thickness of the CTI, a concave CTI morphology, and a prominent Eustachian ridge, were associated with a difficult CTI ablation (P < 0.01). In the main study, 366 consecutive patients were divided into 2 groups: a modulation group (catheter inversion technique for a concave aspect, prominent Eustachian ridge, and steep angle of the CTI or increased output for a thicker CTI) and nonmodulation group (conventional strategy). The duration and total amount of radiofrequency energy delivered were significantly shorter and smaller in the modulation group than those in the nonmodulation group (162.2 ± 153.5 vs 222.7 ± 191.9 seconds, P < 0.01, and 16,962.4 ± 11,545.6 vs 24,908.5 ± 22,804.2 J, P < 0.01, respectively). The recurrence rate of type 1 atrial flutter after the CTI ablation in the nonmodulation group was significantly higher than that in the modulation group (6.3 vs 1.7%, P = 0.02). CONCLUSION: Changing the procedural strategies by adaptating them to the anatomical characteristics improved the outcomes of the CTI ablation.

Evaluation of Inappropriate Positioning of Dosimeters in Medical Workers Based on Dose Equivalent Hp(10).

ABSTRACT: This report presents a new method to characterize the inappropriate positioning of dosimeters based on the dose equivalent Hp(10). The Hp(10) values of medical workers were measured monthly for 12 mo using two personal dosimeters. Using the ratio between the values of Hp(10) recorded from dosimeters worn over and under protective aprons [Hp(10) over and Hp(10) under , respectively], 670 pairs of dosimeter readings were categorized into a proper use group [Hp(10) over /Hp(10) under ≥ 5] and a misuse group [Hp(10) over /Hp(10) under < 5]. Following personal interviews, the readings in the misuse group were classified into the following six subgroups: "reversed," "sometimes reversed," "both under," "both over," "without apron," and "not specified." Ultimately, the scatter plot of "Hp(10) over - Hp(10) under " vs. Hp(10) over was identified as the most promising tool for clarifying the misuse patterns of dosimeters, as individual readings were mapped to the locations of the corresponding subgroups in the obtained graphs. Our results are expected to facilitate efficient and accurate usage of dosimeters by medical workers.

Usefulness of large beam-shaping filters at different tube voltages of newborn chest CT.

BACKGROUND: To investigate optimizing the use of different beam shaping filters (viz. small, medium and large) when using different tube voltages during the newborn chest computed tomography (CT) on a GE Lightspeed VCT scanner. METHODS: We used pediatric anthropomorphic phantoms with a 64 detector-row CT scanner while scanning the chest. A real-time skin dosimeter (RD - 1000; Trek Corporation, Kanagawa, Japan) was positioned into the phantom center of the body, the surface of the body back, and the right and left mammary glands. We performed and compared six scan protocols using small, medium, and large beam shaping filters at 80 and 120 kVp protocols. RESULT: There were no significant differences in the image noise for the chest scan among the different beam shaping filters. By using the large beam shaping filter at 80 kVp, it was possible to reduce the exposure dose by 5% in comparison with the small beam shaping filter, and by 10% in comparison with the medium beam shaping filter. By using the large beam shaping filter at 120 kVp, it was possible to reduce the exposure dose by 15% in comparison with the small beam shaping filter and by 20% in comparison with the medium beam shaping filter (p < 0.01). CONCLUSION: The large beam shaping filter had the most dose reduction effect during newborn chest CT on a GE Lightspeed VCT scanner. The additional copper filtration being present in the large bowtie filter of the GE Lightspeed CT scanner when using different tube voltages is more effective in reducing radiation exposure in children.