Effective Tube Current Research Articles

Assessment of the distribution and volume of air chambers around the inner auditory canal on high-resolution computed tomography scans of the temporal bone.

Assessment of the distribution and volume of air chambers around the inner auditory canal on high-resolution computed tomography scans of the temporal bone.

Radiation dose and cancer risks from radiation exposure during abdominopelvic computed tomography (CT) scans: comparison of diagnostic and radiotherapy treatment planning CT scans.

In the present study, radiation doses and cancer risks resulting from abdominopelvic radiotherapy planning computed tomography (RP-CT) and abdominopelvic diagnostic CT (DG-CT) examinations are compared. Two groups of patients who underwent abdominopelvic CT scans with RP-CT (n = 50) and DG-CT (n = 50) voluntarily participated in this study. The two groups of patients had approximately similar demographic features including mass, height, body mass index, sex, and age. Radiation dose parameters included CTDIvol, dose-length product, scan length, effective tube current, and pitch factor, all taken from the CT scanner console. The ImPACT software was used to calculate the patient-specific radiation doses. The risks of cancer incidence and mortality were estimated based on the BEIR VII report of the US National Research Council. In the RP-CT group, the mean ± standard deviation of cancer incidence risk for all cancers, leukemia, and all solid cancers was 621.58 ± 214.76, 101.59 ± 27.15, and 516.60 ± 189.01 cancers per 100,000 individuals, respectively, for male patients. For female patients, the corresponding risks were 742.71 ± 292.35, 74.26 ± 20.26, and 667.03 ± 275.67 cancers per 100,000 individuals, respectively. In contrast, for DG-CT cancer incidence risks were 470.22 ± 170.07, 78.23 ± 18.22, and 390.25 ± 152.82 cancers per 100,000 individuals for male patients, while they were 638.65 ± 232.93, 62.14 ± 13.74, and 575.73 ± 221.21 cancers per 100,000 individuals for female patients. Cancer incidence and mortality risks were greater for RP-CT than for DG-CT scans. It is concluded that the various protocols of abdominopelvic CT scans, especially the RP-CT scans, should be optimized with respect to the radiation doses associated with these scans.

Radiation Organ Dose Measurement and Cancer Risk Estimation in CT Examination on Trauma Patients

Background: This study intended to measure radiation doses to various organs and calculate the risk of cancer incidence from neck computed tomography and head computed tomography scans of trauma patients by using a thermoluminescent dosimeter. Methods:We assessed 93 patients who presented to the Emergency Department. Based on their health conditions, different computed tomography scans were performed. We used a fixed tube current of 200 mAs and tube voltage of 120 kVp for all patients. Next, we derived the effective radiation dose by multiplying the dose length product and conversion factor of each computed tomography scan based on the International Commission on Radiological Protection 103. Organ dose estimations were calculated from the dosimeter readout. We calculated the life attributable risk for cancer incidence based on the Committee on the Biological Effects of Ionizing Radiation VII preferred models. Results: Neck computed tomography scans had a mean effective dose of 2.18 mSv. The mean effective dose for head computed tomography scans was 1.53 mSv. The highest mean equivalent organ dose was for the thyroid with the neck computed tomography scan and the lenses of the eyes with the head computed tomography scan. There was no significant difference between scan lengths in each computed tomography acquisition. There was a noticeable correlation observed between effective radiation dose and tube current. As anticipated, young people had a higher life attributable risk of cancer compared to the elderly. This amount was less than 0.011 per 100 persons for both computed tomography studies. Conclusion: Our data showed a significant organ radiation dose in both neck and head computed tomography scans, not only for the thyroid and the lenses of the eyes, but also for the chest.

P027] Diagnostic reference levels for computed tomography examinations of adult patients

Purpose Diagnostic Reference Levels (DRLs) are important databases which help to optimize the radiation exposure to patients undergoing similar radiological examinations at different centers operating regionwide, countrywide or worldwide. This study aims to develop regional DRLs for the most common computed tomography (CT) examinations carried out around Izmir, Turkey, and to compare the results with national and international studies present in the literature. Methods Survey data were based on 5 most common adult CT examinations (Head, Neck, Thorax, Abdomen-Pelvis and Thorax-Abdomen-Pelvis) carried out in 4 different radiology departments located in Izmir (n = 50 per protocol for each department; i.e. n = 1000 in total). Collected data included the examination accession number, patient sex, age, effective tube current, tube voltage, Computed Tomography Dose Index-Volume ( CTDI vol ) and Dose Length Product (DLP) for each examination. Among all the exposure parameters, only CTDI vol and DLP values were statistically analyzed, since they account for the overall dosimetric information regarding the examination. CTDI vol information were based on body phantoms for all examinations except head examinations which were based on head phantoms for all departments. Third quartiles of CTDI vol and DLP datasets have been recognized as DRLs parallel to the literature. Statistical analysis has been performed by using IBM SPSS 23 Statistics software program. Results 51.3% of patients were male and 48.7% was female, with a mean age of 57 (between 18 and 93). DRLs for CTDI vol were recorded as 70 mGy, 16 mGy, 15 mGy, 23 mGy and 16 mGy for head, neck, thorax, abdomen-pelvis and thorax-abdomen-pelvis examinations respectively, while DLP results were 1385 mGy.cm, 605 mGy.cm, 567 mGy.cm, 998 mGy.cm and 1180 mGy.cm with respect to the same order. Conclusions This study was carried out on a wide range of patient age and size. Results agree well with national and international data, except for the head examinations which were observed to slightly exceed the DRLs established by other countries. Consequently, it is planned to bring this study to a furtherly comprehensive point based on data collected countrywide.

CT Angiography in the Lower Extremity Peripheral Artery Disease Feasibility of an Ultra-Low Volume Contrast Media Protocol

PurposeThe ALARA principle is not only relevant for effective dose (ED) reduction, but also applicable for contrast media (CM) management. Therefore, the aim was to evaluate the feasibility of an ultra-low CM protocol in the assessment of peripheral artery disease (PAD).Materials and methodsFifty PAD patients were scanned on third-generation dual-source computed tomography, from diaphragm to the forefoot, as follows: tube voltage: 70 kV, reference effective tube current: 90 mAs, collimation: 192 × 2 × 0.6 mm, with individualized acquisition timing. The protocol ED (mSv) was quantified with dedicated software. CM protocol consisted of 15 ml test bolus and 30 ml main bolus (300 mgI/ml) injected at 5 ml/s, followed by a 40 ml saline chaser at the same flow rate. Aorto-popliteal bolus transit time was used to calculate the overall acquisition time and delay. Objective (hounsfield units—HU; contrast-to-noise ratio—CNR) and subjective image quality (four-point Likert score) were assessed at different anatomical regions from the aorta down to the forefoot.ResultsMean attenuation values were exceeding 250 HU from aorta down to the anterior tibial artery with CNR < 13. However, decline in attenuation was observed in more distal region with mean values of 165 and 199 HU, in left and right dorsalis pedis artery, respectively. Mode subjective image quality from the level of aorta down to the popliteal segment was excellent; below the knee mode score was good. The mean ED per protocol was 1.1 ± 0.5 mSv.ConclusionUse of an ultra-low CM volume protocol at 70 kV is feasible in the evaluation of PAD, resulting in good to excellent image quality with mean ED of 1.1 ± 0.5 mSv.Level of evidenceLevel 3, Local non-random sample

Improving CT quality with optimized image parameters for radiation treatment planning and delivery guidance

Abstract Background and purpose CT scan protocols are often created with imaging parameters set to minimize imaging dose with acceptable image quality for diagnostic purpose. This study aimed to optimize CT imaging parameters to help accurately delineate structures for radiation therapy planning and delivery guidance. Materials and methods Imaging parameters were optimized with CT data acquired for a phantom to create image quality enhancement (IQE) protocols, which were subsequently used to scan a prostate and a pancreatic cancer patient who underwent image-guided radiotherapy (IGRT). The patient images were compared with those scanned with standard clinical protocols, the quality of these images was assessed with various methods (survey, inter- and intra-observer variations, and dice coefficient analysis) for the two patient cases. Results An effective tube current–time product of ∼1000 mAs was found to be a reasonable choice to balance CT quality and CT dose. With increased dose and penetration taken into account, 100 and 120 kV tube voltages were found appropriate for the IQE protocols. The inter- and intra-observer variations for the IQE data were smaller than those with the standard protocols. Dice coefficient analysis indicated that the IQE protocols lead to improved dice coefficient by as much as 8 percentage points for the two cases studied. Conclusion CT image quality can be improved with the IQE protocols created in this study, to provide better soft tissue contrast, which would be beneficial for use in radiation therapy, e.g., for planning data acquisition or for IGRT for hypo-fractionated treatments.

Single-energy pediatric chest computed tomography with spectral filtration at 100 kVp: effects on radiation parameters and image quality.

Most of the applied radiation dose at CT is in the lower photon energy range, which is of limited diagnostic importance. To investigate image quality and effects on radiation parameters of 100-kVp spectral filtration single-energy chest CT using a tin-filter at third-generation dual-source CT in comparison to standard 100-kVp chest CT. Thirty-three children referred for a non-contrast chest CT performed on a third-generation dual-source CT scanner were examined at 100kVp with a dedicated tin filter with a tube current-time product resulting in standard protocol dose. We compared resulting images with images from children examined using standard single-source chest CT at 100kVp. We assessed objective and subjective image quality and compared radiation dose parameters. Radiation dose was comparable for children 5years old and younger, and it was moderately decreased for older children when using spectral filtration (P=0.006). Effective tube current increased significantly (P=0.0001) with spectral filtration, up to a factor of 10. Signal-to-noise ratio and image noise were similar for both examination techniques (P≥0.06). Subjective image quality showed no significant differences (P≥0.2). Using 100-kVp spectral filtration chest CT in children by means of a tube-based tin-filter on a third-generation dual-source CT scanner increases effective tube current up to a factor of 10 to provide similar image quality at equivalent dose compared to standard single-source CT without spectral filtration.

Low Dose MDCT with Tube Current Modulation: Role in Detection of Urolithiasis and Patient Effective Dose Reduction

Urolithiasis is one of the major, recurring problem in young individuals and CT being the commonest diagnostic modality used. In order to reduce the radiation dose to the patient who are young and as stone formation is a recurring process; one of the simplest way would be, low dose CT along with tube current modulation. Aim of this study was to compare the sensitivity and specificity of low dose (70mAs) with standard dose (250mAs) protocol in detecting urolithiasis and to define the tube current and mean effective patient dose by these protocols. A prospective study was conducted in 200 patients over a period of 2 years with acute flank pain presentation. CT was performed in 100 cases with standard dose and another 100 with low dose protocol using tube current modulation. Sensitivity and specificity for calculus detection, percentage reduction of dose and tube current with low dose protocol was calculated. Urolithiasis was detected in 138 patients, 67 were examined by high dose and 71 were by low dose protocol. Sensitivity and Specificity of low dose protocol was 97.1% and 96.4% with similar results found in high BMI patients. Tube current modulation resulted in reduction of effective tube current by 12.17%. The mean effective patient dose for standard dose was 10.33 mSv whereas 2.92 mSv for low dose with 51.13-53.8% reduction in low dose protocol. The study has reinforced that low-dose CT with tube current modulation is appropriate for diagnosis of urolithiasis with significant reduction in tube current and patient effective dose.

Entrance skin dosimetry and size-specific dose estimate from pediatric chest CTA

BackgroundSize-specific dose estimate (SSDE), which corrects CT dose index (CTDI) for body diameter and is a better measure of organ dose than is CTDI, has not yet been validated in vivo. ObjectiveThe purpose was to determine the correlation between SSDE and measured breast entrance skin dose (ESD) for pediatric chest CT angiography across a variety of techniques, scanner models, and patient sizes. MethodsDuring 42 examinations done on 4 different scanners over 7 years, we measured mid-sternal ESD as an approximation of breast dose with skin dosimeters. We recorded age, weight, effective tube current, kilovoltage potential, console CTDI, and dose-length product, from which we calculated effective dose. We measured effective chest diameter to convert CTDI to SSDE, and we correlated SSDE with measured ESD, using linear regression. We evaluated image quality to answer the clinical question. ResultsPatient mean (±SD) age was 8.4 ± 6.1 years (median, 7.9 years; range, 0.02–19.5 years); mean weight was 35 ± 27 kg (median, 26 kg; range, 3.5–115 kg); effective chest diameter was 20 ± 7 cm (median, 19 cm; range, 10–35 cm). Mean effective dose was 2.9 ± 2.8 mSv (median, 2.2 mSv; range, 0.1–14.4 mSv). We observed a linear correlation (R2 = 0.98, P < .005) between SSDE (mean, 11 ± 11mGy; median, 7 mGy; range, 0.5–40 mGy) and breast ESD (mean, 12 ± 11 mGy; median, 7 mGy; range, 0.3–44 mGy). Our doses, which compared favorably with those previously reported, decreased significantly (P < .05) during the course of our study, because of the introduction of automatic exposure control, low kilovoltage, and high pitch techniques. All studies were of diagnostic quality. ConclusionSSDE is a valid dose measure in children undergoing chest CT angiography over a wide range of scanner platforms, techniques, and patient sizes, and it may be used to model breast dose and to document the results of dose reduction strategies.

E0703 Radiation dosage comparison between different coronary CT angiography protocols

ObjectiveProspective ECG gated coronary CT angiography (pECG-CCTA) has become an alternative CT protocol. It limits radiation exposure at a narrowed predefined end diastolic time segment instead of during the entire...

Urinary Calculi Composed of Uric Acid, Cystine, and Mineral Salts: Differentiation with Dual-Energy CT at a Radiation Dose Comparable to That of Intravenous Pyelography

To retrospectively evaluate radiation dose, image quality, and the ability to differentiate urinary calculi of differing compositions by using low-dose dual-energy computed tomography (CT). The institutional review board approved this retrospective study; informed consent was waived. A low-dose dual-energy CT protocol (tube voltage and reference effective tube current-time product, 140 kV and 23 mAs and 80 kV and 105 mAs; collimation, 64 × 0.6 mm; pitch, 0.7) for the detection of urinary calculi was implemented into routine clinical care. All patients (n = 112) who were examined with this protocol from July 2008 to August 2009 were included. The composition of urinary calculi was assessed by using commercially available postprocessing software and was compared with results of the reference standard (ex vivo infrared spectroscopy) in 40 patients for whom the reference standard was available. Effective doses were calculated. Image quality was rated subjectively and objectively and was correlated with patient size expressed as body cross-sectional area at the level of acquisition by using Spearman correlation coefficients. One calcified concrement in the distal ureter of an obese patient was mistakenly interpreted as mixed calcified and uric acid. One struvite calculus was falsely interpreted as cystine. All other uric acid, cystine, and calcium-containing calculi were correctly identified by using dual-energy CT. The mean radiation dose was 2.7 mSv. The average image quality was rated as acceptable, with a decrease in image quality in larger patients. Low-dose unenhanced dual-source dual-energy CT can help differentiate between calcified, uric acid, and cystine calculi at a radiation dose comparable to that of conventional intravenous pyelography. Because of decreased image quality in obese patients, only nonobese patients should be examined with this protocol.

TU-E-201B-06: Relative Dose of Fast KV Switching Dual-Energy CT

Purpose: Dual‐energy CT has attracted much attention in recent years. Most recently, a fast‐kVp switching (FKS) dual‐energy method has been presented with clinical and phantom results to demonstrate its efficacy. The purpose of our study was to quantitatively compare the CTDIw of FKS and routine CT exams under the body and head conditions. Material and Method: For a fair comparison, the low contrast detectability (LCD) was matched before measuring dose. In FKS protocols, an x‐ray generator switch rapidly between 140kVp and 80kVp in adjacent views, and the effective tube current is around 600mA. In addition to the tube voltage and current, the flux ratio between high and low kVp is optimized by asymmetric sampling of 35%–65%. The head and body protocols further differ by the gantry speed and type of bowtie filter. For baseline single‐energy, we followed the IEC standard head and body protocols but iteratively adjusted the tube current (mA) in order to match the LCD.CTDIw was measured using either a 16 cm or a 32 cm PMMA phantom of at least 14 cm in length. The LCD was measured using the water section of Catphan 600. To make the study repeatable, the automated statistical LCD measurement tool available on GE Discovery CT750 scanner was used in this work. Result: The mean CTDIw for the head and body single‐energy acquisitions were 57.5mGy and 29.2mGy, respectively. The LCD was measured at 0.45% and 0.42% (slice thickness=5mm, object size=3mm, central 4 images), respectively. The average CTDIw for FKS head and body scans was 70.4mGy and 33.4mGy, respectively, at the optimal monochromatic energy of 65 keV. The corresponding LCD was measured at 0.45% and 0.43%, respectively. Conclusion: This demonstrates that, with matching LCD,CTDIw of FKS is comparable to that of routine CT exams under head and body conditions.

Arm Raising at Exposure-controlled Multidetector Trauma CT of Thoracoabdominal Region: Higher Image Quality, Lower Radiation Dose

To evaluate the effect of arm position on image quality and effective radiation dose in an automatic exposure-controlled (AEC) multidetector thoracoabdominal computed tomography (CT) protocol in trauma patients. This retrospective study of the data of 177 trauma patients (117 male; median age, 39 years) was approved by the institutional ethics board, with informed patient consent waived. Patients underwent scanning by using an AEC 16-detector thoracoabdominal CT protocol in which both arms were raised above the shoulder region (standard-position group, 132 patients), one arm was raised and the other was down (one-arm group, 27 patients), or both arms were down (two-arm group, 18 patients). Objective and subjective image quality was assessed. Individual effective radiation dose was calculated from the effective tube current-time product per exposed section. For this purpose, section location-dependent conversion factors were derived by using a CT dosimetry calculator. The effect of arm position on effective dose was quantified by using linear regression analysis with correction for patient volume and attenuation. Compared with the image quality in the standard-position group, the image quality in the one- and two-arm groups was decreased but within acceptable diagnostic limits. The median corrected effective dose in the standard-position group was 18.6 mSv; the dose in the one-arm group was 18% (95% confidence interval: 11%, 25%) higher than this, and that in the two-arm group was 45% (95% confidence interval: 34%, 57%) higher. Omitting arm raising results in lower but acceptable image quality and a substantially higher effective radiation dose. Hence, effort should be made to position the arms above the shoulder when scanning trauma patients. Clinical trial registration no. NCT00228111.

Characterization of the Relation Between CT Technical Parameters and Accuracy of Quantification of Lung Attenuation on Quantitative Chest CT

The purpose of this study was to assess the compromise between CT technical parameters and the accuracy of CT quantification of lung attenuation. Materials that simulate water (0 H), healthy lung (-650 H), borderline emphysematous lung (-820 H), and severely emphysematous lung (-1,000 H) were placed at both the base and the apex of the lung of an anthropomorphic phantom and outside the phantom. Transaxial CT images through the samples were obtained while the effective tube current was varied from 440 to 10 mAs, kilovoltage from 140 to 80 kVp, and slice thickness from 0.625 to 10 mm. Mean +/- SD attenuation within the samples and the standard quantitative chest CT measurements, the percentage of pixels with attenuation less than -910 H and 15th percentile of attenuation, were computed. Outside the phantom, variations in CT parameters produced less than 2.0% error in all measurements. Within the anthropomorphic phantom at 30 mAs, error in measurements was much larger, ranging from zero to 200%. Below approximately 80 mAs, mean attenuation became increasingly biased. The effects were most pronounced at the apex of the lungs. Mean attenuation of the borderline emphysematous sample of apex decreased 55 H as the tube current was decreased from 300 to 30 mAs. Both the 15th percentile of attenuation and percentage of pixels with less than -910 H attenuation were more sensitive to variations in effective tube current than was mean attenuation. For example, the -820 H sample should have 0% of pixels less than -910 H, which was true at 400 mA. At 30 mA in the lung apex, however, the measurement was highly inaccurate, 51% of pixels being below this value. Decreased kilovoltage and slice thickness had analogous, but lesser, effects. The accuracy of quantitative chest CT is determined by the CT acquisition parameters. There can be significant decreases in accuracy at less than 80 mAs for thin slices in an anthropomorphic phantom, the most pronounced effects occurring in the lung apex.

Radiation Dose Reduction for Augmentation Mammography

Patients who undergo cosmetic augmentation have larger and denser breasts and receive higher radiation doses during mammography than women without implants. In this study we evaluated the dose increase and techniques for dose reduction. Mean glandular dose to the breast during screening mammography was measured for 206 women who had undergone breast augmentation. For 13 of these women, mean glandular dose from preoperative mammography also was measured. Effective tube current, peak kilovoltage, and breast thickness were measured, and mean glandular dose was calculated for 1,632 images. Two screen-film combinations and three target-filter combinations were studied. For four-view augmentation mammography with a molybdenum-molybdenum (Mo-Mo) target-filter combination, mean glandular dose was reduced 35%, from 10.7 to 7.0 mGy, by changing the screen-film combination from 100 to 190 speed. For four-view augmentation mammography, mean glandular dose was reduced 24% by changing the target-filter combination from Mo-Mo to rhodium-rhodium (Rh-Rh) for full views of breasts containing implants. For four-view augmentation mammography, mean glandular dose was reduced 50% by changing the screen-film combination from 100 to 190 speed and changing the target-filter combination from Mo-Mo to Rh-Rh for implant-full views. Mean glandular dose per breast from four-view augmentation mammography with the 100-speed screen-film and Mo-Mo target-filter combinations averaged 10.7 mGy, which is 3.1 times higher than the 3.4 mGy for conventional two-view mammography of breasts without implants. In 40 years of screening, this number represents a more than tripled lifetime attributable risk of radiation-induced breast cancer--an unacceptable level. Use of faster screen-film combinations, use of Rh-Rh target-filter combinations, and acquisition of three rather than four views are dose-reduction methods that together result in a 66% dose reduction, from 10.7 to 3.6 mGy. Mean glandular dose should be kept less than 7.0 mGy per breast for screening mammography of patients with breast implants.

Urinary Stone Disease: Comparison of Standard-Dose and Low-Dose with 4D MDCT Tube Current Modulation

The purpose of this prospective study was to compare the performance of standard-dose MDCT with that of low-dose MDCT with tube current modulation in patients with renal colic. Three hundred patients underwent 6- and 16-MDCT in 150 standard-dose examinations (6-MDCT effective tube current, 95 mAs at 130 kV; 16-MDCT effective tube current, 120 mAs at 120 kV) and 150 low-dose examinations (6-MDCT effective tube current, 51 mAs at 110 kV; 16-MDCT effective tube current, 70 mAs at 120 kV), all performed with 4D tube current modulation. Two experienced radiologists using a clinical workstation and blinded to scan parameters prospectively viewed the images from the 300 examinations. In a second session, one experienced radiologist and two first-year residents using a clinical workstation retrospectively reviewed images from 100 randomly selected standard-dose and 100 randomly selected low-dose examinations. Tube current modulation reduced effective tube current 25-31% in all examinations. Mean effective dose was 1.41-1.58 mSv for low-dose examinations, which reached additional dose reduction of 51.2-64.3% in comparison with standard-dose examinations. Excellent correlation existed between mean tube current and body mass index of the patients. Spearman's correlation coefficient was 0.85-0.88 for all examinations. The sensitivity of low-dose examinations interpreted by two experienced reviewers was 97.3-98.6%; specificity, 93.5%; and accuracy, 95.3%. These findings were comparable with those for standard-dose examinations. Sensitivity, specificity, and accuracy of low-dose examinations of overweight and obese patients reached similar high values: 97-100%, 100%, and 98-100%, respectively. Interobserver agreement for urinary stone detection was excellent between the two reviewers, with kappa values of 0.98 for the low-dose and 0.96 for the standard-dose examinations. An alternative diagnosis was identified in 15% and 16% of cases by two experienced radiologists in the two examinations groups. In the second interpretation session, the residents found an alternative diagnosis in only 10-12% of standard-dose examinations and only 4-5% of low-dose examinations. Low-dose MDCT with tube current modulation can be used as standard procedure in evaluation for urolithiasis, even in overweight and obese patients.

Circle of Willis at CT Angiography: Dose Reduction and Image Quality—Reducing Tube Voltage and Increasing Tube Current Settings

To prospectively assess the effects of lower tube voltage and various effective tube currents on image quality for computed tomographic (CT) angiography of the circle of Willis. Institutional review board approval was obtained. Patients or family provided written informed consent. Signal-to-noise ratios (SNRs) were determined in a head phantom for various effective tube currents with tube voltages of 90, 120, and 140 kVp. Patients were referred for CT angiography because of acute subarachnoid hemorrhage (n = 20) or family history of cerebral aneurysms (n = 20). In each group, 10 patients were scanned with 120 kVp and 200 mAs(eff) and 10 were scanned with 90 kVp and 330 mAs(eff) (CT dose index volumes, 27.2 mGy and 20.6 mGy, respectively). CT numbers were measured in the internal carotid artery at the T junction and compared with a t test. Two radiologists used a five-point scale to subjectively score arterial enhancement, depiction of small arterial detail, image noise, venous contamination, and interference of subarachnoid blood. Mann-Whitney U test was used for statistical analysis. In the phantom, SNR(2) was proportional to effective tube current and CT dose index volume. With an identical effective tube current, SNR(2) was lower at 90 kVp than at 120 or 140 kVp. With identical CT dose index volume, tube voltage of 90 kVp resulted in a 45%-52% increase of SNR(2) compared with SNR(2) at 120 kVp. In patients, mean attenuation in the internal carotid artery T junction was higher with 90 kVp (340 HU) than with 120 kVp (252 HU, P < .001). Although dose at 90 kVp was 30% lower than dose at 120 kVp, scores for arterial enhancement and depiction of small arterial detail were higher at 90 kVp than at 120 kVp (4.0 vs 3.2 and 3.6 vs 3.1, respectively; P < .005). In head phantoms, lower tube voltage improved SNR at equal radiation doses. For CT angiography of the circle of Willis, this translated into superior image quality at 90 kVp.

Comparison of Standard- and Low-Radiation-Dose CT for Quantification of Emphysema

This study was performed to compare standard- and low-radiation-dose techniques in the CT quantification of emphysema. The study population consisted of 36 men and 20 women who were current or former heavy smokers and underwent standard-dose (effective tube current, 100-250 mAs) chest CT at our institution within 6 months of having undergone low-dose (effective tube current, 30-60 mAs) chest CT. All CT scans were reconstructed at 5-mm slice thickness with a smooth filter. CT-measured lung volume, mean and median lung attenuation, and percentage of lung volume with attenuation lower than multiple thresholds (emphysema index values) were compared by Pearson correlation, two-tailed and paired Student's t tests, and regression analysis. There were no significant differences in mean attenuation (-848 vs -846 H, p > 0.35) for the low dose and the standard dose or in median lung attenuation (-879 vs -878 H, p > 0.66). Low- and standard-dose emphysema indexes were correlated at all attenuation thresholds (r = 0.86-0.97). Mean emphysema indexes were higher on the low-dose scans, but the mean difference at all thresholds was less than 3%. The differences were significant (p < 0.05) only at the lower index thresholds, correlated with differences in lung volume (r < or = 0.86), and increased with greater differences in dose. Low-dose technique has minimal effect on CT quantification of emphysema.

Multi-detector row CT scanning in Paleoanthropology at various tube current settings and scanning mode

The purpose of this study was to determine the optimal tube current setting and scanning mode for hominid fossil skull scanning, using multi-detector row computed tomography (CT). Four fossil skulls (La Ferrassie 1, Abri Pataud 1, CroMagnon 2 and Cro-Magnon 3) were examined by using the CT scanner LightSpeed 16 (General Electric Medical Systems) with varying dose per section (160, 250, and 300 mAs) and scanning mode (helical and conventional). Image quality of two-dimensional (2D) multiplanar reconstructions, three-dimensional (3D) reconstructions and native images was assessed by four reviewers using a four-point grading scale. An ANOVA (analysis of variance) model was used to compare the mean score for each sequence and the overall mean score according to the levels of the scanning parameters. Compared with helical CT (mean score=12.03), the conventional technique showed sustained poor image quality (mean score=4.17). With the helical mode, we observed a better image quality at 300 mAs than at 160 in the 3D sequences (P=0.03). Whereas in native images, a reduction in the effective tube current induced no degradation in image quality (P=0.05). Our study suggests a standardized protocol for fossil scanning with a 16 x 0.625 detector configuration, a 10 mm beam collimation, a 0.562:1 acquisition mode, a 0.625/0.4 mm slice thickness/reconstruction interval, a pitch of 5.62, 120 kV and 300 mAs especially when a 3D study is required.

Metallic Prosthesis: Technique to Avoid Increase in CT Radiation Dose with Automatic Tube Current Modulation in a Phantom and Patients

The institutional review board approved this Health Insurance Portability and Accountability Act-compliant study protocol, with waiver of informed consent. The purpose of the study was to retrospectively evaluate the combined automatic tube current modulation technique in patients with orthopedic metallic prostheses. Five hundred abdominal-pelvic computed tomographic (CT) studies performed with combined modulation technique were reviewed to identify nine patients with metallic prostheses (mean age, 66 years; range, 35-86 years; male-female ratio, 5:4). On the basis of age and transverse abdominal images, these patients were matched with nine others with no metallic prostheses (mean age, 56 years; range, 36-72 years; male-female ratio, 4:5) who were control patients. Images were graded for extent and severity of streak artifacts (grade 1, streak artifact present but not substantially compromising evaluation of adjacent structures; grade 2, streak artifact present and slightly compromising evaluation of adjacent structures; and grade 3, streak artifact present and severely compromising evaluation of adjacent structures). Student t test was performed for statistical analysis. There was no difference in mean effective tube current-time product between study and control patients (P > .49). With automatic tube current modulation, an increase in CT dose caused by metallic prostheses can be successfully avoided.