Equal Radiation Doses Research Articles

Photon-Counting Detector CT for Liver Lesion Detection-Optimal Virtual Monoenergetic Energy for Different Simulated Patient Sizes and Radiation Doses.

The aim of this study was to evaluate the optimal energy level of virtual monoenergetic images (VMIs) from photon-counting detector computed tomography (CT) for the detection of liver lesions as a function of phantom size and radiation dose. An anthropomorphic abdominal phantom with liver parenchyma and lesions was imaged on a dual-source photon-counting detector CT at 120 kVp. Five hypoattenuating lesions with a lesion-to-background contrast difference of -30 HU and -45 HU and 3 hyperattenuating lesions with +30 HU and +90 HU were used. The lesion diameter was 5-10 mm. Rings of fat-equivalent material were added to emulate medium- or large-sized patients. The medium size was imaged at a volume CT dose index of 5, 2.5, and 1.25 mGy and the large size at 5 and 2.5 mGy, respectively. Each setup was imaged 10 times. For each setup, VMIs from 40 to 80 keV at 5 keV increments were reconstructed with quantum iterative reconstruction at a strength level of 4 (QIR-4). Lesion detectability was measured as area under the receiver operating curve (AUC) using a channelized Hotelling model observer with 10 dense differences of Gaussian channels. Overall, highest detectability was found at 65 and 70 keV for both hypoattenuating and hyperattenuating lesions in the medium and large phantom independent of radiation dose (AUC range, 0.91-1.0 for the medium and 0.94-0.99 for the large phantom, respectively). The lowest detectability was found at 40 keV irrespective of the radiation dose and phantom size (AUC range, 0.78-0.99). A more pronounced reduction in detectability was apparent at 40-50 keV as compared with 65-75 keV when radiation dose was decreased. At equal radiation dose, detection as a function of VMI energy differed stronger for the large size as compared with the medium-sized phantom (12% vs 6%). Detectability of hypoattenuating and hyperattenuating liver lesions differed between VMI energies for different phantom sizes and radiation doses. Virtual monoenergetic images at 65 and 70 keV yielded highest detectability independent of phantom size and radiation dose.

Improved visualization of the bone-implant interface and osseointegration in ex vivo acetabular cup implants using photon-counting detector CT

BackgroundSuccessful osseointegration of joint replacement implants is required for long-term implant survival. Accurate assessment of osseointegration could enable clinical discrimination of failed implants from other sources of pain avoiding unnecessary surgeries. Photon-counting detector computed tomography (PCD-CT) provides improvements in image resolution compared to conventional energy-integrating detector CT (EID-CT), possibly allowing better visualization of bone-implant-interfaces and osseointegration. The aim of this study was to assess the quality of visualization of bone-implant-interfaces and osseointegration in acetabular cup implants, using PCD-CT compared with EID-CT.MethodsTwo acetabular implants (one cemented, one uncemented) retrieved during revision surgery were scanned using PCD-CT and EID-CT at equal radiation dose. Images were reconstructed using different reconstruction kernels and iterative strengths. Delineation of the bone-implant and bone-cement-interface as an indicator of osseointegration was scored subjectively for image quality by four radiologists on a Likert scale and assessed quantitatively.ResultsDelineation of bone-implant and bone-cement-interfaces was better with PCD-CT compared with EID-CT (p ≤ 0.030). The highest ratings were given for PCD-CT at sharper kernels for the cemented cup (PCD-CT, median 5, interquartile range 4.25–5.00 versus EID-CT, 3, 2.00–3.75, p < 0.001) and the uncemented cup (5, 4.00–5.00 versus 2, 2–2, respectively, p < 0.001). The bone-implant-interface was 35–42% sharper and the bone-cement-interface was 28–43% sharper with PCD-CT compared with EID-CT, depending on the reconstruction kernel.ConclusionsPCD-CT might enable a more accurate assessment of osseointegration of orthopedic joint replacement implants.Key points• The bone-implant interface ex vivo showed superior visualization using photon-counting detector computed tomography (PCD-CT) compared to energy-integrating detector computed tomography.• Harder reconstruction kernels in PCD-CT provide sharper images with lower noise levels.• These improvements in imaging might make it possible to visualize osseointegration in vivo.

CT Angiography of the Aorta Using Photon-counting Detector CT with Reduced Contrast Media Volume.

To develop and evaluate a low-volume contrast media protocol for thoracoabdominal CT angiography (CTA) with photon-counting detector (PCD) CT. This prospective study included consecutive participants (April-September 2021) who underwent CTA with PCD CT of the thoracoabdominal aorta and previous CTA with energy-integrating detector (EID) CT at equal radiation doses. In PCD CT, virtual monoenergetic images (VMI) were reconstructed in 5-keV intervals from 40 to 60 keV. Attenuation of the aorta, image noise, and contrast-to-noise ratio (CNR) were measured, and subjective image quality was rated by two independent readers. In the first group of participants, the same contrast media protocol was used for both scans. CNR gain in PCD CT compared with EID CT served as the reference for contrast media volume reduction in the second group. Noninferiority analysis was used to test noninferior image quality of the low-volume contrast media protocol with PCD CT. The study included 100 participants (mean age, 75 years ± 8 [SD]; 83 men). In the first group (n = 40), VMI at 50 keV provided the best trade-off between objective and subjective image quality, achieving 25% higher CNR compared with EID CT. Contrast media volume in the second group (n = 60) was reduced by 25% (52.5 mL). Mean differences in CNR and subjective image quality between EID CT and PCD CT at 50 keV were above the predefined boundaries of noninferiority (-0.54 [95% CI: -1.71, 0.62] and -0.36 [95% CI: -0.41, -0.31], respectively). CTA of the aorta with PCD CT was associated with higher CNR, which was translated into a low-volume contrast media protocol demonstrating noninferior image quality compared with EID CT at the same radiation dose.Keywords: CT Angiography, CT-Spectral, Vascular, Aorta, Contrast Agents-Intravenous, Technology Assessment© RSNA, 2023See also the commentary by Dundas and Leipsic in this issue.

Awareness of Medical Doctors in Pusat Perubatan Universiti Kebangsaan Malaysia on Diagnostic Radiological Examination Related Radiation Exposure in the Pediatric Population.

Background: When exposed to equal radiation doses, the risks for children and adolescents are more significant than for adults. Children grow quickly, and their cells are more sensitive to radiation. After radiation exposure, children have a higher risk of developing malignancies such as leukemia, thyroid abnormalities, and various types of cancers. The healthcare professionals’ (in this context referring to medical doctors at all levels) awareness of imaging modalities associated with ionizing radiation is essential to ensure optimal patient management of cooperation in dealing with radiation exposure. Therefore, the present study is aimed to evaluate the awareness of healthcare professionals on medical imaging-related radiation exposure in the pediatric population in our center, Pusat Perubatan Universiti Kebangsaan Malaysia. Materials and Methods: A cross-sectional survey was conducted among healthcare professionals using self-administered validated questionnaires in a university hospital for a duration of seven months. Healthcare professionals of all levels participated in this survey. Results: A total of 145 healthcare professionals participated in this study. More than half of the respondents are house officers, 57.2% (n = 83). Results indicated that only 6 out of 145 healthcare professionals who participated in this survey had attended a radiation protection course. This survey showed that 37.2% of the respondents were unaware that chest radiographs would expose patients to ionizing radiation. Finally, results also indicated that senior doctors (21 out of 24 participants) showed better awareness of radiation protection knowledge. Conclusions: In general, healthcare professionals in our institution are inadequate in awareness of medical radiation exposure, particularly among house officers. However, the awareness of radiation safety and exposure improves with the number of years of clinical practice. We propose that some younger healthcare professionals do not take radiation safety seriously. Moreover, we would like to suggest all healthcare professionals must attend a radiation safety course, as we expect this will improve patient outcomes.

A Century of Fractionated Radiotherapy: How Mathematical Oncology Can Break the Rules.

Radiotherapy is involved in 50% of all cancer treatments and 40% of cancer cures. Most of these treatments are delivered in fractions of equal doses of radiation (Fractional Equivalent Dosing (FED)) in days to weeks. This treatment paradigm has remained unchanged in the past century and does not account for the development of radioresistance during treatment. Even if under-optimized, deviating from a century of successful therapy delivered in FED can be difficult. One way of exploring the infinite space of fraction size and scheduling to identify optimal fractionation schedules is through mathematical oncology simulations that allow for in silico evaluation. This review article explores the evidence that current fractionation promotes the development of radioresistance, summarizes mathematical solutions to account for radioresistance, both in the curative and non-curative setting, and reviews current clinical data investigating non-FED fractionated radiotherapy.

High-Pitch Photon-Counting Detector Computed Tomography Angiography of the Aorta: Intraindividual Comparison to Energy-Integrating Detector Computed Tomography at Equal Radiation Dose.

The aims of this study were to determine the objective and subjective image quality of high-pitch computed tomography (CT) angiography of the aorta in clinical dual-source photon-counting detector CT (PCD-CT) and to compare the image quality to conventional dual-source energy-integrating detector CT (EID-CT) in the same patients at equal radiation dose. Patients with prior CT angiography of the thoracoabdominal aorta acquired on third-generation dual-source EID-CT in the high-pitch mode and with automatic tube voltage selection (ATVS, reference tube voltage 100 kV) were included. Follow-up imaging was performed on a first-generation, clinical dual-source PCD-CT scanner in the high-pitch and multienergy (QuantumPlus) mode at 120 kV using the same contrast media protocol as with EID-CT. Radiation doses between scans were matched by adapting the tube current of PCD-CT. Polychromatic images for both EID-CT and PCD-CT (called T3D) and virtual monoenergetic images at 40, 45, 50, and 55 keV for PCD-CT were reconstructed. Computed tomography attenuation was measured in the aorta; noise was defined as the standard deviation of attenuation; contrast-to-noise ratio (CNR) was calculated. Subjective image quality (noise, vessel attenuation, vessel sharpness, and overall quality) was rated by 2 blinded, independent radiologists. Forty patients were included (mean age, 63 years; 8 women; mean body mass index [BMI], 26 kg/m2). There was no significant difference in BMI, effective diameter, or radiation dose between scans (all P's > 0.05). The ATVS in EID-CT selected 70, 80, 90, 100, 110, and 120 kV in 2, 14, 14, 7, 2, and 1 patients, respectively. Mean CNR was 17 ± 8 for EID-CT and 22 ± 7, 20 ± 6, 18 ± 5, 16 ± 5, and 12 ± 4 for PCD-CT at 40, 45, 50, 55 keV, and T3D, respectively. Contrast-to-noise ratio was significantly higher for 40 and 45 keV of PCD-CT as compared with EID-CT (both P's < 0.05). The linear regression model (adjusted R2, 0.38; P < 0.001) revealed that PCD-CT reconstruction (P < 0.001), BMI group (P = 0.007), and kV of the EID-CT scan (P = 0.01) were significantly associated with CNR difference, with an increase by 34% with PCD-CT for overweight as compared with normal weight patients. Subjective image quality reading revealed slight differences between readers for subjective vessel attenuation and sharpness, whereas subjective noise was rated significantly higher for 40 and 45 keV (P < 0.001) and overall quality similar (P > 0.05) between scans. High-pitch PCD-CT angiography of the aorta with VMI at 40 and 45 keV resulted in significantly increased CNR compared with EID-CT with ATVS at matched radiation dose. The CNR gain of PCD-CT increased in overweight patients. Taking into account the subjective analysis, VMI at 45 to 50 keV is proposed as the best trade-off between objective and subjective image quality.

Energy-integrating-detector multi-energy CT: Implementation and a phantom study.

Multi-energy computed tomography (MECT) has a great potential to enable many novel clinical applications such as simultaneous multi-contrast imaging. The purpose of this study was to implement triple-beam MECT on a traditional energy-integrating-detector (EID) CT platform (EID-MECT). This was accomplished by mounting a z-axis split-filter (0.05mm Au, 0.6mm Sn) on Tube A of a dual-source EID CT scanner. With the two split x-ray beams from Tube A and the third beam from Tube B, three beams with different x-ray spectra can be simultaneously acquired. With Tube B operated at 70 or 80kV and Tube A at 120 or 140kV, four different triple-beam configurations were calibrated for MECT measurements: 70/Au120/Sn120, 80/Au120/Sn120, 70/Au140/Sn140, and 80/Au140/Sn140 kV. Iodine (I), gadolinium (Gd), bismuth (Bi) samples, and their mixtures were prepared for 2 three-material-decomposition tasks and 1 four-material-decomposition task. For each task, samples were placed in a water phantom and scanned using each of the four triple-beam configurations. For comparison, the same phantom was also scanned using three other dual-energy CT (DECT) or MECT technologies: twin-beam DECT (TB-DECT), dual-source DECT (DS-DECT), and photon-counting-detector CT (PCD-CT), all with optimal x-ray spectrum settings and at equal volume CT dose index (CTDIvol). The phantom for four-material decomposition (I/Gd/Bi/Water imaging) was scanned using the PCD-CT only (140kV with 25, 50, 75, and 90keV). Image-based material decomposition was performed to acquire material-specific images, on which the mean basis material concentrations and noise levels were measured and compared across all triple-beam configurations in EID-MECT and various DECT/MECT systems. The optimal triple-beam configuration was task-dependent with 70/Au120/Sn120, 70/Au140/Sn140, and 70/Au120/Sn120kV for I/Gd/Water, I/Bi/Water, and I/Gd/Bi/Water material decomposition tasks, respectively. At equal radiation dose level, EID-MECT provided comparable or better quantification accuracy in material-specific images for all three material decomposition tasks, compared to EID-based DECT and PCD-CT systems. In terms of noise level comparison, EID-MECT-derived material-specific images showed lower noise levels than TB-DECT and DS-DECT, but slightly higher than that from PCD-CT in I/Gd/Water imaging. For I/Bi/Water imaging, EID-MECT showed a comparable noise level to DS-DECT, and a much lower noise level than TB-DECT and PCD-CT in all material-specific images. For the four-material decomposition task involving I/Gd/Bi/Water, the bismuth-specific image derived from EID-MECT was slightly noisier, but both iodine- and gadolinium-specific images showed much lower noise levels in comparison to PCD-CT. For the first time, an EID-based MECT system that can simultaneously acquire three x-ray spectra measurements was implemented on a clinical scanner, which demonstrated comparable or better imaging performance than existing DECT and MECT systems.

Scatter-to-primary ratio in dentomaxillofacial cone-beam CT: effect of field of view and beam energy.

The aim of this study was to evaluate the effect of field of view (FOV) and beam energy on the scatter-to-primary ratio (SPR) in dental cone-beam CT (CBCT). An anthropomorphic phantom representing an adult male (ATOM Max 711-HN, Norfolk, VA, USA) was scanned using the 3D Accuitomo 170 CBCT (J. Morita, Kyoto, Japan) using 11 FOVs. During each scan, half of the X-ray beam was blocked. Each scan was performed at three exposure settings with varying beam energy and equal radiation dose: 90 kV 5 mA, 77 kV 7.5 mA and 69 kV 10 mA. The SPR was estimated by measuring the grey values in the blocked and non-blocked regions of the RAW data. The effect of FOV on SPR was evaluated using Dunn's multiple comparison test, and the effect of the exposure settings was compared using a Wilcoxon signed rank test. Larger FOVs showed increased scatter. FOVs with a shorter isocenter-detector distance showed a particularly high SPR. Most intercomparisons between FOVs were statistically significant. The largest difference was found between 17 × 12 cm and 6 × 6 cm (lower jaw), with the former showing a 4.9-fold higher SPR. The effect of beam energy was relatively small and varied between FOV sizes and positions. While the choice of FOV size and position is determined by the diagnostic region of interest, the image quality deterioration for large FOVs due to scatter provides another incentive to limit the FOV size as much as possible.

Comparison of low kVp CT and dual-energy CT for the evaluation of hypervascular hepatocellular carcinoma.

To compare lesion conspicuity and image quality of arterial phase images obtained from low kVp (90-kVp) and dual-energy (DE) scans for the evaluation of hypervascular hepatocellular carcinoma (HCC). This retrospective study included 229 patients with HCC who underwent either 90kVp (n = 106) or DE scan (80- and 150-kVp with a tin filter) (n = 123) during the arterial phase. DE scans were reconstructed into a linearly blended image with a mixed ratio of 0.6 (60% 80kVp and 40% 150kVp) and post-processed for 40keV and 50keV images. The contrast-to-noise ratio (CNR) of HCC to the liver and image noise was measured. Lesion conspicuity, liver parenchymal image quality, and overall image preference were assessed qualitatively by three independent radiologists. DE 40keV images had the highest CNR of HCC, and DE blended images had the lowest image noise among four image sets (p = 0.01 and p < 0.001, respectively). There was no significant difference in mean volume CT dose index and dose-length product between DE and low kVp scan (ps > 0.05). For qualitative analyses, DE blended images had the highest scores for image quality and overall image preference (ps < 0.001). At an equal radiation dose, DE 40keV showed higher CNR of HCC and DE blended image showed higher image quality and image preference compared with low kVp CT.

Relating Linear Energy Transfer to the Formation and Resolution of DNA Repair Foci After Irradiation with Equal Doses of X-ray Photons, Plateau, or Bragg-Peak Protons.

Proton beam therapy is increasingly applied for the treatment of human cancer, as it promises to reduce normal tissue damage. However, little is known about the relationship between linear energy transfer (LET), the type of DNA damage, and cellular repair mechanisms, particularly for cells irradiated with protons. We irradiated cultured cells delivering equal doses of X-ray photons, Bragg-peak protons, or plateau protons and used this set-up to quantitate initial DNA damage (mainly DNA double strand breaks (DSBs)), and to analyze kinetics of repair by detecting γH2A.X or 53BP1 using immunofluorescence. The results obtained validate the reliability of our set-up in delivering equal radiation doses under all conditions employed. Although the initial numbers of γH2A.X and 53BP1 foci scored were similar under the different irradiation conditions, it was notable that the maximum foci level was reached at 60 min after irradiation with Bragg-peak protons, as compared to 30 min for plateau protons and photons. Interestingly, Bragg-peak protons induced larger and irregularly shaped γH2A.X and 53BP1 foci. Additionally, the resolution of these foci was delayed. These results suggest that Bragg-peak protons induce DNA damage of increased complexity which is difficult to process by the cellular repair apparatus.

Turn down the noise—a blinded evaluation of iterative image reconstruction in radiation therapy computed tomography simulation

PurposeThe current standard reconstruction algorithm for computed tomography (CT) scans is filtered back projection. Alternative algorithms using iterative reconstruction (IR)—in our case, “sinogram affirmed iterative reconstruction”—have been increasingly implemented in diagnostic CT imaging. We studied its potential in improving radiation therapy planning images. Methods and materialsRaw planning CT data sets of patients from varied disease sites were reconstructed using filtered back projection and IR levels 1, 3, and 5 with equal radiation dose. For each site, 2-7 patient scans were selected; 2-3 physicians blindly evaluated the 4 3-dimensional image sets. Using a visual analogue scale, they rated the sharpness, noise, perceived ease in delineating gross tumor/clinical target volume and organs at risk, and overall appreciation of the images. Interobserver correlation was calculated with the Spearman correlation coefficient (ρ). Generalized estimating equations assessed the differences in the mean score for each criterion between reconstructions. When significant differences existed, pairwise comparisons compared the least-squares means. The preference for each reconstruction was rank ordered for each observer. The rank occurrences were computed; generalized estimating equations and pairwise comparisons were again calculated. ResultsSixteen physicians reviewed 548 image sets. The sharpness had a ρ = −0.22-0.53, noise ρ = −0.34-0.38, delineating gross tumor/clinical target volume ρ = −0.28-0.53, delineating organs at risk ρ = −0.47-0.42, and overall appreciation ρ = −0.17-0.38, suggesting a low level of agreement among observers. IR 3 and 5 had consistently higher scores and ranks than filtered back projection (P = .02 and P = .015, respectively). Paradoxically, IR 5 scored both highest and worst the most frequently. IR 3 was more consistently well-ranked for all criteria. ConclusionsThis report is the first to clinically evaluate IR in radiation therapy planning. When used to reduce noise in current CT simulation protocols, IR images were generally preferred. Although highly processed images polarized observers, the use of moderate IR was appreciated for most disease sites.

Coronary artery calcification scoring with state-of-the-art CT scanners from different vendors has substantial effect on risk classification.

To determine the intervendor variability of Agatston scoring determined with state-of-the-art computed tomographic (CT) systems from the four major vendors in an ex vivo setup and to simulate the subsequent effects on cardiovascular risk reclassification in a large population-based cohort. Research ethics board approval was not necessary because cadaveric hearts from individuals who donated their bodies to science were used. Agatston scores obtained with CT scanners from four different vendors were compared. Fifteen ex vivo human hearts were placed in a phantom resembling an average human adult. Hearts were scanned at equal radiation dose settings for the systems of all four vendors. Agatston scores were quantified semiautomatically with software used clinically. The ex vivo Agatston scores were used to simulate the effects of different CT scanners on reclassification of 432 individuals aged 55 years or older from a population-based study who were at intermediate cardiovascular risk based on Framingham risk scores. The Friedman test was used to evaluate overall differences, and post hoc analyses were performed by using the Wilcoxon signed-rank test with Bonferroni correction. Agatston scores differed substantially when CT scanners from different vendors were used, with median Agatston scores ranging from 332 (interquartile range, 114-1135) to 469 (interquartile range, 183-1381; P < .05). Simulation showed that these differences resulted in a change in cardiovascular risk classification in 0.5%-6.5% of individuals at intermediate risk when a CT scanner from a different vendor was used. Among individuals at intermediate cardiovascular risk, state-of the-art CT scanners made by different vendors produced substantially different Agatston scores, which can result in reclassification of patients to the high- or low-risk categories in up to 6.5% of cases.

SU-D-217BCD-05: Analytic Determination of Size of Water Cylinder Absorbing Equal Radiation Dose as a System of Concentric Cylinders of Arbitrary Composition: Application for Pediatric CT.

To develop analytic formulae for calculating absorbed dose to a system of concentric cylinders and to use this to determine the size of water cylinder which would absorb the same dose in a matching field. Appropriate scaling of radiation output to patient size is of particular interest in pediatric CT (TG204). For a given CT scanner output, absorbed dose increases as patient size decreases. Analytic functions can calculate the dose delivered to systems of concentric cylinders of varying size and composition. In particular these functions provide useful insight when considering examinations in body regions with large variations in attenuation, such as the chest (which can be modeled as concentric cylinders of heart, lung, rib and soft tissue). Iterative calculations rapidly determine the size water cylinder required to absorb the same dose in matching radiation fields. More general findings put limits on some of the methods for determining size specific dose estimates (SSDE). For the simple chest model, in the absence of scatter or bow tie filter considerations, the equivalent water phantom would have a diameter of just over half the chest equivalent concentric cylinder phantom. A more general Result is that in the limit of very small size, the absorbed dose in a fixed irradiating field depends only on mass attenuation coefficient. The concentric cylinder model developed can be used to study the scaling of radiation dose with patient size. In particular, the water phantom absorbing the same dose as the chest region has only about half the diameter. An important conclusion is that in the limit of small size, absorbed dose depends on mass attenuation coefficient only and that in this limit an equivalent water phantom does not exist.

High-LET Ion Radiolysis of Water: Oxygen Production in Tracks

It is known that molecular oxygen is a product of the radiolysis of water with high-linear energy transfer (LET) radiation, a result that is of particular significance in radiobiology and of practical relevance in radiotherapy. In fact, it has been suggested that the radiolytic formation of an oxygenated microenvironment around the tracks of high-LET heavy ions is an important factor in their enhanced biological efficiency in the sense that this may be due to an "oxygen effect" by O(2) produced by these ions in situ. Using Monte Carlo track simulations of pure, deaerated water radiolysis by 4.8 MeV (4)He(2+) (LET approximately 94 keV/microm) and 24 MeV (12)C(6+) (LET approximately 490 keV/microm) ions, including the mechanism of multiple ionization of water, we have calculated the yields and concentrations of O(2) in the tracks of these irradiating ions as a function of time between approximately 10(-12) and 10(-5) s at 25 and 37 degrees C. The track oxygen concentrations obtained compare very well with O(2) concentrations estimated from the "effective" amounts of oxygen that are needed to produce the observed reduction in oxygen enhancement ratio (OER) with LET (assuming this decrease is attributable to the sole radiolytic formation of O(2) in the tracks). For example, for 24 MeV (12)C(6+) ions, the initial track concentration of O(2) is estimated to be more than three orders of magnitude higher than the oxygen levels present in normally oxygenated and hypoxic tumor regions as well as in normal human cells. Such results, which largely plead in favor of the "oxygen in the heavy-ion track" hypothesis, could explain at least in part the greater efficiency of high-LET radiation for cell inactivation (at equal radiation dose).

Variability of Semiautomated Lung Nodule Volumetry on Ultralow-Dose CT: Comparison with Nodule Volumetry on Standard-Dose CT

The study investigates the effect of a substantial dose reduction on the variability of lung nodule volume measurements by assessing and comparing nodule volumes using a dedicated semiautomated segmentation software on ultralow-dose computed tomography (ULD-CT) and standard-dose computed tomography (SD-CT) data. In 20 patients, thin-slice chest CT datasets (1 mm slice thickness; 20% reconstruction overlap) were acquired at ultralow-dose (120 kV, 5 mAs) and at standard-dose (120 kV, 75 mAs), respectively, and analyzed using the segmentation software OncoTREAT (MeVis, Bremen, Germany; version 1.3). Interobserver variability of volume measurements of 202 solid pulmonary nodules (mean diameter 11 mm, range 3.2-44.5 mm) was calculated for SD-CT and ULD-CT. With respect to interobserver variability, the 95% confidence interval for the relative differences in nodule volume in the intrascan analysis was measured with -9.7% to 8.3% (mean difference -0.7%) for SD-CT and with -12.6% to 12.4% (mean difference -0.2%) for ULD-CT. In the interscan analysis, the 95% confidence intervals for the differences in nodule volume ranged with -25.1% to -23.4% and 26.2% to 28.9% (mean difference 1.4% to 2.1%) dependent on the combination of readers and scans. Intrascan interobserver variability of volume measurements was comparable for ULD-CT and SD-CT data. The calculated variability of volume measurements in the interscan analysis was similar to the data reported in the literature for CT data acquired with equal radiation dose. Thus, the evaluated segmentation software provides nodule volumetry that appears to be independent of the dose level with which the CT source dataset is acquired.

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.

Effect of initial crystallinity on the response of high-density polyethylene to high-energy radiation

Samples of each of two high-density polyethylenes with various initial degrees of crystallinity, but otherwise identical, were exposed under a vacuum to moderate doses of gamma irradiation. The results indicate that, for otherwise initially identical polymer samples, the dose required to reach the gel point increases with increase of the initial degree of crystallinity. Above the critical dose for gelation, the gel content decreases with higher degrees of crystallinity at equal radiation doses. The mechanical behavior of the polymers changed progressively from ductile to brittle as the crystallinity was increased. The extensibility of originally ductile samples decreases with increasing radiation dose. The irradiation of samples having intermediate behavior produces a change to ductile behavior. Mechanical behavior is not modified substantially when brittle samples are irradiated. The initial modulus is little altered by irradiation, while the yield stress shows a slight increase with irradiation. The mechanical properties, such as draw ratio at break and ultimate tensile stress, decrease with dose in ductile samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1375–1384, 1999

Radiosensitivity of jejunal mucosa after whole abdomen irradiation and CDDP pretreatment

Pretreatment of mice with a single radiation dose of 11.5 Gy or with fractionated irradiation (2 × 6.5 or 7.5 Gy, with an interval time of 12 hr) led to a relative decrease in the radiosensitivity of jejunal crypt cells when a second single dose of radiation was delivered 2 months later. When the same irradiation pretreatment was combined with CDDP (6 mg/kg, i.p.) injected 12 hr after single radiation or between two equal doses of radiation, similar crypt cells resistance was obtained. The combination of CDDP with irradiation did not modify the radiosensitivity of jejunal crypts in comparison with irradiation alone, even when the total radiation dose was delivered in 2 split doses. This induced radioresistance was demonstrated to be a reflection of late injury on intestinal tissue, presumably due to hypoxia resulting from vascular damage. It seems that the administration of CDDP did not change the possible hypoxia suspected in crypt cells of mice pretreated with single radiation dose. However, mouse lethality increased significantly when CDDP was combined with irradiation.

Repair of Potentially Lethal X-ray Damage in Fibroblasts Derived from Patients with Hereditary and D-deletion Retinoblastoma

We examined X-ray induced potentially lethal damage repair (PLDR) in density inhibited plateau phase cultures of six fibroblast strains derived from patients with hereditary retinoblastoma and two patients with D-deletion retinoblastoma and compared them to three normal controls. PLD was measured in hereditary retinoblastoma (7 Gy exposure) and normal cells (7 and 9 Gy exposure) after 24 h repair time. PLD survival curves were performed at 2-9 Gy on six retinoblastoma and three normal control cell strains. Thus, PLDR was compared at equitoxic survival levels as well as after exposure to equal doses of radiation. Some retinoblastoma strains showed normal PLDR whereas others were possibly deficient. Implications of PLDR for susceptibility to radiation-induced and spontaneous tumours in hereditary retinoblastoma patients are discussed.

Repair of Potentially Lethal X-ray Damage in Fibroblasts Derived from Patients with Hereditary and D-deletion Retinoblastoma

We examined X-ray induced potentially lethal damage repair (PLDR) in density inhibited plateau phase cultures of six fibroblast strains derived from patients with hereditary retinoblastoma and two patients with D-deletion retinoblastoma and compared them to three normal controls. PLD was measured in hereditary retinoblastoma (7 Gy exposure) and normal cells (7 and 9 Gy exposure) after 24 h repair time. PLD survival curves were performed at 2-9 Gy on six retinoblastoma and three normal control cell strains. Thus, PLDR was compared at equitoxic survival levels as well as after exposure to equal doses of radiation. Some retinoblastoma strains showed normal PLDR whereas others were possibly deficient. Implications of PLDR for susceptibility to radiation-induced and spontaneous tumours in hereditary retinoblastoma patients are discussed.