A comparison of polyacrylamide gels and radiochromic film for source measurements in intravascular brachytherapy

For intravascular brachytherapy with catheter-based systems, AAPM Task Group 60 has recommended measurements that should be made to characterize the sources. Beta emitters, including (90)Sr/(90)Y are ideal for intravascular brachytherapy, but problems arise in measuring dose distributions in the high dose gradient region at short distances from the source. In this paper, measurements of radial and orthogonal dose distributions and dose profiles for a (90)Sr/(90)Y source train using polyacrylamide gel (PAG) dosimetry and a high-field 4.7 Tesla MRI scanner are presented and compared with measurements made with two types of radiochromic film, MD-55 and HD-810. For the PAG system, the dose distributions were determined with in-plane resolutions of 0.4 mm and 0.2 mm. The measurements of absorbed dose distributions both orthogonal and parallel to the source axis show good agreement between the PAG and radiochromic film. The absolute dose at a radial distance of 2 mm in the central 32 mm of a line parallel to the axis was measured. For the PAG the measured absorbed dose was 1.25% lower, for MD-55 4% higher and for the HD-810 1.6% higher when compared with the value given by the source calibration. These results confirm that both absorbed dose and dose distributions for high gradient vascular brachytherapy sources can be measured using PAG but the disadvantages of gel manufacture and the need for access to a high resolution scanner suggests that the use of radiochromic film is the method of choice.     

双源CT单能量成像对肝癌检出影响的初步研究

目的 探索显示肝癌病灶对比噪声比(CNR)和图像质量的最佳keV条件,并与融合能量图像比较,探讨能谱CT单能量成像对肝癌检出的影响.方法 回顾性分析经双源CT双能量双期扫描的30例肝癌患者影像学表现.采用双源分析软件处理产生单能量(40～140 keV,间隔10 keV)图像,测定单能量图像、100 keV和140 keV图像中病灶的CNR和图像噪声.优化单能量图像中检测肝癌的最佳CNR值和图像噪声值.通过两相关样本的非参数秩和检验的方法对单能量图像和混合能量图像的结果进行比较.结果 动脉期图像中所有病灶的最佳CNR的单光子能量水平集中分布在70 keV,所占的比例为81.8％(27/33).图像噪声水平的最低点位于70 keV和80 keV.综合考虑图像质量和病变对比,笔者选择70 keV图像与融合图像进行比较.70 keV单能量图像的CNR与100 keV图像无显著性差异(1.68±1.04,1.88±1.59,P=0.149),>140 keV图像且有显著性差异(1.68±1.04,0.62±0.92,P=0.000).图像噪声<100 keV图像,差异有统计学意(6.52±1.53,8.55±1.11,P=0.000),与140 keV图像差异无统计学意义(6.52±1.53,7.60±2.73,P=0.050).结论 能谱CT 70 keV单能量图像可以在不降低图像质量的前提下有效提高肝癌病灶的CNR,这将有助于病灶的检出.     

胃癌双能量扫描在分期中的应用

目的 探讨胃癌双能量CT优化图像质量,评估其在胃癌术前分期中的作用.方法 收集临床疑有胃癌的患者55例,行双源双能量腹部增强扫描.测量100 kV、70 keV、120 kV图像病灶动静脉期的CT值,信噪比(SNR)、噪声.选择出最佳水平的图像,并评估此水平图像的术前TNM分期,并和常规120 kV图像相对比.结果 动静脉期70 keV和100 kV图像强化程度均高于120 kV(P＜0.001);动脉期70 keV和120 kV的SNR高于100 kV(P＜0.01),静脉期70 keV的SNR高于120 kV和100 kV(P＜0.01);70 keV和120 kV T分期符合率分别为83.7％、72.1％(P=0.25);120 kV和70 keV N分期符合率分别为62.8％、74.4％ (P＜0.05).结论 双能量CT 70 keV单能图像较常规120 kV优化了图像质量,提高了N分期的符合率.     

Imaging of weak-source distributions in LSO-based small-animal PET scanners.

Lutetium oxyorthosilicate (LSO)- or lutetium-yttrium oxyorthosilicate (LYSO)-based PET scanners have intrinsic radioactivity in the scintillator crystals due to the presence of (176)Lu, which decays by beta-emission followed by one or more prompt gamma-ray emissions. This leads to intrinsic true counts that can influence the image when scanning low levels of activity. An evaluation of the effects of this intrinsic activity for low levels of activity and different energy windows is performed on an LSO-based small-animal PET scanner. METHODS: Intrinsic count rate and sensitivity were measured for a range of lower-level discriminators (LLDs) ranging from 100 to 750 keV. The noise equivalent count rate (NECR) as a function of LLD for activity levels from 100 Bq to 100 kBq was estimated using a combination of measurement and previously published data for this scanner. Phantom imaging was performed using three (68)Ge sources of strength 55, 220, and 940 Bq and LLD levels of 250, 350, and 400 keV. The images were assessed using a contrast-to-noise ratio (CNR) analysis and by comparing the observed ratio of source activities to the true ratio value. RESULTS: The intrinsic true count rate is reduced from 940 counts per second (cps) for a 250- to 750-keV energy window to <2 cps for a 400- to 750-keV window. There is a corresponding 2-fold drop in sensitivity for detected true events for external positron sources for these 2 energy windows. The NECR versus LLD curves showed a highly peaked shape, with the optimum LLD being approximately 425 keV. The phantom image results were dominated by the intrinsic true counts when an energy window of 250-750 keV was used. The intrinsic true counts were almost completely removed by raising the LLD to 400 keV. The CNR for each of the sources was higher for the narrow energy window and the 55 Bq could be easily visualized in images acquired with LLD levels of 350 and 400 keV but not when the 250-keV LLD was used. Images acquired with an LLD of 400 keV and reconstructed with 2-dimensional filtered backprojection were the most quantitatively accurate. CONCLUSION: It is possible to visualize sources of <1 kBq in LSO-based animal PET systems by raising the LLD to 400 keV to exclude the majority of the counts due to the intrinsic activity present in the LSO.     

Improving image quality in portal venography with spectral CT imaging

Objective

To investigate the effect of energy spectral CT on the image quality of CT portal venography in cirrhosis patients.

Materials and methods

30 portal hypertension patients underwent spectral CT examination using a single-tube, fast dual tube voltage switching technique. 101 sets of monochromatic images were generated from 40 keV to 140 keV. Image noise and contrast-to-noise ratio (CNR) for portal veins from the monochromatic images were measured. An optimal monochromatic image set was selected for obtaining the best CNR for portal veins. The image noise and CNR of the intra-hepatic portal vein and extra-hepatic main stem at the selected monochromatic level were compared with those from the conventional polychromatic images. Image quality was also assessed and compared.

Results

The monochromatic images at 51 keV were found to provide the best CNR for both the intra-hepatic and extra-hepatic portal veins. At this energy level, the monochromatic images had about 100% higher CNR than the polychromatic images with a moderate 30% noise increase. The qualitative image quality assessment was also statistically higher with monochromatic images at 51 keV.

Conclusion

Monochromatic images at 51 keV for CT portal venography could improve CNR for displaying hepatic portal veins and improve the overall image quality.     

CT能谱成像技术减除金属植入物伪影的定量实验研究

目的 探讨能谱成像技术(GSI)减少金属伪影的价值.方法 选取离体附肉猪腰椎骨模型1具,在相同CT剂量指数(CTDI)条件下分别行GSI和常规120kVp扫描;随后于L2、L4水平植入钛钉并行重复扫描.金属植入前后的GSI图像均以间距为10 keV在40～140 keV间重建11种单能量(Mono)+金属伪影消除技术(MARs)图像.主观评定钛钉植入后120kVp组和GSI组图像质量差异,并量化分析:(1)在金属伪影最重层面自金属边缘由近及远选取3个面积相同的ROI,依次记为ROI近、ROI中、ROI远,分别测量植入前120kVp和Mono组、植入后120 kVp、Mono+MARs组的CT值及CT标准差(SD)值,并采用LSD检验和Bonferroni检验比较3个ROI植入前Mono组和植入后Mono+MARs组CT值的差异.(2)计算对比噪声比(CNR)和伪影指数(AI);比较不同组金属植入前后的CT值、SD值和CNR值;通过伪影指数确定观察金属伪影的最佳keV范围.结果 (1)GSI组图像质量优于常规120kVp组.(2)伪影指数最小的keV范围是80～100 keV.(3)ROI近的植入前Mono组和植入后Mono+MARs组CT值分别为(80.25±16.00)和(30.10±10.45)HU,差异有统计学意义(Z=2.978,P＜0.05);ROI中和ROI远的植入前Mono组、植入后Mono+MARs组CT值分别为(63.21±6.61)和(54.84±10.60)HU、(76.54±9.07)和(73.20±5.39)HU,差异均无统计学意义(t值分别为0.530、0.822,P值均＞0.05).结论 能谱成像技术能准确校正距离金属3 cm范围外的伪影,并提供准确的CT值.     

Single source dual energy CT: What is the optimal monochromatic energy level for the analysis of the lung parenchyma?

ObjectiveTo determine the optimal monochromatic energy level for lung parenchyma analysis in spectral CT.MethodsAll 50 examinations (58% men, 64.8 ± 16yo) from an IRB-approved prospective study on single-source dual energy chest CT were retrospectively included and analyzed.Monochromatic images in lung window reconstructed every 5 keV from 40 to 140 keV were independently assessed by two chest radiologists. Based on the overall image quality and the depiction/conspicuity of parenchymal lesions, each reader had to designate for every patient the keV level providing the best diagnostic and image quality.Results72% of the examinations exhibited parenchymal lesions.Reader 1 picked the 55 keV monochromatic reconstruction in 52% of cases, 50 in 30% and 60 in 18%. Reader 2 chose 50 keV in 52% cases, 55 in 40%, 60 in 6% and 40 in 2%. The 50 and 55 keV levels were chosen by at least one reader in 64% and 76% of all patients, respectively.Merging 50 and 55 keV into one category results in an optimal setting selected by reader 1 in 82% of patients and by reader 2 in 92%, with a 74% concomitant agreement.ConclusionThe best image quality for lung parenchyma in spectral CT is obtained with the 50–55 keV monochromatic reconstructions.     

Virtual Monoenergetic Spectral Detector CT for Preoperative CT Angiography in Liver Donors

ObjectiveThe purpose of this study was to evaluate the use of virtual monoenergetic images (VMI) in pre-operative CT angiography of potential donors for living donor adult liver transplantation (LDALT), and to determine the optimal energy level to maximize vascular signal-to-noise and contrast-to-noise ratios (SNR and CNR, respectively).Materials and methodsWe retrospectively evaluated 29 CT angiography studies performed preoperatively in potential liver donors on a spectral detector CT scanner. All studies included arterial, early venous, and delayed venous phase imaging. Conventional polyenergetic images were generated for each patient, as well as virtual monoenergetic images in 10 keV increments from 40 –100 keV. Arteries (aorta and celiac, superior mesenteric, common hepatic, right and left hepatic arteries) were assessed on arterial phase images; portal venous system branches (splenic, superior mesenteric, main, right, and left portal veins) on early venous phase images; and hepatic veins on late venous phase images. Vascular attenuation, background parenchymal attenuation, and noise were measured on each set of virtual monoenergetic and conventional images.ResultsBackground hepatic and vascular noise decreased with increasing keV, with the lowest noise at 100 keV. Vascular SNR and CNR increased with decreasing keV and were highest at 40 keV, with statistical significance compared with conventional ( P < 0.05).ConclusionsIn preoperative CT angiography for potential liver donors, the optimal keV for assessing the vasculature to improve SNR and CNR is 40 keV. Use of low keV VMI in LDALT CT protocols may facilitate detection of vascular anatomical variants that can impact surgical planning.     

Noise-optimized monoenergetic post-processing improves visualization of incidental pulmonary embolism in cancer patients undergoing single-pass dual-energy computed tomography

Purpose

To evaluate noise-optimized monoenergetic postprocessing of dual-energy CT (DE-CT) on image quality in patients with incidental pulmonary embolism in single-pass portal-venous phase CT (CT_pv).

Materials and methods

20 Consecutive patients with incidental pulmonary embolism in contrast-enhanced oncological follow-up DE-CT_pv examination were included in this study. Images were acquired with a 3rd generation DE-CT system in DE mode (100/Sn150 kV) and activated tube current modulation 90 s after contrast agent administration. Subsequently, virtual monoenergetic images (MEI+) were reconstructed at five different keV levels (40, 55, 70, 85, 100) and compared to the standard linearly blended (M_0.8) CT_pv images. Image quality was assessed qualitatively (vascular contrast and detectability of embolism, image noise, iodine influx artifact; two independent readers; 5-point Likert scale; 5 = excellent) and quantitatively by calculating signal-to-noise (SNR) and contrast-to-noise ratios (CNR).

Results

Highest vessel contrast and highest detectability of embolism were observed in MEI+ at 40 keV (4.7 ± 0.4) and 55 keV (4.2 ± 0.6) with significant differences as compared to CT_pv (3.6 ± 0.5) and high keV reconstructions (70, 85, 100; p ≤ 0.01). Image noise significantly increased at 40 keV MEI+ compared to all other MEI+ reconstructions and CT_pv (p < 0.001). SNR and CNR calculations were highest at 40 keV MEI+ followed by 55 keV and CT_pv with significant differences to high keV MEI+ (85–100).

Conclusions

Computed MEI+ at low keV levels allow for improved vessel contrast and visualisation of incidental pulmonary embolism in patients with portal-venous phase CT scans by substantially increasing CNR and SNR.

     

Dose--response of initial G2-chromatid breaks induced in normal human fibroblasts by heavy ions

PURPOSE: To investigate initial chromatid breaks in prematurely condensed G2 chromosomes following exposure to heavy ions of different LET. MATERIAL AND METHODS: Exponentially growing human fibroblast cells AG1522 were irradiated with gamma-rays, energetic carbon (13 keV/ microm, 80 keV/microm), silicon (55 keV/microm) and iron (140 keV/microm, 185keV/microm, 440keV/microm) ions. Chromosomes were prematurely condensed using calyculin-A. Initial chromatid-type and isochromatid breaks in G2 cells were scored. RESULTS: The dose response curves for total chromatid breaks were linear regardless of radiation type. The relative biological effectiveness (RBE) showed a LET-dependent increase, peaking around 2.7 at 55-80keV/microm and decreasing at higher LET. The dose response curves for isochromatid-type breaks were linear for high-LET radiations, but linear-quadratic for gamma-rays and 13 keV/microm carbon ions. The RBE for the induction of isochromatid breaks obtained from linear components increased rapidly between 13keV/microm (about 7) and 80keV/microm carbon (about 71), and decreased gradually until 440 keV/microm iron ions (about 66). CONCLUSIONS: High-LET radiations are more effective at inducing isochromatid breaks, while low-LET radiations are more effective at inducing chromatid-type breaks. The densely ionizing track structures of heavy ions and the proximity of sister chromatids in G2 cells result in an increase in isochromatid breaks.     

Dose–response of initial G2-chromatid breaks induced in normal human fibroblasts by heavy ions

Purpose : To investigate initial chromatid breaks in prematurely condensed G2 chromosomes following exposure to heavy ions of different LET. Material and methods : Exponentially growing human fibroblast cells AG1522 were irradiated with γ-rays, energetic carbon (13 keV/ μ m, 80keV/ μ m), silicon (55 keV/ μ m) and iron (140 keV/ μ m, 185keV/ μ m, 440keV/ μ m) ions. Chromosomes were prematurely condensed using calyculin-A. Initial chromatid-type and isochromatid breaks in G2 cells were scored. Results : The dose-response curves for total chromatid breaks were linear regardless of radiation type. The relative biological effectiveness (RBE) showed a LET-dependent increase, peaking around 2.7 at 55-80 keV/ μ m and decreasing at higher LET. The dose-response curves for isochromatid-type breaks were linear for high-LET radiations, but linear-quadratic for γ-rays and 13 keV/ μ m carbon ions. The RBE for the induction of isochromatid breaks obtained from linear components increased rapidly between 13 keV/ μ m (about 7) and 80 keV/ μ m carbon (about 71), and decreased gradually until 440keV/ μ m iron ions (about 66). Conclusions : High-LET radiations are more effective at inducing isochromatid breaks, while low-LET radiations are more effective at inducing chromatid-type breaks. The densely ionizing track structures of heavy ions and the proximity of sister chromatids in G2 cells result in an increase in isochromatid breaks.     

90Y bremsstrahlung emission computed tomography using gamma cameras

Objective  This study demonstrates images obtained by ⁹⁰Y bremsstrahlung emission computed tomography (BECT), and characterizes the system performance of gamma cameras. Methods   ⁹⁰Y BECT images of phantoms were acquired using a gamma camera equipped with a medium energy general purpose parallel-hole collimator. Three energy window widths of 50% (57–94 keV) centered at 75 keV, 30% (102–138 keV) at 120 keV, and 50% (139–232 keV) at 185 keV were set on a ⁹⁰Y bremsstrahlung spectrum. The images obtained with three energy windows were reconstructed using filtered back projection (FBP) and ordered subsets expectation maximization (OSEM) methods. The images of the sum window were obtained by fusing the images of the 75, 120, and 185 keV windows. Results  The OSEM method improved the full width at half maximum by 20% and the standard deviation by 9% compared with the FBP method. BECT displayed ⁹⁰Y biodistribution and quantified ⁹⁰Y activity. BECT images obtained with OSEM method using the 120 keV window showed the highest resolution and lowest uncertainty. The sum window showed the highest sensitivity, while its resolution was 10% inferior to that of the 120 keV window. One whole-body image can be taken over 100 min using the sum window. An absorber to cover the body surface reduced background by 30%. Conclusions   ⁹⁰Y BECT imaging can be used for patient assessment without modifying current treatment procedures.     

Direct comparison between protons and alpha-particles of the same LET: I. Irradiation methods and inactivation of asynchronous V79, HeLa and C3H 10T1/2 cells.

A direct comparison was carried out of the biological effectiveness of protons and alpha-particles of the same linear energy transfer (LET) under identical conditions with a variety of in vitro biological systems. Monolayers of mammalian cells were irradiated with accelerated beams of protons (1.2 and 1.4 MeV) and alpha-particles (30 and 35 MeV) corresponding to LETs of 23 and 20 keV microns-1 for each particle type. For V79-4 cells it was observed that the linear term of the dose-response for cell inactivation by protons was significantly greater than that for alpha-particles of the same LET. For HeLa and HeLa S3 cells, also, the linear term appeared to be greater for protons, but this was not observed with more limited data for C3H 10T1/2 cells. The result for V79 cells is in agreement with the report of Belli et al. (1989) who observed that the biological effectiveness of protons rose sharply between 17 and 30 keV microns-1 in strong contrast to alpha-particles which reached a peak effectiveness at greater than 100 keV microns-1. These results place new constraints on the biologically relevant features of the microscopic structure of radiation tracks, and have implications for the mechanistic and practical comparison between radiations.     

Changes in measured size of atherosclerotic plaque calcifications in dual-energy CT of ex vivo carotid endarterectomy specimens: effect of monochromatic keV image reconstructions

Objective

The aim of this study was to compare the size of the calcifications measured on the different keV images to a histological standard.

Methods

Five ex vivo carotid endarterectomy (CEA) specimens were imaged with a dual-energy CT. CT images were reconstructed at different monochromatic spectral energies (40, 60, 77, 80, 100, 120, 140 keV). Cross-sectional area of the plaque calcifications present on each CT image was measured. The histological calcium areas on each corresponding CEA specimen were traced manually on digitised images of Toluidine Blue/Basic Fuchsin stained plastic sections. The CT images and corresponding histology sections were matched. The CT-derived calcium areas on each keV image were compared to the calcified area measurements by histology.

Results

A total of 107 histology sections were matched to corresponding CT images. The average calcified area per section by histology was 7.6?±?7 mm² (range 0–26.4 mm²). There was no significant difference between the calcified areas measured by histology and those measured on CT–virtual monochromatic spectral (VMS) reconstructed images at 77 keV (P?=?0.08), 80 keV (P?=?0.20) and 100 keV (P?=?0.14).

Conclusions

Calcium area measured on the 80 keV image set was most comparable to the amount of calcium measured by histology.

Key Points

? Dual-energy computed tomography allows reconstruction of virtual monochromatic images. ? Virtual monochromatic images reconstructed at different keVs reveal different atherosclerotic calcification quantification. ? Virtual monochromatic images allows better evaluation of calcified atherosclerotic plaques.     

Differential cross section measurements for the 7Li(n,n′γ) reaction at incident neutron energy between 0.5 and 3.0 MeV

Differential cross sections for the production of the 478 keV γ-ray from the interaction of reactor fast neutrons with ⁷Li have been measured at 55°, 90° and 125° angles relative to the incident neutron beam. Secondary neutrons have also been observed at 0° and 180° by large NE-213 scintillation detectors. The direct time-of-flight (n,n′) cross section values were deduced at these two angles relative to the standard values of 847(2⁺) keV level in ⁵⁶Fe. The results were compared with the available experimental, theoretical and evaluated data.     

Electron capture decay of 203Pb

Intensities of γ-transitions emerging from the EC decay of ²⁰³Pb were measured precisely. The obtained relative γ-intensities are 100% (279.2 keV), 4.14 ± 0.08% (401.3 keV) and 0.932 ± 0.022% (680.5 keV). The 279.2 and 680.5 keV level feeding β-branching ratios were deduced to be 95.3 ± 0.1 and 4.7 ± 0.1% respectively. ²⁰³Pb is suggested for calibration purposes.     

Determination of the intensity of X- and gamma-ray emissions in the decay of 153Sm.

The activity of a 153Sm solution was determined by means of liquid scintillation counting and an ionization chamber. Several accurately calibrated X- and gamma-ray spectrometers were used to measure point sources. The use of different detectors results in improvements to the accuracy of the data around 100 keV where the efficiency curve changes significantly. Photon emission intensities have been derived for the main X- and gamma-rays, and the 103-keV emission has a measured intensity of (29.07 (20)) per 100 disintegrations.     

Performance measurement of the microPET focus 120 scanner.

The microPET Focus 120 scanner is a third-generation animal PET scanner dedicated to rodent imaging. Here, we report the results of scanner performance testing. METHODS: A (68)Ge point source was used to measure energy resolution, which was determined for each crystal and averaged. Spatial resolution was measured using a (22)Na point source with a nominal size of 0.25 mm at the system center and various off-center positions. Absolute sensitivity without attenuation was determined by extrapolating the data measured using an (18)F line source and multiple layers of absorbers. Scatter fraction and counting rate performance were measured using 2 different cylindric phantoms simulating rat and mouse bodies. Sensitivity, scatter fraction, and noise equivalent counting rate (NECR) experiments were repeated under 4 different conditions (energy window, 250 approximately 750 keV or 350 approximately 650 keV; coincidence window, 6 or 10 ns). A performance phantom with hot-rod inserts of various sizes was scanned, and several animal studies were also performed. RESULTS: Energy resolution at a 511-keV photopeak was 18.3% on average. Radial, tangential, and axial resolution of images reconstructed with the Fourier rebinning (FORE) and filtered backprojection (FBP) algorithms were 1.18 (radial), 1.13 (tangential), and 1.45 mm full width at half maximum (FWHM) (axial) at center and 2.35 (radial), 1.66 (tangential), and 2.00 mm FWHM (axial) at a radial offset of 2 cm. Absolute sensitivities at transaxial and axial centers were 7.0% (250 approximately 750 keV, 10 ns), 6.7% (250 approximately 750 keV, 6 ns), 4.0% (350 approximately 650 keV, 10 ns), and 3.8% (350 approximately 650 keV, 6 ns). Scatter fractions were 15.9% (mouse phantom) and 35.0% (rat phantom) for 250 approximately 750 keV and 6 ns. Peak NECR was 869 kcps at 3,242 kBq/mL (mouse phantom) and 228 kcps at 290 kBq/mL (rat phantom) at 250 approximately 750 keV and 6 ns. Hot-rod inserts of 1.6-mm diameter were clearly identified, and animal studies illustrated the feasibility of this system for studies of whole rodents and mid-sized animal brains. CONCLUSION: The results of this independent field test showed the improved physical characteristics of the F120 scanner over the previous microPET series systems. This system will be useful for imaging studies on small rodents and brains of larger animals.     

The potential of iodinated contrast reduction in dual-energy CT thoracic angiography; an evaluation of image quality

IntroductionThe purpose of this study was to compare a dual energy CT (DECT) protocol with 50% reduction of iodinated contrast to a single energy CT (SECT) protocol using standard contrast dose in imaging of the thoracic aorta.MethodsDECT with a 50% reduction in iodinated contrast was compared with SECT. For DECT, monoenergetic images at 50, 55, 60, 65, 68, 70, and 74 keV were reconstructed with adaptive statistical iterative reconstruction (ASiR-V) of 50% and 80%. Objective image quality parameters included intravascular attenuation (HU), image noise (SD), contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR). Two independent radiologists subjectively assessed the image quality for the 55 and 68 keV DECT reconstructions and SECT on a five-point Likert scale.ResultsAcross 14 patients, the intravascular attenuation at 50–55 keV was comparable to SECT (p > 0.05). The CNRs were significantly lower for DECT with ASIR-V 50% compared to SECT for all keV-values (p < 0.05 for all). For ASIR-V 80%, CNR was comparable to SECT at energies below 60 keV (p > 0.05). The subjective image quality was comparable between DECT and SECT independent of keV level.ConclusionThis study indicates that a 50% reduction in iodinated contrast may result in adequate image quality using DECT with monoenergetic reconstructions at lower energy levels for the imaging of the thoracic aorta. The best image quality was obtained for ASiR-V 80% image reconstructions at 55 keV.Implications of practiceDual energy CT with a reduction in iodinated contrast may result in adequate image quality in imaging of the thoracic aorta. However, increased radiation dose may limit the use to patients in which a reduction in fluid and iodinated contrast volume may outweigh this risk.     

The low energy X-ray response of the LiF:Mg:Cu:P thermoluminescent dosemeter: a comparison with LiF:Mg:Ti

LiF:Mg:Cu:P thermoluminescent dosemeters (TLD) can be used for the same X-ray dosimetry applications as LiF:Mg:Ti, with each type having the disadvantage of a response dependent on energy, particularly at low energies. Measurements were made of the response per unit air kerma of LiF:Mg:Cu:P and LiF:Mg:Ti to nine quasi-monoenergetic X-ray beams with mean energies from 12 keV to 208 keV. Each measurement was normalized to the value produced by 6 MV X-rays. LiF:Mg:Cu:P was found to under-respond to a majority of these radiations whereas LiF:Mg:Ti over-responded to a majority. Their smallest relative measured response was produced by the lowest energy beam, and the maximum measured relative response of 1.15+/-0.07 and 1.21+/-0.07 for LiF:Mg:Cu:P and LiF:Mg:Ti, respectively, occurred at 33 keV. Energy response coefficients were derived from these measurements to estimate the error introduced by using either type of TLD to measure the dose from an X-ray spectrum different to that used for its absolute response calibration. It was calculated that if the response of either type of TLD was calibrated at 100 kVp, then an error of no more than +/-2% would be introduced into measurements of tube output at potentials of 50-130 kVp. LiF:Mg:Cu:P was found to introduce a larger error (up to 30%) into the measurement of body exit dose than LiF:Mg:Ti at tube potentials of 40-150 kVp, if its absolute response was calibrated using the corresponding body entrance beam. The method should allow this type of error to be estimated in other dosimetry applications for either type of TLD.