kVp Images Research Articles

Quantitative myocardial perfusion imaging in a porcine ischemia model using a prototype spectral detector CT system

We optimized and evaluated dynamic myocardial CT perfusion (CTP) imaging on a prototype spectral detector CT (SDCT) scanner. Simultaneous acquisition of energy sensitive projections on the SDCT system enabled projection-based material decomposition, which typically performs better than image-based decomposition required by some other system designs. In addition to virtual monoenergetic, or keV images, the SDCT provided conventional (kVp) images, allowing us to compare and contrast results. Physical phantom measurements demonstrated linearity of keV images, a requirement for quantitative perfusion. Comparisons of kVp to keV images demonstrated very significant reductions in tell-tale beam hardening (BH) artifacts in both phantom and pig images. In phantom images, consideration of iodine contrast to noise ratio and small residual BH artifacts suggested optimum processing at 70 keV. The processing pipeline for dynamic CTP measurements included 4D image registration, spatio-temporal noise filtering, and model-independent singular value decomposition deconvolution, automatically regularized using the L-curve criterion. In normal pig CTP, 70 keV perfusion estimates were homogeneous throughout the myocardium. At 120 kVp, flow was reduced by more than 20% on the BH-hypo-enhanced myocardium, a range that might falsely indicate actionable ischemia, considering the 0.8 threshold for actionable FFR. With partial occlusion of the left anterior descending (LAD) artery (FFR < 0.8), perfusion defects at 70 keV were correctly identified in the LAD territory. At 120 kVp, BH affected the size and flow in the ischemic area; e.g. with FFR 0.65, the anterior-to-lateral flow ratio was 0.29 ± 0.01, over-estimating stenosis severity as compared to 0.42 ± 0.01 (p < 0.05) at 70 keV. On the non-ischemic inferior wall (not a LAD territory), the flow ratio was 0.50 ± 0.04 falsely indicating an actionable ischemic condition in a healthy territory. This ratio was 1.00 ± 0.08 at 70 keV. Results suggest that projection-based keV imaging with the SDCT system and proper processing could enable useful myocardial CTP, much improved over conventional CT.

Dual-energy CT Aortography with 50% Reduced Iodine Dose Versus Single-energy CT Aortography with Standard Iodine Dose

Because many patients with aortic pathology also have compromised renal function, we wished to investigate dual-energy computed tomography (DECT) aortography with 50% reduced iodine dose compared to single-energy computed tomography (SECT) aortography with standard iodine dose. Fifty patients had DECT aortography with 50% reduced iodine dose. Thirty-four of these patients had prior SECT aortography with standard iodine dose. DECT images were reconstructed at both 50 and 77 keV and were compared to SECT 120 kVp images. Reviewers measured aortic attenuation, image noise, and scored vascular enhancement. Signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were calculated. Volume CT dose index was recorded. Mean iodine dose was 47 g for SECT and 24 g for DECT. Aortic attenuation was highest at reduced iodine dose DECT 50 keV (570 ± 105 Hounsfield units [HU]) compared to 77 keV (239 ± 40 HU) or to standard iodine dose SECT 120 kVp (356 ± 69 HU) (P < 0.05). Image noise was greatest at 50 keV compared to 77 keV and 120 kVp (P < 0.05) but was similar between 77 keV and 120 kVp (P > 0.05). SNR and CNR were the same at 50 keV and 120 kVp (P > 0.05). Mean vascular enhancement scores were all above 3.0 (good, typical enhancement). Volume CT dose index was 11.7 mGy for DECT and 11.8 mGy for SECT (P = 0.37). DECT aortography with 50% reduced iodine reconstructed at 50 keV resulted in significantly greater aortic attenuation, good subjective vascular enhancement, and comparable SNR and CNR compared to standard iodine dose SECT. DECT image noise at 77 keV was similar to SECT at 120 kVp.

Monochromatic Spectral Computed Tomography with Low Iodine Concentration Contrast Medium in a Rabbit VX2 Liver Model:: Investigation of Image Quality and Detection Rate

This study aimed to validate the feasibility of using virtual monochromatic spectral computed tomography (CT) with isotonic low iodine concentration contrast medium for VX2 hepatic tumors. Sixty New Zealand white rabbits with implanted VX2 hepatic tumors underwent two-phase contrast-enhanced spectral CT imaging on the 14th day after tumor implantation. They were randomly divided into groups A, B, and C, with 20 rabbits each (group A: 270 mg I/mL, monochromatic spectral images; group B: 370 mg I/mL, conventional 120 kVp images, 100% filtered back projection [FBP]; group C: 270 mg I/mL, conventional 120 kVp images, 100% FBP). Group A was further divided into two subgroups (subgroup A1: 100% FBP; subgroup A2: 50% FBP + 50% adaptive statistical iterative reconstruction). Objective evaluation (signal-to-noise ratio [SNR], contrast-to-noise ratio [CNR], and image noise), subjective rating score (image noise score, anatomical details score, overall image quality score, and lesion conspicuity score), CT dose index volume, and dose length product were compared between groups during two-phase contrast enhancement. The detection rates of the four groups were calculated as percentages. Image noise (SNR and CNR) among the four groups was statistically significant (P <0.05). The image noise in group A2 was lower than in group A1, but higher than that in groups B and C (P <0.05). SNR and CNR in group A2 were the highest, followed by group A1, and group C was the lowest (P <0.05 for all). The image noise score of group A2 was higher than that of the other three groups. In terms of the anatomic details score, the overall image quality score, and the lesion conspicuity score, the images of group A2 were superior to that of groups A1 and C. For hepatic tumor diameters more than or equal to 1.0 cm and less than 3.0 cm, group A achieved a higher detection rate than groups B and C. The CT dose index volume, dose length product, and effective dose in group A were significantly lower than that in groups B and C (P <0.05). On average, group A reduced the effective radiation dose by 27.2% compared to group B, whereas group B reduced the effective radiation dose by 28% compared to group C. Group A reduced the iodine load by 22.86% compared to group B. The use of monochromatic images combined with 50% adaptive statistical iterative reconstruction with an isotonic low concentration contrast medium of 270 mg I/mL can optimize image quality, reduce image noise, increase detection rate for small tumors, and decrease radiation dose and iodine load in hepatic tumor CT examinations.

Dual-energy CT of liver metastases in patients with uveal melanoma

ObjectiveTo investigate the value of different kVp images of dual-energy CT (DECT) for the detection of liver metastases. Methods20 Patients with uveal melanoma were investigated with DECT of the liver. In each patient contrast-enhanced DECT imaging with arterial delay was performed. Number and size of metastases were documented on arterial phase 80-kVp images, virtual 120-kVp images and following angiographic images (DSA) as part of hepatic chemoperfusion. Attenuation of metastases and several anatomic regions, subjective (image noise, image quality) and objective (SNR, CNR) parameters were documented. ResultsThe mean number of liver metastases detected was significant higher on 80-kVp images than on virtual 120-kVp/DSA images (5.6±2.1 vs. 4.1±1.8/4.3±1.6); (p<0.001). All lesions sizes were significant better detected with 80kVp images than with virtual 120kVp and DSA-Images (80kVp vs. 120kVp: <10mm: 34 vs. 19, p<0.05; 10–20mm:, 33 vs. 25, p<0.05; >20mm: 56 vs. 42, p<0.05/80kVp vs. DSA: <10mm: 34 vs. 18 p<0.05; 10–20mm: 33 vs. 24, p<0.05; >20mm: 56 vs. 41, p<0.05). Number of detected small lesions <10mm with 120kVp compared to DSA-images were significant higher (19 vs. 13; p<0.05), lesions 10–20mm and >20mm were measured statistically equally. Noise, SNR and CNR of 80kVp images were higher compared to 120kVp images. Image quality of 120kVp images was higher compared to 80kVp images. ConclusionLow-kVp images of DECT datasets are more sensitive in detecting liver metastases of patients with uveal melanoma than virtual 120kVp- and DSA images.

Low-Contrast and Low-Radiation Dose Protocol in Cardiac Computed Tomography: Usefulness of Low Tube Voltage and Knowledge-Based Iterative Model Reconstruction Algorithm.

This study aimed to evaluate the feasibility of a low contrast, low-radiation dose protocol of 80-peak kilovoltage (kVp) with prospective electrocardiography-gated cardiac computed tomography (CT) using knowledge-based iterative model reconstruction (IMR). Thirty patients underwent an 80-kVp prospective electrocardiography-gated cardiac CT with low-contrast agent (222-mg iodine per kilogram of body weight) dose. We also enrolled 30 consecutive patients who were scanned with a 120-kVp cardiac CT with filtered back projection using the standard contrast agent dose (370-mg iodine per kilogram of body weight) as a historical control group. We evaluated the radiation dose for the 2 groups. The 80-kVp images were reconstructed with filtered back projection (protocol A), hybrid iterative reconstruction (HIR, protocol B), and IMR (protocol C). We compared CT numbers, image noise, and contrast-to-noise ratio among 120-kVp protocol, protocol A, protocol B, and protocol C. In addition, we compared the noise reduction rate between HIR and IMR. Two independent readers compared image contrast, image noise, image sharpness, unfamiliar image texture, and overall image quality among the 4 protocols. The estimated effective dose (ED) of the 80-kVp protocol was 74% lower than that of the 120-kVp protocol (1.4 vs 5.4 mSv). The contrast-to-noise ratio of protocol C was significantly higher than that of protocol A. The noise reduction rate of IMR was significantly higher than that of HIR (P < 0.01). There was no significant difference in almost all qualitative image quality between 120-kVp protocol and protocol C except for image contrast. A 80-kVp protocol with IMR yields higher image quality with 74% decreased radiation dose and 40% decreased contrast agent dose as compared with a 120-kVp protocol, while decreasing more image noise compared with the 80-kVp protocol with HIR.

Spectral CT with monochromatic imaging and metal artifacts reduction software for artifacts reduction of ¹²⁵I radioactive seeds in liver brachytherapy.

To investigate the optimal monochromatic energy for artifacts reduction from (125)I seeds as well as image improvement in the vicinity of seeds on monochromatic images with and without metal artifacts reduction software (MARS) and to compare this with traditional 120-kVp images, so as to evaluate the application value of gemstone spectral imaging for reducing artifacts from (125)I seeds in liver brachytherapy. A total of 45 tumors from 25 patients treated with (125)I seed brachytherapy in the liver were enrolled in this study. Multiphasic spectral computed tomography (CT) scanning was performed for each patient. After a delay time of 15 s of portal vein phase, a traditional 120-kVp scan was performed, focusing on several planes of (125)I seeds only. The artifact index (AI) in the vicinity of seeds and the standard deviation (SD) of the CT density of region of interest in the outside liver parenchyma were calculated. Artifact appearance was evaluated and classified on reconstructed monochromatic S and 120-kVp images. Image quality in the vicinity of seeds of three data sets were evaluated using a 1-5 scale scoring method. The Friedman rank-sum test was used to estimate the scoring results of image quality. The greatest noise in monochromatic images was found at 40 keV (SD = 27.38, AI = 206.40). The optimal monochromatic energy was found at 75 keV, which provided almost the least image noise (SD = 10.01) and good performance in artifact reduction (AI = 102.73). Image noise and AI reduction at 75 keV was decreased by 63.44 and 50.23%, compared with at 40 keV. Near-field thick artifacts were obvious in all 45 lesions, in 120-kVp images, and 75-keV images, but basically reduced in 75 keV MARS images and artifacts completely invisible in 7 lesions. The number of diagnosable images (score ≥3) was significantly more in the 75-keV MARS group (28/45), and the 75-keV group (22/45) than in the 120-kVp group (11/45) (p < 0.0167 for both). Compared with 120-kVp images alone, 75-keV images plus 75-keV MARS images can increase tumor visibility around seeds and increase the proportion of diagnostic images to 84.4% (38/45). Spectral CT producing 75-keV MARS images could substantially reduce near-field thick artifacts caused by (125)I seeds and improve image quality, even to a state of being completely free from artifacts. Spectral CT imaging (with and without MARS) can provide more accurate CT images for estimating efficacy after (125)I seed brachytherapy in the liver.

Correlation of quantitative dual-energy computed tomography iodine maps and abdominal computed tomography perfusion measurements: are single-acquisition dual-energy computed tomography iodine maps more than a reduced-dose surrogate of conventional computed tomography perfusion?

Study objectives were the quantitative evaluation of whether conventional abdominal computed tomography (CT) perfusion measurements mathematically correlate with quantitative single-acquisition dual-energy CT (DECT) iodine concentration maps, the determination of the optimum time of acquisition for achieving maximum correlation, and the estimation of the potential for radiation exposure reduction when replacing conventional CT perfusion by single-acquisition DECT iodine concentration maps. Dual-energy CT perfusion sequences were dynamically acquired over 51 seconds (34 acquisitions every 1.5 seconds) in 24 patients with histologically verified pancreatic carcinoma using dual-source DECT at tube potentials of 80 kVp and 140 kVp. Using software developed in-house, perfusion maps were calculated from 80-kVp image series using the maximum slope model after deformable motion correction. In addition, quantitative iodine maps were calculated for each of the 34 DECT acquisitions per patient. Within a manual segmentation of the pancreas, voxel-by-voxel correlation between the perfusion map and each of the iodine maps was calculated for each patient to determine the optimum time of acquisition topt defined as the acquisition time of the iodine map with the highest correlation coefficient. Subsequently, regions of interest were placed inside the tumor and inside healthy pancreatic tissue, and correlation between mean perfusion values and mean iodine concentrations within these regions of interest at topt was calculated for the patient sample. The mean (SD) topt was 31.7 (5.4) seconds after the start of contrast agent injection. The mean (SD) perfusion values for healthy pancreatic and tumor tissues were 67.8 (26.7) mL per 100 mL/min and 43.7 (32.2) mL per 100 mL/min, respectively. At topt, the mean (SD) iodine concentrations were 2.07 (0.71) mg/mL in healthy pancreatic and 1.69 (0.98) mg/mL in tumor tissue, respectively. Overall, the correlation between perfusion values and iodine concentrations was high (0.77), with correlation of 0.89 in tumor and of 0.56 in healthy pancreatic tissue at topt. Comparing radiation exposure associated with a single DECT acquisition at topt (0.18 mSv) to that of an 80 kVp CT perfusion sequence (2.96 mSv) indicates that an average reduction of Deff by 94% could be achieved by replacing conventional CT perfusion with a single-acquisition DECT iodine concentration map. Quantitative iodine concentration maps obtained with DECT correlate well with conventional abdominal CT perfusion measurements, suggesting that quantitative iodine maps calculated from a single DECT acquisition at an organ-specific and patient-specific optimum time of acquisition might be able to replace conventional abdominal CT perfusion measurements if the time of acquisition is carefully calibrated. This could lead to large reductions of radiation exposure to the patients while offering quantitative perfusion data for diagnosis.

Possible Contrast Media Reduction with Low keV Monoenergetic Images in the Detection of Focal Liver Lesions: A Dual-Energy CT Animal Study.

ObjectiveTo investigate the feasibility of dual-energy CT for contrast media (CM) reduction in the diagnosis of hypervascular and hypovascular focal liver lesions (FLL).Subjects and MethodsThe Institutional Animal Care and Use Committee approved this study. VX2 tumors were implanted in two different segments of the liver in 13 rabbits. After 2 weeks, two phase contrast enhanced CT scans including the arterial phase (AP) and portal-venous phase (PVP) were performed three times with 24-hour intervals with three different concentrations of iodine, 300 (I300), 150 (I150) and 75 mg I/mL (I75). The mean HU and standard deviation (SD) were measured in the liver, the hypervascular portion of the VX2 tumor which represented hypervascular tumors, and the central necrotic area of the VX2 tumor which represented hypovascular tumors in 140kVp images with I300 as a reference standard and in monoenergetic images (between 40keV and 140keV) with I150 and I75. The contrast-to-noise ratio (CNR) for FLLs and the ratio of the CNRs (CNRratio) between monoenergetic image sets with I150 and I75, and the reference standard were calculated.ResultsFor hypervascular lesions, the CNRratio was not statistically different from 1.0 between 40keV and 70keV images with I150, whereas the CNRratio was significantly lower than 1.0 in all keV images with I75. For hypovascular lesions, the CNRratio was similar to or higher than 1.0 between 40keV and 80keV with I150 and between 40keV and 70keV with I75.ConclusionsWith dual-energy CT, the total amount of CM might be halved in the diagnosis of hypervascular FLLs and reduced to one-fourth in the diagnosis of hypovascular FLLs, while still preserving CNRs.

Effects of the difference in tube voltage of the CT scanner on dose calculation

Computed tomography (CT) measures the attenuation coefficient of an object and converts the value assigned to each voxel into a CT number. In radiation therapy, the CT number, which is directly proportional to the linear attenuation coefficient, must be converted to an electron density for radiation dose calculations for cancer treatment. However, if various tube voltages are applied to take the patient’s CT image without applying the specific CT number to the electron density conversion curve, the accuracy of the dose calculation is not assured. In this study, changes in CT numbers for different materials due to changes in the tube voltage were demonstrated, and the dose calculation errors in the percentage depth dose (PDD), along with a clinical case were analyzed. The maximum dose difference in the PDD from the treatment planning system (TPS) dose calculation and from the Monte Carlo simulation were 1.3% and 1.1%, respectively, when applying the same CT number to the electron density conversion curve for the 80-kVp and 140-kVp images. In the clinical case, different CT number to electron density conversion curves at tube voltage of 80 kVp and 140 kVp were applied to the same image and the maximum differences in the mean, maximum, and minimum doses were 1.1%, 1.2%, and 1.0%, respectively, at the central region of the phantom and 0.6%, 0.9%, and 0.8%, respectively, at the peripheral region of the phantom.

Evaluation of image quality, radiation dose and diagnostic performance of dual-energy CT datasets in patients with hepatocellular carcinoma

To evaluate image quality and diagnostic accuracy of different dual-energy computed tomography (DECT) datasets for identification of hepatocellular carcinoma (HCC), assess the reliability of virtual unenhanced (VU) images in replacing standard unenhanced (SU) images, and quantify effective dose (ED) at different tube voltages. Thirty cirrhotic patients underwent liver contrast-enhanced DECT. Two blinded observers retrospectively evaluated conventional unenhanced and VU images, 140 kVp/80 kVp/mixed tube potential arterial datasets and conventional portal-venous/late phases in consensus. Final diagnosis was based on pathological proof or imaging criteria. Image quality, ED, sensitivity, and specificity of arterial datasets were calculated. Thirty-eight HCC and 18 benign lesions were detected at 80 kVp, 33 HCC and 22 benign lesions were detected at 140 kVp, and 36 HCC and 20 benign lesions were detected at mixed tube potentials. Final diagnosis confirmed 37 HCC and 20 benign lesions. There was no significant difference in diagnostic confidence between 80 kVp, 140 kVp, and mixed tube potential arterial datasets (p>0.05). Image quality was adequate for all datasets, with increased quality at higher tube potential (80 versus 140 kVp, p=0.001; mixed versus 140 kVp, p=0.001; 80 kVp versus mixed, p=0.0024). Significant ED reduction was observed between 140 and 80 kVp datasets (p<0.001). The 140 kVp dataset provided higher image quality. The 80 kVp images were more sensitive in detecting HCC. VU images are adequate in replacing SU images. The ED of the 80 kVp dataset was significantly lower.

Feasibility Study of Using Gemstone Spectral Imaging (GSI) and Adaptive Statistical Iterative Reconstruction (ASIR) for Reducing Radiation and Iodine Contrast Dose in Abdominal CT Patients with High BMI Values.

PurposeTo prospectively investigate the effect of using Gemstone Spectral Imaging (GSI) and adaptive statistical iterative reconstruction (ASIR) for reducing radiation and iodine contrast dose in abdominal CT patients with high BMI values.Materials and Methods26 patients (weight > 65kg and BMI ≥ 22) underwent abdominal CT using GSI mode with 300mgI/kg contrast material as study group (group A). Another 21 patients (weight ≤ 65kg and BMI ≥ 22) were scanned with a conventional 120 kVp tube voltage for noise index (NI) of 11 with 450mgI/kg contrast material as control group (group B). GSI images were reconstructed at 60keV with 50%ASIR and the conventional 120kVp images were reconstructed with FBP reconstruction. The CT values, standard deviation (SD), signal-noise-ratio (SNR), contrast-noise-ratio (CNR) of 26 landmarks were quantitatively measured and image quality qualitatively assessed using statistical analysis.ResultsAs for the quantitative analysis, the difference of CNR between groups A and B was all significant except for the mesenteric vein. The SNR in group A was higher than B except the mesenteric artery and splenic artery. As for the qualitative analysis, all images had diagnostic quality and the agreement for image quality assessment between the reviewers was substantial (kappa = 0.684). CT dose index (CTDI) values for non-enhanced, arterial phase and portal phase in group A were decreased by 49.04%, 40.51% and 40.54% compared with group B (P = 0.000), respectively. The total dose and the injection rate for the contrast material were reduced by 14.40% and 14.95% in A compared with B.ConclusionThe use of GSI and ASIR provides similar enhancement in vessels and image quality with reduced radiation dose and contrast dose, compared with the use of conventional scan protocol.

Simultaneous achievement of accurate CT number and image quality improvement for myocardial perfusion CT at 320-MDCT volume scanning

PurposeTo investigate differences in image-to-image variations between full- and half-scan reconstruction on myocardial CT perfusion (CTP) study. MethodsUsing a cardiac phantom we performed ECG-gated myocardial CTP on a second-generation 320-multidetector CT volume scanner. The heart rate was set at 60 bpm; once per second for a total of 24 s were performed. CT images were acquired at 80- and 120 kVp and subjected to full- and half-scan reconstruction. On images acquired at the same slice level we then measured image-to-image variations, coefficients of variance (CV), and image noise. ResultsThe image-to-image variations with full- and half-scan reconstruction were 1.3 HU vs. 27.2 HU at 80 kVp (p < 0.001) and 0.70 HU vs. 9.3 HU at 120 kVp (p < 0.001) even though the mean HU value was almost the same for both reconstruction methods. The CV of 80- and 120-kVp images of the left ventricular cavity decreased by 0.16% and 0.17%, respectively, with full-scan reconstruction; with half-scan reconstruction it decreased by 3.34% and 2.30%, respectively. Compared with half-scan reconstruction, the image noise was reduced by 27.2% at 80 kVp and by 28.0% at 120 kVp with full-scan reconstruction. ConclusionMyocardial CTP with full-scan reconstruction substantially decreased image-to-image variations and provided accurate CT attenuation.

Dual energy computed tomography thermometry during hepatic microwave ablation in an ex-vivo porcine model

BackgroundMicrowave thermoablation (MTA) is a treatment method used to destroy hepatic tumors. ObjectiveTo investigate temperature changes during MTA of ex-vivo porcine liver using dual-energy computed tomography (DECT) imaging. MethodsThree MTA experiments were performed using ex-vivo porcine liver (15 × 15 × 15 cm3) and DECT imaging with 80/Sn140 kVp spectral and 0.5-weighted reconstructions. Images were acquired from basic organ temperature to 100 °C with 10 °C difference during microwave heating and cooling phases. Three fluoro-optic thermometers were used for temperature measurements; two were placed at 1 cm and third one positioned at 2 cm distance from the applicator. Tissue temperature, ablation-region-conspicuity (ARC), ablation-region dimensions and image quality were determined. Regression analysis was performed determining thermal sensitivity during heating and cooling phases. ResultsDetermined thermal sensitivities during heating phase were: −0.59 Hounsfield Unit/°C (80 kVp), −0.60HU/°C (0.5-weighted) and −0.59HU/°C (140 kVp); furthermore, during cooling: −0.56HU/°C (80 kVp), −0.55HU/°C (0.5-weighted) and −0.55HU/°C (140 kVp). ARC showed significantly higher (all P < 0.05) values for thermometer positions −1 and −2 compared to −3; however, comparison between positions −1 and −2 was insignificant (P > 0.05). Signal-to-noise ratios were higher for 0.5-weighted but ARC values were higher for 80 kVp images. ConclusionMicrowave thermal sensitivity on tissue was inversely linear with DECT image datasets. Heating phase showed higher influence of temperature on HU compared to cooling; ARC and ablation-region were increased with increase in temperature.

Evaluation of image quality and dose reduction of 80 kVp neck computed tomography in patients with suspected peritonsillar abscess

To evaluate neck computed tomography (CT) with a reduced tube voltage of 80 kVp in patients with suspected peritonsillar abscess (PTA) regarding objective and subjective image quality, and the potential for dose reduction. Forty-seven patients with clinically suspected PTA were retrospectively analysed. Patients were examined using dual-source CT in dual-energy mode. The objective and subjective image quality of 80 kVp images were compared with linearly blended 120 kVp images (M_0.3; 30% of 80 kV, 70% of 140 kV spectrum). Attenuation of abscess rim enhancement, central necrosis, and several other anatomical landmarks were measured. The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and rim-to-abscess CNR (raCNR) were calculated. Radiation dose was assessed as size-specific dose estimates (SSDE). Subjective image quality was assessed according to the European guidelines on quality criteria for CT. Interobserver agreement was calculated using the intraclass correlation coefficient (ICC). Attenuation of inflamed soft tissue (141.7 ± 16.3 versus 93.7 ± 9.3 HU, p < 0.001), CNR (9.6 ± 4.8 versus 5.6 ± 3.8, p = 0.001), raCNR (14.3 ± 5.9 versus 12.4 ± 4.4, p = 0.02), and subjective image sharpness (3.6 ± 0.6 versus 2.8 ± 0.7, p < 0.001) were significantly increased in the 80 kVp compared to 120 kVp, whereas subjective and objective image noise were significantly increased with 80 kVp acquisition (p < 0.001). Overall interobserver agreement was almost perfect (ICC, 0.87). Calculated SSDE of 80 kVp acquisition was decreased by 49.7% compared to 120 kVp (10.58 ± 0.76 versus 21.04 ± 1.43 mGy, p < 0.001). Low-tube-voltage 80 kVp neck CT provides increased enhancement of soft-tissue inflammation, CNR, raCNR, and improved abscess delineation in patients with PTA compared to standard 120 kVp acquisition while resulting in a significant reduction of radiation exposure.

Examining Practitioners' Assessments of Perceived Aesthetic and Diagnostic Quality of High kVp–Low mAs Pelvis, Chest, Skull, and Hand Phantom Radiographs

This study investigated the usefulness of the dose optimization strategy of increased tube voltage (kVp) and decreased tube current-exposure time product (mAs) (or high kVp–low mAs) by examining practitioners' assessments of perceived aesthetic and diagnostic quality of direct digital radiographs acquired using this strategy. Ninety-one practitioners (radiologists, radiology residents, radiographers, and radiography students) from eight clinical sites in Ontario examined three types of radiographs (“standard” image, +20 kVp image, and +30 kVp image) for anthropomorphic pelvis, chest, skull, and hand phantoms and rated (on a five-point scale) each image in regard to its perceived aesthetic quality, perceived diagnostic quality, and visualization of anatomic structures. Our primary findings are that for the pelvis, skull, and hand–although not the chest–images acquired using standard technical factors were rated significantly higher in diagnostic and aesthetic quality than those acquired using the high kVp–low mAs strategy. Despite this, both standard and dose-optimized images of the pelvis, skull, and hand were rated to be of acceptable diagnostic quality for clinical use. In conclusion, for the pelvis, skull, and hand, an increase of 20 kVp was an effective strategy to reduce dose while still acquiring images of diagnostic quality.

Reducing the Radiation Dose for CT Colonography: Effect of Low Tube Voltage and Iterative Reconstruction

The purpose of this study was to assess the effect of a low-tube-voltage technique and iterative reconstruction (IR) on the radiation dose and image quality of computed tomography colonography (CTC). We studied 30 patients (14 women and 16 men; mean age, 64.5±13.1years; range, 39-90years) with colorectal cancer referred for surgical treatment. All underwent CTC with fecal tagging under a standard 120-kVp protocol in the supine position and a 100-kVp protocol in the prone position. The 120-kVp images were reconstructed with filtered back projection (FBP). The 100-kVp images were postprocessed using FBP and a hybrid type of IR (adaptive iterative dose reduction 3D). The effective radiation dose (ED), image noise, and contrast-to-noise ratio (CNR) were compared among the three protocols. The visual image quality was scored on a four-point scale. The mean ED was significantly lower under the 100-kVp protocol than the 120-kVp protocol, resulting in a 27% radiation dose decrease (3.5±2.0 vs 2.5±1.5mSv; P<.01). Image noise decreased by 48%, and the mean attenuation of tagged fluid increased from 452 to 558 HU on images acquired at 100 kVp with IR compared to that in the 120-kVp protocol; these differences were significant. The mean CNR was significantly higher under the 100 kVp with IR than the other two protocols. We found no significant differences in the visual scores for diagnostic utility between the 100 kVp with IR and the 120 kVp with FBP protocol (P=.10). Low-tube-voltage CTC reduced the radiation dose by approximately 27% while maintaining the image quality.

Renal cyst pseudoenhancement: intraindividual comparison between virtual monochromatic spectral images and conventional polychromatic 120-kVp images obtained during the same CT examination and comparisons among images reconstructed using filtered back projection, adaptive statistical iterative reconstruction, and model-based iterative reconstruction.

The purpose of this study was to compare renal cyst pseudoenhancement between virtual monochromatic spectral (VMS) and conventional polychromatic 120-kVp images obtained during the same abdominal computed tomography (CT) examination and among images reconstructed using filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR).Our institutional review board approved this prospective study; each participant provided written informed consent. Thirty-one patients (19 men, 12 women; age range, 59–85 years; mean age, 73.2 ± 5.5 years) with renal cysts underwent unenhanced 120-kVp CT followed by sequential fast kVp-switching dual-energy (80/140 kVp) and 120-kVp abdominal enhanced CT in the nephrographic phase over a 10-cm scan length with a random acquisition order and 4.5-second intervals. Fifty-one renal cysts (maximal diameter, 18.0 ± 14.7 mm [range, 4–61 mm]) were identified. The CT attenuation values of the cysts as well as of the kidneys were measured on the unenhanced images, enhanced VMS images (at 70 keV) reconstructed using FBP and ASIR from dual-energy data, and enhanced 120-kVp images reconstructed using FBP, ASIR, and MBIR. The results were analyzed using the mixed-effects model and paired t test with Bonferroni correction.The attenuation increases (pseudoenhancement) of the renal cysts on the VMS images reconstructed using FBP/ASIR (least square mean, 5.0/6.0 Hounsfield units [HU]; 95% confidence interval, 2.6–7.4/3.6–8.4 HU) were significantly lower than those on the conventional 120-kVp images reconstructed using FBP/ASIR/MBIR (least square mean, 12.1/12.8/11.8 HU; 95% confidence interval, 9.8–14.5/10.4–15.1/9.4–14.2 HU) (all P < .001); on the other hand, the CT attenuation values of the kidneys on the VMS images were comparable to those on the 120-kVp images.Regardless of the reconstruction algorithm, 70-keV VMS images showed a lower degree of pseudoenhancement of renal cysts than 120-kVp images, while maintaining kidney contrast enhancement comparable to that on 120-kVp images.

Objective and subjective image quality of primary and recurrent squamous cell carcinoma on head and neck low-tube-voltage 80-kVp computed tomography.

To investigate low-tube-voltage 80-kVp computed tomography (CT) of head and neck primary and recurrent squamous cell carcinoma (SCC) regarding objective and subjective image quality. We retrospectively evaluated 65 patients (47 male, 18 female; mean age: 62.1 years) who underwent head and neck dual-energy CT (DECT) due to biopsy-proven primary (n = 50) or recurrent (n = 15) SCC. Eighty peak kilovoltage and standard blended 120-kVp images were compared. Attenuation and noise of malignancy and various soft tissue structures were measured. Tumor signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Subjective image quality was rated by three reviewers using 5-point grading scales regarding overall image quality, lesion delineation, image sharpness, and image noise. Radiation dose was assessed as CT dose index volume (CTDIvol). Interobserver agreement was calculated using intraclass correlation coefficient (ICC). Mean tumor attenuation (153.8 Hounsfield unit (HU) vs. 97.1 HU), SNR (10.7 vs. 8.3), CNR (8.1 vs. 4.8), and subjective tumor delineation (score, 4.46 vs. 4.13) were significantly increased (all P < 0.001) with 80-kVp acquisition compared to standard blended 120-kVp images. Noise of all measured structures was increased in 80-kVp acquisition (P < 0.001). Overall interobserver agreement was good (ICC, 0.86; 95 % confidence intervals: 0.82-0.89). CTDIvol was reduced by 48.7 % with 80-kVp acquisition compared to standard DECT (4.85 ± 0.51 vs. 9.94 ± 0.81 mGy cm, P < 0.001). Head and neck CT with low-tube-voltage 80-kVp acquisition provides increased tumor delineation, SNR, and CNR for CT imaging of primary and recurrent SCC compared to standard 120-kVp acquisition with an accompanying significant reduction of radiation exposure.

Dynamic Myocardial Perfusion in a Porcine Balloon-induced Ischemia Model using a Prototype Spectral Detector CT.

Myocardial CT perfusion (CTP) imaging is an application that should greatly benefit from spectral CT through the significant reduction of beam hardening (BH) artifacts using mono-energetic (monoE) image reconstructions. We used a prototype spectral detector CT (SDCT) scanner (Philips Healthcare) and developed advanced processing tools (registration, segmentation, and deconvolution-based flow estimation) for quantitative myocardial CTP in a porcine ischemia model with different degrees of coronary occlusion using a balloon catheter. The occlusion severity was adjusted with fractional flow reserve (FFR) measurements. The SDCT scanner is a single source, dual-layer detector system, which allows simultaneous acquisitions of low and high energy projections, hence enabling accurate projection-based material decomposition and effective reduction of BH-artifacts. In addition, the SDCT scanner eliminates partial scan artifacts with fast (0.27s), full gantry rotation acquisitions. We acquired CTP data under different hemodynamic conditions and reconstructed conventional 120kVp images and projection-based monoenergetic (monoE) images for energies ranging from 55keV-to-120keV. We computed and compared myocardial blood flow (MBF) between different reconstructions. With balloon completely deflated (FFR=1), we compared the mean attenuation in a myocardial region of interest before iodine arrival and at peak iodine enhancement in the left ventricle (LV), and we found that monoE images at 70keV effectively minimized the difference in attenuation, due to BH, to less than 1 HU compared to 14 HU with conventional 120kVp images. Flow maps under baseline condition (FFR=1) were more uniform throughout the myocardial wall at 70keV, whereas with 120kVp data about 12% reduction in blood flow was noticed on BH-hypoattenuated areas compared to other myocardial regions. We compared MBF maps at different keVs under an ischemic condition (FFR < 0.7), and we found that flow-contrast-to-noise-ratio (CNR f ) between LAD ischemic and remote healthy territories attains its maximum (2.87 ± 0.7) at 70keV. As energies diverge from 70keV, we noticed a steady decrease in CNRf and an overestimation of mean-MBF. Flow overestimation was also noticed for conventional 120kVp images in different myocardial regions.

Image quality and optimal energy level of spectral CT virtual monochromatic series in atypical osteoblastic metastases in patients with lung cancer

Objective To assess image quality and optimal keV levels of spectral CT virtual monochromatic series in atypical vertebral osteoblastic metastases of lung cancer. Methods Patients with pathologically proven lung cancer who had undergone spectral CT (Discovery CT750 HD, GE) of the chest or abdomen more than twice were analyzed retrospectively. Vertebral osteoblastic metastases were confirmed by follow-up CT examinations, biopsy ,emission CT, PET/CT. The bone lesions were missed due to atypicalappearance or presented with suspicious density at the first exmaination were chosen. A total of twenty two patients with 72 lesions were enrolled. Conventional polychromatic images (140 kVp) and monochromatic images were generated (40 to 140 keV at an interval of 10 keV). The signal to noise ratio(SNR) and contrast to noise ratio (CNR) of the lesions were measured and calculated at all the 12 series images by two radiologists. The two radiologists scored the different series of images independently. Paired sample t test was used to compare SNR and CNR among 40 to 140 keV and 140 kVp images. The inter-observer agreement between the two radiologists was evaluated using Kappa statistics and the difference of different images intrarobserver was compared using Wilcoxon signed rank test. Results The SNR of 140 kVp was 48.03±20.17, and those of 50, 60 70 keV images were 58.52±22.92, 64.07±24.88, 59.54±22.04. SNR of 50, 60, 70 keV images was higher than that of 140 kVp (t values were 13.366,16.278, 18.889,P<0.01), 60 keV images had the highest SNR. The CNR of 140 kVp was 7.64±4.52 and those of 50, 60, 70 and 80 keV images were 7.95±4.99, 8.12±5.08, 8.16±5.05, 7.89±4.81. CNR of 50, 60, 70 and 80 keV images were higher than that of 140 kVp image (t values were 3.519, 5.050, 6.231, 4.413, P<0.01), 60 keV and 70 keV images had the higher CNR than 50 keV and 80 keV. Good interobserver agreement was found for the evaluation of image quality (Kappa =0.864,P<0.05).Moreover, the scores of both the two observes for 60 keV images were higher than 140 kVp images and higher than other monochromatic images. Conclusion Atypical vertebral osteoblastic metastases of lung cancer are more conspicuous in virtual monochromatic images as compared wtih 140 kVp polychromatic images and the optimal energy level was 60 keV, repectively. Key words: Lung neoplasms; Bone neoplasms; Neoplasm metastasis; Tomography, X-ray computed