Difference In Contrast-to-noise Ratio Research Articles

Dual source abdominal computed tomography: the effect of reduced X-ray tube voltage and intravenous contrast media dosage in patients with reduced renal function.

X-ray tube voltage (kVp) reduction increases intravenous contrast medium (CM) attenuation at computed tomography (CT), but tube output limits its use in large patients. To evaluate the feasibility and image quality of reducing CM dose by low kVp and using dual X-ray source at liver CT. Patients with estimated glomerular filtration rate (eGFR) < 45 mL/min (n = 43) aged 60-91 years (75 ± 7.7), weighing 42-114 kg (75 ± 15) were prospectively scanned using a reduced CM dose of 0.25 or 0.3 g iodine (I)/kg with 70 or 80 kVp respectively, using either single-source or dual-source CT depending on patient size. Liver contrast-to-noise ratio (CNR), liver noise, and muscle noise were quantitatively compared with those of 43 consecutive patients aged > 65 years with eGFR > 45 mL/min scanned using a standard abdominal protocol at 120 kVp after receiving 0.5 gI/kg. There was no statistically significant difference in CNR, liver noise, or muscle noise at reduced CM protocols compared to the standard protocol: CNR was 4.6 (95% CI = 4.2-5.0) vs. 5.0 (95% CI = 4.5-5.5), liver noise was 11.1 (95% CI = 10.7-11.6) vs. 11.0 (95% CI = 10.5-11.6), muscle noise was 11.7 (95% CI = 11.2-12.1) vs. 10.8 (95% CI = 10.1-11.4). The mean SSDE was 70% higher with the reduced CM protocol. CM dosage can be reduced by 40-50% with maintained measured noise and CNR in patients with BMIs of 15-36 kg/m2 by lowering the tube voltage and dual-source CT scanning of the liver.

Anti-scatter grid artifact elimination for high-resolution x-ray imaging detectors without a prior scatter distribution profile.

Using anti-scatter grids with high-resolution imaging detectors could result in grid-line artifacts, with increasing severity as detector resolution improves. Grid-line mask subtraction can result in residual artifacts that are due to residual scatter penetrating the grid and not subtracted. By subtracting this residual scatter, the grid artifacts can be minimized. In the previous works, an initial residual-scatter estimate was derived by placing lead markers on a test object; however, any change in the object geometry requires a new scatter estimate. Such a method is impractical to implement during a clinical procedure. In this work, we present a new method to derive the initial scatter estimate to eliminate grid-line artifacts during a procedure. A standard stationary Smit-Roentgen x-ray grid (line density - 70 lines/cm, grid ratio - 13:1) was used with a high-resolution CMOS detector (Dexela Model 1207, pixel size - 75 μm) to image an anthropomorphic head phantom. The initial scatter estimate was derived from the image itself and the grid artifacts were eliminated using recursive correction estimation; this result was compared to that with the estimate derived from placing lead markers on the phantom. In both cases, the contrast-to-noise ratio (CNR) was improved compared to the original image with grid artifacts. Percentage differences in CNR's for three regions between the images corrected with the two estimates were less than 5%. With the new method no a priori scatter distribution profiles are needed, eliminating the need to have libraries of pre-calculated scatter profiles and making the implementation more clinically practical.

Application of preset adaptive statistical iterative reconstruction-V in dual-enhanced abdominal CT

Objective: To analyze the effect of preset adaptive statistical iterative reconstruction-V (ASIR-V) on image quality and radiation dose in dual-enhanced abdominal CT and to investigate the optimal ASIR-V in clinic use. Methods: From February 13 to April 30 in 2017, one hundred and eighty patients who received up abdominal CT scan in the First Affiliated Hospital of Zhengzhou University were collected prospectively. All patients underwent arterial phase (AP) and portal venous phase (PVP) enhanced abdominal CT(120 kVp, noise index 10) and were randomly divided into 6 groups according to random number table (A-F, 30 cases in each group). In group A-F, 0-50% preset ASIR-V (an interval of 10%) was applied, respectively. Qualitative parameters (subjective image quality, diagnosis confidence and radiation dose) and quantitative parameters[image noise, CT number and contrast to noise ratio (CNR)]were measured and compared among the groups by using one-way analysis of variance or Kruskal-Wallis H test. Results: The CT dose index volume (CTDIvol) decreased with the increasing of preset ASIR-V. The effective radiation dose (ED) was significant different among groups (F=27.598, P<0.05), and the ED of group B-F dropped by 10.8%, 21.7%, 31.2%, 44.9% and 61.9% respectively when compared with that in group A. Group E showed the optimal image quality (Z=18.675, 27.548, 19.761, all P<0.05) and diagnosis confidence(Z=21.387, 17.693, 22.459, all P<0.05) in plain scan, AP and PVP phases. There was no significant differences in image noise and CT value of liver, pancreas and muscle among groups (F=1.468, 0.337, 0.592, 0.284, all P>0.05). There were significant differences in CNRs in liver and portal vein in PVP phase among the groups (F=3.980, 4.681, both P<0.05). Conclusion: In abdominal CT, 40% preset ASIR-V can provides the best image quality and it can reduce radiation dose for 44.9%.

Contrast-Enhanced CT with Knowledge-Based Iterative Model Reconstruction for the Evaluation of Parotid Gland Tumors: A Feasibility Study.

ObjectiveThe purpose of this study was to determine the diagnostic utility of low-dose CT with knowledge-based iterative model reconstruction (IMR) for the evaluation of parotid gland tumors.Materials and MethodsThis prospective study included 42 consecutive patients who had undergone low-dose contrast-enhanced CT for the evaluation of suspected parotid gland tumors. Prior or subsequent non-low-dose CT scans within 12 months were available in 10 of the participants. Background noise (BN), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were compared between non-low-dose CT images and images generated using filtered back projection (FBP), hybrid iterative reconstruction (iDose4; Philips Healthcare), and knowledge-based IMR. Subjective image quality was rated by two radiologists using five-point grading scales to assess the overall image quality, delineation of lesion contour, image sharpness, and noise.ResultsWith the IMR algorithm, background noise (IMR, 4.24 ± 3.77; iDose4, 8.77 ± 3.85; FBP, 11.73 ± 4.06; p = 0.037 [IMR vs. iDose4] and p < 0.001 [IMR vs. FBP]) was significantly lower and SNR (IMR, 23.93 ± 7.49; iDose4, 10.20 ± 3.29; FBP, 7.33 ± 2.03; p = 0.011 [IMR vs. iDose4] and p < 0.001 [IMR vs. FBP]) was significantly higher compared with the other two algorithms. The CNR was also significantly higher with the IMR compared with the FBP (25.76 ± 11.88 vs. 9.02 ± 3.18, p < 0.001). There was no significant difference in BN, SNR, and CNR between low-dose CT with the IMR algorithm and non-low-dose CT. Subjective image analysis revealed that IMR-generated low-dose CT images showed significantly better overall image quality and delineation of lesion contour with lesser noise, compared with those generated using FBP by both reviewers 1 and 2 (4 vs. 3; 4 vs. 3; and 3–4 vs. 2; p < 0.05 for all pairs), although there was no significant difference in subjective image quality scores between IMR-generated low-dose CT and non-low-dose CT images.ConclusionIterative model reconstruction-generated low-dose CT is an alternative to standard non-low-dose CT without significantly affecting image quality for the evaluation of parotid gland tumors.

Application of the Dual-layer Spectral Detector CT in the CT Angiography of Superior Vena Cava.

Objective To evaluate the application of the dual-layer spectral detector CT in the CT angiography of superior vena cava (SVC). Methods Totally 30 consecutive patients who underwent chest enhanced CT in our center were enrolled in this study. Eight series of images were reconstructed,including the conventional images at 120 kVp and seven series of virtual monoenergetic spectral images at 40,50,60,70,80,90,and 100 keV. The regions of interest (ROIs) were placed at the level of the proximal end,middle part,and distal end in the SVC vessel. The CT values and standard deviations of these three ROIs and the lipid on prothroax wall were measured. The signal to noise ratio (SNR),contrast to noise ratio (CNR),and effective dose (ED) were calculated. In addition,the quality of images was evaluated by two blinded readers using a grading scheme. The differences in CT values,SNR,and CNR among groups were analyzed using the independent t-test. The quality of all images was compared using non-parametric test between two readers,and the consistency between two radiologists were evaluated by using Kappa (κ) value. Results There was no significantly different attenuation value among three ROIs of the SVC for each monoenergetic images (all P>0.05). The SVC showed significantly higher attenuation value (223.51±40.35)HU,SNR 13.56±4.18 and CNR 24.15±6.58 in the 40 keV group than in other keV groups and the conventional group [attenuation value:(97.70±13.85)HU;SNR:4.59±1.41;CNR:9.69±2.81] (P<0.005). The mean ED was(2.04±0.63) mSv. The subjective diagnostic scores accessed from two radiologists were 1 (1,2) and 1 (1,2) (Z=-0.358,P=0.720). The subjective diagnostic quality values evaluated by two observers showed excellent consistency (κ=0.863,P=0.000). Conclusion An optimal imaging of the SVC can be achieved on monoenergetic reconstructions at 40 keV by using the dual-layer spectral detector CT.

Image quality and radiation dose of low-tube-voltage CT with reduced contrast media for right adrenal vein imaging

ObjectivesTo compare image quality and radiation dose of right adrenal vein (RAV) imaging computed tomography (CT) among conventional, low kV, and low kV with reduced contrast medium protocols. MethodsOne-hundred-and-twenty patients undergoing adrenal CT were randomly assigned to one of three protocols: contrast dose of 600mgI/kg at 120-kV tube voltage setting (600-120 group), 600mgI/kg at 80kV (600-80 group), and 360mgI/kg at 80kV (360-80 group). Iterative reconstruction was used for 80-kV groups. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the RAV and size-specific dose estimates (SSDE) were measured. Three radiologists evaluated 4-point visualisation scores of RAV by consensus reading. ResultsThe RAV detectability was 95%, 97.2%, and 97.3% for 600-120, 600-80, and 360-80 groups, respectively (p=1.000). Visualisation scores were not significantly different among the groups (p=0.152). There were no significant differences in CNR or SNR between the 600-120 and 360-80 groups. SSDE of the 360-80 group was significantly lower than that of the 600-120 group (5.86mGy±1.44 vs. 7.27mGy±1.81, p<0.001). Conclusions80-kV scans with 360 mgI/kg contrast media showed comparable detectability of RAV to conventional scans, while reducing 19% of SSDE.

Variable refocusing flip angle single-shot fast spin echo imaging of liver lesions: increased speed and lesion contrast.

To evaluate acquisition time and clinical image quality of a variable refocusing flip angle (vrf) single-shot fast spin echo (SSFSE) sequence in comparison with a conventional SSFSE sequence for imaging of liver lesions in patients undergoing whole-body PET/MRI for oncologic staging. A vrfSSFSE sequence was acquired in 43 patients with known pancreatic neuroendocrine tumors undergoing 68Ga-DOTA-TOC PET on a simultaneous time-of-flight 3.0T PET/MRI. Liver lesions≥1.5cm with radionucleotide uptake were analyzed. Contrast-to-noise ratios (CNRs) were measured, and four blinded radiologists assessed overall image quality. Differences in repetition time and CNR were assessed using a paired Student's t test with p<0.05 considered statistically significant. Inter-reader variability was assessed with Fleiss' kappa statistic. 53 eligible lesions in 27 patients were included for analysis. vrfSSFSE demonstrated higher mean lesion CNR compared to SSFSE (9.9±4.1 vs. 6.7±4.1, p<0.001). Mean repetition time (TR) was 679±97ms for the vrfSSFSE sequence compared to 1139±106ms for SSFSE (p<0.0001), corresponding to a 1.7-fold decrease in acquisition time. Overall quality of liver lesion and common bile duct images with the vrfSSFSE sequence was graded as superior than or equivalent to the SSFSE sequence for 59% and 67% of patients, respectively. Compared to conventional SSFSE, vrfSSFSE resulted in improved lesion contrast on simultaneous PET/MRI in patients with liver metastases. Due to decreased SAR demands, vrfSSFSE significantly decreased TR, allowing coverage of the entire liver in a single twenty-second breath hold. This may have important clinical implications in the setting of PET/MRI, where scan time is limited by the necessity of whole-body image acquisition in addition to bed specific imaging.

Assessment of thoracic vasculature in patients with central bronchogenic carcinoma by unenhanced magnetic resonance angiography: comparison between 2D free-breathing TrueFISP, 2D breath-hold TrueFISP and 3D respiratory-triggered SPACE.

Preoperative assessment of the integrity of major thoracic vessels in central bronchogenic carcinoma is vital for tumor staging and treatment planning. Contrast-enhanced CT is currently the first choice of modality for this purpose in clinical practice with limitations including exposure to ionizing radiation and the use of iodinated contrast material. MRI has been increasingly employed for the staging of lung cancer. More recently, unenhanced magnetic resonance angiography (MRA) which is totally non-invasive and contrast-free has been reported able to show thoracic vessels. This study was to compare image qualities of three unenhanced-MRAs and to evaluate accuracy of them in assessing thoracic vessel invasion by using contrast-enhanced CT as a reference standard. A total of 30 patients with central bronchogenic carcinoma confirmed by pathology were examined by CT and unenhanced MRA including 2D free-breathing (FB)-TrueFISP, breath-holding (BH)-TrueFISP and 3D respiratory-triggered (RT)-SPACE. Image qualities of pulmonary arteries and veins, thoracic aorta and vena cava were scored for each MRA sequence. Vessel to lung tissue signal contrast-to-noise ratio (CNR), vessel to tumor signal contrast ratio (VTR), and tumor to background signal contrast ratio (TBR) were calculated. On each method, vessel invasion was evaluated according to types of morphological relationships between the tumor and major vessels. The three MRAs showed no significant difference in CNR (P=0.518) while TrueFISP MRAs were better than SPACE in terms of VTR (P=0.000) and image quality (P=0.002). Excellent consistency with CT was found for all three MRAs in assessment of the morphological relationships between tumors and major vessels (FB-TrueFISP: kappa =0.821; BH-TrueFISP: kappa =0.862; RT-SPACE: kappa =0.811). Both TrueFISP and SPACE allow satisfactory visualization of major mediastinal and hilar vessels and are comparable to MDCT in assessment of vessel invasion in patients with central lung cancer. TrueFISP sequences are better than SPACE in regard to image quality and VTR.

Feasibility of dual-low scheme combined with iterative reconstruction technique in acute cerebral infarction volume CT whole brain perfusion imaging.

The feasibility of application of low-concentration contrast agent and low tube voltage combined with iterative reconstruction in whole brain computed tomography perfusion (CTP) imaging of patients with acute cerebral infarction was investigated. Fifty-nine patients who underwent whole brain CTP examination and diagnosed with acute cerebral infarction from September 2014 to March 2016 were selected. Patients were randomly divided into groups A and B. There were 28 cases in group A [tube voltage, 100 kV; contrast agent, iohexol (350 mg I/ml), reconstructed by filtered back projection] and 31 cases in group B [tube voltage, 80 kV; contrast agent, iodixanol (270 mg I/ml), reconstructed by algebraic reconstruction technique]. The artery CT value, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), dose length product, effective dose (ED) of radiation and brain iodine intake of both groups were measured and statistically analyzed. Two physicians carried out kappa (κ) analysis on the consistency of image quality evaluation. The difference in subjective image quality evaluation between the groups was tested by χ2. The differences in CT value, SNR, CNR, CTP and CT angiography subjective image quality evaluation between both groups were not statistically significant (P>0.05); the diagnosis rate of the acute infarcts between the two groups was not significantly different; while the ED and iodine intake in group B (dual low-dose group) were lower than group A. In conclusion, combination of low tube voltage and iterative reconstruction technique, and application of low-concentration contrast agent (270 mg I/ml) in whole brain CTP examination reduced ED and iodine intake without compromising image quality, thereby reducing the risk of contrast-induced nephropathy.

Novel contrast-injection protocol for high-resolution abdominal CT-angiography: vascular visualization improvement with vasodilator.

To evaluate the usefulness of a novel contrast-injection protocol for high-resolution abdominal computed tomography angiography (CTA) using nitroglycerin (NTG). Abdominal CTA was performed in 80 patients using two 64-detector-row CT scanners. Forty patients were examined after administration of sublingual NTG (NTG group), while 40 were examined without NTG administration (non-NTG group). Arterial phase images were acquired with maximum intensity projection and volume rendering. Reduction rates: vessel cross-sectional areas ratio of 10 cm distal to origin at the superior mesenteric artery, contrast enhancements, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were assessed. Three reviewers evaluated degree of depiction of the peripancreatic vasculature using a four-point scale (1=poor, 4=excellent). Reduction rates were significantly lower in the NTG group (P<0.001), while there were no significant differences in contrast enhancements, SNR, or CNR between groups. Visual evaluation results of the NTG group were significantly better than those of the non-NTG group (P<0.01). Abdominal CTA using NTG improved visualization of the abdominal peripheral vessels. This improved arterial view may be beneficial for preoperative evaluation of the arterial anatomy.

Split-bolus intravenous contrast material injection vs. single-bolus injection in patients following endovascular abdominal aortic repair (EVAR).

To investigate the feasibility and accuracy of a split-bolus contrast injection CTA (SB-CTA) compared to a single-bolus injection CTA (SI-CTA) protocol of post-EVAR patients. In this IRB-approved study, patients who underwent SB-CTA and SI-CTA after EVAR were evaluated. Attenuation and contrast-to-noise ratio (CNR) of vessels and parenchymal organs were assessed. Subjective enhancement of vessels, quality of 3D reconstructions, and enhancement phase of parenchymal organs were assessed by two independent readers. Endoleak visibility and incidental findings were evaluated. Fifty-six patients with SB-CTA and SI-CTA at two different time points after EVAR were included in the study (112 imaging studies, mean age 75±9years). There was no difference in attenuation and CNR for aorta between SB-CTA and SI-CTA (310±87 vs. 311±80HU, p=0.88; 31.1±12.6 vs. 29.0±12.2, p=0.20), although both were improved in the venous structures and parenchymal organs with SB-CTA (portal vein: 149±33 vs. 88±32HU, 11.6±5.6 vs. 4.3±3.4; liver: 91±19 vs. 68±20HU, 4.4±2.8 vs. 2.1±2.0; pancreas: 108±27 vs. 82±23HU, 6.4±3.1 vs. 3.6±2.4; p<0.0001). Subjectively, enhancement of veins, liver, spleen, bowel, and kidneys was improved (p<0.001), while there was no difference for the aorta (p=0.46) and 3D reconstructions (p=0.58). None of the 18/56 (32.1%) endoleaks was missed with the SB-CTA. More incidental findings were detected with SB-CTA (158/56) compared to SI-CTA (135/56), p<0.001. SB-CTA was able to adequately characterize 7/15 (47%) of the findings that needed further evaluation in SI-CTA. 4/15 (26%) incidental findings that were missed with SI-CTA but seen with SB-CTA required further evaluation. Split-bolus injection CTA in the follow-up of EVAR patients allows reliable visualization of endoleaks with improved subjective and objective image quality.

Overall evaluability of low dose protocol for computed tomography angiography of thoracic aorta using 80kV and iterative reconstruction algorithm using different concentration contrast media.

Multidetector Computed Tomography Angiography (MDCTA) is presently the imaging modality of choice for aortic disease. However, the effective radiation dose and the risk related to the use of contrast agents associated with MDCTA is an issue of concern. Aim of this study was to assess image quality of a low dose ECG-gated MDCTA of thoracic aorta using different concentration contrast media without tailored injection protocol. Two-hundred patients were randomised into four different scan protocols: Group A (Iodixanol 320 and 80 Kvp tube voltage), Group B (Iodixanol 320 and 100Kvp tube voltage), Group C (Iomeprol 400 and 80Kvp tube voltage) and Group D (Iomeprol 400 and 100Kvp tube voltage). Image quality, noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and effective dose (ED) were compared among groups. No significant differences in image noise, SNR and CNR between groups with the same tube voltage. Significant differences in SNR and CNR were found among groups with 80kV versus groups using 100kV but without differences in terms of image quality. ED was significantly lower in groups with 80kV. Multidetector Computed Tomography Angiography protocols using 80kV and low concentration contrast media are feasible without need of tailored injection protocols.

Diagnosis of small posterior fossa stroke on brain CT: effect of iterative reconstruction designed for brain CT on detection performance

In this study, we aimed to determine whether iterative model reconstruction designed for brain CT (IMR-neuro) would improve the accuracy of posterior fossa stroke diagnosis on brain CT. We enrolled 37 patients with ischaemic stroke in the posterior fossa and 37 patients without stroke (controls). Using axial images reconstructed using filtered back-projection (FBP) and IMR-neuro, we compared the CT numbers in infarcted areas, image noise in the pons, and contrast-to-noise ratios (CNRs) of infarcted and non-infarcted areas on scans subjected to IMR-neuro and FBP. To analyse the performance of hypo-attenuation detection, we used receiver-operating characteristic (ROC) curve techniques. The image noise was significantly lower (2.2 ± 0.5 vs. 5.1 ± 0.9 Hounsfield units, p < 0.01) and the difference in CNR between the infarcted and non-infarcted areas was significantly higher with IMR-neuro than with FBP (2.2 ± 1.7 vs. 4.0 ± 3.6, p < 0.01). Furthermore, the average area under the ROC curve was significantly higher with IMR-neuro (0.90 vs. 0.86 for FBP, p = 0.04). IMR-neuro yielded better image quality and improved hypo-attenuation detection in patients with ischaemic stroke. • Iterative model reconstruction of brain CT data can facilitate the diagnosis of ischaemic stroke. • IMR improved the detectability of low-contrast lesions in the posterior fossa. • IMR-neuro yielded better image quality and improved observer performance.

Application of High-pitch CT Pulmonary Angiography at 70 kV Tube Voltage with 15 ml Contrast Medium Using Third-generation Dual-source CT.

Objective To assess the application of high-pitch CT pulmonary angiography (CTPA) at 70 kV tube voltage with 15 ml contrast medium using third-generation dual-source CT. Methods A total of 70 patients with clinically suspected pulmonary embolism were randomly divided into two groups: group A (n=35) underwent CTPA on conventional scanning mode (120 kV,80 ml contrast medium);and group B (n=35) underwent CTPA on high-pitch scanning mode at 70 kV tube voltage with 15 ml contrast medium. The CT values and standard deviations of the main pulmonary artery,apical segment of right upper pulmonary lobe (S1),and posterior basal segment of the right lower pulmonary lobe (S10),anterior thoracic air,and back muscles were measured. The signal to noise ratio (SNR),contrast to noise ratio (CNR),and effective dose (ED) were calculated. The overall image quality was evaluated by two blinded radiologists. The quality image was compared using non-parametric test on two independent samples. The potential differences in CT value,SNR,CNR,and ED were analyzed using the independent sample t-test. Results The CT values of main pulmonary artery [(300.62±77.54)HU vs.(332.80±102.80)HU;t=-1.53,P=0.13],S1 [(361.72±84.92)HU vs. (325.37±87.86)HU;t=1.81,P=0.08],and S10 [(359.54±89.61)HU vs. (318.26±87.19)HU;t=2.00,P=0.05] of right lung were not significantly different between group A and group B. The CNR of S1 (22.81±6.05 vs. 19.80±6.60;t=2.05,P=0.04) and S10 (22.65±6.37 vs. 19.28±6.63;t=2.23,P=0.03) of right lung in group A was significantly higher than in group B. The SNR of main pulmonary artery,S1,and S10 of right lung were not significantly different between group A and B. The subjective diagnostic quality values of group A and B were 1 (1,1) and 1 (1,1),respectively (Z=-0.08,P=0.93). The subjective diagnostic quality values evaluated by two radiologists showed excellent consistency(κ=0.87,P=0.01). The mean ED was 79% lower in group B [(0.92±0.23)mSv] than in group A [(4.33±1.80) mSv] (t=11.72,P=0.00).Conclusion Application of high-pitch mode in CTPA at 70 kV with 15 ml contrast medium using third-generation dual-source CT can remarkably reduce radiation dose without affecting image quality.

Initial Experience of the Application of Automated Tube Potential Selection Technique in High-pitch Dual-source CT Angiography of Whole Aorta Using Third-generation Dual-source CT Scanner.

Objective To evaluate the application of automated tube potential selection technique in high-pitch dual-source CT aortic angiography on a third-generation dual-source CT scanner. Methods Whole aorta angiography were indiated in 59 patients,who were divided into 2 groups using a simple random method:in group 1 there were 31 patients who underwent the examination with automated tube potential selection using a vascular setting with a preferred image quality of 288 mA/100 kV;in group 2 there were 28 patients who underwent the examination with a tube voltage of 100 kV and automated tube current modulation using a reference tube current of 288 mA. Both groups were scanned on a third generation dual-source CT device operated in dual-source high-pitch ECG-gating mode with a pitch of 3.0,collimation of 2×192×0.6 mm,and a rotation time of 0.25 s. Iterative reconstruction algorithm was used. For group 1,the volume and flow of contrast medium and chasing saline were adapted to the tube voltage. For group 2,a contrast material bolus of 45 ml with a flow of 4.5 ml/s followed by a 50 ml saline chaser at 5 ml/s was used. CTA scan was automatically started using a bolus tracking technique at the level of the original part of aorta after a trigger threshold of 100 HU was reached. The start delay was set to 6 s in both groups. Effective dose (ED),signal to noise ratio (SNR),contrast to noise ratio (CNR),and subjective diagnostic quality of both groups were evaluated. Results The mean ED were 21.3% lower (t=-3.099,P=0.000) in group 1 [(2.48±0.80) mSv] than in group 2 [(3.15±0.86) mSv]. Two groups showed no significant difference in attenuation,SD,SNR,or CNR at all evaluational parts of aorta (ascending aorta,aortic arch,diaphragmatic aorta,or iliac bifurcation)(all P>0.05). There was no significant difference in subjective diagnostic quality values of two groups [(1.41±0.50) scores vs. (1.39±0.50) scores;W=828.5,P=0.837]. Conclusion Compared with automated tube current modulation,the automated tube potential selection technique in aorta CT angiography on a third-generation dual-source CT can dramatically reduce radiation dose without affecting image quality.

Prospective comparison of dual-energy CT aortography using 70% reduced iodine dose versus single-energy CT aortography using standard iodine dose in the same patient.

To compare dual-energy computed tomography (DECT) aortography using a 70% reduced iodine dose to single-energy CT (SECT) aortography using a standard iodine dose in the same patient. Twenty-one patients with a prior SECT aortography using standard iodine dose had DECT aortography using 70% reduced iodine dose. Section120 kVp images were compared to DECT images reconstructed at both 50 and 77keV. Reviewers measured image noise and attenuation in the aorta at eight locations from proximal to distal and subjectively scored vascular enhancement on a four-point scale. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The volume CT dose index (CTDIvol) for each exam was recorded. Mean iodine dose was 50g for SECT and 15g for DECT (70% reduction). Mean aortic attenuation was similar for section120 kVp (350±67 HU) and DECT 50keV (338±57 HU, p=0.547) but was lower at 77keV (152±23 HU). Measured image noise was greatest at 50keV (12±5 HU) and was lowest at 77keV (7±2 HU, p>0.001). There was no difference in SNR or CNR between 120 kVp and 50keV (p>0.05). Mean subjective vascular enhancement scores for SECT were between good and excellent (3.33-3.69), and for DECT at 50keV were between moderate and good (2.54-2.93, p<0.0001). CTDIvol was 13.6mGy for SECT and 13.1mGy for DECT (p=0.637). 70% Reduced iodine DECT aortography may result in similar aortic attenuation, CNR, SNR, and lower although acceptable subjective image scores when compared to standard iodine SECT aortography in the same patient.

The Value of the T2-Weighted Multipoint Dixon Sequence in MRI of Sacroiliac Joints for the Diagnosis of Active and Chronic Sacroiliitis.

The objective of this study was to determine the value of the T2-weighted multipoint Dixon technique as a single sequence in MRI of the sacroiliac joints for the diagnosis of active and chronic sacroiliitis. The T2-weighted multipoint Dixon sequence with water-only, in-phase, opposed-phase, and fat-only images was added to a routine MRI protocol, which included T1-weighted, fat-saturated T2-weighted, and contrast-enhanced fat-saturated T1-weighted sequences, for imaging 73 patients. Images obtained as part of the routine protocol were reviewed first by two radiologists. Then, the T2-weighted multipoint Dixon images were reviewed separately. Signs of active inflammation detected on fat-saturated T2-weighted and contrast-enhanced fat-saturated T1-weighted images were compared with the water-only images. Signs of chronic sacroiliitis detected on T1-weighted images were compared with the fat-only, in-phase, and opposed-phase images. Contrast-to-noise ratios (CNRs) of all lesions were statistically analyzed. ANOVA and posthoc Tukey tests were used to compare CNR data. The mean CNR of 34 lesions with bone marrow edema or osteitis was greater on the water-only images (CNR, 176) than on the fat-saturated T2-weighted images (CNR, 82) and the contrast-enhanced fat-saturated T1-weighted images (CNR, 56), and this difference in mean CNRs was statistically significant (p < 0.01). There were also statistically significant differences in CNRs between sequences (p < 0.01). The highest mean CNR for subchondral sclerosis in 23 lesions was noted on in-phase images, and the highest mean CNR for periarticular fat deposition in 29 lesions was noted on opposed-phase images. Qualitative analyses also revealed that T2-weighted multipoint Dixon images were superior in showing signs of both active and chronic sacroiliitis. The T2-weighted multipoint Dixon sequence is superior to conventional MRI sequences in depicting diagnostic signs of active and chronic sacroiliitis and therefore may be used as a single sequence.

The value of spectral imaging to reduce artefacts in the body after 125 I seed implantation.

To explore the value of gemstone spectral imaging (GSI) and metal artefact reduction sequence (MARs) to reduce the artefacts of metal seeds. Thirty-five patients with 125 I seed implantation in their abdomens underwent GSI CT. Six types of monochromatic images and the corresponding MARs images at 60-110keV (interval of 10keV) were reconstructed. The differences in the quality of the images of three imaging methods were subjectively assessed by three radiologists. Length of artefacts, the CT value and noise value of tissue adjacent to 125 I seeds, contrast-to-noise ratio (CNR), and artefact index (AI) were recorded. The differences in subjective scoring were statistically significant (t=10.87, P<0.001). Images at 70keV showed the best CNR (0.84±0.17) of tissues adjacent to 125 I seeds, and received the highest subjective score (2.82±0.18). Images at 80keV had the lowest AI (70.67±19.17). Images at 110keV had the shortest artefact lengths. High-density metal artefacts in the MARs spectral images were reduced. The length of metal artefacts in images at 110keV was shorter than that of the polychromatic images and MARs spectral images (t=3.35, 3.89, P<0.05). The difference in CNR between MARs spectral images and polychromatic images, and images at 70keV was statistically significant (t=3.57, 4.16, P<0.01). Gemstone spectral imaging technique can reduce metal artefacts of 125 I seeds effectively in CT images, and improve the quality of images, and improve the display of tissues adjacent to 125 I seeds after implantation. MARs technique cannot reduce the artefacts caused by radioactive seeds effectively.

Image quality assessment of clinically-applied CBCT protocols using a QAT phantom.

This study has two main purposes: (1) to evaluate the effect of various clinically applied protocols [changing field of view (FOV), voxel size and tube voltage (kVp)] on CS 9300 CBCT (CareStream SM 749, Rochester, NY) image quality using its quality assurance test (QAT) phantom and (2) to evaluate the efficacy of a newly-designed prototype plugin on ImageJ (National Institutes of Health, Bethesda, MD) which was introduced to measure modulation transfer function (MTF) using a modified slanted-edge method. Using a specifically constructed QAT phantom, five image quality parameters were assessed-image uniformity, signal-to-noise ratio, contrast, position checking and the MTF-for ten variables, clinically applied protocols on a CS 9300 PREMIUM three-dimensional CBCT device. With FOV and voxel size fixed, high-dose protocols resulted in less image noise and more uniformity. On the other hand, less image uniformity was achieved with less kVp. Moreover, high-dose protocols resulted in a high contrast-to-noise ratio (CNR). There were significant differences in CNR between 60 and 70 kVp as well as between 70 and 90 kVp. Our study identified no difference between MTF and either voxel size or FOV. The image quality of the CS 9300 CBCT varied with variability in exposure protocols and different voxel sizes. The negative association between greater spatial resolution (smaller voxel size) and the MTF shows that the slanted edge method is not ideal for MTF evaluation of CBCT and is therefore not recommended for using it for this purpose.

Evaluation of the effects of positioning and configuration on contrast-to-noise ratio in the quality control of a 3D Accuitomo 170 dental CBCT system.

This study evaluated the effect of phantom positioning and the configuration of phantom inserts on the measurement of contrast-to-noise ratio (CNR) in dental CBCT. The work aimed to make pragmatic suggestions for the remedial tolerances for CNR measurements in the routine quality control (QC) of a three-dimensional Accuitomo 170 dental CBCT system (J Morita, Kyoto, Japan). Images of the SEDENTEXCT (safety and efficacy of a new and emerging dental X-ray modality) IQ (image quality) dental CBCT phantom (Leeds Test Objects Ltd, Boroughbridge, UK) were acquired and measurements of CNR were obtained in three configurations of inserts and in six phantom orientations for one of the configurations. Five consecutive images were acquired in each case, to assess the reproducibility of measurements. Reproducibility of measurements ranged from 1.8% to 4.6%. For the CNR measurements in the three phantom configurations, the ratio of the measured CNR to the minimum value was 2.1 ± 0.2 times the minimum value for Delrin(®) (DuPont UK Ltd, Stevenage, UK). For aluminium, there was no significant variation between configurations and for the other three materials, the ratio ranged from 20% to 50%. Significant variations in CNR with phantom position were observed, with differences between the maximum and minimum values ranging from 10% to 60%. Absolute differences in CNR from the minimum value ranged from <0.1 to 2.1 with phantom configuration and from 1.2 to 4.5 with phantom position. The effects of phantom configuration and positioning on CNR measurements for dental CBCT QC were investigated and possible remedial tolerances suggested.