CT Protocol Research Articles

IMAGE QUALITY STUDY OF RADIATION-REDUCED COMBINED CHEST AND ABDOMEN/PELVIS CT COMPARED WITH A STANDARD PROTOCOL

The purpose of this study is to examine radiation doses and image quality of a low-dose (LD) protocol for chest and abdomen/pelvis (CAP) CT compared with a standard (STD) protocol. A total of 361 patients were included between October 2019 and April 2020; 104 patients with LD-protocol (100kV, ref mAs 80 (chest)/145 (abdomen/pelvis)) and 257 patients with STD-protocol (100kV, ref mAs 100 (chest)/180 (abdomen/pelvis)) at second-generation dual-source CT. Radiation doses for CTDIvol and DLP, and objective and subjective image qualities of 50 examinations from each group were evaluated. The LD-protocol applied significantly lower radiation doses compared with the STD-protocol (p<0.001), achieving a dose reduction by 37% for the median DLP in chest, 19% in abdomen/pelvis and 22% in total. Median total DLP was 342mGy·cm (LD) vs. 436mGy·cm (STD). The LD-CAP CT protocol achieved a significant dose reduction far below national diagnostic reference levels, ensuring acceptable and good image quality.

Rhinoplasty Pre-Surgery Models by Using Low-Dose Computed Tomography, Magnetic Resonance Imaging, and 3D Printing.

Rhinoplasty and surgical reconstruction of cartilaginous structures still remain a great challenge today. This study aims to identify an imaging strategy in order to merge the information from CT scans and magnetic resonance imaging (MRI) acquisitions and build a 3D printed model true to the patient’s anatomy, for better surgical planning. Using MRI, information can be obtained about the cartilage structures of which the nose is composed. Ten rhinoplasty candidate patients underwent both a low-dose protocol CT scan and a specific MRI for characterization of nasal structures. Bone and soft tissue segmentations were performed in CT, while cartilage segmentations were extrapolated from MRI and validated by both an expert radiologist and surgeon. Subsequently, a 3D model was produced in materials and colors reproducing the density of the three main structures (bone, soft tissue, and cartilage), useful for pre-surgical evaluation. This study has highlighted that the optimization of a CT and MR dedicated protocol has allowed to reduce the CT radiation dose up to 60% compared to standard acquisitions with the same machine, and MR acquisition time of about 20%. Patient-tailored 3D models and pre-surgical planning have reduced the mean operative time by 20 minutes.

Detectability of Lung Nodules in Ultra-low Dose CT.

Investigation of the influence of different ultra-low dose computed tomography (ULDCT) protocols on the detection of solid and subsolid nodules in a phantom study. A chest phantom with pulmonary nodules was scanned with different CT protocols ranging from ultra-low dose settings with spectral shaping to a standard low dose lung cancer screening protocol. Image analysis was performed with different reconstruction algorithms and dedicated computer aided detection (CAD), which was compared to manual readout. The highest sensitivity rates (83%) were achieved for the 90 mAs and 120 mAs protocols when reconstructed with ADMIRE 3 or 5 and manual readout. The only statistically significant difference was found for subsolid nodules with preference of manual readout compared to CAD (p<0.05). Dose levels for the mAs settings ranged from 0.029 to 0.2 mSv. Reliable detectability rates for solid nodules were achieved; CAD software did not prove reliable for subsolid nodules.

Diagnostic performance and image quality of low-tube voltage and low-contrast medium dose protocol with hybrid iterative reconstruction for hepatic dynamic CT.

To evaluate the diagnostic performance and image quality of the low-tube voltage and low-contrast medium dose protocol for hepatic dynamic CT. This retrospective study was conducted between January and May 2018. All patients underwent hepatic dynamic CT using one of the two protocols: tube voltage, 80 kVp and contrast dose, 370 mgI/kg with hybrid iterative reconstruction or tube voltage, 120 kVp and contrast dose, 600 mgI/kg with filtered back projection. Two radiologists independently scored lesion conspicuity and image quality. Another radiologist measured the CT numbers of abdominal organs, muscles, and hepatocellular carcinoma (HCC) in each phase. Lesion detectability, HCC diagnostic ability, and image quality of the arterial phase were compared between the two protocols using the non-inferiority test. CT numbers and HCC-to-liver contrast were compared between the protocols using the Mann-Whitney U test. 424 patients (70.5 ± 10.1 years) were evaluated. The 80-kVp protocol showed non-inferiority in lesion detectability and diagnostic ability for HCC (sensitivity, 85.7-89.3%; specificity, 96.3-98.6%) compared with the 120-kVp protocol (sensitivity, 91.0-93.3%; specificity, 93.6-97.3%) (p < 0.001-0.038). The ratio of fair image quality in the 80-kVp protocol also showed non-inferiority compared with that in the 120-kVp protocol in assessments by both readers (p < 0.001). HCC-to-liver contrast showed no significant differences for all phases (p = 0.309-0.705) between the two protocols. The 80-kVp protocol with hybrid iterative reconstruction for hepatic dynamic CT can decrease iodine doses while maintaining diagnostic performance and image quality compared with the 120-kVp protocol. The 80- and 120-kVp protocols showed equivalent hepatic lesion detectability, diagnostic ability for HCC, image quality, and HCC-to-liver contrast.The 80-kVp protocol showed a 38.3% reduction in iodine dose compared with the 120-kVp protocol.

OPTIMIZATION OF LUNG CT PROTOCOL FOR THE DIAGNOSTIC EVALUATION OF COVID-19 LUNG DISEASE.

This study intends to evaluate the different lung CT scan protocols used for the diagnostic evaluation of COVID-19-induced lung disease in Iranian imaging centers in terms of radiation dose and image quality. After data collecting, subjective image quality, radiation dose and objective image quality such as noise, SNR and CNR were assessed.Statistically significant differences in effective dose and image quality were evident among different lung CT protocols. Lowest and highest effective dose was1.31 ± 0.53 mSv related to a protocol with activated AEC (reference mAs = 20) and 6.15 ± 0.57 mSv related to a protocol with Fixed mAs (mAs = 100), respectively.A protocol with enabled tube current modulation with 70 mAs as a reference mAs, and protocol with 20 mAs and enabled AEC had the best and lowest image quality, respectively. To optimize the scan parameters, AEC must be used, and a range of tube currents (between 20 and 50 mAs) can produce acceptable images in terms of diagnostic quality and radiation dose for the diagnosis of COVID-19-induced lung disease.

Design of a 3D printed coronary artery model for CT optimization

IntroductionTo design a custom phantom of the coronary arteries to optimize CT coronary angiography (CCTA) protocols. MethodsCharacteristics of the left and right coronary arteries (mean Hounsfield Unit (HU) values and diameters) were collected from consecutive CCTA examinations (n = 43). Four different materials (two mixtures of glycerine, gelatine and water, pig hearts, Ecoflex™ silicone) were scanned inside a Lungman phantom using the CCTA protocol to find the closest model to in vivo data. A 3D printed model of the coronary artery tree was created using CCTA data by exporting a CT volume rendering into Autodesk Meshmixer™ software. The model was placed in an acid bath for 5 h, then covered in Ecoflex™, which was removed after drying. Both the Ecoflex™ and pig heart were later filled with a mixture of contrast (Visipaque 320 mg I/ml), NaCl and gelatin and scanned with different levels of tube current and iterative reconstruction (ASiR-V). Objective (HU, noise and size (vessel diameter) and subjective analysis were performed on all scans. ResultsThe gelatine mixtures had HU values of 130 and 129, Ecoflex™ 65 and the pig heart 56. At the different mA/ASiR-V levels the contrast filled Ecoflex™ had a mean HU 318 ± 4, noise 47±7HU and diameter of 4.4 mm. The pig heart had a mean HU of 209 ± 5, noise 38±4HU and a diameter of 4.4 mm. With increasing iterative reconstruction level the visualisation of the pig heart arteries decreased so no measurements could be performed. ConclusionThe use of a 3D printed model of the arteries and casting with the Ecoflex™ silicone is the most suitable solution for a custom-designed phantom. Implications for practiceCustom designed phantoms using 3D printing technology enable cost effective optimisation of CT protocols.

Assessing the Relative Value of CT Perfusion Compared to Non-contrast CT and CT Angiography in Prognosticating Reperfusion-Eligible Acute Ischemic Stroke Patients.

In the present study we sought to measure the relative statistical value of various multimodal CT protocols at identifying treatment responsiveness in patients being considered for thrombolysis. We used a prospectively collected cohort of acute ischemic stroke patients being assessed for IV-alteplase, who had CT-perfusion (CTP) and CT-angiography (CTA) before a treatment decision. Linear regression and receiver operator characteristic curve analysis were performed to measure the prognostic value of models incorporating each imaging modality. One thousand five hundred and sixty-two sub-4.5 h ischemic stroke patients were included in this study. A model including clinical variables, alteplase treatment, and NCCT ASPECTS was weak (R2 0.067, P < 0.001, AUC 0.605) at predicting 90 day mRS. A second model, including dynamic CTA variables (collateral grade, occlusion severity) showed better predictive accuracy for patient outcome (R2 0.381, P < 0.001, AUC 0.781). A third model incorporating CTP variables showed very high predictive accuracy (R2 0.488, P < 0.001, AUC 0.899). Combining all three imaging modalities variables also showed good predictive accuracy for outcome but did not improve on the CTP model (R2 0.439, P < 0.001, AUC 0.825). CT perfusion predicts patient outcomes from alteplase therapy more accurately than models incorporating NCCT and/or CT angiography. This data has implications for artificial intelligence or machine learning models.

Parapelvic cyst: A rare cause of ureteropelvic junction obstruction in a pediatric patient managed with robotic cyst decortication

We report a case of a right parapelvic renal cyst causing intermittent ureteropelvic junction obstruction (UPJO). A 13-year-old male was referred for right flank pain. Stone protocol CT revealed renal pelvis dilation with punctate stones. Due to concern for intermittently obstructive calculi, he underwent ureteroscopy, which was unremarkable. A diuretic renogram showed symmetric uptake with partial emptying on the right with pain after diuretic administration. In office, we potentiated a Dietl's crisis with ultrasound obtained before and after fluid intake. Comparison of ultrasounds revealed a parapelvic cyst causing calyceal dilation. He was counseled for robotic cyst decortication and possible pyeloplasty. A robotic cyst decortication was performed. Once decorticated, the cyst base was fulgurated and pararenal fat was interposed into the cyst base. Console time was 70min with minimal blood loss. The patient was discharged post-operative day 1. Follow-up renal ultrasound at 4 months demonstrated resolution of hydronephrosis and parapelvic cyst. Parapelvic renal cysts causing intermittent UPJO is a rare entity that may be missed on a diuretic renogram. Clinical suspicion and appropriate imaging with ultrasound or magnetic resonance imaging are useful. Robotic cyst decortication is a technically feasible approach to treat this condition.

A Protocol of Low Dose Chest CT to Verify Suspected COVID -19 infection

Chest CT scanning is significant in verifying COVID-19 infection in patients with clinical symptoms,although CT scanning uses ionizing radiation. So we aim to investigate the demonstration of relevance andaccuracy of chest tomography using a low-dose protocol compared to the standard auto-modulation protocolof 50 – 210 mAs. Moreover, to assess whether any distinguishing signs in patients might help determinethe severity of the respiratory infection from COVID-19. A standard auto-modulation protocol of 50 – 210mAs was performed for all patients (120 patients), Rotation time 0.5 second. Of the 120 patients whoseCT scan showed signs of COVID-19 infection, 47 patients aged over 50 years were selected. Low doseCT scanning (30 mAs) was performed on these patients immediately. Of the 120 patients over the age of50 with COVID-19 according to a PCR underwent a CT chest, only 47 showed signs of COVID-19.Whencompared to standard-dose, low-dose demonstrated excellent sensitivity in detecting typical findings ofCOVID-19 (coefficient of significance (C.S) = 0.98–0.99, P-values &lt; 0.05 one reader and P-values &lt; 0.01two readers). The mean effective dose values were 6.32±2.82 and 1.45±0.29mSvin the stander and lowdose,respectively.A low dose protocol can be used with high reliability and accuracy to reduce the ionizingradiation risks in the state of reproducible assessment. On the other hand, we emphasize there are indicatorswith high reliability of a relationship between infection with COVID-19 and its severity and the work nature,environment, age, body mass index (BMI) and Patient Health Status.

Dual-Contrast Biphasic Liver Imaging With Iodine and Gadolinium Using Photon-Counting Detector Computed Tomography: An Exploratory Animal Study.

The aims of this study were to develop a single-scan dual-contrast protocol for biphasic liver imaging with 2 intravenous contrast agents (iodine and gadolinium) and to evaluate its effectiveness in an exploratory swine study using a photon-counting detector computed tomography (PCD-CT) system. A dual-contrast CT protocol was developed for PCD-CT to simultaneously acquire 2 phases of liver contrast enhancement, with the late arterial phase enhanced by 1 contrast agent (iodine-based) and the portal venous phase enhanced by the other (gadolinium-based). A gadolinium contrast bolus (gadobutrol: 64 mL, 8 mL/s) and an iodine contrast bolus (iohexol: 40 mL, 5 mL/s) were intravenously injected in the femoral vein of a healthy domestic swine, with the second injection initiated after 17 seconds from the beginning of the first injection; PCD-CT image acquisition was performed 12 seconds after the beginning of the iodine contrast injection. A convolutional neural network (CNN)-based denoising technique was applied to PCD-CT images to overcome the inherent noise magnification issue in iodine/gadolinium decomposition task. Iodine and gadolinium material maps were generated using a 3-material decomposition method in image space. A set of contrast samples (mixed iodine and gadolinium) was attached to the swine belly; quantitative accuracy of material decomposition in these inserts between measured and true concentrations was calculated using root mean square error. An abdominal radiologist qualitatively evaluated the delineation of arterial and venous vasculatures in the swine liver using iodine and gadolinium maps obtained using the dual-contrast PCD-CT protocol. The iodine and gadolinium samples attached to the swine were quantified with root mean square error values of 0.75 mg/mL for iodine and 0.45 mg/mL for gadolinium from the contrast material maps derived from the denoised PCD-CT images. Hepatic arteries containing iodine and veins containing gadolinium in the swine liver could be clearly visualized. Compared with the original images, better distinctions between 2 liver phases were achieved using CNN denoising, with approximately 60% to 80% noise reduction in contrast material maps acquired with the denoised PCD-CT images compared with the original images. Simultaneous biphasic liver imaging in a single multienergy PCD-CT acquisition using a dual-contrast (iodine and gadolinium) injection protocol and CNN denoising was demonstrated in a swine study, where the enhanced hepatic arteries (containing iodine) and the enhanced hepatic veins (containing gadolinium) could be clearly visualized and delineated in the swine liver.

Augmented-Reality-Assisted K-Wire Placement for Glenoid Component Positioning in Reversed Shoulder Arthroplasty: A Proof-of-Concept Study.

The accuracy of the implant’s post-operative position and orientation in reverse shoulder arthroplasty is known to play a significant role in both clinical and functional outcomes. Whilst technologies such as navigation and robotics have demonstrated superior radiological outcomes in many fields of surgery, the impact of augmented reality (AR) assistance in the operating room is still unknown. Malposition of the glenoid component in shoulder arthroplasty is known to result in implant failure and early revision surgery. The use of AR has many promising advantages, including allowing the detailed study of patient-specific anatomy without the need for invasive procedures such as arthroscopy to interrogate the joint’s articular surface. In addition, this technology has the potential to assist surgeons intraoperatively in aiding the guidance of surgical tools. It offers the prospect of increased component placement accuracy, reduced surgical procedure time, and improved radiological and functional outcomes, without recourse to the use of large navigation or robotic instruments, with their associated high overhead costs. This feasibility study describes the surgical workflow from a standardised CT protocol, via 3D reconstruction, 3D planning, and use of a commercial AR headset, to AR-assisted k-wire placement. Post-operative outcome was measured using a high-resolution laser scanner on the patient-specific 3D printed bone. In this proof-of-concept study, the discrepancy between the planned and the achieved glenoid entry point and guide-wire orientation was approximately 3 mm with a mean angulation error of 5°.

Opportunities to reduce the radiation exposure during computed tomography to assess the changes in the lungs in patients with COVID-19: use of adaptive statistical iterative reconstruction

BACKGROUND: Several COVID-19 patients are subjected to multiple imaging examinations during hospitalization, the cumulative effect of which can significantly increase the total dose of radiation received. The effective radiation dose can be reduced by lowering the current and voltage of the X-ray tube, but this reduces image quality. One possible solution is to use adaptive statistical iterative reconstruction technology on the raw CT data. Recently, data on the efficacy of low-dose CT (LDCT) in the diagnosis of COVID-19 have appeared in the literature. AIM: To analyze the quality and diagnostic value of LDCT images of the lungs after applying an iterative processing algorithm and to assess the possibility of reducing the radiation load on the patient when diagnosing COVID-19. MATERIALS AND METHODS: Patients from the Infectious Diseases Department of the Moscow State University Hospital participated in the prospective study. CT examinations were performed at the time of patient admission and discharge and were repeated as needed during hospitalization. In the first study, a standard CT protocol with a tube voltage of 120 kV and automatic current modulation in the range of 200400 mA was used; in repeated CT scans, the LDKT protocol was used with reduced tube voltage parameters (100 or 110 kV) and automatic current modulation in the range of 40120 mA. To assess the diagnostic value of LDCT in comparison with standard CT, a survey was conducted among doctors from the Department of Radiation Diagnostics at Moscow State University Hospital. The questionnaire included a comparison of the two methods for identifying the following pathological processes: ground-glass opacities, compaction of the lung tissue with reticular changes, areas of lung tissue consolidation, and lymphadenopathy. RESULTS: The study included 151 patients. The average age was 5814.2 years, with men accounting for 53.6% of the population. During LDCT the radiation load was reduced by 2.96 times on average, CTDI by 2.6 times, DLP by 3.1 times, the current on the tube by 1.83 times, and the voltage on the tube by 1.2 times. The results indicate that the effectiveness of detecting the main signs of viral pneumonia and assessing the dynamics of the patients condition does not differ significantly from CT performed according to the standard protocol. CONCLUSIONS: The results of a comparison of standard and low-dose CT show that there is no significant loss of diagnostic information and image quality as the radiation load is reduced. Thus, chest LDCT can be used to successfully diagnose COVID-19 in routine practice.

P49. Cervical spine CT scans can miss fractures when football equipment is in place

<h3>BACKGROUND CONTEXT</h3> Iatrogenic worsening of a spinal injury can result in significant harm to football athletes and complicate its management when equipment is removed in the acute setting by inexperienced personnel. Spine imaging before removal of protective equipment mitigates this risk. There is a controversy regarding the ideal timing of equipment removal and whether current diagnostic imaging modalities are effective to detect these injuries without equipment removal. Prior data suggests that CT is a diagnostic modality for this purpose, however, radiologists' accuracy in detecting specific fractures must be investigated. However, there is no established modality to perform imaging in these patients with protective equipment in place. <h3>PURPOSE</h3> 1) Does the introduction of football equipment result in a reduction in sensitivity for cervical spine fracture detection? (2 What proportion of images that were determined to be of adequate diagnostic quality by experienced radiologists contained missed fractures that were previously identified in the images without football equipment? <h3>STUDY DESIGN/SETTING</h3> Diagnostic Study. <h3>PATIENT SAMPLE</h3> A total of 13 cadaveric specimens were used for testing to replicate a clinical setting. <h3>OUTCOME MEASURES</h3> 1) Sensitivity of CT for c-spine fracture 2) Proportion of fractures missed in CT studies with football equipment on that were deemed diagnostic by participation radiologists. <h3>METHODS</h3> A pendulum device was engineered to deliver a measured axial load to the crown of cadavers [PM1] to produce a variety of cervical spine fractures. The cadavers were then imaged using a standardized CT protocol first without and then with protective football equipment. The images were presented to three board-certified radiologists [SSL3] to identify all fractures from the occiput to T1 and assess their diagnostic quality. A sensitivity analysis was performed against a reference standard of fractures produced by the consensus of all radiologists in this study to determine if there was any reduction in radiologists' ability to detect fractures once football equipment was in place. <h3>RESULTS</h3> The radiologists in this study observed a 26.7% reduction in sensitivity for spine fracture detection once football equipment was in place (Overall, we observed a 26.7% reduction in sensitivity (51.3% (1.54/3) versus 78.0% (2.34/3), 95% CI 40.2% to 62.4%; p = 0.0032). Although the study radiologists considered 92% (72/82) of the CT images in the presence of football equipment to be of diagnostic quality, they failed to identify 51 (40.0%) total cervical spine fractures once the football equipment was introduced. <h3>CONCLUSIONS</h3> The sensitivity of cervical spine fracture detection using CT is diminished in the setting of protective football equipment. These findings contradict previous studies that determined CT to be a diagnostic imaging modality to image the cervical spine through equipment. Although the interpreting radiologists consistently deemed CTs performed in the presence of helmets and shoulder pads to have subjectively diagnostic quality, numerous fractures that had been detected in the absence of equipment were missed in their presence. The sensitivity of cervical spine fracture detection using CT is diminished in the setting of protective football equipment. Furthermore, this study established that subjective approval of the appearance of an imaging study based on the ability to recognize anatomic landmarks is insufficient to reliably determine the diagnostic quality of a CT image. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Intra-scan inter-tissue variability can help harmonize radiomics features in CT.

We studied the repeatability and the relative intra-scan variability across acquisition protocols in CT using phantom and unenhanced abdominal series. We used 17 CT scans from the Credence Cartridge Radiomics Phantom database and 20 unenhanced multi-site non-pathologic abdominal patient series for which we measured spleen and liver tissues. We performed multiple measurements in extracting 9 radiomics features. We defined a "tandem" as the measurement of a given tissue (or material) by a given radiomics. For each tandem, we assessed the proportion of the variability attributable to repetitions, acquisition protocols, material, or patient. We analyzed the distribution of the intra-scan correlation between pairs of tandems and checked the impact of correlation coefficient greater than 0.90 in comparing paired and unpaired differences. The repeatability of radiomics features depends on the measured material; 56% of tandems were highly repeatable. Histogram-derived radiomics were generally less repeatable. Nearly 60% of relative radiomics measurements had a correlation coefficient higher than 0.90 allowing paired measurements to improve reliability in detecting the difference between two materials. The analysis of liver and spleen tissues showed that measurement variability was negligible with respect to other variabilities. As for phantom data, we found that gray level zone length matrix (GLZLM)-derived radiomics and gray level co-occurrence matrix (GLCM)-derived radiomics were the most correlating features. For these features, relative intra-scan measurements improved the detection of different materials or tissues. We identified radiomics features for which the intra-scan measurements between tissues are linearly correlated. This property represents an opportunity to improve tissue characterization and inter-site harmonization. • The repeatability of radiomics features on CT depends on the measured material or tissue. • Some tandems of radiomics features/tissues are linearly affected by the variability of acquisition protocols on CT. • Relative intra-scan measurements are an opportunity for improving quantitative imaging on CT.

PO-1642 Feasibility of incorporating bead TLDs for in vivo dosimetry into current Radiotherapy CT protocols

PO-1642 Feasibility of incorporating bead TLDs for in vivo dosimetry into current Radiotherapy CT protocols

Anatomic Variations of the Hepatic Artery in 5625 Patients.

To analyze the origin and anatomic course of the hepatic arteries by using digital subtraction angiography (DSA) and multidetector CT in a large study sample. This retrospective study included 5625 patients who underwent liver CT and chemoembolization between January 2005 and December 2018 (mean age, 60 years ± 11 [range, 11-99 years]; 4464 males). The CT and DSA images were reviewed to evaluate the visceral arterial anatomy for variations in the celiac axis and hepatic arteries. Aberrant right hepatic arteries (aRHAs) and aberrant left hepatic arteries (aLHAs) were defined on the basis of their origin and anatomic course. Statistical analyses were performed to evaluate the association between aRHAs and aLHAs and the association between variations in the hepatic artery and celiac axis. Right hepatic arteries were categorized as being aRHAs (if originating from the proximal to middle common hepatic artery, gastroduodenal artery, superior mesenteric artery [SMA], celiac axis, aorta, splenic artery, or left gastric artery [LGA]) or as being aLHAs (if arising from the LGA, celiac axis, aorta, or SMA). The prevalence of aRHAs (15.63%; 879 of 5625) and the prevalence aLHAs (16.32%; 918 of 5625) were similar. Patients with an aRHA were more likely to have an aLHA than those without an aRHA (29.01% vs 13.97%; P < .001), and patients with an aLHA were more likely to have an aRHA than those without an aLHA (27.78% vs 13.26%; P < .001). There was no association between the hepatic arterial variations and celiac axis variations. A hypothetical anatomic model summarizing the observed variations was created. A comprehensive list of hepatic arterial variations and a three-dimensional hypothetical model for the observed variations were described.Keywords: CT, Angiography, Liver, Anatomy, Arteries© RSNA, 2021 Supplemental material is available for this article. See also commentary by Sutphin and Kalva in this issue.

Optimisation of CT protocols in PET-CT across different scanner models using different automatic exposure control methods and iterative reconstruction algorithms

BackgroundA significant proportion of the radiation dose from a PET-CT examination is dependent on the CT protocol, which should be optimised for clinical purposes. Matching protocols on different scanners within an imaging centre is important for the consistency of image quality and dose. This paper describes our experience translating low-dose CT protocols between scanner models utilising different automatic exposure control (AEC) methods and reconstruction algorithms.MethodsThe scanners investigated were a newly installed Siemens Biograph mCT PET with 64-slice SOMATOM Definition AS CT using sinogram affirmed iterative reconstruction (SAFIRE) and two GE Discovery 710 PET scanners with 128-slice Optima 660 CT using adaptive statistical reconstruction (ASiR). Following exploratory phantom work, 33 adult patients of various sizes were scanned using the Siemens scanner and matched to patients scanned using our established GE protocol to give 33 patient pairs. A comparison of volumetric CT dose index (CTDIvol) and image noise within these patient pairs informed optimisation, specifically for obese patients. Another matched patient study containing 27 patient pairs was used to confirm protocol matching. Size-specific dose estimates (SSDEs) were calculated for patients in the second cohort. With the acquisition protocol for the Siemens scanner determined, clinicians visually graded the images to identify optimal reconstruction parameters.ResultsIn the first matched patient study, the mean percentage difference in CTDIvol for Siemens compared to GE was − 10.7% (range − 41.7 to 50.1%), and the mean percentage difference in noise measured in the patients’ liver was 7.6% (range − 31.0 to 76.8%). In the second matched patient study, the mean percentage difference in CTDIvol for Siemens compared to GE was − 20.5% (range − 43.1 to 1.9%), and the mean percentage difference in noise was 19.8% (range − 27.0 to 146.8%). For these patients, the mean SSDEs for patients scanned on the Siemens and GE scanners were 3.27 (range 2.83 to 4.22) mGy and 4.09 (range 2.81 to 4.82) mGy, respectively. The analysis of the visual grading study indicated no preference for any of the SAFIRE strengths.ConclusionsGiven the different implementations of acquisition parameters and reconstruction algorithms between vendors, careful consideration is required to ensure optimisation and standardisation of protocols.

Assessment of task-based image quality for abdominal CT protocols linked with national diagnostic reference levels

ObjectivesTo assess task-based image quality for two abdominal protocols on various CT scanners. To establish a relationship between diagnostic reference levels (DRLs) and task-based image quality.MethodsA protocol for the detection of focal liver lesions was used to scan an anthropomorphic abdominal phantom containing 8- and 5-mm low-contrast (20 HU) spheres at five CTDIvol levels (4, 8, 12, 16, and 20 mGy) on 12 CTs. Another phantom with high-contrast calcium targets (200 HU) was scanned at 2, 4, 6, 10, and 15 mGy using a renal stones protocol on the same CTs. To assess the detectability, a channelized Hotelling observer was used for low-contrast targets and a non-prewhitening observer with an eye filter was used for high contrast targets. The area under the ROC curve and signal to noise ratio were used as figures of merit.ResultsFor the detection of 8-mm spheres, the image quality reached a high level (mean AUC over all CTs higher than 0.95) at 11 mGy. For the detection of 5-mm spheres, the AUC never reached a high level of image quality. Variability between CTs was found, especially at low dose levels. For the search of renal stones, the AUC was nearly maximal even for the lowest dose level.ConclusionsComparable task-based image quality cannot be reached at the same dose level on all CT scanners. This variability implies the need for scanner-specific dose optimization.Key Points• There is an image quality variability for subtle low-contrast lesion detection in the clinically used dose range.• Diagnostic reference levels were linked with task-based image quality metrics.• There is a need for specific dose optimization for each CT scanner and clinical protocol.

Analysis of Reduction Effective Dose for Eye in Phantom Using Eye TLD with Implementation of Organ Dose Modulation (ODM) Software and Eyeshield on Head CT Protocol with GE Revolution Evo 128 Slice Tool

The eye is one of the sensitive organs that need attention in the head CT-Scan. This study aims to reduce the effective eye dose on a head CT-Scan using ODM (Organ Dose Modulation) software and use eyeshield on the phantom. The study was conducted using a CT-Scan tool GE Revolution Evo 128 Slice. The research method was carried out by placing three pairs of eye TLDs (Hp3 Dosimeters) on the phantom for the three examination configurations, CT-Scan standard (routine) examinations, examinations using ODM software, and examinations using ODM software and eyeshield. The estimated effective dose calculation based on TLD reading for the eye lens on a standard CT-Scan (routine) is 1.29 mSv. Examination with ODM software is 1.03 mSv. Examination with ODM software and eyeshield of 0.9 mSv. Based on the results obtained, a head CT-Scan with ODM software can reduce the dose by 20% from a routine head CT-Scan, and if added with an eyeshield, it can reduce the dose by 30%. The quality of the image produced by implementing ODM software, SNR value decreased from 39 to 35 in the anterior phantom, central and posterior parts remained. However, the change in SNR value is not significant, so it does not change the image quality. Furthermore, the addition of eyeshield does not alter the SNR value, which means that the addition eyeshield does not cause artifacts that affect image quality. Using ODM and eyeshield software is indeed a little more complicated than a routine head CT-Scan. Still, the benefits obtained are pretty significant, reducing the effective dose received by the eye without reducing image quality.

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.