An Investigation into the Infrastructure and Management of Computerized Tomography Units in Ghana.

INTRODUCTION: In Ghana, there is a need to document computed tomography (CT) infrastructure and management systems for the development of interventions to promote CT practices while ensuring patient protection through the establishment of diagnostic reference levels and improved dose management systems. METHODS: A quantitative inquiry using a descriptive, cross-sectional approach was used to collect data, using a semistructured questionnaire related to CT infrastructure and management from the technical heads responsible for CT scanners. Data collected included the scanner characteristics, basic management system and organizational arrangements, number of attending practitioners, clinical indications for CT examinations, and the operation of CT facilities in Ghana. RESULTS: Of the 35 CT scanners installed across the country, 31 were involved in the study. The majority (29%) were Toshiba models. Equipment slices ranged from 1 to 640, of which 45.2% were 16-slice scanners. Many (n = 28, 90.3%) were functioning, and most were installed in the capital city, Accra. The equipment mean age was 7.3 ± 4.4 years, and 25.6% were 10 or more years old. There were 107 operating radiographers, 60 reporting radiologists, and 10 medical physicists employed across the facilities. A total of 204,760 CT examinations were performed yearly (6.8 CT procedures per 1000 people in Ghana). Head CT procedures were the most common, and suspicion of cerebrovascular accident or stroke (32.8%) was the most common indication. Some basic quality management system and policy driving CT infrastructure in Ghana were lacking. CONCLUSION: The results have provided essential information on the status of CT infrastructure and management systems for policy development and planning in CT facilities in Ghana. This study provides those interested in CT services, jobs, or medical equipment investment in Ghana the information needed to make appropriate decisions.

Use of computed tomography volumetric measurements to predict operative techniques in paraesophageal hernia repair.

BACKGROUND: Despite advances in diagnostic imaging capabilities, little information exists concerning the impact of physical dimensions of a paraesophageal hernia (PEH) on intraoperative decision making. The authors hypothesized that computerized volumetric analysis and multidimensional visualization to measure hiatal defect area (HDA) and intrathoracic hernia sac volume (HSV) would correlate to operative findings and required surgical techniques performed. METHODS: Using volumetric analysis software (Aquarius iNtuition, TeraRecon, Inc), HDA and HSV were measured in PEH patients with preoperative computerized tomography (CT) scans, and used to predict the likelihood of intraoperative variables. Multidimensional rotation of images enabled visualization of the entire hiatal defect in a plane mimicking the surgeon's view during repair. The intrathoracic hernia sac was outlined producing volume measurements based on a summation of exact dimensions. RESULTS: A total of 213 PEHR patients had preoperative CT imaging, with 14.1% performed emergently. Primary cruroplasty was performed in 89.2%, salvage gastropexy in 10.3%, and diaphragmatic relaxing incisions in 4.2%. Median HDA was 25.7 cm2 (IQR17.8-35.6 cm2); median HSV was 365.0 cm3 (IQR150.0-611.0 cm3). Incremental 5 cm2 increase in HDA was associated with greater likelihood of presenting emergently (OR 1.27; 95%CI 1.124-1.428, p = 0.0001), incarceration (OR 1.27; 1.074-1.499, p = 0.005), gastric volvulus (OR 1.13; 1.021-1.248, p = 0.02), and requiring either relaxing incision (OR 1.43; 1.203-1.709, p < 0.0001) or salvage gastropexy (OR 1.13; 1.001-1.274, p = 0.04). Similarly, HSV increases of 100 cm3 were associated with 23% greater likelihood of emergent repair (CI 1.121-1.353, p < 0.0001), and were more likely to require a relaxing incision (OR 1.18; 1.043-1.339, p = 0.009) or salvage gastropexy (1.19; 1.083-1.312, p = 0.0003). CONCLUSIONS: Utilization of CT volumetric measurements is a valuable adjunct in preoperative planning, allowing the surgeon to anticipate complexity of repair and operative approach, as incremental increases in HSV by 100 cm3 and HDA by 5 cm2 are more likely to require complex techniques or bailout procedures and/or present emergently.

ComBat harmonization for radiomic features in independent phantom and lung cancer patient computed tomography datasets.

This work seeks to evaluate the combatting batch effect (ComBat) harmonization algorithm's ability to reduce the variation in radiomic features arising from different imaging protocols and independently verify published results. The Gammex computed tomography (CT) electron density phantom and Quasar body phantom were imaged using 32 different chest imaging protocols. 107 radiomic features were extracted from 15 spatially varying spherical contours between 1.5 cm and 3 cm in each of the lung300 density, lung450 density, and wood inserts. The Kolmogorov-Smirnov test was used to determine significant differences in the distribution of the features and the concordance correlation coefficient (CCC) was used to measure the repeatability of the features from each protocol variation class (kVp, pitch, etc) before and after ComBat harmonization. P-values were corrected for multiple comparisons using the Benjamini-Hochberg-Yekutieli procedure. Finally, the ComBat algorithm was applied to human subject data using six different thorax imaging protocols with 135 patients. Spherical contours of un-irradiated lung (2 cm) and vertebral bone (1 cm) were used for radiomic feature extraction. ComBat harmonization reduced the percentage of features from significantly different distributions to 0%-2% or preserved 0% across all protocol variations for the lung300, lung450 and wood inserts. For the human subject data, ComBat harmonization reduced the percentage of significantly different features from 0%-59% for bone and 0%-19% for lung to 0% for both. This work verifies previously published results and demonstrates that ComBat harmonization is an effective means to harmonize radiomic features extracted from different imaging protocols to allow comparisons in large multi-institution datasets. Biological variation can be explicitly preserved by providing the ComBat algorithm with clinical or biological variables to protect. ComBat harmonization should be tested for its effect on predictive models.

CNN-based PET sinogram repair to mitigate defective block detectors.

Positron emission tomography (PET) scanners continue to increase sensitivity and axial coverage by adding an ever expanding array of block detectors. As they age, one or more block detectors may lose sensitivity due to a malfunction or component failure. The sinogram data missing as a result thereof can lead to artifacts and other image degradations. We propose to mitigate the effects of malfunctioning block detectors by carrying out sinogram repair using a deep convolutional neural network. Experiments using whole-body patient studies with varying amounts of raw data removed are used to show that the neural network significantly outperforms previously published methods with respect to normalized mean squared error for raw sinograms, a multi-scale structural similarity measure for reconstructed images and with regard to quantitative accuracy.

Technical Note: Proof of concept for radiomics-based quality assurance for computed tomography.

PURPOSE: Routine quality assurance (QA) testing to identify malfunctions in medical imaging devices is a standard practice and plays an important role in meeting quality standards. However, current daily computed tomography (CT) QA techniques have proven to be inadequate for the detection of subtle artifacts on scans. Therefore, we investigated the ability of a radiomics phantom to detect subtle artifacts not detected in conventional daily QA. METHODS: An updated credence cartridge radiomics phantom was used in this study, with a focus on two of the cartridges (rubber and cork) in the phantom. The phantom was scanned using a Siemens Definition Flash CT scanner, which was reported to produce a subtle line pattern artifact. Images were then imported into the IBEX software program, and 49 features were extracted from the two cartridges using four different preprocessing techniques. Each feature was then compared with features for the same scanner several months previously and with features from controlled CT scans obtained using 100 scanners. RESULTS: Of 196 total features for the test scanner, 79 (40%) from the rubber cartridge and 70 (36%) from the cork cartridge were three or more standard deviations away from the mean of the controlled scan population data. Feature values for the artifact-producing scanner were closer to the population mean when features were preprocessed with Butterworth smoothing. The feature most sensitive to the artifact was co-occurrence matrix maximum probability. The deviation from the mean for this feature was more than seven times greater when the scanner was malfunctioning (7.56 versus 1.01). CONCLUSIONS: Radiomics features extracted from a texture phantom were able to identify an artifact-producing scanner as an outlier among 100 CT scanners. This preliminary analysis demonstrated the potential of radiomics in CT QA to identify subtle artifacts not detected using the currently employed daily QA techniques.

Diagnostic performance of computed tomography for bowel endometriosis: A systematic review and meta-analysis.

PURPOSE: To perform a systematic review and meta-analysis regarding the performance of CT for diagnosis of bowel endometriosis. MATERIALS AND METHODS: Pubmed and EMBASE were systematically searched up to March 28, 2019. Diagnostic accuracy studies using CT for diagnosis of bowel endometriosis using laparoscopy followed by histopathology as the reference standard were included. Methodological quality of the included studies was evaluated using Quality Assessment of Diagnostic Accuracy Studies-2. Sensitivity and specificity were pooled using hierarchical summary receiver operating modelling. Meta-regression analysis was done to explore heterogeneity. RESULTS: Twelve studies (1091 patients) were included. Pooled sensitivity and specificity were 0.92 (95% confidence interval [CI], 0.83-0.97) and 0.95 (95% CI, 0.88-0.98), respectively. Substantial heterogeneity was present: I2 = 92.38% for sensitivity and 89.09% for specificity. Deeks' asymmetry test suggested publication bias (p = 0.04). At meta-regression analysis, history of prior surgery for endometriosis was the only significant factor affecting heterogeneity (p < 0.01). Specifically, studies that included patients with such history demonstrated significantly greater specificity than studies that did not (0.95 [95% CI, 0.91-1.00] vs 0.75 [95% CI, 0.43-1.00]). CONCLUSIONS: CT shows excellent performance in the diagnosis of bowel endometriosis. Due to small number of included studies and publication bias, further studies may be needed to validate these results.

3D cone-beam CT of the ankle using a novel twin robotic X-ray system: Assessment of image quality and radiation dose.

PURPOSE: To evaluate image quality (IQ) and radiation dose in cone-beam computed tomography (CBCT) of the ankle using a novel twin robotic X-ray system. METHOD: We examined 16 cadaveric ankles with standard-dose (FD) and low-dose (LD) protocols using the new system's CBCT mode. For comparison, we performed multi-slice CT imaging (MSCT) with a clinical protocol. Three radiologists assessed IQ, noise and artifacts in bone and soft tissue on a five-point Likert scale (1= poor IQ; strong noise or artifacts; 5= excellent IQ; minimal noise or artifacts). Volume CT dose indices (CTDIvol) were calculated for radiation dose comparison between CBCT and MSCT. RESULTS: Overall IQ was described as very good or excellent by reader 1/2/3 in 62.5/87.5/56.3% of LD, 87.5/87.5/81.3% of FD and 100/87.5/87.5% of MSCT studies. Readers agreed that IQ was better in MSCT than LD (R1/R2/R3; p ≤ 0.008), two also found advantages of MSCT over FD (R1/R3; p ≤ 0.034). Soft tissue noise and artifacts were stronger in FD (all p ≤ 0.002) and LD (all p ≤ 0.001). In bone, artifacts and noise were also more severe in LD (all p < 0.001) and FD (all p ≤ 0.003). CTDIvol for clinical MSCT scans without dose modulation (15.0 ± 0.0 mGy) were higher than for FD (5.3 ± 1.0 mGy) and LD studies (2.9 ± 0.6 mGy; both p < 0.001). CONCLUSIONS: Despite MSCT providing better overall IQ than the twin robotic X-ray system's CBCT mode, both cone-beam protocols offer very good IQ in most studies and are suitable for clinical ankle imaging. Standard-dose and especially low-dose CBCT studies deliver up to five times less radiation dose than MSCT imaging.

Characterization of dynamic collimation mechanisms for helical CT scans with direct measurements.

Dynamic collimation is an important dose reduction mechanism for helical CT scans, especially for modern wide-beam scanner models. Its implementation and efficacy need to be studied to optimize CT scan protocols and to reduce unnecessary patient dose. The purpose of this study is to evaluate dynamic beam collimation for modern wide-beam CT scanners with direct measurements and to estimate the efficacy for dose reduction. By using a linear-array solid state detector, primary x-ray beam coverage was measured for four CT scanner models: GE Revolution CT, Siemens Somatom Force, Philips iQon, and GE LightSpeed VCT. Supported independently from patient table, the detector remained stationary at the isocenter during helical scans. Data lines were recorded every 0.24 ms throughout one entire helical scan, with a spatial resolution of 0.8 mm along the craniocaudal direction. The measurements were repeated for various scan parameters related to dynamic collimation, including beam collimation width, pitch, rotation time, and scan length. The recorded beam coverage area was used as a surrogate to total primary dose, to model different dynamic collimation mechanisms. The directly measured total radiation range was compared to table travel distance and nominal scan length which equals to the ratio between DLP and CTDIvol. Equations to calculate the percentage dose reduction with dynamic collimation were derived for different mechanisms. Three different dynamic collimation mechanisms were revealed and related linear model parameters were reported for different helical scan parameters. The nominal scan length used to calculate DLP was shown to vary for different dynamic collimation mechanisms. For typical head and abdomen scans with nominal scan lengths of 17.5 cm and 25 cm, percentage dose reduction from dynamic collimation ranged from 2% to 32%. In conclusion, with direct measurements of primary x-ray beam coverage, dynamic collimation mechanisms and related dose reduction effects were characterized for four modern wide-beam CT scanners.

NATIONAL DIAGNOSTIC REFERENCE LEVELS AND ACHIEVABLE DOSES FOR 13 ADULT CT PROTOCOLS AND A PAEDIATRIC HEAD CT PROTOCOL: NATIONAL SURVEY OF KOREAN HOSPITALS.

To develop a second set of diagnostic reference levels (DRLs) and achievable doses (ADs) for 13 adult computed tomography (CT) protocols and a paediatric head CT protocol in Korea. A survey of 13,625 CT examinations was performed based on 13 adult CT protocols and a paediatric non-contrast brain CT protocol using 369 CT systems, with patients grouped according to age. Most CT protocols in this survey had DRLs similar to those reported in other countries. However, chest and abdomen-pelvic CT had lower DRLs than those reported in the first Korean national survey and those from other countries. Paediatric non-contrast brain CT in each age group, with the exception of the 11-15-year age group, had lower DRLs than those reported in other countries. The DRLs presented here are similar to (or lower than for some protocols) those reported in the first Korean national survey and those from other countries.

Assessment of Image Quality and Dosimetric Performance of CT Simulators.

BACKGROUND: CT simulator for radiation therapy aims to produce high-quality images for dose calculation and delineation of target and organs at risk in the process of treatment planning. Selection of CT imaging protocols that achieve a desired image quality while minimizing patient dose depends on technical CT parameters and their relationship with image quality and radiation dose. For similar imaging protocols using comparable technical CT parameters, there are also variations in image quality metrics between different CT simulator models. Understanding the relationship and variation is important for selecting appropriate imaging protocol and standardizing QC process. Here, we proposed an automated method to determine the relationship between image quality and radiation dose for various CT technical parameters. MATERIAL AND METHOD: The impact of scan parameters on various aspects of image quality and volumetric CT dose index for a Philips Brilliance Big Bore and a Toshiba Aquilion One CT scanners were determined by using commercial phantom and automated image quality analysis software and cylindrical radiation dose phantom. RESULTS AND DISCUSSION: Both scanners had very similar and satisfactory performance based on the diagnostic acceptance criteria recommended by ACR, International Atomic Energy Agency, and American Association of Physicists in Medicine. However, our results showed a compromise between different image quality components such as low-contrast and spatial resolution with the change of scanning parameters and revealed variations between the two scanners on their image quality performance. Measurement using a generic phantom and analysis by automated software was unbiased and efficient. CONCLUSION: This method provides information that can be used as a baseline for CT scanner image quality and dosimetric QC for different CT scanner models in a given institution or across sites.

The effects of mis-centering on radiation dose during CT head examination: A phantom study.

There are several factors that may contribute to the increase in radiation dose of CT including the use of unoptimized protocols and improper scanning technique. In this study, we aim to determine significant impact on radiation dose as a result of mis-centering during CT head examination. The scanning was performed by using Toshiba Aquilion 64 slices multi-detector CT (MDCT) scanner and dose were measured by using calibrated ionization chamber. Two scanning protocols of routine CT head; 120 kVp/ 180 mAs and 100 kVp/ 142 mAs were used represent standard and low dose, respectively. As reference measurement, the dose was first measured on standard cylindrical polymethyl methacrylate (PMMA) phantom that positioned at 104 cm from the floor (reference isocenter). The positions then were varied to simulate mis-centering by 5 cm from isocenter, superiorly and inferiorly at 109 cm, 114 cm, 119 cm, 124 cm and 99 cm, 94 cm, 89 cm, 84 cm, respectively. Scanning parameter and dose information from the console were recorded for the radiation effective dose (E) measurement. The highest mean CTDIvol value for MCS and MCI were 105.06 mGy (at +10 cm) and 105.51 mGy (at - 10 cm), respectively which differed significantly (p < 0.05) as compared to the isocenter. There were large significant different (p < 0.05) of mean Dose Length Product (DLP) recorded between isocenter to the MCS (85.8 mGy.cm) and MCI (93.1 mGy.cm). As the low dose protocol implemented, the volume CTDI (CTDIvol) were significantly increase (p < 0.05) for MCS (at +10 cm) and MCI (at - 10 cm) when compared to the isocenter. The phantom study revealed a noticeable different in radiation dose between isocenter and experimental groups due to degradation of the bowtie filter performance. It is anticipated that these noteworthy findings may emphasize the importance of accurate patient centering at the isocenter of CT gantry, so that CT optimization practice can be achieved.

COMPARISON OF RADIATION EXPOSURE TO THE PATIENT AND CONTRAST DETAIL RESOLUTIONS ACROSS LOW DOSE 2D/3D SLOT SCANNER AND TWO CONVENTIONAL DIGITAL RADIOGRAPHY X-RAY IMAGING SYSTEMS.

PURPOSE: To assess and compare the radiation dose and image quality of the low dose 2D/3D EOS slot scanner (LDSS) to conventional digital radiography (DR) X-ray imaging systems for chest and knee examination protocols. METHODS AND MATERIALS: The effective doses (ED) to the patient in the chest and knee clinical examination protocols for LDSS and DR X-ray imaging systems were determined using the dose area product and PCXMC Monte Carlo simulation software. The CDRAD phantom was imaged with 19 cm, and 13 cm thick Polymethyl Methacrylate (PMMA) blocks to simulate the chest and knees respectively of a patient of average adult size. The contrast detail resolution was calculated using image analysis software. RESULTS: The EDs for the LDSS default setting were up to 69% and 51% lower than for the DR systems for the chest (speed 4) and knee (speed 6) protocols, respectively, while for the increased dose level setting then the EDs were up to 42% and 35% lower than for the DR systems for the chest (speed 6) and knee (speed 8) protocols respectively. At the default setting, the contrast detail was lowest for the default setting of the 2D/3D low dose slot scanner (LDSS) for both chest and knee examinations, but at the highest dose levels then the threshold were equal or higher than the contrast resolution of DR imaging systems. CONCLUSION: The LDSS has the potential to be used for clinical diagnosis of chest and knee examinations using the higher dose level. For speed 6 in chest protocol and speed 8 in knee protocol, the measured contrast detail resolution was comparable with the DR systems but at a lower effective dose.

Mini EXPLORER II: a prototype high-sensitivity PET/CT scanner for companion animal whole body and human brain scanning.

As part of the EXPLORER total-body positron emission tomography (PET) project, we have designed and built a high-resolution, high-sensitivity PET/CT scanner, which is expected to have excellent performance for companion animal whole body and human brain imaging. The PET component has a ring diameter of 52 cm and an axial field of view of 48.3 cm. The detector modules are composed of arrays of lutetium (yttrium) oxyorthosilicate (LYSO) crystals of dimensions 2.76 × 2.76 × 18.1 mm3 coupled to silicon photomultipliers (SiPMs) for read-out. The CT component is a 24 detector row CT scanner with a 50 kW x-ray tube. PET system time-of-flight resolution was measured to be 409 ± 39 ps and average system energy resolution was 11.7% ± 1.5% at 511 keV. The NEMA NU2-2012 system sensitivity was found to be 52-54 kcps MBq-1. Spatial resolution was 2.6 mm at 10 mm from the center of the FOV and 2.0 mm rods were clearly resolved on a mini-Derenzo phantom. Peak noise-equivalent count (NEC) rate, using the NEMA NU 2-2012 phantom, was measured to be 314 kcps at 9.2 kBq cc-1. The CT scanner passed the technical components of the American College of Radiology (ACR) accreditation tests. We have also performed scans of a Hoffman brain phantom and we show images from the first canine patient imaged on this device.

Validation of A Method to Compensate Multicenter Effects Affecting CT Radiomics.

Background Radiomics extracts features from medical images more precisely and more accurately than visual assessment. However, radiomics features are affected by CT scanner parameters such as reconstruction kernel or section thickness, thus obscuring underlying biologically important texture features. Purpose To investigate whether a compensation method could correct for the variations of radiomic feature values caused by using different CT protocols. Materials and Methods Phantom data involving 10 texture patterns and 74 patients in cohorts 1 (19 men; 42 patients; mean age, 60.4 years; September-October 2013) and 2 (16 men; 32 patients; mean age, 62.1 years; January-September 2007) scanned by using different CT protocols were retrospectively included. For any radiomic feature, the compensation approach identified a protocol-specific transformation to express all data in a common space that were devoid of protocol effects. The differences in statistical distributions between protocols were assessed by using Friedman tests before and after compensation. Principal component analyses were performed on the phantom data to evaluate the ability to distinguish between texture patterns after compensation. Results In the phantom data, the statistical distributions of features were different between protocols for all radiomic features and texture patterns (P < .05). After compensation, the protocol effect was no longer detectable (P > .05). Principal component analysis demonstrated that each texture pattern was no longer displayed as different clusters corresponding to different imaging protocols, unlike what was observed before compensation. The correction for scanner effect was confirmed in patient data with 100% (10 of 10 features for cohort 1) and 98% (87 of 89 features for cohort 2) of P values less than .05 before compensation, compared with 30% (three of 10) and 15% (13 of 89) after compensation. Conclusion Image compensation successfully realigned feature distributions computed from different CT imaging protocols and should facilitate multicenter radiomic studies. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Steiger and Sood in this issue.

Radiation dose reduction for musculoskeletal computed tomography of the pelvis with preserved image quality.

OBJECTIVE: To analyze the impact of pelvic computed tomography (CT) technique optimization on estimated dose and subjective and objective image quality. MATERIALS AND METHODS: An institutional review board (IRB)-approved retrospective records review was performed with waived informed consent. Five CT scanners (various manufacturers/models) were standardized to match the lowest dose profile on campus via subjective assessment of clinical images by experienced musculoskeletal radiologists. The lowest dose profile had previously been established through image assessment by experienced musculoskeletal radiologists after a department-wide radiation dose reduction initiative. A consecutive series of 60 pre- and 59 post-optimization bony pelvis CTs were analyzed by two residents, who obtained signal-to-noise ratio for femoral cortex and marrow, gluteus medius muscle, and subcutaneous and visceral fat in a standardized fashion. Two blinded attending radiologists ranked image quality from poor to excellent. RESULTS: Pre- and post-optimization subjects exhibited no difference in gender, age, or BMI (p > 0.2). Mean CT dose index (CTDIvol) and dose-length product (DLP) decreased by approximately 45%, from 39± 14 to 18± 12 mGy (p < 0.0001) and 1,227± 469 to 546± 384 mGy-cm (p < 0.0001). Lower body mass index (BMI) was associated with a larger dose reduction and higher BMI with higher DLP regardless of pre- or post-optimization examination. Inter-observer agreement was 0.64-0.92 for SNR measurements. Cortex SNR increased significantly for both observers (p < 0.02). Although qualitative image quality significantly decreased for one observer (p < 0.01), adequate mean quality (3.3 out of 5) was maintained for both observers. CONCLUSION: Subjective and objective image quality for pelvic CT examination remains adequate, despite a substantially reduced radiation dose.

Leadless Cardiac Pacemaker (LCP) without Diagnostic Relevant Artifacts in DualSource and DualEnergy-CT Examinations in First- to Third-Generation DSCT Scanner.

RATIONALE AND OBJECTIVES: To identify the influence and artifact burden in cardiac CT imaging of a leadless cardiac pacemaker (LCP) performed with all three generations of DualSource CT (DSCT) Scanners. MATERIALS AND METHODS: The LCP was examined in DSCT scanners of the first to third generation using DualEnergy (DECT) and DSCT as well as alterations of the current-time product. For DECT examinations, virtual monoenergetic images were computed manually on a dedicated workstation. Virtual voltage was manually selected by subjective assessment of the lowest artifact burden. Systematic variations of the pacemaker angle to the gantry were assessed, too. The angle was successively increased by 10°, ranging from 0° to 90°. Artifact burden was quantified on a five-point Likert scale (1- no artifacts, 2- few artifacts, 3- moderate artifacts, 4- many artifacts, and 5- massive artifacts). Likert values of 1-3 were considered diagnostic and assessed by two board-certified radiologists in consensus. RESULTS: In total, 200 examinations were analyzed, a mean Likert value of 1.93 ± 0.61 was found overall. None of the images were assessed Likert value >3. The positioning evaluation showed a clear and significant reduction of artifact burden toward lower angles, (0°: 1.4 ± 0.5 vs. 90° 2.55 ± 0.51). At scanner level, second-generation DSCT performed significantly better (1.68 ± 0.47) than both other scanners. Comparison of technique (DECT vs. DSCT) revealed a significantly improved image quality in DSCT examinations. CONCLUSION: LCP can be safely examined in DSCT scanner of the first to third generation with the evaluated protocols and techniques, which are currently in use. Artifact burden can be significantly reduced by aligning or approaching the LCP's longitudinal axis toward the scanner's z-axis.

Statistical analysis for obtaining optimum number of CT scanners in patient dose surveys for determining national diagnostic reference levels.

OBJECTIVES: To statistically determine an 'optimum number of CT scanners' for obtaining 'diagnostic reference levels' (DRLs) in CT examinations as close as possible to 'ideal DRLs' when all available CT scanners are considered. METHODS: First, six 'ideal DRLs' (CTDIVol and DLP) were determined for head, chest and abdomen/pelvis examinations by using patient-dose survey data of 100 CT scanners of different models in Tehran. Then, a 'random sampling method' was applied to different percent fractions of patient dose data of 100 CT scanners. The percent differences (PD) of the DRLs obtained from 'ideal DRLs' and their coefficients of variation (CVs) were calculated. The 'optimum number of CT scanners' determined met those of 'ideal DRL' criteria; i.e. precision (CV ≤ 10%) and accuracy (PD ≤ 10%). RESULTS: 'Optimum number of CT scanners' for determining DRLs as close as possible to 'ideal DRLs', fulfilling the stated criteria, is 43 instead of using 100. CONCLUSION: 'Optimum number of CT scanners' for obtaining DRLs as close as possible to 'ideal DRLs' was determined. This optimum number can be effectively applied in patient-dose survey situations with limited resources in a time- and cost-effective manner. KEY POINTS: • Ideal DRLs were determined by a CT patient-dose survey applied to available scanners. • 'Optimum number of CT scanners' statistically determined for DRLs is 43%. • Optimum number can be used for DRLs as if 'ideal DRLs' were determined by all scanners.

Diagnostic accuracy of diagnostic imaging for lumbar disc herniation in adults with low back pain or sciatica is unknown; a systematic review.

Main text: We aim to summarize the available evidence on the diagnostic accuracy of imaging (index test) compared to surgery (reference test) for identifying lumbar disc herniation (LDH) in adult patients.For this systematic review we searched MEDLINE, EMBASE and CINAHL (June 2017) for studies that assessed the diagnostic accuracy of imaging for LDH in adult patients with low back pain and surgery as the reference standard. Two review authors independently selected studies, extracted data and assessed risk of bias. We calculated summary estimates of sensitivity and specificity using bivariate analysis, generated linked ROC plots in case of direct comparison of diagnostic imaging tests and assessed the quality of evidence using the GRADE-approach.We found 14 studies, all but one done before 1995, including 940 patients. Nine studies investigated Computed Tomography (CT), eight myelography and six Magnetic Resonance Imaging (MRI). The prior probability of LDH varied from 48.6 to 98.7%. The summary estimates for MRI and myelography were comparable with CT (sensitivity: 81.3% (95%CI 72.3-87.7%) and specificity: 77.1% (95%CI 61.9-87.5%)). The quality of evidence was moderate to very low. Conclusions: The diagnostic accuracy of CT, myelography and MRI of today is unknown, as we found no studies evaluating today's more advanced imaging techniques. Concerning the older techniques we found moderate diagnostic accuracy for all CT, myelography and MRI, indicating a large proportion of false positives and negatives.

Coronary artery calcium quantification using contrast-enhanced dual-energy computed tomography scans in comparison with unenhanced single-energy scans.

Extracting coronary artery calcium (CAC) scores from contrast-enhanced computed tomography (CT) images using dual-energy (DE) based material decomposition has been shown feasible, mainly through patient studies. However, the quantitative performance of such DE-based CAC scores, particularly per stenosis, is underexamined due to lack of reference standard and repeated scans. In this work we conducted a comprehensive quantitative comparative analysis of CAC scores obtained with DE and compare to conventional unenhanced single-energy (SE) CT scans through phantom studies. Synthetic vessels filled with iodinated blood mimicking material and containing calcium stenoses of different sizes and densities were scanned with a third generation dual-source CT scanner in a chest phantom using a DE coronary CT angiography protocol with three exposures/CTDIvol: auto-mAs/8 mGy (automatic exposure), 160 mAs/20 mGy and 260 mAs/34 mGy and 10 repeats. As a control, a set of vessel phantoms without iodine was scanned using a standard SE CAC score protocol (3 mGy). Calcium volume, mass and Agatston scores were estimated for each stenosis. For DE dataset, image-based three-material decomposition was applied to remove iodine before scoring. Performance of DE-based calcium scores were analyzed on a per-stenosis level and compared to SE-based scores. There was excellent correlation between the DE- and SE-based scores (correlation coefficient r: 0.92-0.98). Percent bias for the calcium volume and mass scores varied as a function of stenosis size and density for both modalities. Precision (coefficient of variation) improved with larger and denser stenoses for both DE- and SE-based calcium scores. DE-based scores (20 mGy and 34 mGy) provided comparable per-stenosis precision to SE-based (3 mGy). Our findings suggest that on a per-stenosis level, DE-based CAC scores from contrast-enhanced CT images can achieve comparable quantification performance to conventional SE-based scores. However, DE-based CAC scoring required more dose compared with SE for high per-stenosis precision so some caution is necessary with clinical DE-based CAC scoring.