Standardization of scan protocols for RT CT simulator from different vendors using quantitative image quality technique.

OBJECTIVE: To investigate the feasibility of standardizing RT simulation CT scanner protocols between vendors using target-based image quality (IQ) metrics. METHOD AND MATERIALS: A systematic assessment process in phantom was developed to standardize clinical scan protocols for scanners from different vendors following these steps: (a) images were acquired by varying CTDIvol and using an iterative reconstruction (IR) method (IR: iDose and model-based iterative reconstruction [IMR] of CTp-Philips Big Bore scanner, SAFIRE of CTs-Siemens biograph PETCT scanner), (b) CT exams were classified into body and brain protocols, (c) the rescaled noise power spectrum (NPS) was calculated, (d) quantified the IQ change due to varied CTDIvol and IR, and (e) matched the IR strength level. IQ metrics included noise and texture from NPS, contrast, and contrast-to-noise ratio (CNR), low contrast detectability (d'). Area under curve (AUC) of the receiver operation characteristic curve of d' was calculated and compared. RESULTS: The level of change in the IQ ratio was significant (>0.6) when using IMR. The IQ ratio change was relatively low to moderate when using either iDose in CTp (0.1-0.5) or SAFIRE in CTs (0.1-0.6). SAFIRE-2 in CTs showed a closer match to the reference body protocol when compared to iDose-3 in CTp. In the brain protocol, iDose-3 in CTp could be matched to the low to moderate level of SAFIRE in CTs. The AUC of d' was highest when using IMR in CTp with lower CTDIvol, and SAFIRE in CTs performed better than iDose in CTp CONCLUSION: It is possible to use target-based IQ metrics to evaluate the performance of the system and operations across various scanners in a phantom. This can serve as an initial reference to convert clinical scanned protocols from one CT simulation scanner to another.

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.

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.

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.

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.

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.

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.

Image quality and absorbed dose comparison of single- and dual-source cone-beam computed tomography.

PURPOSE: Dual-source cone-beam computed tomography (DCBCT) is currently available in the Vero4DRT image-guided radiotherapy system. We evaluated the image quality and absorbed dose for DCBCT and compared the values with those for single-source CBCT (SCBCT). METHODS: Image uniformity, Hounsfield unit (HU) linearity, image contrast, and spatial resolution were evaluated using a Catphan phantom. The rotation angle for acquiring SCBCT and DCBCT images is 215° and 115°, respectively. The image uniformity was calculated using measurements obtained at the center and four peripheral positions. The HUs of seven materials inserted into the phantom were measured to evaluate HU linearity and image contrast. The Catphan phantom was scanned with a conventional CT scanner to measure the reference HU for each material. The spatial resolution was calculated using high-resolution pattern modules. Image quality was analyzed using ImageJ software ver. 1.49. The absorbed dose was measured using a 0.6-cm3 ionization chamber with a 16-cm-diameter cylindrical phantom, at the center and four peripheral positions of the phantom, and calculated using weighted cone-beam CT dose index (CBCTDIw ). RESULTS: Compared with that of SCBCT, the image uniformity of DCBCT was slightly reduced. A strong linear correlation existed between the measured HU for DCBCT and the reference HU, although the linear regression slope was different from that of the reference HU. DCBCT had poorer image contrast than did SCBCT, particularly with a high-contrast material. There was no significant difference between the spatial resolutions of SCBCT and DCBCT. The absorbed dose for DCBCT was higher than that for SCBCT, because in DCBCT, the two x-ray projections overlap between 45° and 70°. CONCLUSIONS: We found that the image quality was poorer and the absorbed dose was higher for DCBCT than for SCBCT in the Vero4DRT.

[Application of Quality Control Circle Activity in CT Quality Control Management].

To explore the effect and experience of quality control circle(QCC) in quality control testing for CT scanners, the quality control circle group was set up to determine the theme of quality control circle, and the causes of the failure of the quality control testing for CT scanners were analyzed, then the corresponding corrective measures were formulated and carried out. After the activity of the quality control circle, the qualified rate of CT quality control testing in the second level 2nd Class of public hospitals and private hospitals in Shanghai increased from 40.6% to 86.1%. By conducting quality control circle activities, we found the problems existed in the quality control testing of CT scanners, and put forward many corresponding corrective measures and solutions which finally improved the qualified rate of CT quality control testing.

100 days with scans of the same Catphan phantom on the same CT scanner.

Quality control (QC) of CT scanners is important to evaluate image quality and radiation dose. Different QC phantoms for testing image quality parameters on CT are commercially available, and Catphan phantoms are widely used for this purpose. More data from measured image quality parameters on CT are necessary to assess test methods, tolerance levels, and test frequencies. The aim of this study was to evaluate the stability of essential image quality parameters for axial and helical scans on one CT scanner over time. A Catphan 600 phantom was scanned on a Philips Ingenuity CT scanner for 100 days over a period of 6 months. At each day of testing, one helical scan covering the entire phantom and four axial scans covering four different modules in the phantom were performed. All images were uploaded into Image Owl for automatic analysis of CT numbers, modular transfer function (MTF), low-contrast resolution, noise, and uniformity. In general, the different image quality parameters for both scan techniques were stable over time compared to given tolerance levels. Average measured CT numbers differed between axial and helical scans, while MTF was almost identical for helical and axial scans. Axial scans had better low-contrast resolution and less noise than helical scans. The uniformity was relatively similar for axial and helical scans. Most standard deviations of measured values were larger for helical scans compared to axial scans. Test results in this study were stable over time for both scan techniques, but further studies on different CT scanners are required to confirm that this also holds true for other systems.

Coronary CT Angiography: Variability of CT Scanners and Readers in Measurement of Plaque Volume.

Purpose To determine reader and computed tomography (CT) scan variability for measurement of coronary plaque volume. Materials and Methods This HIPAA-compliant study followed Standards for Reporting of Diagnostic Accuracy guidelines. Baseline coronary CT angiography was performed in 40 prospectively enrolled subjects (mean age, 67 years ± 6 [standard deviation]) with asymptomatic hyperlipidemia by using a 320-detector row scanner (Aquilion One Vision; Toshiba, Otawara, Japan). Twenty of these subjects underwent coronary CT angiography repeated on a separate day with the same CT scanner (Toshiba, group 1); 20 subjects underwent repeat CT performed with a different CT scanner (Somatom Force; Siemens, Forchheim, Germany [group 2]). Intraclass correlation coefficients (ICCs) and Bland-Altman analysis were used to assess interreader, intrareader, and interstudy reproducibility. Results Baseline and repeat coronary CT angiography scans were acquired within 19 days ± 6. Interreader and intrareader agreement rates were high for total, calcified, and noncalcified plaques for both CT scanners (all ICCs ≥ 0.96) without bias. Scanner variability was ±18.4% (coefficient of variation) with same-vendor follow-up. However, scanner variability increased to ±29.9% with different-vendor follow-up. The sample size to detect a 5% change in noncalcified plaque volume with 90% power and an α error of .05 was 286 subjects for same-CT scanner follow-up and 753 subjects with different-vendor follow-up. Conclusion State-of-the-art coronary CT angiography with same-vendor follow-up has good scan-rescan reproducibility, suggesting a role of coronary CT angiography in monitoring coronary artery plaque response to therapy. Differences between coronary CT angiography vendors resulted in lower scan-rescan reproducibility. © RSNA, 2016 Online supplemental material is available for this article.

Evaluation of commercial extension plates for the ACR CT accreditation phantom.

The American College of Radiology (ACR) Computed Tomography (CT) Accreditation Program requires submission of phantom scans acquired with the ACR accreditation phantom. There is a known issue with some wide-beam scanners in which the Hounsfield unit (HU) value of water may be correct when using the scanner manufacturer's phantom, but will be out of range in some scan modes when scanning the accreditation phantom. The phantom manufacturer has developed a product known as Extension Plates to eliminate the water HU value issue. The purpose of this technical note is to evaluate the effectiveness of the Extension Plates in alleviating the water HU issue. The ACR phantom was scanned on nine different CT scanners representing four CT manufacturers at eight different facilities. Scanner models included 16- and 64-channel geometries from each manufacturer. All scanners passed routine daily water HU testing per the manufacturer's instructions. The accreditation phantom was scanned in helical and axial modes both with and without the Extension Plates present. Regions of interest were placed on the linearity test objects as well as the water HU test object in Module 1 of the phantom. Mean values were recorded and compared with the acceptable ranges specified by the ACR accreditation phantom testing instructions. Water HU values failed for one scanner model when scanned in helical mode using the widest collimation available and the Extension Plates were not present. All other scanner models passed the water HU linearity test with or without the Extension Plates in both axial and helical scan modes. Three of the four manufacturers tested failed the linearity test for different materials. The presence of the Extension Plates only affected the HU measurement for the water test object.

Method and phantom to study combined effects of in-plane (x,y) and z-axis resolution for 3D CT imaging.

Increasingly, the advent of multislice CT scanners, volume CT scanners, and total body spiral acquisition modes has led to the use of Multi Planar Reconstruction and 3D datasets. In considering 3D resolution properties of a CT system it is important to note that both the in-plane (x,y) and z-axis (slice thickness) influence the visual-ization and detection of objects within the scanned volume. This study investigates ways to consider both the in-plane resolution and the z-axis resolution in a single phantom wherein analytic or visualized analysis can yield information on these combined effects. A new phantom called the "Wave Phantom" is developed that can be used to sample the 3D resolution properties of a CT image, including in-plane (x,y) and z-axis information. The key development in this Wave Phantom is the incorporation of a z-axis aspect of a more traditional step (bar) resolution gauge phantom. The phantom can be examined visually wherein a cutoff level may be seen; and/or the analytic analysis of the various characteristics of the waveform profile by including amplitude, frequency, and slope (rate of climb) of the peaks, can be extracted from the Wave Pattern using mathematical analysis such as the Fourier transform. The combined effect of changes in in-plane resolution and z-axis (thickness), are shown, as well as the effect of changes in either in-plane resolu-tion, or z-axis thickness. Examples of visual images of the Wave pattern as well as the analytic characteristics of the various harmonics of a periodic Wave pattern resulting from changes in resolution filter and/or slice thickness, and position in the field of view are shown. The Wave Phantom offers a promising way to investigate 3D resolution results from combined effect of in-plane (x-y) and z-axis resolution as contrasted to the use of simple 2D resolution gauges that need to be used with separate measures of z-axis dependency, such as angled ramps. It offers both a visual pattern as well as a pattern amenable to analytic analysis using Fourier Transform methods, and is believed to offer an image quality test closer to the diagnostic task where the 2D image has the hidden third (z) axis effects.

A routine quality assurance test for CT automatic exposure control systems.

The study purpose was to develop and validate a quality assurance test for CT automatic exposure control (AEC) systems based on a set of nested polymethylmethacrylate CTDI phantoms. The test phantom was created by offsetting the 16 cm head phantom within the 32 cm body annulus, thus creating a three part phantom. This was scanned at all acceptance, routine, and some nonroutine quality assurance visits over a period of 45 months, resulting in 115 separate AEC tests on scanners from four manufacturers. For each scan the longitudinal mA modulation pattern was generated and measurements of image noise were made in two annular regions of interest. The scanner displayed CTDIvol and DLP were also recorded. The impact of a range of AEC configurations on dose and image quality were assessed at acceptance testing. For systems that were tested more than once, the percentage of CTDIvol values exceeding 5%, 10%, and 15% deviation from baseline was 23.4%, 12.6%, and 8.1% respectively. Similarly, for the image noise data, deviations greater than 2%, 5%, and 10% from baseline were 26.5%, 5.9%, and 2%, respectively. The majority of CTDIvol and noise deviations greater than 15% and 5%, respectively, could be explained by incorrect phantom setup or protocol selection. Barring these results, CTDIvol deviations of greater than 15% from baseline were found in 0.9% of tests and noise deviations greater than 5% from baseline were found in 1% of tests. The phantom was shown to be sensitive to changes in AEC setup, including the use of 3D, longitudinal or rotational tube current modulation. This test methodology allows for continuing performance assessment of CT AEC systems, and we recommend that this test should become part of routine CT quality assurance programs. Tolerances of ± 15% for CTDIvol and ± 5% for image noise relative to baseline values should be used.

CT radiation profile width measurement using CR imaging plate raw data.

This technical note demonstrates computed tomography (CT) radiation profile measurement using computed radiography (CR) imaging plate raw data showing it is possible to perform the CT collimation width measurement using a single scan without saturating the imaging plate. Previously described methods require careful adjustments to the CR reader settings in order to avoid signal clipping in the CR processed image. CT radiation profile measurements were taken as part of routine quality control on 14 CT scanners from four vendors. CR cassettes were placed on the CT scanner bed, raised to isocenter, and leveled. Axial scans were taken at all available collimations, advancing the cassette for each scan. The CR plates were processed and raw CR data were analyzed using MATLAB scripts to measure collimation widths. The raw data approach was compared with previously established methodology. The quality control analysis scripts are released as open source using creative commons licensing. A log-linear relationship was found between raw pixel value and air kerma, and raw data collimation width measurements were in agreement with CR-processed, bit-reduced data, using previously described methodology. The raw data approach, with intrinsically wider dynamic range, allows improved measurement flexibility and precision. As a result, we demonstrate a methodology for CT collimation width measurements using a single CT scan and without the need for CR scanning parameter adjustments which is more convenient for routine quality control work.

Three-dimensional evaluation of the repeatability of scanned conventional impressions of prepared teeth generated with white- and blue-light scanners.

STATEMENT OF PROBLEM: Digital scanning is increasingly used in prosthodontics. Three-dimensional (3D) evaluations that compare the repeatability of the blue-light scanner with that of the white-light scanner are required. PURPOSE: The purpose of this in vitro study was to evaluate the repeatability of conventional impressions of abutment teeth digitized with white- and blue-light scanners and compare the findings for different types of abutment teeth. MATERIAL AND METHODS: Impressions of the canine, premolar, and molar abutment teeth were made and repeatedly scanned with each scanner type to obtain 5 sets of 3D data for each tooth. Point clouds were compared, and error sizes per tooth and scanner type were measured (n=10). One-way ANOVA with Tukey honest significant differences multiple comparison and independent t tests were performed to evaluate repeatability (α=.05). RESULTS: Repeatability (mean ±SD) of the white- and blue-light scanners for canine, premolar, and molar teeth was statistically significant (means: P=.001, P<.001, P<.001; ±SD: P<.001, P<.001, P=.003). Means of discrepancies with the white-light scanner (P<.001) were 5.8 µm for the canine, 5.9 µm for the premolar, and 8.6 µm for the molar teeth and 4.4 µm, 2.9 µm, and 3.2 µm, respectively, with the blue-light scanner (P<.001). Corresponding SDs of discrepancies with the white-light scanner (P<.001) were 15.9 µm for the canine, 23.2 µm for the premolar, and 14.6 µm for the molar teeth and 9.8 µm, 10.6 µm, and 11.2 µm, respectively, with the blue-light scanner (P=.73). CONCLUSIONS: On evaluation of the digitized abutment tooth impressions, the blue-light scanner exhibited greater repeatability than the white-light scanner.

Preparing for the costs of XR-29 a new standard for CT radiation dose monitoring.

A new standard for computed tomography (CT) scanners, established by the Medical Imaging and Technology Alliance, is aimed at ensuring CT studies are performed on safe equipment that delivers high-quality images at the lowest possible radiation dose to patients. Starting in January, the Centers for Medicare & Medicaid Services will implement a new payment incentive, authorized by Congress in 2014, aimed at promoting healthcare providers' adoption of the new standard for all outpatient CT studies. Organizations that perform CT studies on an outpatient basis will need to develop a process to comply with the standards or face a reduction in payment per study.

Performance evaluation of computed tomography scanners in Indonesia: recommendation from a nation-wide study.

In this study, an evaluation of the compliance test data from 684 computed tomography (CT)-scanners in Indonesia for the 2019-22 test period was carried out. The study was aimed to describe the performance profile of CT-scanners in Indonesia and evaluate the testing protocol. A total of 87.8% of the CT-scanners unconditionally passed the tests, 8.8% passed the tests with conditions and 3.4% failed the tests. Of the devices conditionally passed the tests, the top two causes were water CT number accuracy (45.2%) and laser position accuracy (41.9%). Meanwhile, 75.0% of the failed devices were due to failing to meet the patient dose test criteria. The failure of the test for the water CT number accuracy parameter was caused by variations in the type of phantom used in the test, where several types of phantoms did not use water as material of the homogeneity module. Failures in laser position accuracy test were caused by the passing criteria that adjust to the minimum slice thickness, so that modern CT-scanner with small detector sizes and collimations tend not to pass. On the other hand, the failure on dose aspects was due to the frequent unavailability of baseline values for comparison. Of these top three failure causes, two of them, namely the CT number and dose test parameters, have been accommodated in the latest regulation (BAPETEN Regulation No. 2/2022) with a change in the evaluation method, while for the laser position accuracy test it is recommended to alter the passing criteria to an absolute value, namely 1 mm.

A proposed protocol for acceptance and constancy control of computed tomography systems: a Nordic Association for Clinical Physics (NACP) work group report.

BACKGROUND: Quality assurance (QA) of computed tomography (CT) systems is one of the routine tasks for medical physicists in the Nordic countries. However, standardized QA protocols do not yet exist and the QA methods, as well as the applied tolerance levels, vary in scope and extent at different hospitals. PURPOSE: To propose a standardized protocol for acceptance and constancy testing of CT scanners in the Nordic Region. MATERIAL AND METHODS: Following a Nordic Association for Clinical Physics (NACP) initiative, a group of medical physicists, with representatives from four Nordic countries, was formed. Based on international literature and practical experience within the group, a comprehensive standardized test protocol was developed. RESULTS: The proposed protocol includes tests related to the mechanical functionality, X-ray tube, detector, and image quality for CT scanners. For each test, recommendations regarding the purpose, equipment needed, an outline of the test method, the measured parameter, tolerance levels, and the testing frequency are stated. In addition, a number of optional tests are briefly discussed that may provide further information about the CT system. CONCLUSION: Based on international references and medical physicists' practical experiences, a comprehensive QA protocol for CT systems is proposed, including both acceptance and constancy tests. The protocol may serve as a reference for medical physicists in the Nordic countries.