R2* relaxometry analysis for mapping of white matter alteration in Parkinson's disease with mild cognitive impairment.

BACKGROUND: R2* relaxometry analysis combined with quantitative susceptibility mapping (QSM), which has high sensitivity to iron deposition, can distinguish microstructural changes of the white matter (WM) and iron deposition, thereby providing a sensitive and biologically specific measure of the WM owing to the changes in myelin and its surrounding environment. This study aimed to explore the microstructural WM alterations associated with cognitive impairment in patients with Parkinson's disease (PD) using R2* relaxometry analysis combined with QSM. MATERIALS AND METHODS: We enrolled 24 patients with PD and mild cognitive impairment (PD-MCI), 22 patients with PD and normal cognition (PD-CN), and 19 age- and sex-matched healthy controls (HC). All participants underwent Montreal Cognitive Assessment (MoCA) and brain magnetic resonance imaging, including structural three-dimensional T1-weighted images and multiple spoiled gradient echo sequence (mGRE). The R2* and susceptibility maps were estimated from the multiple magnitude images of mGRE. The susceptibility maps were used for verifying iron deposition in the WM. The voxel-based R2* of the entire WM and its correlation with cognitive performance were analyzed. RESULTS: In the voxel-based group comparisons, the R2* in the PD-MCI group was lower in some WM regions, including the corpus callosum, than R2* in the PD-CN and HC groups. The mean susceptibility values in almost all brain regions were negative and close-to-zero values, indicating no detectable paramagnetic iron deposition in the WM of all subjects. There was a significant positive correlation between R2* and MoCA in some regions of the WM, mainly the corpus callosum and left hemisphere. CONCLUSION: R2* relaxometry analysis for WM microstructural changes provided further biologic insights on demyelination and changes in the surrounding environment, supported by the QSM results demonstrating no iron existence. This analysis highlighted the potential for the early evaluation of cognitive decline in patients with PD.

Delineation of prostatic calcification using quantitative susceptibility mapping: Spatial accuracy for magnetic resonance-only radiotherapy planning.

To investigate the spatial accuracy of delineating prostatic calcifications by quantitative susceptibility mapping (QSM) in comparison with computed tomography (CT), we conducted phantom and human studies. Five differently-sized spherical hydroxyapatites mimicking prostatic calcification (pseudo-calcification) were arranged in the order of their sizes at the center of a plastic container filled with gelatin. This calcification phantom underwent magnetic resonance (MR) imaging, including the multiple spoiled gradient-echo sequences (SPGR) for the QSM and CT as a reference. The volume of each pseudo-calcification and center-to-center distance between the pseudo-calcifications delineated by QSM and CT were measured. In the human study, eight patients with prostate cancer who underwent radiation therapy and had some prostatic calcifications were included. The patients underwent CT and SPGR and modified DIXON sequence for MR-only simulation. The hybrid QSM processing combined with the complex signals in the SPGR and water and fat fraction maps estimated from the modified DIXON sequence were used to reconstruct the pelvic susceptibility map in humans. The threshold of CT numbers was set at 130 HU, while the QSM images were manually segmented in the calcification phantom and human studies. In the phantom study, there was an excellent agreement in the pseudo-calcification volumes between QSM and CT (y = 1.02x - 7.38, R2  = 0.99). The signal profiles had similar trends in CT and QSM. The center-to-center distances between the pseudo-calcifications in the phantom were also identical in QSM and CT. The calcification volumes were almost identical between the QSM and CT in the human study (y = 0.95x - 9.32, R2  = 1.00). QSM can offer geometric and volumetric accuracies to delineate prostatic calcifications, similar to CT. The prostatic calcification delineated by QSM may facilitate image-guided radiotherapy in the MR-only simulation workflow.

[Examination of the Quality Control Items for Digital Breast Tomosynthesis System in Japan].

Mammography equipment attached to the digital breast tomosynthesis (DBT) system is widespread in Japan. However, there are no guidelines for quality control methods for DBT in Japan. Therefore, it is necessary to rapidly establish a performance evaluation procedure and a quality control procedure for DBT. In this study, we conducted basic experiments using DBTs of five companies (Canon Medical, Fujifilm Medical, GE Healthcare, Hologic, Siemens) already sold in Japan and examined feasible common items. We aimed to establish a quality control method for DBT in Japan. The measurement was performed based on the European Reference Organisation for Quality Assured Breast Screening and Diagnostic Services (EUREF) breast tomosynthesis quality control protocol, version 1.03. In this study, we tried to measure 18 items in DBT. We examined whether the 18 items could be measured using each device; it is not an evaluation of device performance based on the measured values. There were some management items that were difficult to implement due to the specifications of DBT, such as devices that required pressure on DBT operation, problems due to the shape of bucky, and devices that did not have stationary mode. There were also problems with measurement data; for example, devices could not retrieve projection data and reconstruction data. This study clarified points to be considered for establishing common quality control items. In the future, we will carefully refer to the recently published IEC 61223-3-6, consider international harmonization, and establish DBT guidelines customized for the Japanese market.

[Relationship between Radiation Quality and Image Quality in Digital Chest Radiography: Validation Study Using Human Soft Tissue-equivalent Phantom].

PURPOSE: To evaluate image quality for chest radiography at different radiation qualities, using phantoms with scatter fractions similar to those of lungs. METHODS: Two base phantoms with 10 and 4 cm thicknesses, respectively, made of a soft tissue-equivalent material, were used to mimic the X-ray attenuation of the human lung. Two plates with soft tissue- and bone-equivalent materials, respectively, were placed on the base phantom as contrast objects. The image data were obtained with the same entrance surface dose in each radiation quality. Six radiation qualities generated using 120 and 90 kV, and additional copper filters with thicknesses 0, 0.1, and 0.2 mm were selected. The signal-difference-to-noise ratio (SdNR) and a contrast ratio of the soft tissue to the bone were measured for the six radiation qualities. RESULTS: The thicker the additional filter, the better the SdNR at both tube voltages. The SdNR values were not significantly different between 120 and 90 kV for the same filter thickness. The contrast ratio was higher at 120 than at 90 kV by approximately 8%. CONCLUSIONS: Because of the advantage of the contrast ratio and the highest SdNR, the radiation quality with 120 kV and 0.2-mm copper filtration was the best. It was indicated that the conventional tube voltage of 120 kV remains to be better than the lower tube voltage of 90 kV.

Decreasing iron susceptibility with temperature in quantitative susceptibility mapping: A phantom study.

To clarify the temperature dependence of susceptibility estimated by quantitative susceptibility mapping (QSM) analysis, we investigated the relationship between temperature and susceptibility using a cylinder phantom with varying temperatures. Six solutions with various concentrations of superparamagnetic iron oxide (SPIO) nanoparticles were employed. These tubes were placed in a cylinder phantom and surrounded with water. The temperature of the circulated water was adjusted to change the temperature in the cylinder phantom from 25.8 °C to 42.5 °C. The cylinder phantom was scanned via a three-dimensional multiple spoiled gradient-echo sequence for R2* and QSM analyses with varying temperatures. The relationships between temperature, susceptibility, and R2* values were determined. Moreover, the temperature coefficients of susceptibility (χ-Tc) and (R2*-Tc) were calculated at each concentration and the linearities in these indices against each SPIO concentration were validated. Significant inverse correlations were found between temperature, susceptibility, and R2* values at each SPIO concentration due to the decrease in paramagnetic iron susceptibility that occurred with increasing temperature based on Curie's law. Moreover, although there were significant correlations between the susceptibility and R2* values at any temperature, the slopes of the regression lines grew in height with greater temperatures. The percentage of difference per Celsius degree in susceptibility in any SPIO concentration was lower than the corresponding finding among the R2* results. There were strong linearities between the SPIO concentration, χ-Tc (r = -0.994; p < 0.001), and R2*-Tc (r = -0.998; p < 0.001). The χ-Tc and R2*-Tc outcomes in a particular voxel varied considerably with the iron contents. Although there was an inverse correlation noted between temperature and susceptibility, the susceptibility analysis showed smaller temperature dependence relative to the R2* analysis. QSM analysis might be a more suitable option for magnetic resonance-based iron quantification in comparison with R2* relaxometry.

Signal-to-noise ratio improvements using anti-scatter grids with different object thicknesses and tube voltages.

PURPOSE: The appropriate object thickness to start using anti-scatter grids (grids) has not sufficiently investigated in previous studies, and thus we rigorously investigated the effectiveness of two generally used grids with grid ratios of 6 and 10 (G6 and G10) for different 50-200 mm thicknesses at tube voltages of 60-100 kV. METHODS: Acrylic phantoms with 30 × 30 cm2 and different thicknesses were used to measure the signal-to-noise ratio improvement factors (SIFs) of grids. To evaluate the infants' conditions, field sizes of 225, 400, and 625 cm2 were also evaluated at 60-80 kV. In addition, the signal difference-to-noise ratio (SDNR) was used to evaluate tube voltage dependencies of grids for each thickness. RESULTS: SIF values exceeded 1.0 for ≥70 mm thicknesses and mostly exceeded 1.07 for the 100 mm thickness with 400 cm2 field size corresponding to a 1-year-old infant abdomen. The estimated dose reduction capabilities for a 1-year-old infant were approximately 15% using G10 at 70 and 80 kV. The tube voltage dependencies for grid use was almost not prominent for all conditions tested, except for some conditions that are not clinically realistic. CONCLUSIONS: G6 and G10 can improve SNR for  ≥100 mm thickness. The results from this work demonstrate approximately 15% dose reduction or image quality improvements at the same dose level for the use of G6 and G10 grids for 100 mm thickness, traditionally excluded from the recommended grid use conditions.

Simultaneous voxel-based magnetic susceptibility and morphometry analysis using magnetization-prepared spoiled turbo multiple gradient echo.

This study aimed to develop and test a simultaneous acquisition and analysis pipeline for voxel-based magnetic susceptibility and morphometry (VBMSM) on a single dataset using young volunteers, elderly healthy volunteers, and an Alzheimer's disease (AD) group. 3D T1 -weighted and multi-echo phase images for VBM and quantitative susceptibility mapping (QSM) were simultaneously acquired using a magnetization-prepared spoiled turbo multiple gradient echo sequence with inversion pulse for QSM (MP-QSM). The magnitude image was split into gray matter (GM) and white matter (WM) and was spatially normalized. The susceptibility map was reconstructed from the phase images. The segmented image and susceptibility map were compared with those obtained from conventional multiple spoiled gradient echo (mGRE) and MP-spoiled gradient echo (MP-GRE) in healthy volunteers to validate the availability of MP-QSM by numerical measurements. To assess the feasibility of the VBMSM analysis pipeline, voxel-based comparisons of susceptibility and morphometry in MP-QSM were conducted in volunteers with a bimodal age distribution, and in elderly volunteers and the AD group, using spatially normalized GM and WM volume images and a susceptibility map. GM/WM contrasts in MP-QSM, MP-GRE, and mGRE were 0.14 ± 0.011, 0.17 ± 0.015, and 0.045 ± 0.010, respectively. Segmented GM and WM volumes in the MP-QSM closely coincided with those in the MP-GRE. Region of interest analyses indicated that the mean susceptibility values in MP-QSM were completely in agreement with those in mGRE. In an evaluation of the aging effect, a significant increase and decrease in susceptibility and volume were found by VBMSM in deep GM and WM, respectively. Between the elderly volunteers and the AD group, the characteristic susceptibility and volume changes in GM and WM were observed. The proposed MP-QSM sequence makes it possible to acquire acceptable-quality images for simultaneous analysis and determine brain atrophy and susceptibility distribution without image registration by using voxel-based analyses.

Improvement of Signal Inhomogeneity Induced by Radio-frequency Transmit-related Phase Error for Single-step Quantitative Susceptibility Mapping Reconstruction.

To mitigate the susceptibility inhomogeneity induced by radio-frequency transmit phase error through the whole brain in quantitative susceptibility mapping (QSM) using single-echo gradient echo sequence, we developed a novel single-step QSM reconstruction algorithm and compared it with a previous algorithm in five healthy volunteers. The proposed algorithm had effectively suppressed the susceptibility inhomogeneity through the whole brain and achieved acceptable quality, similar to that of the susceptibility map calculated from a multi-echo gradient echo sequence.

Geometric discrepancy of image-guided radiation therapy in patients with prostate cancer without implanted fiducial markers using a commercial pseudo-CT generation method.

MR-only simulations provide pseudo-CT images which are segmented into 5 kinds of tissues from DIXON-based images. However, it is difficult to register pseudo-CT images to cone-beam CT (CBCT) images collected for image-guided radiation therapy (IGRT), because of the lack of contrasts among tissues. We validated gaps of IGRT between pseudo-CT or planning CT and CBCT for patients without implanted markers. We also propose calcification-assisted registration for MR-only simulation. We conducted retrospective analyses to verify the registration accuracy in 15 patients who underwent volumetric modulated arc therapy (VMAT) for prostate cancer. They underwent planning CT and pseudo-CT. Pseudo-CT images after deformable image registration (DIR) to planning CT images were rendered automatic pelvic bone matching to CBCT images. Patient positions on the pseudo-CT images after DIR were shifted on the basis of tissues around the prostate. We compared registration gaps between the images of planning CT and pseudo-CT with DIR, assuming that the tissue-based matching between the planning CT and CBCT was the gold standard. To the pseudo-CT images with DIR, calcifications detected on planning CT were added. We validated IGRT accuracy for a calcification-assisted registration. The absolute registration errors of the pseudo-CT, in comparison with the planning CT, were 0.34 ± 0.50 (lateral), 1.3 ± 1.3 (longitudinal), and 1.1 ± 1.0 mm (vertical). The absolute registration errors of the pseudo-CT with calcification contouring, in comparison with the planning CT, were 0.41 ± 1.0 (lateral), 0.87 ± 0.92 (longitudinal), and 0.74 ± 0.64 mm (vertical). Reduced absolute registration errors were observed in the proposed approach in the longitudinal (P < 0.01) and vertical (P < 0.01) dimensions when using calcification-assisted registration. The tissue-based registration using the MR-only simulation was not sufficient for use in patients with prostate cancer without implanted markers. The calcification-assisted registration might help to improve IGRT accuracy using MRI alone.

Background field removal technique based on non-regularized variable kernels sophisticated harmonic artifact reduction for phase data for quantitative susceptibility mapping.

PURPOSE: We developed a non-regularized, variable kernel, sophisticated harmonic artifact reduction for phase data (NR-VSHARP) method to accurately estimate local tissue fields without regularization for quantitative susceptibility mapping (QSM). We then used a digital brain phantom to evaluate the accuracy of the NR-VSHARP method, and compared it with the VSHARP and iterative spherical mean value (iSMV) methods through in vivo human brain experiments. MATERIALS AND METHODS: Our proposed NR-VSHARP method, which uses variable spherical mean value (SMV) kernels, minimizes L2 norms only within the volume of interest to reduce phase errors and save cortical information without regularization. In a numerical phantom study, relative local field and susceptibility map errors were determined using NR-VSHARP, VSHARP, and iSMV. Additionally, various background field elimination methods were used to image the human brain. RESULTS: In a numerical phantom study, the use of NR-VSHARP considerably reduced the relative local field and susceptibility map errors throughout a digital whole brain phantom, compared with VSHARP and iSMV. In the in vivo experiment, the NR-VSHARP-estimated local field could sufficiently achieve minimal boundary losses and phase error suppression throughout the brain. Moreover, the susceptibility map generated using NR-VSHARP minimized the occurrence of streaking artifacts caused by insufficient background field removal. CONCLUSION: Our proposed NR-VSHARP method yields minimal boundary losses and highly precise phase data. Our results suggest that this technique may facilitate high-quality QSM.

Quantitative susceptibility mapping using principles of echo shifting with a train of observations sequence on 1.5T MRI.

PURPOSE: To evaluate the accuracy of susceptibility estimated from the principles of echo shifting with a train of observations (PRESTO) sequence using a 1.5T MRI system, we conducted experiments on the human brain using the PRESTO sequence and compared our results with the susceptibility obtained from spoiled gradient-recalled echo (GRE) sequence with flow compensation using quantitative susceptibility mapping (QSM) reconstruction. MATERIALS AND METHODS: Experiments on the human brain were conducted on 12 healthy volunteers (27±4years) using PRESTO and spoiled GRE sequences on a 1.5T scanner. The PRESTO sequence is an echo-shifted gradient echo sequence that allows high susceptibility sensitivity and rapid acquisition because of TE>TR compared with the spoiled GRE sequence. QSM analysis was performed on the obtained phase images using the iLSQR method. Estimated susceptibility maps were used for region of interest analyses and estimation of line profiles through iron-rich tissue and major vessels. RESULTS: Our results demonstrated that susceptibility maps were accurately estimated, without error, by QSM analysis of PRESTO and spoiled GRE sequences. Acquisition time in the PRESTO sequence was reduced by 43% compared with that in the spoiled GRE sequence. Differences did exist between susceptibility maps in PRESTO and spoiled GRE sequences for visualization and quantitative values of major blood vessels and the areas around them CONCLUSION: The PRESTO sequence enables correct estimation of tissue susceptibility with rapid acquisition and may be useful for QSM analysis of clinical use of 1.5T scanners.

Background field removal technique using regularization enabled sophisticated harmonic artifact reduction for phase data with varying kernel sizes.

An effective background field removal technique is desired for more accurate quantitative susceptibility mapping (QSM) prior to dipole inversion. The aim of this study was to evaluate the accuracy of regularization enabled sophisticated harmonic artifact reduction for phase data with varying spherical kernel sizes (REV-SHARP) method using a three-dimensional head phantom and human brain data. The proposed REV-SHARP method used the spherical mean value operation and Tikhonov regularization in the deconvolution process, with varying 2-14mm kernel sizes. The kernel sizes were gradually reduced, similar to the SHARP with varying spherical kernel (VSHARP) method. We determined the relative errors and relationships between the true local field and estimated local field in REV-SHARP, VSHARP, projection onto dipole fields (PDF), and regularization enabled SHARP (RESHARP). Human experiment was also conducted using REV-SHARP, VSHARP, PDF, and RESHARP. The relative errors in the numerical phantom study were 0.386, 0.448, 0.838, and 0.452 for REV-SHARP, VSHARP, PDF, and RESHARP. REV-SHARP result exhibited the highest correlation between the true local field and estimated local field. The linear regression slopes were 1.005, 1.124, 0.988, and 0.536 for REV-SHARP, VSHARP, PDF, and RESHARP in regions of interest on the three-dimensional head phantom. In human experiments, no obvious errors due to artifacts were present in REV-SHARP. The proposed REV-SHARP is a new method combined with variable spherical kernel size and Tikhonov regularization. This technique might make it possible to be more accurate backgroud field removal and help to achive better accuracy of QSM.

Application of a variable filter for presampled modulation transfer function analysis with the edge method.

We devised a new noise filtering method to reduce the noise in the line spread function (LSF) for presampled modulation transfer function (MTF) analysis with the edge method. A filter was designed to reduce noise effectively using a position-dependent filter controlled by the boundary frequency b for low-pass filtering, which is calculated by 1/2d (d: distance from the LSF center). In this filtering process, strong filters with very low b can be applied to regions distant from the LSF center, and the region near the LSF center can be maintained simultaneously by a correspondingly high b. Presampled MTF accuracies derived by use of the proposed method and an edge spread function (ESF)-fitting method were compared by use of simulated ESFs with and without noise, resembling a computed radiography (CR) and an indirect-type flat panel detector (FPD), respectively. In addition, the edge images of clinical CR, indirect-type FPD, and direct-type FPD systems were examined. For a simulated ESF without noise, the calculated MTFs of the variable filtering method agreed precisely with the true MTFs. The excellent noise-reduction ability of the variable filter was demonstrated for all simulated noisy ESFs and those of three clinical systems. Although the ESF-fitting method provided excellent noise reduction only for the CR-like simulated ESF with noise, its noise elimination performance could not be demonstrated due to the lesser robustness of the fitting.

Investigation of measurement accuracy of factors used for detective quantum efficiency measurement in digital radiography.

In the detective quantum efficiency (DQE) evaluation of detectors for digital radiography (DR) systems, physical image quality indices such as modulation transfer function (MTF) and normalized noise power spectrum (NNPS) need to be accurately measured to obtain highly accurate DQE evaluations. However, there is a risk of errors in these measurements. In this study, we focused on error factors that should be considered in measurements using clinical DR systems. We compared the incident photon numbers indicated in IEC 62220-1 with those estimated using a Monte Carlo simulation based on X-ray energy spectra measured employing four DR systems. For NNPS, influences of X-ray intensity non-uniformity, tube voltage and aluminum purity were investigated. The effects of geometric magnifications on MTF accuracy were also examined using a tungsten edge plate at distances of 50, 100 and 150 mm from the detector surface at a source-image receptor distance of 2000 mm. The photon numbers in IEC 62220-1 coincided with our estimates of values, with error rates below 2.5%. Tube voltage errors of approximately ±5 kV caused NNPS errors of within 1.0%. The X-ray intensity non-uniformity caused NNPS errors of up to 2.0% at the anode side. Aluminum purity did not affect the measurement accuracy. The maximum MTF reductions caused by geometric magnifications were 3.67% for 1.0-mm X-ray focus and 1.83% for 0.6-mm X-ray focus.

Examination of the optimal temporal resolution required for computed tomography coronary angiography.

Sub-second multidetector-row computed tomography systems provide great potential for the further improvement of CT coronary angiography (CTCA). However, because the temporal resolution (TR) of such CT systems is insufficient, blurring and artifacts produced by fast cardiac motion remain as unresolved issues. Previous TR investigations of CTCA were based on the retrospective electrocardiogram-gated multisegment reconstruction technique. However, the results obtained may not necessarily be correct because the TR of multisegment reconstruction may not be substantial due to the insufficient periodicity of cardiac motion. The optimal TR required for better CTCA images was evaluated with use of a dual-source CT system, which has various substantial TR modes (83, 125, and 165 ms). CTCA images of 147 patients with heart rates (HRs) ranging from 36 to 117 beats/minute (bpm) were evaluated visually on a 4-point scale. Our results revealed not only that the 165-ms TR is sufficient for low HRs (≤60 bpm), but also that the 83- and 125-ms TRs are unnecessary for such HRs. The image quality with the 125-ms TR mode was acceptable for the left anterior descending artery, left circumflex artery, and right coronary artery at low to intermediate HRs (≤70 bpm). At high HRs (>70 bpm), the 83-ms TR mode resulted in an excellent image quality for all cases except those with very rapid RCA motion. Adequate TRs for a wide range of heart rates (52-106 bpm) are thus clarified.

[Physical image properties of digital radiography systems in low dose range].

We measured physical image properties of a flat panel detector (FPD) system and a computed radiography (CR) system, targeting to a low dose range (reference dose: 2.58×10(-7) C/kg: to 1/20 dose). Input-output properties, pre-sampled modulation transfer functions (pre-sampled MTFs), and normalized noise power spectra for an FPD system equipped with a CsI scintillator (FPDcsi) and a CR system with an imaging plate coated with storage phosphor (CR) were measured at the low dose range for radiation quality of RQA3 (≍50 skV) and RQA5 (≍70 kV), and detective quantum efficiencies (DQEs) were calculated. In addition, in order to validate the DQE results, component fractions of Poisson and multiplicative and additive noise were analyzed using relative standard deviation analysis. The DQE values of FPDcsi were decreased with dose decrease, and contrarily to these, those of CR were increased. At the 1/10 and 1/20 doses for RQA3, the DQEs of FPDcsi and CR became almost the same. From the results of RSD analysis, it was proved that the main cause of DQE deterioration on FPDcsi are non-negligible additive (electronic) noise, and the DQE improvement on CR was caused by both of significant multiplicative (structure) noise and very low electronic noise. The DQE results were validated by comparing burger phantom images of each dose and radiation quality.

[Investigation of error factors in analysis of digital noise power spectrum].

The noise power spectrum (NPS) measurement is important for assessing noise properties of digital radiography systems, and its measurement method was standardized in International Electrotechnical Commission 62220-1 (IEC). However, improvement of its accuracy is not easy due to random data analysis. In this study, regarding error factors in the NPS measurement using 2-dimensional (2D) Fast Fourier transform, we investigated effects of overlap of region of interests (ROIs), number of average lines in 2D frequency space, directional dependence of frequency property, and detrending techniques. If the number of average lines was set so as to obtain a similar frequency range to IEC, total matrix size was the most important factor and error rate was decreased with increasing of the size. For images, including many trends, detrending using 256 x 256-pixels ROI and second-order polynomial fitting was the most effective. Consistent with the previous report, the overlap of ROIs was not effective for improving accuracy. Contrary to the previous report that indicated effectiveness of 128 x 128-pixels ROI for detrending, we demonstrated less affectivity of the ROI size, other than 256 x 256-pixels.

[Influence of angle-measurement error on pre-sampled MTF and proposal of an optimal technique of angle measurement].

The presampled modulation transfer function (MTF) is recognized as the established metric for characterizing the resolution performance of a digital imaging system. In the past, the three general approaches for assessing the presampled MTF were using the angulated slit, angulated edge, and angulated square-wave test pattern all of which are tilted slightly against the column direction of the detector. In all methods, it is important to determine the exact angle of the respective test devices. In this study, we examined the influence of angle-measurement error in three test devices and the optimal technique of angle measurement. These results demonstrated that the influences of angle-measurement error in each method were equal. We also investigated three angle-measurement techniques using trace of objects, Hough transfer, and comparative observation of synthetic profiles. These results suggested that the technique using synthetic profiles was the most optimal technique in the angle measurement. Through use of the technique, angle-measurement error was completely overcome. This technique will contribute to improved accuracy of presampled MTF measurements.