Shinsuke Tsukagoshi

Improvement of spatial resolution in the longitudinal direction for isotropic imaging in helical CT.

Experiments were conducted to confirm the isotropic spatial resolution of multislice CT with a 0.5 mm slice thickness. Isotropic spatial resolution means that the spatial resolution in the transaxial plane (X-Y plane) and that in the longitudinal direction (Z direction) are equivalent. To obtain point spread function (PSF) values in the X-Y-Z directions, three-dimensional voxel data were obtained by helical scanning of a bead phantom. The modulation transfer function (MTF) values were then obtained by three-dimensional Fourier transform of the PSF. Evaluation of the spatial resolution in the X-Y-Z directions by the MTF values showed that the spatial resolution in the Z direction does not depend on the reconstruction kernel used. It was also found that the spatial resolution in the Z direction, as compared with that in the X-Y plane, is superior with the standard kernel for the abdomen and is inferior with the high-definition kernel for the ears/bones. By performing sharpening filter processing in the Z direction with a high-definition kernel, comparable spatial resolution could be obtained in the X-Y-Z directions. It was confirmed that adjusting the spatial resolution in the Z direction with the reconstruction kernel used is an effective method for isotropic imaging.

Ultra-High-Resolution Computed Tomography of the Lung: Image Quality of a Prototype Scanner

Purpose The image noise and image quality of a prototype ultra-high-resolution computed tomography (U-HRCT) scanner was evaluated and compared with those of conventional high-resolution CT (C-HRCT) scanners. Materials and Methods This study was approved by the institutional review board. A U-HRCT scanner prototype with 0.25 mm x 4 rows and operating at 120 mAs was used. The C-HRCT images were obtained using a 0.5 mm x 16 or 0.5 mm x 64 detector-row CT scanner operating at 150 mAs. Images from both scanners were reconstructed at 0.1-mm intervals; the slice thickness was 0.25 mm for the U-HRCT scanner and 0.5 mm for the C-HRCT scanners. For both scanners, the display field of view was 80 mm. The image noise of each scanner was evaluated using a phantom. U-HRCT and C-HRCT images of 53 images selected from 37 lung nodules were then observed and graded using a 5-point score by 10 board-certified thoracic radiologists. The images were presented to the observers randomly and in a blinded manner. Results The image noise for U-HRCT (100.87 ± 0.51 Hounsfield units [HU]) was greater than that for C-HRCT (40.41 ± 0.52 HU; P < .0001). The image quality of U-HRCT was graded as superior to that of C-HRCT (P < .0001) for all of the following parameters that were examined: margins of subsolid and solid nodules, edges of solid components and pulmonary vessels in subsolid nodules, air bronchograms, pleural indentations, margins of pulmonary vessels, edges of bronchi, and interlobar fissures. Conclusion Despite a larger image noise, the prototype U-HRCT scanner had a significantly better image quality than the C-HRCT scanners.

Three-dimensional perfusion imaging of hepatocellular carcinoma using 256-slice multidetector-row computed tomography.

PurposeThe aim of this study was to evaluate the clinical capability of three-dimensional (3D) perfusion imaging of hepatocellular carcinoma (HCC) by performing dynamic scanning using a 256-slice multidetector-row CT (MDCT) scanner.Materials and methodsTwo patients with HCC were examined in this study. They were scheduled to undergo transcatheter arterial infusion therapy using an arterial infusion reservoir system. The CT system used was a newly developed prototype scanner of 256-slice MDCT. Dynamic CT scanning was performed with intraarterial injection via the reservoir route, and perfusion analysis was done based on the 3D data.ResultsThe blood flow volume per unit volume in the tumors was significantly increased compared with that in normal hepatic parenchyma. Using a 3D workstation, 3D perfusion images could be displayed by fusing CT images with perfusion images about blood flow volume.ConclusionThree-dimensional perfusion images, which enable 3D evaluation of perfusion in HCCs, can be generated using 256-slice MDCT.

Image quality improvement and exposure dose reduction with the combined use of X-ray modulation and Boost3D

Multislice CT with a larger number of detector rows has recently become the mainstream. As a result, scanning with a thin slice thickness is more frequently performed. However, a large number of obvious raster-type artifacts occur when X-ray absorption in the lateral direction is extremely high, such as in the shoulder and the pelvis. There are two methods to solve this problem. In one method, X-ray output is modulated during rotation so that the exposure dose is increased in regions with high X-ray absorption and reduced in regions with low X-ray absorption. In the other method, regions that are responsible for artifacts are filter-processed using image processing to minimize artifacts. From the viewpoints of image quality and exposure dose, we have evaluated a method we have developed that combines X-ray modulation technology (X-ray Modulation) and artifact elimination processing (Boost3D). An acrylic elliptical phantom was used for evaluation. Assuming a constant image SD level, it was found that the exposure dose can be reduced by approximately 25% with the combined use of X-ray Modulation and Boost3D.

Automated continuous quantitative measurement of proximal airways on dynamic ventilation CT: initial experience using an ex vivo porcine lung phantom

Background The purpose of this study was to evaluate the feasibility of continuous quantitative measurement of the proximal airways, using dynamic ventilation computed tomography (CT) and our research software. Methods A porcine lung that was removed during meat processing was ventilated inside a chest phantom by a negative pressure cylinder (eight times per minute). This chest phantom with imitated respiratory movement was scanned by a 320-row area-detector CT scanner for approximately 9 seconds as dynamic ventilatory scanning. Obtained volume data were reconstructed every 0.35 seconds (total 8.4 seconds with 24 frames) as three-dimensional images and stored in our research software. The software automatically traced a designated airway point in all frames and measured the cross-sectional luminal area and wall area percent (WA%). The cross-sectional luminal area and WA% of the trachea and right main bronchus (RMB) were measured for this study. Two radiologists evaluated the traceability of all measurable airway points of the trachea and RMB using a three-point scale. Results It was judged that the software satisfactorily traced airway points throughout the dynamic ventilation CT (mean score, 2.64 at the trachea and 2.84 at the RMB). From the maximum inspiratory frame to the maximum expiratory frame, the cross-sectional luminal area of the trachea decreased 17.7% and that of the RMB 29.0%, whereas the WA% of the trachea increased 6.6% and that of the RMB 11.1%. Conclusion It is feasible to measure airway dimensions automatically at designated points on dynamic ventilation CT using research software. This technique can be applied to various airway and obstructive diseases.

Evaluation of dose efficiency index compared to receiver operating characteristics for assessing CT low-contrast performance

The dose efficiency index (DEI) is a dose independent measure that quantifies the low-contrast performance of CT scanners. The purpose of this paper is to compare the results of DEI analysis with those of ROC analysis. A custom-made phantom consisting of diluted contrast targets of various sizes and densities was scanned at 80 & 120 kV on a multislice CT scanner (Hispeed Advantage RP, GE). Eight radiographers reviewed the images and identified discernable targets. The likelihood of detection was measured as a function of the target size and scan conditions. The results of the DEI & ROC analyses showed that the low-contrast resolution was higher at 80kV than at 120kV. The p-value obtained by the paired-t test was 0.000 for both analyses, indicating that the difference was significant. Under the conditions used in this study, the DEI analysis was found to be an effective alternative to ROC analysis for characterizing the low-contrast performance of CT scanners. The evaluation time was about 1/6 compared with ROC analysis. It is much simpler to calculate than ROC and is useful in comparing scanners from different manufacturers or as part of ongoing quality assurance.

Phantom Study of In-Stent Restenosis at High-Spatial-Resolution CT

Purpose To examine the diagnostic performance of high-spatial-resolution (HSR) CT with 0.25-mm section thickness for evaluating renal artery in-stent restenosis. Materials and Methods A 0.05-mm wire phantom and vessel phantoms with renal stents with in-stent stenotic sections of varying diameters were scanned with both an HSR CT scanner equipped with 160-section multi-detector rows (0.25-mm section thickness) and a conventional CT scanner. The wire phantom was used to analyze modulation transfer function (MTF). With the vessel phantoms, the error rates were calculated as the absolute difference between the measured diameters and true diameters divided by the true diameters at the narrowing sections. For qualitative evaluation, overall image quality and diagnostic accuracy for evaluating stenosis in three stages were assessed by two radiologists. Statistical analyses included the paired t test, Wilcoxon signed-rank test, and McNemar test. Results HSR CT achieved 24.3 line pairs per centimeter ± 0.5 (standard deviation) and 29.1 line pairs per centimeter ± 0.4 at 10% and 2% MTF, respectively; and conventional CT was 12.5 line pairs per centimeter ± 0.1 and 14.3 line pairs per centimeter ± 0.1 at 10% and 2% MTF, respectively. The mean error rate of the measured diameter at HSR CT (8.0% ± 5.8) was significantly lower than that at at conventional CT (16.9% ± 9.3; P < .001). Image quality at HSR CT was significantly better than that at conventional CT (P < .001), but HSR CT was not significantly superior to conventional CT in terms of diagnostic accuracy. Conclusion Compared with conventional CT, high-spatial-resolution CT achieved spatial resolutions of up to 29 line pairs per centimeter at 2% modulation transfer function and yielded improved measurement accuracy for the evaluation of in-stent restenosis in a phantom study of renal artery stents. Published under a CC BY 4.0 license.

Subjective and objective comparisons of image quality between ultra-high-resolution CT and conventional area detector CT in phantoms and cadaveric human lungs

ObjectivesTo compare the image quality of the lungs between ultra-high-resolution CT (U-HRCT) and conventional area detector CT (AD-CT) images.MethodsImage data of slit phantoms (0.35, 0.30, and 0.15 mm) and 11 cadaveric human lungs were acquired by both U-HRCT and AD-CT devices. U-HRCT images were obtained with three acquisition modes: normal mode (U-HRCTN: 896 channels, 0.5 mm × 80 rows; 512 matrix), super-high-resolution mode (U-HRCTSHR: 1792 channels, 0.25 mm × 160 rows; 1024 matrix), and volume mode (U-HRCTSHR-VOL: non-helical acquisition with U-HRCTSHR). AD-CT images were obtained with the same conditions as U-HRCTN. Three independent observers scored normal anatomical structures (vessels and bronchi), abnormal CT findings (faint nodules, solid nodules, ground-glass opacity, consolidation, emphysema, interlobular septal thickening, intralobular reticular opacities, bronchovascular bundle thickening, bronchiectasis, and honeycombing), noise, artifacts, and overall image quality on a 3-point scale (1 = worst, 2 = equal, 3 = best) compared with U-HRCTN. Noise values were calculated quantitatively.ResultsU-HRCT could depict a 0.15-mm slit. Both U-HRCTSHR and U-HRCTSHR-VOL significantly improved visualization of normal anatomical structures and abnormal CT findings, except for intralobular reticular opacities and reduced artifacts, compared with AD-CT (p < 0.014). Visually, U-HRCTSHR-VOL has less noise than U-HRCTSHR and AD-CT (p < 0.00001). Quantitative noise values were significantly higher in the following order: U-HRCTSHR (mean, 30.41), U-HRCTSHR-VOL (26.84), AD-CT (16.03), and U-HRCTN (15.14) (p < 0.0001). U-HRCTSHR and U-HRCTSHR-VOL resulted in significantly higher overall image quality than AD-CT and were almost equal to U-HRCTN (p < 0.0001).ConclusionsBoth U-HRCTSHR and U-HRCTSHR-VOL can provide higher image quality than AD-CT, while U-HRCTSHR-VOL was less noisy than U-HRCTSHR.Key Points• Ultra-high-resolution CT (U-HRCT) can improve spatial resolution.• U-HRCT can reduce streak and dark band artifacts.• U-HRCT can provide higher image quality than conventional area detector CT.• In U-HRCT, the volume mode is less noisy than the super-high-resolution mode.• U-HRCT may provide more detailed information about the lung anatomy and pathology.

Influence of gantry rotation time and scan mode on image quality in ultra-high-resolution CT system

OBJECTIVES To investigate the image quality of helical scan (HS) mode and non-helical scan (non-HS) mode on ultra-high-resolution CT in different gantry rotation time. METHODS non-HS with 0.35 s/rot (non-HS200 mA/0.35 s). Three observers compared each non-HS image with HS image, and scored non-HS images by using 3-point scale, paying attention to normal findings, abnormal findings, noise, streak artifact, and overall image quality. Statistical analysis was performed with Steel-Dwass test. RESULTS Overall image quality (score: 2.45) and noise (score: 2.42) of non-HS 200 mA/1.5s was statistically best (p < 0.0005). Overall Image quality and noise of non-HS200 mA/0.75 s (score: 2.0) was comparable to that of HS200 mA/1.5 s. CTDIvol of HS200 mA/1.5 s is 23.2 mGy. CTDIvol of non-HS200 mA/1.5 s, non-HS200 mA/0.75 s, non-HS200 mA/0.35 s is 19.2 mGy, 9.8 mGy, 4.7 mGy. CONCLUSION Overall image quality and noise of non-helical scan is better than that of helical scan in the same rotation time. Overall Image quality of non-HS200 mA/0.75 s is comparable to that of HS200 mA/1.5 s, though the radiation dose of non-HS200 mA/0.75 s is lower than that of HS200 mA/1.5 s.

Effect of Matrix Size on the Image Quality of Ultra-high-resolution CT of the Lung: Comparison of 512 × 512, 1024 × 1024, and 2048 × 2048

RATIONALE AND OBJECTIVES This study aimed to assess the effect of matrix size on the spatial resolution and image quality of ultra-high-resolution computed tomography (U-HRCT). MATERIALS AND METHODS Slit phantoms and 11 cadaveric lungs were scanned on U-HRCT. Slit phantom scans were reconstructed using a 20-mm field of view (FOV) with 1024 matrix size and a 320-mm FOV with 512, 1024, and 2048 matrix sizes. Cadaveric lung scans were reconstructed using 512, 1024, and 2048 matrix sizes. Three observers subjectively scored the images on a three-point scale (1 = worst, 3 = best), in terms of overall image quality, noise, streak artifact, vessel, bronchi, and image findings. The median score of the three observers was evaluated by Wilcoxon signed-rank test with Bonferroni correction. Noise was measured quantitatively and evaluated with the Tukey test. A P value of <.05 was considered significant. RESULTS The maximum spatial resolution was 0.14 mm; among the 320-mm FOV images, the 2048 matrix had the highest resolution and was significantly better than the 1024 matrix in terms of overall quality, solid nodule, ground-glass opacity, emphysema, intralobular reticulation, honeycombing, and clarity of vessels (P < .05). Both the 2048 and 1024 matrices performed significantly better than the 512 matrix (P < .001), except for noise and streak artifact. The visual and quantitative noise decreased significantly in the order of 512, 1024, and 2048 (P < .001). CONCLUSION In U-HRCT scans, a large matrix size maintained the spatial resolution and improved the image quality and assessment of lung diseases, despite an increase in image noise, when compared to a 512 matrix size.