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Showing 8 results for Image Quality
E. Raeisi, Dr H. Rajabi, Dr S.m.r. Aghamiri, Volume 4, Issue 2 (9-2006)
Abstract
ABTRACT
Background: In nuclear medicine,
phantoms are mainly used to evaluate the overall performance of the imaging
systems and practically there is no phantom exclusively designed for the
evaluation of the software performance. In this study the Hoffman brain phantom
was used for quantitative evaluation of reconstruction techniques. The phantom
is modified to acquire tomographic and planar image of the same structure. The
planar image may be used as the reference image to evaluate the quality of
reconstructed slices using the companion software developed in MATLAB.
Methods and Materials: The designed
phantom is composed of 4 independent 2D slices that may be placed juxtapose to
form the 3D phantom. Each slice is composed of objects of different size
and shape e.g. circle, triangle, and rectangle. Each 2D slice was imaged at the
distances from 0 to 15 cm from the collimator surface. The phantom in 3D
configuration was imaged acquiring 128 views of 128×128 matrix size.
Reconstruction was performed using different filtering condition and the
reconstructed images were compared to the corresponding planar images. The
modulation transfer function, scatter fraction and attenuation map were
calculated for each reconstructed image
Results: Since all the parameters of the
acquisition were identical for the 2D and the 3D imaging. It was assumed that
the difference in the quality of the images was exclusively due to
reconstruction condition. The planar images were assumed to be the most perfect
images that could be obtained with the system. Comparing the reconstructed
slices to the corresponding planar images yielded the optimum reconstruction
condition. The results clearly showed that Wiener
filter yields superior quality image among the entire filter tested. The extent
of the improvement has been quantified in terms of universal image quality
index.
Conclusion: The
phantom and the accompanying software were evaluated and found to be quite
useful in determining the optimum filtering condition and mathematical
evaluation of the scatter and attenuation in tomographic images.
Y. Zhuang, W. Huang, Y. Shi, G. Bo, D. Lu, J. Zhang, D. Kong, Y. Shi, Dr. B. Wang, Volume 16, Issue 2 (4-2018)
Abstract
Background: Prospectively electrocardiography (ECG)-triggered high-pitch spiral coronary computed tomography angiography (CCTA) is a unique scan mode for dual-source CT (DSCT). Our reports aim to compare image quality and radiation dose of CCTA using high-pitch spiral or sequential acquisition mode in patients with low and stable heart rates. Materials and Methods: Patients with low and stable heart rates (HR) (HR ≤ 70 beats per minute [bpm]; heart rate variability [HRV] < 10 bpm) were randomly assigned to high-pitch spiral mode (group A; n = 80) or sequential acquisition mode (group B; n = 80). Image quality scores, image noise, effective radiation dose and influencing factors on image quality were assessed. Results: Mean image quality scores were 1.51 ± 0.32 and 1.70 ± 0.38 for groups A and B (P < 0.05), respectively. Image noises of the two groups were 19.05±4.70 Hu and 27.21±8.88 Hu (P < 0.05). Contrast media cost in group A was lower than group B (P < 0.05). No statistical difference was found in the rate of diagnostic patients between the two groups (P = 0.416). The estimated radiation dose of group A was 26.0% reduced compared with group B (0.74 ± 0.34 mSv vs. 1.00 ± 0.48 mSv, P < 0.05). Conclusion: In patients with regular and low heart rates, the prospectively high-pitch spiral acquisition mode can reduce radiation dose and contrast media cost while maintaining image quality compared with the prospectively sequential mode.
J. Zhang, Z.r. Bao, X.t. Huang, D.z. Jiang, C.h. Xie, Y.f. Zhou, Dr. H. Liu, Volume 17, Issue 2 (4-2019)
Abstract
Background: Cone-beam computed tomography (CBCT) scanners for image-guided radiotherapy are in clinical use today, but there has been no consensus on uniform acceptance to verify the CBCT image quality yet. The present work proposed new methods to fully evaluate the performance of CBCT in its three-dimensional (3D) reconstruction space. Materials and Methods: Compared to the traditional methods with only two-dimensional axial slice evaluated, the new methods were designed to evaluate the CBCT image quality not only in the axial slices but also along three dimensions and three sections. Image parameters were evaluated by scanning the corresponding phantom. Results: The new methods demonstrated the high spatial resolution, the image uniformity, the high CT numbers linearity, geometric accuracy and relatively poor performance in low contrast resolution, compared to the results of plan CT. Additionally, the spatial resolution, the CT number linearity and the image uniformity proved to be more superior along the z direction and in the cross-section. Furthermore, the spatial resolution and the CT value linearity decreased gradually when deviating from the center of rotation axis and accelerates the reduction towards the periphery area, suggesting that locating the target within the range of 4 cm around the isocenter during radiotherapy ensure the optimal spatial resolution and the CT value linearity. Conclusion: Results indicate that the proposed three-dimensional image quality evaluation holds the potential to complement existing standards to provide sufficient information for the CBCT image performance and thereby guiding the clinical applications of CBCT.
Priyanka, M.d., R. Kadavigere, S. Sukumar, Volume 20, Issue 4 (10-2022)
Abstract
Background: There is an increase in pediatric Computed Tomography (CT) imaging with advancement in technology but CT radiation dose produces significant adverse effects. The objective of this experimental phantom study is to develop an age-based low-dose pediatric CT head protocol. Materials and Methods: Polymethyl methacrylate (PMMA) pediatric head mimicking phantom scanning was performed on a CT scanner using various combinations of tube voltage (kV) and product of tube current and exposure time (mAs) setting. Images were reconstructed by iterative reconstruction iDose4 level 1-5. Quantitative assessment of image quality (IQ) was done by calculating Signal to Noise Ratio (SNR), Contrast to Noise Ratio (CNR), and Image Noise (IN). Radiation dose indices (RDI) were measured by recording Volumetric CT Dose Index (CTDIv) and Dose length product (DLP). Figure of Merit (FOM) was calculated to study overall effects between IQ and RDI. IQ and RDI obtained using different exposure settings were compared. Result: Optimized age-based low-dose protocols were developed based on IQ analysis and RDI. For pediatric CT head, with age less than one year kV and mAs of 80 and 150 and for one–five years age kV and mAs of 100 and 200 with iDose4 level-3 was found to be optimum low dose protocol. Conclusion: The experimental phantom study concluded that with use of low kVp and mAs, radiation dose was reduced to 62% for less than 1-year age group and 51% for 1-5 year age group and also with use of iterative reconstruction technique iDose4 level-3 diagnostic image quality was maintained.
H. Ragab, D.m. Abdelaziz, M.m. Khalil, M.n. Yasein Elbakry, Volume 21, Issue 3 (7-2023)
Abstract
Background: To assess and compare image quality characteristics of x-ray computed tomography (CT) and cone beam (CBCT) imaging systems of the Varian linear accelerator. Materials and Methods: The CatPhan®504, was examined on the CT simulator (SOMATOM Definition AS, VA48A) and two CBCTs (TrueBeam™ and Clinac® iX linear accelerators) attached to Varian linear accelerator. Image quality parameters including pixel value stability, spatial linearity, pixel size verification, uniformity, noise, spatial resolution, low contrast resolution, and contrast-to-noise ratio (CNR) were assessed using different scanning protocols. Results: The mean pixel values of regions of interest were stable for CT, TB, and iX-CBCT imaging. Noise on CT was slightly lower and was seen to decrease with increasing mAs, while CNR increased with CT mAs and two CBCTs. For all schemes, the Modulation Transfer Function (MTF) of the reconstructed image was limited by the pixel size. Low contrast targets for TB-CBCT were visible, with up to 6 and 2 targets for 1% and 0.5% for contrast, respectively. However, up to 4 targets of 1% contrast on iX-CBCT images are visible for the low-contrast objectives. Also, up to 8, 4, and 1 targets of 1%, 0.5%, and 0.3% contrast were visible for the low-contrast targets on CT images. Conclusions: CT and CBCT image quality parameters have been quantified and compared for clinical protocols in different mAs conditions. Selecting the right protocol will boost contrast, based on image quality criteria. The mAs can be decreased to minimize patient dosage.
E. Kim, H. Park, H. Choi, Dr. J. Kim, Volume 21, Issue 3 (7-2023)
Abstract
Background: Light and portable handheld X-ray devices are being used more often for diagnosis because they allow radiography procedures to be performed on patients in settings where there may not be stationary X-ray devices, such as islands or mountainous regions. In this study, the performances of handheld X-ray devices (HXD) and stationary X-ray devices (SXD) were compared to determine whether the handheld device could produce diagnostically acceptable image quality outside of hospitals, particularly during a global pandemic. Materials and Methods: For performance evaluation, the accuracy of tube voltage, reproducibility of X-ray dose, linearity, leakage dose, and accuracy of focal spot size were obtained. The accuracy of the tube voltage and the reproducibility and linearity of the X-ray dose were measured to reduce the frequency of patient reimaging as a performance evaluation of the devices. Results: After conducting various experiments, it was found that the percentage average error (PAE) value of the tube voltage was -0.01% for the HXD, and the error of the tube voltage was 0.01% for the SXD, which is lower than the standard 10%. Additionally, when using an HXD according to these standards, medical staff is considered safe from exposure to leakage dose because the leakage dose is 0.26 mSv/year without the use of a partition. Conclusion: Our results provide evidence that images of appropriate quality can be taken with an HXD, offering comparable diagnostic value. It was concluded that the leakage radiation dose would be safe at 0.26 mSv/year without using a radiation shielding partition.
X. Li, Y. Duan, W. Liu, Z. Han, Z. Liang, Ph.d., R. Wang, Volume 21, Issue 4 (10-2023)
Abstract
Background: The study aimed to elucidate the clinical application significance of prospective ECG-gated dual-source CT in central venous (CV) imaging. Materials and Methods: Eighty patients who took CT imaging of CV (CTV) check using dual-source Force CT were enrolled. The control group (helical pitch, 0.8; rotation speed, 0.5 s) and the experimental group (rotation speed, 0.25 s). For both groups, image quality and radiation dose were computed. Results: Cases in the experimental group required longer scanning durations than those in the contro lgroup. In respect to the experimental group, the image quality scores of the superior vena cava and left and right brachiocephalic veins of the patients sharply increased relative to those in the control group. Individuals in the experimental group also presented better image quality scores in left and right subclavian veins, left and right jugular veins, however, this difference was not statistically significant. Lastly, no increase in the radiation dose was bited with the application of prospective ECG gating. Conclusion: The clinical use of prospective ECG-gated technology significantly reduced cardiovascular pulsing artifact interference on the central vein, especially the superior vena cava segment, and remarkably improved the image quality without increasing the radiation dose to patients.
M. Papaioannou, A. Tsikrika, V. Roka, P. Lavda, N. Pantazis, G.k. Sakkas, E. Dardiotis, A. Bakas, P. Mavroidis, Ph.d., E. Lavdas, Volume 23, Issue 1 (1-2025)
Abstract
Background: Comparison of three different sagittal sequences with fat suppression in the lumbar spine magnetic resonance imaging (MRI), evaluating several image characteristics and changing the phase direction. Materials and Methods: Forty-five subjects (20 males, 25 females, mean age 50 years old) participated in this retrospective study in an MRI machine of 1.5 Tesla (GE Signa Hdx). We compared three fat-saturated sequences {T2 Weighted (T2W) Fast Spin Echo (FSE) Fat Saturation (FS) with phase direction superior-inferior (S/I), T2W Short Tau Inversion Recovery (STIR) with phase direction superior-inferior (S/I) and T2W STIR with phase direction (A/P)}. A qualitative analysis was performed, while two experienced radiologists evaluated the images. The statistical analysis was determined by Kruskal–Wallis non-parametric test. Results: The T2W FSE FS was superior in almost all studied parameters {total image quality, presence of artifacts, artifacts in 4th lumbar vertebra (L4) - 1st Sacral vertebra (S1), depiction of lesions on vertebral bodies, depiction of lesions on L4-S1 region, sharpness} in comparison with T2W STIR sequences with statistically significant difference (p<0.001). The STIR sequences exceeded the T2W FSE FS in the fat saturation effectiveness with a statistically significant difference (p<0.001). Conclusion: The T2 Weighted (T2W) Fast Spin Echo (FSE) Fat Saturation (FS) was superior in the depiction of pathology and normal anatomy, eliminating many artifacts in comparison with T2 Short Tau Inversion Recovery (STIR) sequences, especially in the L4 vertebra– S1 vertebra anatomic region, between three under-study sequences. Choosing the appropriate sagittal fat-saturated sequence in each clinical question is useful to avoid misdiagnosis due to technical artifacts.
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