Consistent Image Quality Research Articles

Fully automatic multi-atlas segmentation of CTA for partial volume correction in cardiac SPECT/CT

Anatomical-based partial volume correction (PVC) has been shown to improve image quality and quantitative accuracy in cardiac SPECT/CT. However, this method requires manual segmentation of various organs from contrast-enhanced computed tomography angiography (CTA) data. In order to achieve fully automatic CTA segmentation for clinical translation, we investigated the most common multi-atlas segmentation methods. We also modified the multi-atlas segmentation method by introducing a novel label fusion algorithm for multiple organ segmentation to eliminate overlap and gap voxels. To evaluate our proposed automatic segmentation, eight canine 99mTc-labeled red blood cell SPECT/CT datasets that incorporated PVC were analyzed, using the leave-one-out approach. The Dice similarity coefficient of each organ was computed. Compared to the conventional label fusion method, our proposed label fusion method effectively eliminated gaps and overlaps and improved the CTA segmentation accuracy. The anatomical-based PVC of cardiac SPECT images with automatic multi-atlas segmentation provided consistent image quality and quantitative estimation of intramyocardial blood volume, as compared to those derived using manual segmentation. In conclusion, our proposed automatic multi-atlas segmentation method of CTAs is feasible, practical, and facilitates anatomical-based PVC of cardiac SPECT/CT images.

A specific absorption rate reduction method for simultaneous multislice magnetic resonance imaging.

This study proposes a modified Shinnar-Le Roux method to synthesize the excitation radio frequency (RF) pulse for a 2D gradient echo (GRE) based simultaneous multi-slice (SMS) magnetic resonance imaging (MRI) with features of low specific absorption rate (SAR) and small out-of-slice ripple. This synthesis method for SMS RF pulses employs thinner slice bandwidth and lower multislice offset frequencies to reduce SAR values and adopts a weighted Parks-McClellan algorithm to reduce sidelobes. Formulas for estimating relative SAR values of the SMS pulses are also introduced. Relative SAR values and out-of-slice ripples of the proposed and typical RF pulses with different parameters are presented. In simultaneous 5-slice phantom and 3-slice human brain imaging, SMS pulses synthesized with the proposed method achieve 32% and 28% SAR values of standard pulses while providing similar image qualities. Typical RF pulses such as sinc x cos can also take advantage of the proposed method and offer lower SAR values for SMS imaging. The RF pulse synthesized using the proposed method features low SAR, small sidelobes, and consistent image quality for 2D GRE-based SMS MRI. This method is applicable to the synthesis of typical SMS RF pulses for significant SAR reduction.

Patient-specific optimisation of administered activity and acquisition times for 18F-FDG PET imaging

BackgroundThe purpose of this study is to identify a method for optimising the administered activity and acquisition time for 18F-FDG PET imaging, yielding images of consistent quality for patients with varying body sizes and compositions, while limiting radiation doses to patients and staff. Patients referred for FDG scans had bioimpedance measurements. They were injected with 3 MBq/kg of 18F up to 370 MBq and scanned on a Siemens Biograph mCT at 3 or 4 min per bed position. Data were rebinned to simulate 2- and 1-min acquisitions. Subjective assessments of image quality made by an experienced physician were compared with objective measurements based on signal-to-noise ratio and noise equivalent counts (NEC). A target objective measure of image quality was identified. The activity and acquisition time required to achieve this were calculated for each subject. Multiple regression analysis was used to identify expressions for the activity and acquisition time required in terms of easily measurable patient characteristics.ResultsOne hundred and eleven patients were recruited, and subjective and objective assessments of image quality were compared for 321 full and reduced time scans. NEC-per-metre was identified as the objective measure which best correlated with the subjective assessment (Spearman rank correlation coefficient 0.77) and the best discriminator for images with a subjective assessment of “definitely adequate” (area under the ROC curve 0.94). A target of 37 Mcount/m was identified. Expressions were identified in terms of patient sex, height and weight for the activity and acquisition time required to achieve this target. Including measurements of body composition in these expressions was not useful. Using these expressions would reduce the mean activity administered to this patient group by 66 MBq compared to the current protocol.ConclusionsExpressions have been identified for the activity and acquisition times required to achieve consistent image quality in FDG imaging with reduced patient and staff doses. These expressions might need to be adapted for other systems and reconstruction protocols.

Edge-based singular value decomposition for full reference colour image quality assessment

Due to intense use of digital visual aids, image quality plays a crucial role in today's life. Images are subjected to degradations during image acquisition and image processing. This affects their naturalness and usefulness in different applications. Literature shows efforts are made to develop an HVS consistent image quality metric since last few decades. New image quality metrics, extension of existing image quality algorithms and their applications are being developed by researcher's community. Singular value decomposition is one of the measures which are used to quantify the amount of distortion at different distortion levels. Based on the hypothesis that the human eye is adapted to extract edge information from any natural scene, this paper presents a novel approach of introducing edge information in SVD-based image quality metric. The results are compared with SVD-based metric available in related work in literature. Proposed metric outperforms the existing metric. Also, it is extended for evaluation of colour images.

Edge-based singular value decomposition for full reference colour image quality assessment

Due to intense use of digital visual aids, image quality plays a crucial role in today's life. Images are subjected to degradations during image acquisition and image processing. This affects their naturalness and usefulness in different applications. Literature shows efforts are made to develop an HVS consistent image quality metric since last few decades. New image quality metrics, extension of existing image quality algorithms and their applications are being developed by researcher's community. Singular value decomposition is one of the measures which are used to quantify the amount of distortion at different distortion levels. Based on the hypothesis that the human eye is adapted to extract edge information from any natural scene, this paper presents a novel approach of introducing edge information in SVD-based image quality metric. The results are compared with SVD-based metric available in related work in literature. Proposed metric outperforms the existing metric. Also, it is extended for evaluation of colour images.

SU‐G‐JeP4‐13: Continuous Intra‐Fractional Monitoring of the Prostate Using Dynamic KV Collimation and Tube Current Modulation

Purpose:The focus of this work is to improve the available kV image quality for continuous intra‐fraction monitoring of the prostate. This is investigated using a novel blade collimation system enabling modulated volume‐of‐interest (VOI) imaging of prostate fiducial markers.Methods:A four‐blade dynamic kV collimator was used to track a VOI during gantry rotation. Planar image quality was investigated as a function of collimator dimension, while maintaining the same dose to isocenter, for a 22.2 cm diameter cylindrical water phantom with a 9 mm diameter bone insert. A sample prostate anatomy was defined in the planning system, including three fiducial markers within the CTV. The VOI margin around each marker was set to be 2σ of the population covariance matrix characterizing prostate motion. DRRs were used to calculate the kV attenuation for each VOI as a function of angle. The optimal marker and tube current were determined using kV attenuation. Monte Carlo simulations were used to calculate the imaging dose to the phantom and MV scatter dose to the imaging panel.Results:Preliminary measurements show an increase in CNR by a factor of 1.3 with the VOI method, when decreasing from an 6×6 to 2×2 cm2 field. Attenuation calculations show a change in kV fluence at the detector by a factor of 21.6 with fiducial optimization; resultant tube current modulation increases maximum dose by a factor of 1.4 compared to no modulation. MV scatter contribution to the kV detector changes by approximately a factor of two over a complete gantry rotation.Conclusion:The dynamic collimation system allows single fiducial marker tracking at a very low dose, with reduction of scatter and improvement of image quality, compared to imaging the entire prostate. The approach is compatible with tube current modulation, which enables consistent image quality throughout the range of gantry rotation.This project was funded by Varian Medical Systems.

A Filter Design Approach for Consistent Image Quality

A Filter Design Approach for Consistent Image Quality

Optimization of oncological ¹⁸F-FDG PET/CT imaging based on a multiparameter analysis.

This paper describes a method to achieve consistent clinical image quality in (18)F-FDG scans accounting for patient habitus, dose regimen, image acquisition, and processing techniques. Oncological PET/CT scan data for 58 subjects were evaluated retrospectively to derive analytical curves that predict image quality. Patient noise equivalent count rate and coefficient of variation (CV) were used as metrics in their analysis. Optimized acquisition protocols were identified and prospectively applied to 179 subjects. The adoption of different schemes for three body mass ranges (<60 kg, 60-90 kg, >90 kg) allows improved image quality with both point spread function and ordered-subsets expectation maximization-3D reconstruction methods. The application of this methodology showed that CV improved significantly (p < 0.0001) in clinical practice. Consistent oncological PET/CT image quality on a high-performance scanner was achieved from an analysis of the relations existing between dose regimen, patient habitus, acquisition, and processing techniques. The proposed methodology may be used by PET/CT centers to develop protocols to standardize PET/CT imaging procedures and achieve better patient management and cost-effective operations.

Noninvasive imaging of the thirteen-lined ground squirrel photoreceptor mosaic.

Ground squirrels are an increasingly important model for studying visual processing, retinal circuitry, and cone photoreceptor function. Here, we demonstrate that the photoreceptor mosaic can be longitudinally imaged noninvasively in the 13-lined ground squirrel (Ictidomys tridecemlineatus) using confocal and nonconfocal split-detection adaptive optics scanning ophthalmoscopy using 790 nm light. Photoreceptor density, spacing, and Voronoi analysis are consistent with that of the human cone mosaic. The high imaging success rate and consistent image quality in this study reinforce the ground squirrel as a practical model to aid drug discovery and testing through longitudinal imaging on the cellular scale.

Characteristic image quality of a third generation dual-source MDCT scanner: Noise, resolution, and detectability.

The purpose of this work was to assess the inherent image quality characteristics of a new multidetector computed tomography system in terms of noise, resolution, and detectability index as a function of image acquisition and reconstruction for a range of clinically relevant settings. A multisized image quality phantom (37, 30, 23, 18.5, and 12 cm physical diameter) was imaged on a SOMATOM Force scanner (Siemens Medical Solutions) under variable dose, kVp, and tube current modulation settings. Images were reconstructed with filtered back projection (FBP) and with advanced modeled iterative reconstruction (ADMIRE) with iterative strengths of 3, 4, and 5. Image quality was assessed in terms of the noise power spectrum (NPS), task transfer function (TTF), and detectability index for a range of detection tasks (contrasts of approximately 45, 90, 300, -900, and 1000 HU, and 2-20 mm diameter) based on a non-prewhitening matched filter model observer with eye filter. Image noise magnitude decreased with decreasing phantom size, increasing dose, and increasing ADMIRE strength, offering up to 64% noise reduction relative to FBP. Noise texture in terms of the NPS was similar between FBP and ADMIRE (<5% shift in peak frequency). The resolution, based on the TTF, improved with increased ADMIRE strength by an average of 15% in the TTF 50% frequency for ADMIRE-5. The detectability index increased with increasing dose and ADMIRE strength by an average of 55%, 90%, and 163% for ADMIRE 3, 4, and 5, respectively. Assessing the impact of mA modulation for a fixed average dose over the length of the phantom, detectability was up to 49% lower in smaller phantom sections and up to 26% higher in larger phantom sections for the modulated scan compared to a fixed tube current scan. Overall, the detectability exhibited less variability with phantom size for modulated scans compared to fixed tube current scans. Image quality increased with increasing dose and decreasing phantom size. The CT system exhibited nonlinear noise and resolution properties, especially at very low-doses, large phantom sizes, and for low-contrast objects. Objective image quality metrics generally increased with increasing dose and ADMIRE strength, and with decreasing phantom size. The ADMIRE algorithm could offer comparable image quality at reduced doses or improved image quality at the same dose. The use of tube current modulation resulted in more consistent image quality with changing phantom size.

A practical method to standardise and optimise the Philips DoseRight 2.0 CT automatic exposure control system

Given the increasing use of computed tomography (CT) in the UK over the last 30 years, it is essential to ensure that all imaging protocols are optimised to keep radiation doses as low as reasonably practicable, consistent with the intended clinical task. However, the complexity of modern CT equipment can make this task difficult to achieve in practice. Recent results of local patient dose audits have shown discrepancies between two Philips CT scanners that use the DoseRight 2.0 automatic exposure control (AEC) system in the ‘automatic’ mode of operation. The use of this system can result in drifting dose and image quality performance over time as it is designed to evolve based on operator technique.The purpose of this study was to develop a practical technique for configuring examination protocols on four CT scanners that use the DoseRight 2.0 AEC system in the ‘manual’ mode of operation. This method used a uniform phantom to generate reference images which form the basis for how the AEC system calculates exposure factors for any given patient.The results of this study have demonstrated excellent agreement in the configuration of the CT scanners in terms of average patient dose and image quality when using this technique. This work highlights the importance of CT protocol harmonisation in a modern Radiology department to ensure both consistent image quality and radiation dose. Following this study, the average radiation dose for a range of CT examinations has been reduced without any negative impact on clinical image quality.

TH-CD-303-09: Respiratory Motion Guided 4DCBCT On a Linear Accelerator with Lung Cancer Patient Breathing Traces

Purpose: Image quality from Four Dimensional Cone Beam Computed Tomography (4DCBCT) is poor due to projection clustering and under sampling. We have developed a novel method called respiratory motion guided 4DCBCT (RMG-4DCBCT) in which the gantry speed and projection frequency are varied in response to the patients real-time respiratory signal. The method has been shown theoretically to improve image quality by 63% on average. The purpose of this study was to implement RMG-4DCBCT on a linear accelerator for a variety of lung cancer patient breathing rates. Methods: In house software was developed to process RPM breathing traces from lung cancer patients and compute the optimal gantry trajectory and projection pulse rate schedule so that projections were uniformly distributed in each of 10 phase bins. The computed schedule was then programmed into developer mode of the Varian True Beam linear accelerator and the Scandidos Hexamotion phantom was modified to move the Catphan phantom according to the breathing trace. Four lung cancer patient breathing traces were selected with an average breathing period of 3, 4, 5 and 6 seconds respectively. We assess streaking artefacts by examining the variation in the angular separation between projections with a value of zero indicating uniformly space projects and larger values indicating more streaking in the reconstructed images. Results: RMG-4DCBCT with 60 projections per phase produces similar image quality to conventional 4DCBCT with 120 projections per phase. The image quality with RMG-4DCBCT is similar for all breathing rates with an average variation between projections of 1.3°. Conventional 4DCBCT acquiring 60 projections per phase had a variation of 5°, 6.1°, 7.3° and 8.1° for the 3, 4, 5 and 6 second breathing periods respectively. Conclusion: RMG-4DCBCT halves the imaging dose over conventional 4DCBCT with consistent image quality for a range of breathing rates. This project is supported by an NHMRC Australia Fellowship, NHMRC project grant 1034060 and Cancer Australia grant number 1084566.

SU-F-207-03: Dosimetric Effect of the Position of Arms in Torso CT Scan with Tube Current Modulation

Purpose: To evaluate the patient organ dose differences between the arms-raised and arms-lowered postures in Torso multidetector computed tomography (MDCT) scan protocols with tube current modulation (TCM). Methods: Patient CT organ doses were simulated using the Monte Carlo method with human phantoms and a validated CT scanner model. A set of adult human phantoms with arms raised and arms lowered postures were developed using advanced BREP-based mesh surface geometries. Organ doses from routine Torso scan protocols such as chest, abdomen-pelvis, and CAP scans were simulated. The organ doses differences caused by two different posutres were investigated when tube current modulation (TCM) were applied during the CT scan. Results: With TCM applied, organ doses of all the listed organs of arms-lowered posture phantom are larger than those of arms raised phantom. The dose difference for most of the organs or tissues are larger than 50%, and the skin doses difference for abdomen-pelvis scan even reaches 112.03%. This is due to the fact that the tube current for patient with arms-lowered is much higher than for the arms raised posture. Conclusion: Considering CT scan with TCM, which is commonly applied clinically, patients who could not raise their arms will receive higher radiation dose than the arms raised patient, with dose differences for some tissues such as the skin being larger than 100%. This is due to the additional tube current necessary to penetrate the arms while maintaining consistent image quality. National Nature Science Foundation of China(No.11475047)

Derivation of the scan time requirement for maintaining a consistent PET image quality

Objectives: the image quality of PET for larger patients is relatively poor, even though the injection dose is optimized considering the NECR characteristics of the PET scanner. This poor image quality is due to the lower level of maximum NECR that can be achieved in these large patients. The aim of this study was to optimize the PET scan time to obtain a consistent PET image quality regardless of the body size, based on the relationship between the patient specific NECR (pNECR) and body weight.Methods: eighty patients (M/F=53/27, body weight: 059 ± 1 kg) underwent whole-body FDG PET scans using a Philips GEMINI GS PET/CT scanner after an injection of 0.14 mCi/kg FDG. The relationship between the scatter fraction (SF) and body weight was determined by repeated Monte Carlo simulations using a NEMA scatter phantom, the size of which varied according to the relationship between the abdominal circumference and body weight. Using this information, the pNECR was calculated from the prompt and delayed PET sinograms to obtain the prediction equation of NECR vs. body weight. The time scaling factor (FTS) for the scan duration was finally derived to make PET images with equivalent SNR levels.Results: the SF and NECR had the following nonlinear relationships with the body weight: SF=0.15 ⋅ body weight0.3 and NECR = 421.36 (body weight)−0.84. The equation derived for FTS was 0.01⋅ body weight + 0.2, which means that, for example, a 120-kg person should be scanned 1.8 times longer than a 70 kg person, or the scan time for a 40-kg person can be reduced by 30%.Conclusion: the equation of the relative time demand derived in this study will be useful for maintaining consistent PET image quality in clinics.

Fabrication of thin film x-ray sensor using particle-in-binder method for automatic exposure control in digital radiography

An automatic exposure control (AEC) detector is a control device that ensures consistent x-ray image quality and limits patient exposure in digital radiography. Among several kinds of AEC detectors, solid-state sensors offer several advantages such as geometric efficiency due to small thickness, high sensitivity, fast reaction time, and excellent stability. Commercially, the use of single-crystal silicon sensors for AEC detector has grown over time, but is still severely limited by large-area production techniques and mechanically fragile properties. Therefore, our study focused on developing a method of fabricating solid-state sensors that do not suffer from these limitations. The particle-in-binder method was used to fabricate silicon dioxide-based photoconductor films. Because silicon dioxide has a low atomic number and a low work function, it is a suitable material for generating sufficient electron-hole pairs by incident x-rays as well as not negatively affect the image detector of the digital radiography. To verify the feasibility of the silicon dioxide film as an AEC detector, electrical properties such as x-ray transmission and x-ray linearity were measured and compared with those of a commercialized silicon film. Over 90% x-ray transmission was achieved using a 500 μ m silicon dioxide film, which is suitable for an AEC detector. Also, an error below 3% was obtained from both x-ray current and voltage linearity tests. The results of bending tests demonstrated the properties of the silicon dioxide film to be more mechanically strong and stable compared with the commercialized silicon film. These properties were a result of the use of binder materials, which resulted in the flexibility of the film.

Overdrive technology compensating for ambient temperature

We propose an overdrive (OD) technology to precisely compensate for the temperature-dependent response characteristics of liquid-crystal displays (LCDs). The optical responses of LCDs are highly dependent on ambient temperature. After analyzing the optimized OD values, the new OD technology uses simple calculation logic instead of bulky OD lookup tables to obtain OD values of rising transitions over a wide range of ambient temperatures. We also show that it is possible to automatically adjust the optimum OD values depending on the ambient temperature. The results show that the proposed OD technology can improve motion image quality without any motion artifacts regardless of the ambient temperature. We expect that our proposed OD technology will ensure that LCD products have a consistent motion image quality regardless of the ambient temperature without any increase in cost.

TH-C-18A-06: Combined CT Image Quality and Radiation Dose Monitoring Program Based On Patient Data to Assess Consistency of Clinical Imaging Across Scanner Models

Purpose: One of the principal challenges of clinical imaging is to achieve an ideal balance between image quality and radiation dose across multiple CT models. The number of scanners and protocols at large medical centers necessitates an automated quality assurance program to facilitate this objective. Therefore, the goal of this work was to implement an automated CT image quality and radiation dose monitoring program based on actual patient data and to use this program to assess consistency of protocols across CT scanner models. Methods: Patient CT scans are routed to a HIPPA compliant quality assurance server. CTDI, extracted using optical character recognition, and patient size, measured from the localizers, are used to calculate SSDE. A previously validated noise measurement algorithm determines the noise in uniform areas of the image across the scanned anatomy to generate a global noise level (GNL). Using this program, 2358 abdominopelvic scans acquired on three commercial CT scanners were analyzed. Median SSDE and GNL were compared across scanner models and trends in SSDE and GNL with patient size were used to determine the impact of differing automatic exposure control (AEC) algorithms. Results: There was a significant difference in both SSDE and GNL across scanner models (9–33% and 15–35% for SSDE and GNL, respectively). Adjusting all protocols to achieve the same image noise would reduce patient dose by 27–45% depending on scanner model. Additionally, differences in AEC methodologies across vendors resulted in disparate relationships of SSDE and GNL with patient size. Conclusion: The difference in noise across scanner models indicates that protocols are not optimally matched to achieve consistent image quality. Our results indicated substantial possibility for dose reduction while achieving more consistent image appearance. Finally, the difference in AEC methodologies suggests the need for size-specific CT protocols to minimize variability in image quality across CT vendors.

Methods for CT Automatic Exposure Control Protocol Translation Between Scanner Platforms

An imaging facility with a diverse fleet of CT scanners faces considerable challenges when propagating CT protocols with consistent image quality and patient dose across scanner makes and models. Although some protocol parameters can comfortably remain constant among scanners (eg, tube voltage, gantry rotation time), the automatic exposure control (AEC) parameter, which selects the overall mA level during tube current modulation, is difficult to match among scanners, especially from different CT manufacturers. Objective methods for converting tube current modulation protocols among CT scanners were developed. Three CT scanners were investigated, a GE LightSpeed 16 scanner, a GE VCT scanner, and a Siemens Definition AS+ scanner. Translation of the AEC parameters such as noise index and quality reference mAs across CT scanners was specifically investigated. A variable-diameter poly(methyl methacrylate) phantom was imaged on the 3 scanners using a range of AEC parameters for each scanner. The phantom consisted of 5 cylindrical sections with diameters of 13, 16, 20, 25, and 32 cm. The protocol translation scheme was based on matching either the volumetric CT dose index or image noise (in Hounsfield units) between two different CT scanners. A series of analytic fit functions, corresponding to different patient sizes (phantom diameters), were developed from the measured CT data. These functions relate the AEC metric of the reference scanner, the GE LightSpeed 16 in this case, to the AEC metric of a secondary scanner. When translating protocols between different models of CT scanners (from the GE LightSpeed 16 reference scanner to the GE VCT system), the translation functions were linear. However, a power-law function was necessary to convert the AEC functions of the GE LightSpeed 16 reference scanner to the Siemens Definition AS+ secondary scanner, because of differences in the AEC functionality designed by these two companies. Protocol translation on the basis of quantitative metrics (volumetric CT dose index or measured image noise) is feasible. Protocol translation has a dependency on patient size, especially between the GE and Siemens systems. Translation schemes that preserve dose levels may not produce identical image quality.

A liquid crystal display with consistent moving image quality regardless of viewing angles

This paper proposes a new overdrive (OD) technology to precisely compensate for the viewing angle dependent characteristics of LCDs. This paper reports that optical response of liquid crystal displays (LCDs) is considerably dependent on viewing angles for the first time. The new OD technology applies different OD look-up tables (LUTs) depending on the viewing angles. In addition, we combine a new OD technology with an eye tracker that is usually adopted for autostereoscopic 3D LCD systems. The application results show that a new OD technology improves the motion image quality perfectly regardless of viewing angles. We expect that our proposed method will definitely enable the LCD products to have consistent motion image quality regardless of viewing angles. • This paper reports that optical response of liquid crystal displays (LCDs) are considerably dependent on viewing angles for the first time. • We propose a new overdrive (OD) technology to precisely compensate for the viewing angle dependent characteristics of LCDs. • The new OD technology applies different OD look-up tables (LUTs) depending on the viewing angles. • We also combine a new OD technology with an eye tracker that is usually adopted for autostereoscopic 3D LCD systems. • Application results show that the new OD technology improves the motion image quality perfectly regardless of viewing angles.

High resolution 3D diffusion MRI of carotid plaque on 3T

Background Diffusion MRI (DWI and ADC) has been shown to provide excellent contrast for characterizing carotid plaque components such as necrotic lipid core and intraplaque hemorrhage ex vivo [1] and in vivo [2]. However, conventional 2D EPI-based methods have suboptimal image quality and limited spatial resolution leading to difficulties in ADC calculation, limiting the clinical utility of this technique. The purpose of this work is to develop a new diffusion imaging method for carotid plaque characterization that (1) allows 3D imaging; (2) improves spatial resolution (0.6 × 0.6 × 2 mm3); and (3) provides consistent and high image quality.