Cardiac CT blooming artifacts:clinical significance,root causes and potential solutions

This review paper aims to summarize cardiac CT blooming artifacts,how they present clinically and what their root causes and potential solutions are.A literature survey was performed covering any publications with a specific interest in calcium blooming and stent blooming in cardiac CT.The claims from literature are compared and interpreted,aiming at narrowing down the root causes and most promising solutions for blooming artifacts.More than 30 journal publications were identified with specific relevance to blooming artifacts.The main reported causes of blooming artifacts are the partial volume effect,motion artifacts and beam hardening.The proposed solutions are classified as high-resolution CT hardware,high-resolution CT reconstruction,subtraction techniques and post-processing techniques,with a special emphasis on deep learning(DL)techniques.The partial volume effect is the leading cause of blooming artifacts.The partial volume effect can be minimized by increasing the CT spatial resolution through higherresolution CT hardware or advanced high-resolution CT reconstruction.In addition,DL techniques have shown great promise to correct for blooming artifacts.A combination of these techniques could avoid repeat scans for subtraction techniques.

Combined surface electromyography,near-infrared spectroscopy and acceleration recordings of muscle contraction:The effect of motion

Noninvasive techniques,surface electromyography(sEMG)in particular,are being increasingly employed for assessing muscle activity.In these studies,local oxygen consumption and muscle metabolism are of great interest.Measurements can be performed noninvasively using optics-based methods such as near-infrared spectroscopy(NIRS).By combining energy con-sumption data provided by NIRS with muscle level activation data from sEMG,we may gain an insight into the metabolic and functional characteristics of muscle tissue.However,muscle mo-tion may induce artifacts into EMG and NIRS.Thus,the inclusion of simultaneous motion measurements using accelerometers(ACMs)enhances possibilities to perceive the effects of motion on NIRS and EMG signals.This paper reviews the current state of noninvasive EMG and NIRS-based methods used to study muscle function.In addition,we built a combined sEMG/NIRS/ACM sensor to perform simultaneous measurements for static and dynamic exercises of a biceps brachii muscle.Further,we discuss the effect of muscle motion in response of NIRS and EMG when measured noninva-sively.Based on our preliminary studies,both NIRS and EMG supply specific information on muscle activation,but their signal responses also showed similarities with acceleration signals which,in this case,were supposed to be solely sensitive to motions.

A quantitative comparison of five optical coherence tomography angiography systems in clinical performance

AIM： To compare the clinical performance of 4 spectraldomain（SD） optical coherence tomography angiography（OCTA） systems： AngioVueTM, AngioPlexTM, Spectralis？ OCTA, AngioScan, and 1 swept-source（SS） OCTA SS OCT AngioTM. METHODS： Twenty-seven undilated right eyes of 27 participants underwent OCTA examination using five different systems respectively for both 3×3 and 6×6 mm^2 scan pattern（Spectralis OCTA for 3×3 mm^2 scan only）. Image quality, including vessel valid visibility and the number of motion artifacts, and acquisition time were evaluated. Repeated measures analysis of variance（ANOVA） with Bonferroni＇s post-test and Friedman test with Dunn＇s posttest were used to compare measurements.RESULTS： The age of the subjects was 28.19±5.55 y（range, 23-49 y）. The spherical equivalent refraction was-2.55±1.84 D（range, 0.00 to-5.25 D）. Significant difference was observed in the evaluation of vessel valid visibility（Angio Vue the highest： 0.111±0.031 for 3×3 mm^2 scan and 0.128±0.020 for 6×6 mm^2 scan）, number of motion artifacts（AngioVue the fewest： 0.778±1.086 for 3×3 mm^2 scan and 0.333±0.620 for 6×6 mm^2 scan） and acquisition time（AngioPlex the shortest： 8.537±1.921 s for 3×3 mm^2 scan and 8.298±1.741 s for 6×6 mm^2 scan; all P〈0.001）. CONCLUSION： There is poor agreement of measurements among systems. AngioVue provides images with the highest vessel valid visibility and the fewest motion artifacts. AngioPlex achieves the shortest acquisition.

Assessment of cerebral oxygenation response to hemodialysis using near-infrared spectroscopy (NIRS):Challenges and solutions

To date,the clinical use of functional near-infrared spectroscopy(NIRS)to detect cerebral ischemia has been largely limited to surgical settings,where motion artifacts are minimal.In this study,we present novel techniques to address the challenges of using NIRS to monitor ambu-latory patients with kidney disease during approximately eight hours of hemodialysis(HD)treatment.People with end-stage kidney disease who require HD are at higher risk for cognitive impairment and dementia than age-matched controls.Recent studies have suggested that HD-related declines in cerebral blood flow might explain some of the adverse outcomes of HD treatment.However,there are currently no established paradigms for monitoring cerebral per-fusion in real-time during HD treatment.In this study,we used NIRS to assess cerebral hemo-dynamic responses among 95 prevalent HD patients during two consecutive HD treatments.We observed substantial signal attenuation in our predominantly Black patient cohort that required probe modifications.We also observed consistent motion artifacts that we addressed by devel-oping a novel NIRS methodology,called the HD cerebral oxygen demand algorithm(HD-CODA),to identify episodes when cerebral oxygen demand might be outpacing supply during HD treatment.We then examined the association between a summary measure of time spent in cerebral deoxygenation,derived using the HD-CODA,and hemodynamic and treatment-related variables.We found that this summary measure was associated with intradialytic mean arterial pressure,heart rate,and volume removal.Future studies should use the HD-CODA to implement studies of real-time NIRS monitoring for incident dialysis patients,over longer time frames,and in other dialysis modalities.

Motion-Compensated Reconstruction Method Based on Rigid Motion Model with Multi-Object

This paper gives an efficient approach to reconstruct moving multiple objects （multi-object）. Each object has independently rigid motion which includes translation and rotation. The traditional FBP algorithm can resolve the one-object motion problem rather well. However, it suffers from perceptible motion artifacts in multi-object cases. This paper proposes a new motion-compensated reconstruction approach with a pdori knowledge of the rigid motion model. Both an FBP-type and an ART-type algorithm were derived. In an effort to evaluate the proposed algorithms, we have performed numerical studies by using different rigid motion models. Quantitative results demonstrate that the proposed FBP-type and ART-type algorithms can recon- struct multi-object free of motion artifacts.

Motion robust 4D-MRI sorting based on anatomic feature matching: A digital phantom simulation study

Purpose:Motion artifacts induced by breathing variations are common in 4D-MRI images.This study aims to reduce the motion artifacts by developing a novel,robust 4D-MRI sorting method based on anatomic feature matching and applicable in both cine and sequential acquisition.Method:The proposed method uses the diaphragm as the anatomic feature to guide the sorting of 4D-MRI images.Initially,both abdominal 2D sagittal cine MRI images and axial MRI images were acquired.The sagittal cine MRI images were divided into 10 phases as ground truth.Next,the phase of each axial MRI image is determined by matching its diaphragm position in the intersection plane to the ground truth cine MRI.Then,those matched phases axial images were sorted into 10-phase bins which were identical to the ground truth cine images.Finally,10-phase 4D-MRI were reconstructed from these sorted axial images.The accuracy of reconstructed 4D-MRI data was evaluated by comparing with the ground truth using the 4D eXtended Cardiac Torso(XCAT)digital phantom.The effects of breathing signal,including both regular(cosine function)and irregular(patient data)in both axial cine and sequential scanning modes,on reconstruction accuracy were investigated by calculating total relative error(TRE)of the 4D volumes,Volume-Percent-Difference(VPD)and Center-of-Mass-Shift(COMS)of the estimated tumor volume,compared with the ground truth XCAT images.Results:In both scanning modes,reconstructed 4D-MRI images matched well with ground truth with minimal motion artifacts.The averaged TRE of the 4D volume,VPD and COMS of the EOE phase in both scanning modes are 0.32%/1.20%/0.05 mm for regular breathing,and 1.13%/4.26%/0.21 mm for patient irregular breathing.Conclusion:The preliminary evaluation results illustrated the feasibility of the robust 4D-MRI sorting method based on anatomic feature matching.This method provides improved image quality with reduced motion artifacts for both cine and sequential scanning modes.

Sample entropy analysis of laser speckle fluctuations to suppress motion artifact on blood flow monitoring

Laser speckle imaging is a common technique to monitor blood flow.The fluctuations in speckle intensity can be related to the blood flow by calculating the speckle contrast,the ratio between the standard deviation of speckle fluctuations and the average intensity.However,this simple statistic calculation is easily affected by motion artifacts.In this study,we applied sample entropy analysis instead of calculating standard deviations of the speckle fluctuations.Similar to the traditional method,sample entropy-based speckle contrast increases linearly with flow rate but was shown to be more immune to sudden movements during an upper arm occlusion test.

Numerical method for axial motion artifact correction in retinal spectral-domain optical coherence tomography

A numerical method that compensates image distortions caused by random fluctuations of the distance to an object in spectral-domain optical coherence tomography(SD OCT)has been proposed and verified experimentally.The proposed method is based on the analysis of the phase shifts between adjacent scans that are caused by micrometer-scale displacements and the subsequent compensation for the displacements through phase-frequency correction in the spectral space.The efficiency of the method is demonstrated in model experiments with harmonic and random movements of a scattering object as well as during in vivo imaging of the retina of the human eye.

The energy-efficient implementation of an adaptive-filtering-based QRS complex detection method for wearable devices

Electrocardiogram（ECG） can be used as a valid way for diagnosing heart disease.To fulfill ECG processing in wearable devices by reducing computation complexity and hardware cost,two kinds of adaptive filters are designed to perform QRS complex detection and motion artifacts removal,respectively.The proposed design achieves a sensitivity of 99.49% and a positive predictivity of 99.72%,tested under the MIT-BIH ECG database.The proposed design is synthesized under the SMIC 65-nm CMOS technology and verified by post-synthesis simulation.Experimental results show that the power consumption and area cost of this design are of 160 μW and 1.09×10^5 μm^2,respectively.