Motion-artifact-free single shot two-beam optical coherence elastography system.

Significance: The assessment of the biomechanical properties of the skin using various imaging techniques has been used as a diagnostic tool in dermatology. Optical coherence elastography (OCE) is one of the techniques that allows for the measurement of elastic properties. OCE relies on measuring tissue displacements induced by external sources. Measuring the tissue's mechanical properties in vivo using OCE is often challenging due to bulk tissue movement. Aim: This study aimed to develop an OCE system that allows for minimizing the effects of bulk tissue movements. To achieve this, we designed a two-beam OCE system that simultaneously measures the tissue displacement at two locations on the sample. This allows for cancelling the effect of the tissue bulk movement, which is common to both measurement points. Approach: We used a piezoelectric transducer to generate surface acoustic waves (SAW) in the sample. The velocity of the excited waves, which is proportional to the rigidity of the sample, was measured by calculating the phase delay of the SAW at two locations on the sample. Simultaneous measurement at two locations was achieved by dividing a single light beam into two by focusing on the sample at two different locations. The two beams travel different optical path lengths, and the reflected signals were depth encoded in a single optical coherence tomography scan using a single reference beam. Results: The system was characterized using different tissue-mimicking phantoms and the skin of healthy volunteers at the wrist and the palm. We achieved an approximately 50-fold increase in phase sensitivity measurement. Conclusions: We designed a simple two-beam OCE system that effectively minimizes the effect of tissue movement. We believe that the presented system will find immediate applications in the clinic to monitor the progression of systemic sclerosis disease.

RAVE-T2/T1 - Feasibility of a new hybrid MR-sequence for free-breathing abdominal MRI in children and adolescents.

BACKGROUND: The new radial volumetric encoding RAVE-T2/T1 hybrid sequence is a modern three-dimensional sequence with multiparametric approach, which includes T2- and T1-weighted contrasts obtained in identical slice position during one measurement. However, the RAVE-T2/T1 hybrid sequence is not yet being used in clinical routine. PURPOSE: The aim of this study was to evaluate the RAVE-T2/T1 hybrid sequence in a pediatric population with a clinical indication for an abdominal MRI examination to demonstrate that the hybrid imaging may be less challenging to perform on children. MATERIALS AND METHODS: Our retrospective observational study included pediatric patients of all age groups and required for an abdominal MRI examination. Non-contrast standard axial T1 DIXON and non-contrast RAVE-T2/T1 hybrid sequence were obtained at 3 T. MRI studies were analyzed independently by two pediatric radiologists using a 5-point Likert-type scale in five different categories. T1- and T2-weighted sequences were each compared with the RAVE-T2/T1-sequence using a Wilcoxon signed-rank test. RESULTS: The analysis included 15 children (mean age, 11 years and 4 months, 7 girls and 8 boys). The Cohens Kappa of interrater agreement measured 0.62. The T2 weighted part of the RAVE-T2/T1 sequence was significantly better than the standard T2 HASTE sequence in four of five image quality categories: overall image quality (2.2 ± 0.7 vs 1.8 ± 0,7, p = 0.03), respiratory motion artefacts (3.8 ± 0.4 vs 2.0 ± 0.7, p <= 0.01), portal vein clarity (3.3 ± 0.8 vs 2.2 ± 0.7, p <= 0.01), hepatic margin sharpness (2.4 ± 1,0 vs 1.8 ± 0.7, p <= 0.01). The T1 weighted part of the RAVE-T2/T1 sequence was significantly better than the standard T1 DIXON weighted sequence in three of five image quality categories: respiratory motion artefacts (4.0 ± 0.2 vs 3.6 ± 0.8, p = 0.01), portal vein clarity (2.7 ± 0.9 vs 2.1 ± 0.7, p <= 0.01), hepatic margin sharpness (3.2 ± 0.7 vs 2.6 ± 0.9, p <= 0.01). CONCLUSIONS: The RAVE-T2/T1 hybrid sequence is feasible and equal compared to standard T1- and T2-weighted sequences in the assessment of abdominal organs in a pediatric population. Due to non-inferiority to the current standard sequences for abdominal imaging, the RAVE-T2/T1 hybrid sequence is a good alternative for children who cannot be examined in breath-hold technique.

Real-time measurement of repetitive micro bulk motion vector and motion noise removal in optical coherence tomography angiography.

In this work, we developed a motion estimation and correction method which real-time obtained the direction and displacement of repetitive micro bulk motion (such as cardiac and respiratory motion) on an SS-OCT system without additional tracking hardware, and reduced the motion noise in optical coherence tomography angiography (OCTA). In the approach, the direction of repetitive micro bulk motion was considered fixed, and proportional relationships between the motion components in three directions were determined; Then we performed one-dimension cross-correlation to obtain depth displacement which was further used to obtain other two motion components, and greatly reduced the computation; The processing speed on a graphic processing unit was 478 pairs of B-Scans per second, and the measurement range was larger than the range of the angiogram-based methods. Lastly, corrupt angiograms were recovered by adaptive scan protocol, and reduced acquisition time in comparison with the previous work.

Interplane bulk motion analysis and removal based on normalized cross-correlation in optical coherence tomography angiography.

Bulk motion seriously degrades the image quality of optical coherence tomography angiography (OCTA). Conventional correction methods focus on in-plane displacement, while the bulk motion component perpendicular to B-scans also introduces noise. This work first presents an evaluation of this component using a specific scan protocol and an approximate expression derived from peak-normalized cross-correlation values, and then quantitatively assesses how interplane bulk motion noise reduce the sensitivity of cross-sectional angiograms. Finally, we developed a repetitive bulk motion correction method based on the estimated displacements and redundant volume scans. The correction does not require registration and angiogram reconstruction of low flow sensitivity frames, and the results of in vivo mice skin OCTA imaging experiments show that the proposed method can effectively reduce bulk motion noise caused by cardiac and respiratory motion and occasional shaking, and improve OCTA image quality, which has practical significance for clinical OCTA diagnosis and analysis.

Body motion detection and correction in cardiac PET: Phantom and human studies.

PURPOSE: Patient body motion during a cardiac positron emission tomography (PET) scan can severely degrade image quality. We propose and evaluate a novel method to detect, estimate, and correct body motion in cardiac PET. METHODS: Our method consists of three key components: motion detection, motion estimation, and motion-compensated image reconstruction. For motion detection, we first divide PET list-mode data into 1-s bins and compute the center of mass (COM) of the coincidences' distribution in each bin. We then compute the covariance matrix within a 25-s sliding window over the COM signals inside the window. The sum of the eigenvalues of the covariance matrix is used to separate the list-mode data into "static" (i.e., body motion free) and "moving" (i.e. contaminated by body motion) frames. Each moving frame is further divided into a number of evenly spaced sub-frames (referred to as "sub-moving" frames), in which motion is assumed to be negligible. For motion estimation, we first reconstruct the data in each static and sub-moving frame using a rapid back-projection technique. We then select the longest static frame as the reference frame and estimate elastic motion transformations to the reference frame from all other static and sub-moving frames using nonrigid registration. For motion-compensated image reconstruction, we reconstruct all the list-mode data into a single image volume in the reference frame by incorporating the estimated motion transformations in the PET system matrix. We evaluated the performance of our approach in both phantom and human studies. RESULTS: Visually, the motion-corrected (MC) PET images obtained using the proposed method have better quality and fewer motion artifacts than the images reconstructed without motion correction (NMC). Quantitative analysis indicates that MC yields higher myocardium to blood pool concentration ratios. MC also yields sharper myocardium than NMC. CONCLUSIONS: The proposed body motion correction method improves image quality of cardiac PET.

Motion-robust sub-millimeter isotropic diffusion imaging through motion corrected generalized slice dithered enhanced resolution (MC-gSlider) acquisition.

PURPOSE: To develop an efficient MR technique for ultra-high resolution diffusion MRI (dMRI) in the presence of motion. METHODS: gSlider is an SNR-efficient high-resolution dMRI acquisition technique. However, subject motion is inevitable during a prolonged scan for high spatial resolution, leading to potential image artifacts and blurring. In this study, an integrated technique termed Motion Corrected gSlider (MC-gSlider) is proposed to obtain high-quality, high-resolution dMRI in the presence of large in-plane and through-plane motion. A motion-aware reconstruction with spatially adaptive regularization is developed to optimize the conditioning of the image reconstruction under difficult through-plane motion cases. In addition, an approach for intra-volume motion estimation and correction is proposed to achieve motion correction at high temporal resolution. RESULTS: Theoretical SNR and resolution analysis validated the efficiency of MC-gSlider with regularization, and aided in selection of reconstruction parameters. Simulations and in vivo experiments further demonstrated the ability of MC-gSlider to mitigate motion artifacts and recover detailed brain structures for dMRI at 860 µm isotropic resolution in the presence of motion with various ranges. CONCLUSION: MC-gSlider provides motion-robust, high-resolution dMRI with a temporal motion correction sensitivity of 2 s, allowing for the recovery of fine detailed brain structures in the presence of large subject movements.

Motion-corrected k-space reconstruction for interleaved EPI diffusion imaging.

PURPOSE: To develop a new approach to correct for physiological and macroscopic motion in multishot, interleaved echo-planar diffusion imaging. THEORY: This work built on the previous SPIRiT (iterative self-consistent parallel imaging reconstruction) based reconstruction for physiological motion correction in multishot diffusion-weighted imaging to account for macroscopic motion. In-plane rotation, translation correction, data rejection, and weighted combination are integrated in SPIRiT-based reconstruction to correct for ghosting artifacts, blurring, altered b-matrix, and residual artifacts caused by motion. METHODS: Numerical simulations (one data set was obtained from the Human Connectome Project) and in vivo experiments with deliberate bulk motion were performed to demonstrate the effectiveness of the proposed method. Diffusion images and quantitative tensor parameters were calculated to evaluate the correction performance. RESULTS: The proposed method provided images with reduced artifacts and diffusion tensors with improved accuracy in both simulations and in vivo experiments. For in vivo experiments with deliberate motion, the percentage error of fractional anisotropy in the genu of the corpus callosum was significantly reduced from 17.01 ± 12.64 to 5.73 ± 3.77 through motion correction. CONCLUSIONS: The proposed method can effectively correct for physiological and macroscopic motion artifacts in multishot interleaved echo-planar imaging, generate high resolution diffusion images, and improve the accuracy of tensor calculation. Magn Reson Med 79:1992-2002, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Adaptive bulk motion exclusion for improved robustness of abdominal magnetic resonance imaging.

Non-Cartesian magnetic resonance imaging (MRI) sequences have shown great promise for abdominal examination during free breathing, but break down in the presence of bulk patient motion (i.e. voluntary or involuntary patient movement resulting in translation, rotation or elastic deformations of the body). This work describes a data-consistency-driven image stabilization technique that detects and excludes bulk movements during data acquisition. Bulk motion is identified from changes in the signal intensity distribution across different elements of a multi-channel receive coil array. A short free induction decay signal is acquired after excitation and used as a measure to determine alterations in the load distribution. The technique has been implemented on a clinical MR scanner and evaluated in the abdomen. Six volunteers were scanned and two radiologists scored the reconstructions. To show the applicability to other body areas, additional neck and knee images were acquired. Data corrupted by bulk motion were successfully detected and excluded from image reconstruction. An overall increase in image sharpness and reduction of streaking and shine-through artifacts were seen in the volunteer study, as well as in the neck and knee scans. The proposed technique enables automatic real-time detection and exclusion of bulk motion during MR examinations without user interaction. It may help to improve the reliability of pediatric MRI examinations without the use of sedation.