Temporal Resolution Sequences Research Articles

Speckle Tracking Accuracy Enhancement by Temporal Super-Resolution of Three-Dimensional Echocardiography Images.

Background:Speckle tracking has always been a challenging issue in echocardiography images due to the lowcontrast and noisy nature of ultrasonic imaging modality. While in ultrasound imaging, framerate is limited by image size and sound speed in tissue, speckle tracking results get worse inthree-dimensional imaging due to its lower frame rate. Therefore, numerous techniques have beenreported to overcome this limitation and enhance tracking accuracy.Methods:In this work, we have proposedto increase the frame rate temporally for a sequence of three-dimensional (3D) echocardiographyframes to make tracking more accurate. To increase the number of frames, cubic B-spline is usedto interpolate between intensity variation time curves extracted from every single voxel in theimage during the cardiac cycle. We have shown that the frame rate increase will result in trackingaccuracy improvement.Results:To prove the efficiency of the proposed method, numerical evaluation metricsfor tracking are reported to make a comparison between high temporal resolution sequences andlow temporal resolution sequences. Anatomical affine optical flow is selected as the state-of-the-artspeckle tracking method, and a 3D echocardiography dataset is used to evaluate the proposedmethod.Conclusion:Results show that it is beneficial for speckle tracking to perform on temporally condensedframes rather than ordinary clinical 3D echocardiography images. Normalized mean enhancementvalues for mean absolute error, Hausdorff distance, and Dice index for all cases and all frames are0.44 ± 0.09, 0.42± 0.09, and 0.36 ± 0.06, respectively.

Assessment of proximal pulmonary arterial stiffness using magnetic resonance imaging: effects of technique, age and exercise.

IntroductionTo compare the reproducibility of pulmonary pulse wave velocity (PWV) techniques, and the effects of age and exercise on these.Methods10 young healthy volunteers (YHV) and 20 older healthy volunteers (OHV) with no cardiac or lung condition were recruited. High temporal resolution phase contrast sequences were performed through the main pulmonary arteries (MPAs), right pulmonary arteries (RPAs) and left pulmonary arteries (LPAs), while high spatial resolution sequences were obtained through the MPA. YHV underwent 2 MRIs 6 months apart with the sequences repeated during exercise. OHV underwent an MRI scan with on-table repetition. PWV was calculated using the transit time (TT) and flow area techniques (QA). 3 methods for calculating QA PWV were compared.ResultsPWV did not differ between the two age groups (YHV 2.4±0.3/ms, OHV 2.9±0.2/ms, p=0.1). Using a high temporal resolution sequence through the RPA using the QA accounting for wave reflections yielded consistently better within-scan, interscan, intraobserver and interobserver reproducibility. Exercise did not result in a change in either TT PWV (mean (95% CI) of the differences: −0.42 (−1.2 to 0.4), p=0.24) or QA PWV (mean (95% CI) of the differences: 0.10 (−0.5 to 0.9), p=0.49) despite a significant rise in heart rate (65±2 to 87±3, p<0.0001), blood pressure (113/68 to 130/84, p<0.0001) and cardiac output (5.4±0.4 to 6.7±0.6 L/min, p=0.004).ConclusionsQA PWV performed through the RPA using a high temporal resolution sequence accounting for wave reflections yields the most reproducible measurements of pulmonary PWV.

SU‐D‐18C‐04: The Feasibility of Quantifying MRI Contrast Agent in Pulsatile Flowing Blood Using DCE‐MRI

Purpose:To assess the feasibility of accurately quantifying the concentration of MRI contrast agent (CA) in pulsatile flowing blood by measuring its T1, as is common for the purposes of obtaining a patientspecific arterial input function (AIF). Dynamic contrast enhanced (DCE) – MRI and pharmacokinetic (PK) modelling is widely used to produce measures of vascular function but accurate measurement of the AIF undermines their accuracy. A proposed solution is to measure the T1 of blood in a large vessel using the Fram double flip angle method during the passage of a bolus of CA. This work expands on previous work by assessing pulsatile flow and the changes in T1 seen with a CA bolus.Methods:A phantom was developed which used a physiological pump to pass fluid of a known T1 (812ms) through the centre of a head coil of a clinical 1.5T MRI scanner. Measurements were made using high temporal resolution sequences suitable for DCE‐MRI and were used to validate a virtual phantom that simulated the expected errors due to pulsatile flow and bolus of CA concentration changes typically found in patients.Results:: Measured and virtual results showed similar trends, although there were differences that may be attributed to the virtual phantom not accurately simulating the spin history of the fluid before entering the imaging volume. The relationship between T1 measurement and flow speed was non‐linear. T1 measurement is compromised by new spins flowing into the imaging volume, not being subject to enough excitations to have reached steady‐state. The virtual phantom demonstrated a range of recorded T1 for various simulated T1 / flow rates.Conclusion:T1 measurement of flowing blood using standard DCE‐MRI sequences is very challenging. Measurement error is non‐linear with relation to instantaneous flow speed. Optimising sequence parameters and lowering baseline T1 of blood should be considered.

Highly accelerated real-time T2-weighted imaging with through-time radial GRAPPA and low-latency GPU reconstruction

Background T2-weighted cardiac images are commonly used for edema detection [1-4]. However, neither black-blood TSE nor cine images can offer real-time edema monitoring, and are therefore not suitable for the guidance of cardiac ablation procedures. We proposed a radial T2weighted interrupted balanced SSFP (rT2W-iSSFP), a real-time high temporal resolution sequence targeted at monitoring edema.

An efficient content-adaptive motion-compensated 3-D DWT with enhanced spatial and temporal scalability

We propose a novel, content adaptive method for motion-compensated three-dimensional wavelet transformation (MC 3-D DWT) of video. The proposed method overcomes problems of ghosting and nonaligned aliasing artifacts which can arise in regions of motion model failure, when the video is reconstructed at reduced temporal or spatial resolutions. Previous MC 3-D DWT structures either take the form of MC temporal DWT followed by a spatial transform ("t+2D"), or perform the spatial transform first ("2D + t"), limiting the spatial frequencies which can be jointly compensated in the temporal transform, and hence limiting the compression efficiency. When the motion model fails, the "t + 2D" structure causes nonaligned aliasing artifacts in reduced spatial resolution sequences. Essentially, the proposed transform continuously adapts itself between the "t + 2D" and "2D + t" structures, based on information available within the compressed bit stream. Ghosting artifacts may also appear in reduced frame-rate sequences due to temporal low-pass filtering along invalid motion trajectories. To avoid the ghosting artifacts, we continuously select between different low-pass temporal filters, based on the estimated accuracy of the motion model. Experimental results indicate that the proposed adaptive transform preserves high compression efficiency while substantially improving the quality of reduced spatial and temporal resolution sequences.

Magnetic Resonance Imaging of the Spleen and Pancreas

MRI of the spleen and pancreas requires specialized sequences which diminish artifacts in the upper abdomen. High temporal resolution sequences (e.g., spoiled gradient echo) acquired immediately after intravenous Gd-DTPA administration are necessary for imaging both the spleen and pancreas. In evaluating the spleen, early post Gd-DTPA images are essential as many focal disease processes (e.g., lymphomatous deposits or metastases) equilibrate rapidly (< 2 min) with splenic parenchyma. Complete pancreatic examination also requires the use of T1-weighted fat suppressed spin echo. T2-weighted images provide complementary information in a number of settings, in particular in the evaluation of islet cell tumors. Pancreatic ductal carcinoma is low signal on T1-weighted images and enhances in a diminished fashion on immediate post Gd-DTPA images. These tumors are well differentiated from focal chronic pancreatitis and islet celltumors based on their appearances on combined T1, T2-weighted and immediate post Gd-DTPA enhanced images.