Non-contrast pulmonary perfusion MRI in patients with cystic fibrosis.

PURPOSE: This study aimed to assess the feasibility of Self-gated Non-Contrast-Enhanced Functional Lung (SENCEFUL) MRI for detection of pulmonary perfusion deficits in patients with cystic fibrosis. METHODS: Twenty patients with cystic fibrosis and 20 matched healthy controls underwent SENCEFUL-MRI at 1.5 T with reconstruction of perfusion and perfusion phase maps (i.e. comparable to pulse wave delays). Four blinded readers rated both types of maps separately followed by simultaneous assessment thereof. Perfusion phase data was plotted in histograms and a Peak-to-Offset ratio was calculated for comparison to subjective scoring and correlation (Spearman) to lung function parameters. Sensitivity, specificity and positive and negative predictive values were calculated for subjective scoring and Peak-to-Offset ratios. Intraclass correlation (ICC) was used to assess the interrater agreement. RESULTS: Readers attributed pathological ratings 2.2-3.5 times more frequently to the CF-group. The sensitivity with regard to a correct assignment to CF was similar between ratings (perfusion only vs. perfusions phase only vs. simultaneous assessment: 0.54-0.56), while specificity increased from 0.75 to 0.85 for simultaneous assessment. ICC was 0.77-0.84 for subjective scoring. ROC-analysis of Peak-to-Offset ratios on a mean per-subject basis revealed a sensitivity of 0.75 and specificity of 0.85 (PPV 0.83, NPV 0.77). Functional pulmonary parameters indicative of bronchial obstruction and Peak-to-Offset ratios showed positive correlation (FEV1: 0.77; FEF75: 0.76). CONCLUSIONS: SENCEFUL-MRI bears the potential for monitoring CF including disease-associated patterns of altered pulmonary perfusion. The proposed Peak-to-Offset ratio derived from pulmonary perfusion phase measurements could represent an objective future marker for perfusion impairment.

Field camera versus phantom-based measurement of the gradient system transfer function (GSTF) with dwell time compensation.

PURPOSE: The gradient system transfer function (GSTF) can be used to describe the dynamic gradient system and applied for trajectory correction in non-Cartesian MRI. This study compares the field camera and the phantom-based methods to measure the GSTF and implements a compensation for the difference in measurement dwell time. METHODS: The self-term GSTFs of a MR system were determined with two approaches: 1) using a dynamic field camera and 2) using a spherical phantom-based measurement with standard MR hardware. The phantom-based GSTF was convolved with a box function to compensate for the dwell time dependence of the measurement. The field camera and phantom-based GSTFs were used for trajectory prediction during retrospective image reconstruction of 3D wave-CAIPI phantom images. RESULTS: Differences in the GSTF magnitude response were observed between the two measurement methods. For the wave-CAIPI sequence, this led to deviations in the GSTF predicted trajectories of 4% compared to measured trajectories, and residual distortions in the reconstructed phantom images generated with the phantom-based GSTF. Following dwell-time compensation, deviations in the GSTF magnitudes, GSTF-predicted trajectories, and resulting image artifacts were eliminated (< 0.5% deviation in trajectories). CONCLUSION: With dwell time compensation, both the field camera and the phantom-based GSTF self-terms show negligible deviations and lead to strong artifact reduction when they are used for trajectory correction in image reconstruction.

Power-Doppler perfusion phenotype in RA patients is dependent on anti-citrullinated peptide antibody status, not on rheumatoid factor.

It is not known whether there are any consistent non-serological differences between seropositive and seronegative rheumatoid arthritis, and if any, whether they depend upon rheumatoid factor (RF), anti-citrullinated peptide antibodies (ACPA), or both. In a pilot study, we showed that the two forms could be differentiated using power-Doppler sonography (PDS), and that the difference is ACPA dependent. This extended study explored whether the previous findings could be confirmed. 103 patients 51 ACPA positive (ACPA +), 52 ACPA negative (ACPA -) with active wrist arthritis were examined using PDS. By means of a temporal image series, pulsatility was evaluated over a 3-5-s period, maximum and minimum perfusion signal were determined using a computer program counting the number of coloured pixels for each frame. Maxima (Pmax) and minima (Pmin) were determined, and the standardized peak-to-peak amplitude sA was calculated (sA = (Pmax - Pmin)/Pmax). This parameter was then compared for ACPA + and ACPA- patients. In addition, a multivariate regression was performed, to determine which factors influence sA. sA differed significantly between ACPA + and ACPA- patients [20% (13-26) vs. 41% (32-57), p < 0. 0001]. In the multivariate analysis, age (t = 2.5, p = 0.02) and ACPA status (t = - 4.8, p < 0.0001) were independent predictors of sA. PDS perfusion patterns are different in seropositive and seronegative RA. The difference appears to be ACPA, not RF dependent. This suggests that the underlying pathophysiological process is different in ACPA-positive and ACPA-negative RA.

UTE-SENCEFUL: first results for 3D high-resolution lung ventilation imaging.

PURPOSE: This study aimed to develop a 3D MRI technique to assess lung ventilation in free-breathing and without the administration of contrast agent. METHODS: A 3D-UTE sequence with a koosh ball trajectory was developed for a 3 Tesla scanner. An oversampled k-space was acquired, and the direct current signal from the k-space center was used as a navigator to sort the acquired data into 8 individual breathing phases. Gradient delays were corrected, and iterative SENSE was used to reconstruct the individual timeframes. Subsequently, the signal changes caused by motion were eliminated using a 3D image registration technique, and ventilation-weighted maps were created by analyzing the signal changes in the lung tissue. Six healthy volunteers and 1 patient with lung cancer were scanned with the new 3D-UTE and the standard 2D technique. Image quality and quantitative ventilation values were compared between both methods. RESULTS: UTE-based self-gated noncontrast-enhanced functional lung (SENCEFUL) MRI provided a time-resolved reconstruction of the breathing motion, with a 49% increase of the SNR. Ventilation quantification for healthy subjects was in statistical agreement with 2D-SENCEFUL and the literature, with a mean value of 0.11 ± 0.08 mL/mL for the whole lung. UTE-SENCEFUL was able to visualize and quantify ventilation deficits in a patient with lung tumor that were not properly depicted by 2D-SENCEFUL. CONCLUSION: UTE-SENCEFUL represents a robust MRI method to assess both morphological and functional information of the lungs in 3D. When compared to the 2D approach, 3D-UTE offered ventilation maps with higher resolution, improved SNR, and reduced ventilation artifacts.

Whole-heart cine MRI in a single breath-hold--a compressed sensing accelerated 3D acquisition technique for assessment of cardiac function.

PURPOSE: The aim of this study was to perform functional MR imaging of the whole heart in a single breath-hold using an undersampled 3 D trajectory for data acquisition in combination with compressed sensing for image reconstruction. MATERIALS AND METHODS: Measurements were performed using an SSFP sequence on a 3 T whole-body system equipped with a 32-channel body array coil. A 3 D radial stack-of-stars sampling scheme was utilized enabling efficient undersampling of the k-space and thereby accelerating data acquisition. Compressed sensing was applied for the reconstruction of the missing data. A validation study was performed based on a fully sampled dataset acquired by standard Cartesian cine imaging of 2 D slices on a healthy volunteer. The results were investigated with regard to systematic errors and resolution losses possibly introduced by the developed reconstruction. Subsequently, the proposed technique was applied for in-vivo functional cardiac imaging of the whole heart in a single breath-hold of 27  s. The developed technique was tested on three healthy volunteers to examine its reproducibility. RESULTS: By means of the results of the simulation (temporal resolution: 47  ms, spatial resolution: 1.4 × 1.4 × 8  mm, 3 D image matrix: 208 × 208 × 10), an overall acceleration factor of 10 has been found where the compressed sensing reconstructed image series shows only very low systematic errors and a slight in-plane resolution loss of 15 %. The results of the in-vivo study (temporal resolution: 40.5  ms, spatial resolution: 2.1 × 2.1 × 8  mm, 3 D image matrix: 224 × 224 × 12) performed with an acceleration factor of 10.7 confirm the overall good image quality of the presented technique for undersampled acquisitions. CONCLUSION: The combination of 3 D radial data acquisition and model-based compressed sensing reconstruction allows high acceleration factors enabling cardiac functional imaging of the whole heart within only one breath-hold. The image quality in the simulated dataset and the in-vivo measurement highlights the great potential of the presented technique for an efficient assessment of cardiac functional parameters.

[High-resolution functional cardiac MR imaging using density-weighted real-time acquisition and a combination of compressed sensing and parallel imaging for image reconstruction]. / Hochaufgelöste funktionelle Herz-MR Bildgebung mithilfe dichtegewichteter Echtzeit-Datenaufnahme und einer Kombination von Compressed Sensing und paralleler Bildgebung in der Rekonstruktion.

PURPOSE: The aim of this study was to perform high-resolution functional MR imaging using accelerated density-weighted real-time acquisition (DE) and a combination of compressed sensing (CO) and parallel imaging for image reconstruction. MATERIALS AND METHODS: Measurements were performed on a 3 T whole-body system equipped with a dedicated 32-channel body array coil. A one-dimensional density-weighted spin warp technique was used, i. e. non-equidistant phase encoding steps were acquired. The two acceleration techniques, compressed sensing and parallel imaging, were performed subsequently. From a complete Cartesian k-space, a four-fold uniformly undersampled k-space was created. In addition, each undersampled time frame was further undersampled by an additional acceleration factor of 2.1 using an individual density-weighted undersampling pattern for each time frame. Simulations were performed using data of a conventional human in-vivo cine examination and in-vivo measurements of the human heart were carried out employing an adapted real-time sequence. RESULTS: High-quality DECO real-time images using parallel acquisition of the function of the human heart could be acquired. An acceleration factor of 8.4 could be achieved making it possible to maintain the high spatial and temporal resolution without significant noise enhancement. CONCLUSION: DECO parallel imaging facilitates high acceleration factors, which allows real-time MR acquisition of the heart dynamics and function with an image quality comparable to that conventionally achieved with clinically established triggered cine imaging.