Fast Dynamic MRI Research Articles

Compressed sensing plus motion (CS+M): A new perspective for improving undersampled MR image reconstruction.

We address the problem of reconstructing high quality images from undersampled MRI data. This is a challenging task due to the highly ill-posed nature of the problem. In particular, in dynamic MRI scans, the interaction between the target structure and the physical motion affects the acquired measurements leading to blurring artefacts and loss of fine details. In this work, we propose a framework for dynamic MRI reconstruction framed under a new multi-task optimisation model called Compressed Sensing Plus Motion (CS+M). Firstly, we propose a single optimisation problem that simultaneously computes the MRI reconstruction and the physical motion. Secondly, we show our model can be efficiently solved by breaking it up into two computationally tractable problems. The potentials and generalisation capabilities of our approach are demonstrated in different clinical applications including cardiac cine, cardiac perfusion and brain perfusion imaging. We show, through numerical experiments, that the proposed scheme reduces blurring artefacts, and preserves the target shape and fine details in the reconstruction. We also report the highest quality reconstruction under high undersampling rates in comparison to several state of the art techniques.

Feasibility of Fast Dynamic MRI for Noninvasive Monitoring During Ectopic Liver Cell Transplantation to the Spleen in a Porcine Model

Liver cell transplantation is a promising approach for the treatment of metabolic liver disorders. However, a method for noninvasive monitoring during liver cell transplantation is not available clinically. The aim of this study was to investigate the feasibility of fast dynamic MRI monitoring during liver cell infusion to the spleen, which is considered an ectopic implantation site for liver cell transplantation. Porcine liver cells were labeled with micron-sized iron oxide particles and infused to the spleens of pigs (n = 5) via the lineal artery. MRI was performed using a 3-T MR scanner. Initially, T1- and T2-weighted pulse sequences were tested. Thereafter, fast dynamic MRI was performed during cell infusion. MR findings were verified by immunohistological examinations. Images from static MRI (TR/TE, 2500/105.2) showed significantly lower signal intensity and signal-to-noise ratio after cell infusion compared with pretransplant images. T2-weighted fast dynamic MRI enabled visualization of signal decrease of the spleen during cell infusion. When cells were infused systemically, no signal changes in the spleen were observed. This study shows that fast dynamic MRI can enable noninvasive monitoring during liver cell transplantation to the spleen. This approach could be useful for preclinical studies and for quality control of clinical liver cell transplantation.

Dynamic MR assessment of the anorectal angle and puborectalis muscle in pediatric patients with anismus: Technique and feasibility

To assess the feasibility of dynamic breath-hold MRI for evaluating changes in the anorectal angle and movements of the pelvic-floor musculature (puborectalis) during resting and straining states in pediatric patients presenting with anismus. Six pediatric patients (7-13 years old) with chronic constipation and manometric evidence of anismus were assessed by dynamic breath-hold MRI. Changes in the anorectal angle, the degree of pelvic-floor descent, and the thickness and length of the puborectalis muscles were measured during rest and straining. The findings were compared with those obtained in six age- and sex-matched controls. The children with anismus had a smaller anorectal angle during straining, and the angle decreased from rest to defecation. The puborectalis also became paradoxically shortened and thickened during straining in the anismus group. There were significant differences between the two groups in terms of the change of degree of the anorectal angle, and the thickness and length of the puborectalis muscle during straining. Fast dynamic MRI is feasible for evaluating pelvic-floor movement in pediatric patients. Preliminary results suggest that children with anismus have a smaller anorectal angle and a different puborectalis configuration compared to controls.

Post-radiotherapy contrast enhancement changes in fast dynamic MRI of cervical carcinoma.

This pilot study determines fast dynamic gadolinium enhanced MRI contrast enhancement parameters (onset of enhancement and time to peak enhancement) before and after radiotherapy in 10 cervical carcinoma patients. Before radiotherapy, onset of enhancement and time to peak enhancement were early, with a median of 4.5 and 5.2 seconds, respectively. High-grade tumors showed early enhancement, compared with low-grade. After radiotherapy, contrast enhancement patterns differed. In survivors, onset of enhancement after radiotherapy was later than before radiotherapy. In non-survivors, onset of enhancement after radiotherapy was still early. The median difference in onset of enhancement before and after radiotherapy in survivors and non-survivors was an increase of 3.2 and a decrease of 1.1 seconds, respectively. Early onset of enhancement after radiotherapy was a better predictor for survival than a high-signal intensity zone on post radiotherapy unenhanced T1/T2-weighted MRI. It is concluded that enhancement parameters from fast dynamic Gd-enhanced MR images can provide additional functional information with regard to tumor vascularization, and may have prognostic significance. It complements clinical examination and unenhanced MRI in determining the effectiveness of radiotherapy treatment in cervical carcinoma. Future studies will focus on the clinical utility and improvements of the estimation of contrast-enhanced parameters with this new technique.

Fast magnetic resonance imaging of the heart

Fast MR imaging techniques have multiple applications for evaluation of cardiac disease. Cine MRI and MR tagging have been shown to be highly accurate and reproducible in evaluating regional and global myocardial function. Segmented k-space cine MRI and echo-planar imaging (EPI) can considerably improve time efficiency and thereby the clinical utility of these techniques. Double IR fast spin-echo sequences enable breath-hold acquisition of T2 weighted MRI with good suppression of the blood signal. Myocardial perfusion can be assessed with fast dynamic MRI after administration of contrast media. Multi-shot EPI improves temporal resolution and also provides full coverage of the left ventricle. Substantial progress has been made in respiratory gated 3D coronary artery MR angiography with navigator echoes. The newer approaches for coronary arterial imaging including breath-hold three-dimensional segmented EPI and high resolution spiral MRI may further improve clinical usefulness of coronary MR angiography. Assessment of coronary blood flow and flow reserve with phase contrast MRI has the potential for the non-invasive evaluating of the presence and significance of stenosis in the native coronary artery and bypass grafts. Fast cardiac MRI may emerge as a cost effective modality for comprehensive assessments of both cardiac morphology, function, blood flow and perfusion.

Fast dynamic contrast-enhanced colour-coded MRI in uterine cervix carcinoma: Useful for tumour staging?

To quantify first-pass enhancement of cervix carcinoma using fast dynamic MRI. To assess the accuracy of dynamic contrast-enhanced colour-coded MRI for determining tumour invasion into surrounding pelvic tissues. Gadolinium enhanced dynamic MRI at one image every 2 s was performed in 47 patients with cervical carcinoma and five controls. First-pass contrast enhancement of cervix carcinoma and surrounding pelvic tissues was quantified. Automated colour-coded images were constructed using the dynamic parameters slope, amplitude and timing of enhancement. Of 47 patients, 28 underwent surgery and colour coded images were correlated with histological findings. First-pass contrast enhancement imaging of cervix carcinoma required a temporal resolution of dynamic MRI of one image every 3-4 s. Cervix carcinoma first-pass was more rapid and intense than that of other pelvic tissues (P<0.001) with the exception of normal myometrium (P>0.05). Binary colour coding, however, was not reliable for tumour delineation or for accurate assessment of tumour invasion into the parametria or the bladder wall. Overestimation of the extent of tumour invasion occurred in 15, 16 and nine out of 28 patients, respectively, using amplitude, slope and timing of enhancement as parameters. Dynamic contrast-enhanced colour-coded MRI of cervix carcinoma has limited value for assessing the extent of tumour spread and tumour staging.

Fast dynamic contrast enhanced mr imaging of cervical carcinoma

The first pass phase of contrast material is most important to study vascularization and perfusion of tissue and can be studied using dynamic magnetic resonance (MR) imaging. The purpose of this prospective study was to evaluate the usefulness of pre-contrast vs. post-contrast and fast dynamic MR imaging in the preoperative staging of cervical carcinomas. To assess the normal onset of enhancement of the uterus and cervix 15 volunteers underwent dynamic MR imaging. Forty-two consecutive patients with invasive cervical cancer underwent preoperative evaluation using MR imaging. The results of the MR examinations were correlated with clinical (FIGO) staging under anesthesia (n = 42) and with histopathological findings after operation (n = 26). The staging results of precontrast T1-weighted and T2-weighted turbo spin-echo (TSE) MR images, pre-contrast MR images plus post-contrast enhanced (two-dimensional fast low angle shot (FLASH 2-D) post contrast), pre-contrast MR images plus post-contrast enhanced plus fast dynamic enhanced (single slice turbo fast low angle shot (turbo FLASH)) MR images compared to histopathology (n = 26) were 77%, 81%, and 85%, respectively. The improvement was statistically not significant. The result of MR staging compared to clinical staging (n = 42) with pre-contrast MR images was correct in 79% of the cases. Pre-contrast MR images combined with post-contrast MR images did not significantly improve staging accuracy (83%). Pre-contrast plus post-contrast plus fast dynamic MR imaging improved staging to 91%. However, the improvement was only statistically significant for one reader (p = 0.01), whereas the improvement of the second reader was not significant (p = 0.07). The single slice turbo FLASH images showed enhancement of all squamous cell carcinomas (n = 32) with an average onset of 5 seconds (range 4–8 seconds during the first 45 seconds of bolus injection of gadolinium. The normal cervix showed enhancement with an average of 10 seconds (range 6–14 seconds). FLASH 2-D post-contrast images showed less intense enhancement of the cervical tumors with respect to the parametria and other surrounding structures. Fast dynamic MR imaging and to a lesser degree post-contrast MR imaging showed a higher level of confidence than pre-contrast MR. Fast dynamic MRI compared with clinical staging (n = 42) was correct in 91% (38/42) and to histopathology in 85% (22/26). Comparison of clinical staging with histopathology was 85% (22/26). In conclusion, fast dynamic MR imaging is superior to post-contrast and pre-contrast MR imaging and is at least as good as clinical staging in the evaluation of cervical carcinoma.

Fast dynamic contrast enhanced MR imaging of cervical carcinoma

The first pass phase of contrast material is most important to study vascularization and perfusion of tissue and can be studied using dynamic magnetic resonance (MR) imaging. The purpose of this prospective study was to evaluate the usefulness of pre-contrast vs. post-contrast and fast dynamic MR imaging in the pre-operative staging of cervical carcinomas. To assess the normal onset of enhancement of the uterus and cervix 15 volunteers underwent dynamic MR imaging. Forty-two consecutive patients with invasive cervical cancer underwent pre-operative evaluation using MR imaging. The results of the MR examinations were correlated with clinical (FIGO) staging under anaesthesia (n = 42) and with histopathological findings after operation (n = 26). The staging results of pre-contrast T1-weighted and T2-weighted turbo spin-echo (TSE) MR images, pre-contrast MR images plus post-contrast enhanced (two dimensional fast low angle shot (FLASH 2-D) post contrast), pre-contrast MR images plus post-contrast enhanced plus fast dynamic enhanced (single slice turbo fast low angle shot (turbo FLASH)) MR images compared to histopathology (n = 26) were 77%, 81% and 85% respectively. The improvement was statistically not significant. The result of MR staging compared to clinical staging (n = 42) with pre-contrast MR images was correct in 79% of the cases. Pre-contrast MR images combined with post-contrast MR images did not significantly improve staging accuracy (83%). Pre-contrast plus post-contrast plus fast dynamic MR imaging improved staging to 91%. However, the improvement was only statistically significant for one reader (P = 0.01), whereas the improvement of the second reader was not significant (P = 0.07). The single slice turbo FLASH images showed enhancement of all squamous cell carcinomas (n = 32) with an average onset of 5s (range 4-8s) during the first 45s of bolus injection of gadolinium. The normal cervix showed enhancement with an average of 10s (range 6-14 s). FLASH 2-D post-contrast images showed less intense enhancement of the cervical tumours with respect to the parametria and other surrounding structures. Fast dynamic MR imaging and to a lesser degree post-contrast MR imaging showed a higher level of confidence than pre-contrast MR. Fast dynamic MRI compared with clinical staging (n = 42) was correct in 91% (38/42) and to histopathology in 85% (22/26). Comparison of clinical staging with histopathology was 85% (22/26). In conclusion, fast dynamic MR imaging is superior to post-contrast and pre-contrast MR imaging and is at least as good as clinical staging in the evaluation of cervical carcinoma.