Magnetic resonance velocity mapping of 3D cerebrospinal fluid flow dynamics in hydrocephalus: preliminary results.

OBJECTIVES: To investigate the detectability of CSF flow alterations in the ventricular system of patients with hydrocephalus using time-resolved 3D MR velocity mapping. METHODS: MR velocity mapping was performed in 21 consecutive hydrocephalus patients and 21 age-matched volunteers using a 3D phase-contrast (PC) sequence. Velocity vectors and particle path lines were calculated for visualisation of flow dynamics. CSF flow was classified as "hypomotile flow" if it showed attenuated dynamics and as "hypermotile flow" if it showed increased dynamics compared with volunteers. Diagnostic efficacy was compared with routine 2D cine PC-MRI. RESULTS: Seven patients showed hypomotile CSF flow: six had non-communicating hydrocephalus due to aqueductal stenosis. One showed oscillating flow between the lateral ventricles after craniotomy for intracranial haemorrhage. Seven patients showed normal flow: six had hydrocephalus ex vacuo due to brain atrophy. One patient who underwent ventriculostomy 10 years ago showed a flow path through the opening. Seven patients showed hypermotile flow: three had normal pressure hydrocephalus, three had dementia, and in one the diagnosis remained unclear. The diagnostic efficacy of velocity mapping was significantly higher except for that of aqueductal stenosis. CONCLUSIONS: Our approach may be useful for diagnosis, therapy planning, and follow-up of different kinds of hydrocephalus.

Triggered non-contrast enhanced MR angiography of peripheral arteries: optimization of systolic and diastolic time delays for electrocardiographic triggering.

The purpose of this study was to determine the optimal systolic and diastolic time delays for electrocardiographic triggering of a non-contrast media enhanced MR angiography using a 3-dimensional fast spin echo sequence in patients suffering from peripheral arterial disease. 12 patients with suspected peripheral arterial disease were examined on a 1.5 T Philips Achieva MR scanner. A cardiac-triggered Volumetric Isotropic T2-weighted fast spin echo sequence was performed using variable trigger delays for systolic and diastolic phase. The signal in the popliteal arteries and anterior tibial arteries of the systolic and diastolic images was measured and optimal delay times for systolic and diastolic phase were determined. Minimum signal to noise ratio (SNR) appears at the time difference ΔT=-21 ms on systolic images of the popliteal arteries. In the anterior tibial arteries the minimum SNR is significantly higher and appears at the time difference ΔT=-14 ms. Diastolic delay times must be chosen as long or as short as possible depending on heart rate. In peripheral vessels triggered non-contrast MR angiography can yield results which are comparable with contrast enhanced MRA techniques. It is crucial to optimize timing parameters.

Insight into the patterns of cerebrospinal fluid flow in the human ventricular system using MR velocity mapping.

The patterns of cerebrospinal fluid (CSF) flow within the human ventricular system are still not fully understood in all their complexity. Knowledge is based on either the interpretation of CSF flow curves or computational simulations. Both approaches only provide an incomplete insight into the spatial and temporal dynamics of CSF flow. Time-resolved three-dimensional magnetic resonance velocity mapping has previously been used to investigate normal and pathologic blood flow patterns in the human vascular system. Here we used this technique to study the spatial and temporal dynamics of CSF flow in the ventricular system of 40 normal volunteers. Classification of the patterns of CSF flow based on calculation of three-dimensional particle path lines over the cardiac cycle revealed one uniform flow pattern for the lateral ventricles, three categories for the third and two categories for the fourth ventricle. We found no significant aging effects on either the presence of a specific CSF flow pattern or on CSF flow velocities. Our results provide the first detailed demonstration of the patterns of CSF flow within the human ventricular system.

Accelerated time-resolved three-dimensional MR velocity mapping of blood flow patterns in the aorta using SENSE and k-t BLAST.

PURPOSE: To assess the feasibility and potential limitations of the acceleration techniques SENSE and k-t BLAST for time-resolved three-dimensional (3D) velocity mapping of aortic blood flow. Furthermore, to quantify differences in peak velocity versus heart phase curves. MATERIALS AND METHODS: Time-resolved 3D blood flow patterns were investigated in eleven volunteers and two patients suffering from aortic diseases with accelerated PC-MR sequences either in combination with SENSE (R=2) or k-t BLAST (6-fold). Both sequences showed similar data acquisition times and hence acceleration efficiency. Flow-field streamlines were calculated and visualized using the GTFlow software tool in order to reconstruct 3D aortic blood flow patterns. Differences between the peak velocities from single-slice PC-MRI experiments using SENSE 2 and k-t BLAST 6 were calculated for the whole cardiac cycle and averaged for all volunteers. RESULTS: Reconstruction of 3D flow patterns in volunteers revealed attenuations in blood flow dynamics for k-t BLAST 6 compared to SENSE 2 in terms of 3D streamlines showing fewer and less distinct vortices and reduction in peak velocity, which is caused by temporal blurring. Solely by time-resolved 3D MR velocity mapping in combination with SENSE detected pathologic blood flow patterns in patients with aortic diseases. For volunteers, we found a broadening and flattering of the peak velocity versus heart phase diagram between the two acceleration techniques, which is an evidence for the temporal blurring of the k-t BLAST approach. CONCLUSION: We demonstrated the feasibility of SENSE and detected potential limitations of k-t BLAST when used for time-resolved 3D velocity mapping. The effects of higher k-t BLAST acceleration factors have to be considered for application in 3D velocity mapping.

Diffusion-weighted MR imaging with background body signal suppression (DWIBS) for the diagnosis of malignant and benign breast lesions.

The purpose of this study was to evaluate the efficacy of diffusion-weighted MR imaging with background body signal suppression (DWIBS) and a conventional DWI (cDWI) sequence for the detection of breast lesions. Fifty consecutive patients with suspected breast lesions underwent DWIBS and cDWI at 1.5 T. The routine protocol consisted of a short TI inversion recovery (STIR) sequence and a dynamic contrast-enhanced T1-weighted sequence. Apparent diffusion coefficient (ADC) and exponential ADC (eADC) values of the lesions were calculated. Receiver operating characteristic (ROC) analyses and qualitative evaluation of lesion detectability and conspicuity were performed. Thirty-six lesions were detected in 30 patients by using the routine protocol. DWIBS detected 34 lesions (94%) and cDWI detected 26 lesions (72%). The conspicuity of fibroadenomas was significantly (P = 0.007) better for DWIBS. ADC and eADC values of tumour were significantly different between DWIBS and cDWI. DWIBS is superior to cDWI in the visualization of malignant and benign lesions in the breast.

Accelerated phase-contrast MR imaging: comparison of k-t BLAST with SENSE and Doppler ultrasound for velocity and flow measurements in the aorta.

PURPOSE: To evaluate differences in velocity and flow measurements in the aorta between accelerated phase-contrast (PC) magnetic resonance imaging (MRI) using SENSE and k-t BLAST and in peak velocity to Doppler ultrasound. MATERIALS AND METHODS: Two-dimensional PC-MRI perpendicular to the ascending and descending aorta was performed in 11 volunteers using SENSE (R = 2) and k-t BLAST (2-, 4-, 6-, and 8-fold). Peak velocity, mean velocity, and stroke volume of the accelerated PC-MRI experiments were correlated. Peak velocities were compared to Doppler ultrasound. RESULTS: All acceleration techniques showed significant correlations for peak velocity with Doppler ultrasound. However, k-t BLAST 6 and 8 showed a significant underestimation. Strong correlations between SENSE and k-t BLAST were found for all three parameters. Significant differences in peak velocity were found between SENSE and all k-t BLAST experiments, but not for 2-fold k-t BLAST in the ascending aorta, and 2- and 4-fold k-t BLAST in the descending aorta. For mean velocity no significant differences were found. Stroke volume showed significant differences for all k-t BLAST experiments in the ascending and for 6- and 8-fold k-t BLAST in the descending aorta. CONCLUSION: Peak velocity of accelerated PC-MRI correlated with CW Doppler measurements, but high k-t BLAST acceleration factors lead to a significant underestimation. SENSE with R = 2 and 2-fold k-t BLAST are most highly correlated in phase-contrast flow measurements.