Steady-state Precession Sequence Research Articles

Dynamic 1.5-Tvs3-T true fast imaging with steady-state precession (trueFISP)-MRI sequences for assessment of velopharyngeal function

To compare the image quality of MRI scans produced with 1.5- and 3.0-T devices during functional test condition. 65 MRI scans obtained with 1.5- (n = 43) or 3.0-T (n = 22) true fast imaging with steady-state precession (trueFISP) sequences from patients with a history of a cleft palate were evaluated. Two experts assessed the MRI scans, independently of each other, and blinded to the MRI technique used. Subjective ratings were entered on a five-point Likert scale. The median planes of three anatomical structures (velum, tongue and pharyngeal wall) were assessed in three functional states (at rest, during phonation of sustained "e" and during articulation of "kkk"). In addition, MRI scans taken during velopharyngeal closure were evaluated. Under blinded conditions, both observers (radiologist and orthodontist) independently rated the quality of 1.5-T scans higher than that of 3.0 T. Statistical analysis of pooled data showed that the differences were highly significant (p < 0.009) in 4 out of 10 test conditions. The greatest differences in favour of 1.5 T were observed for MRI scans of the velum. 1.5 T used with trueFISP may be preferable over 3.0-T trueFISP for the evaluation of the velopharyngeal structures in the clinical routine.

Investigation of sagittal image acquisition for 4D-MRI with body area as respiratory surrogate.

The authors have recently developed a novel 4D-MRI technique for imaging organ respiratory motion employing cine acquisition in the axial plane and using body area (BA) as a respiratory surrogate. A potential disadvantage associated with axial image acquisition is the space-dependent phase shift in the superior-inferior (SI) direction, i.e., different axial slice positions reach the respiratory peak at different respiratory phases. Since respiratory motion occurs mostly in the SI and anterior-posterior (AP) directions, sagittal image acquisition, which embeds motion information in these two directions, is expected to be more robust and less affected by phase-shift than axial image acquisition. This study aims to develop and evaluate a 4D-MRI technique using sagittal image acquisition. The authors evaluated axial BA and sagittal BA using both 4D-CT images (11 cancer patients) and cine MR images (6 healthy volunteers and 1 cancer patient) by comparing their corresponding space-dependent phase-shift in the SI direction (δSPS (SI)) and in the lateral direction (δSPS (LAT)), respectively. To evaluate sagittal BA 4D-MRI method, a motion phantom study and a digital phantom study were performed. Additionally, six patients who had cancer(s) in the liver were prospectively enrolled in this study. For each patient, multislice sagittal MR images were acquired for 4D-MRI reconstruction. 4D retrospective sorting was performed based on respiratory phases. Single-slice cine MRI was also acquired in the axial, coronal, and sagittal planes across the tumor center from which tumor motion trajectories in the SI, AP, and medial-lateral (ML) directions were extracted and used as references from comparison. All MR images were acquired in a 1.5 T scanner using a steady-state precession sequence (frame rate ∼ 3 frames/s). 4D-CT scans showed that δSPS (SI) was significantly greater than δSPS (LAT) (p-value: 0.012); the median phase-shift was 16.9% and 7.7%, respectively. Body surface motion measurement from axial and sagittal MR cines also showed δSPS (SI) was significantly greater than δSPS (LAT). The median δSPS (SI) and δSPS (LAT) was 11.0% and 9.2% (p-value = 0.008), respectively. Tumor motion trajectories from 4D-MRI matched with those from single-slice cine MRI: the mean (±SD) absolute differences in tumor motion amplitude between the two were 1.5 ± 1.6 mm, 2.1 ± 1.9 mm, and 1.1 ± 1.0 mm in the SI, ML, and AP directions from this patient study. Space-dependent phase shift is less problematic for sagittal acquisition than for axial acquisition. 4D-MRI using sagittal acquisition was successfully carried out in patients with hepatic tumors.

Functional evaluation of transplanted kidneys using arterial spin labeling MRI

To investigate non-contrast-enhanced arterial spin labeling (ASL) MRI for functional assessment of transplanted kidneys at 1.5 Tesla (T) and 3T. This study was approved by the local ethics committee, and written informed consent was obtained from all participants. Ninety eight renal allograft recipients (mean age, 51.5 ± 14.6 years) were prospectively included in this study. ASL MRI was performed at 1.5T (n = 65) and 3T (n = 33) using a single-slice flow-sensitive alternating inversion recovery true-fast imaging with steady-state precession (FAIR True-FISP) sequence in the paracoronal plane. ASL perfusion was regional analyzed for the renal cortex on parameter maps. ASL was compared between patients with good or moderate allograft function (Group a; estimated glomerular filtration rate [eGFR] > 30 mL/min/1.73 m(2)) and patients with heavily impaired allograft function (Group b; eGFR ≤ 30 mL/min/1.73 m(2)) and correlated to renal function as determined by eGFR. ASL perfusion and eGFR were comparable at 1.5T (246.9 ± 66.8 mL/100 g/min and 41.9 ± 22.7 mL/min/1.73 m(2)) and 3T (236.5 ± 102.3 mL/100 g/min and 35.9 ± 22.9 mL/min/1.73 m(2)). ASL perfusion was significantly higher in group a (282.7 ± 60.8 mL/100 g/min) as compared to group b (178.2 ± 63.3 mL/100 g/min) (P < 0.0001). ASL perfusion values exhibited a significant correlation with renal function as determined by eGFR (r = 0.59; P < 0.0001). Cortical ASL perfusion values differ between patients with good or moderate allograft function and poor allograft function and correlate significantly with allograft function. Our results highlight the potential of ASL MRI for functional evaluation of renal allografts.

1039Time after contrast injection is crucial to determine infarct transmurality and myocardial functional recovery after an acute myocardial infarction

Background: In acute myocardial infarction (MI), contrast hyperenhancement include infarcted myocardium (late enhancement), and area at risk (early enhancement). There is no information about the optimal timing to differentiate these 2 time periods in order to better determine infarct size. Aims: To determine whether the time after contrast injection influences the size of hyperenhancement in acute and chronic MI, and the time that better predicts infarct size and functional recovery.9 Table Table Methods: Subjects were evaluated using CMR the first week (n= 60) and 3 months (n = 47) after an STEMI percutaneously revascularized. Short-axis cine views (SSFP sequences) were performed to quantify volumes, ejection fraction and determine the wall motion score index (WMSI). Inversion-recovery single-shot true fast imaging with steady-state precession (ss-IR) and segmented inversion-recovery gradient-echo (seg-IR) sequences were used. SS-IR was acquired 1, 3, 5, 7, 10, 15, 20, and 25 min after administration of 0.2 mmol/kg Gd-DTPA to analyze dynamic changes. Seg-IR was acquired starting at 10 min after contrast and were used for comparison to ss-IR. Inversion time was properly adjusted to null normal myocardium. All images were blinded, randomized, and measured for hyperenhancement volumes. Results: In acute MI, there was a significant decrease in infarct mass over time (p = 0.005). Hyperenhancement volume was maximum 3 min after contrast injection and stable after 20 min. Nevertheless, infarct mass remained constant over time in chronic MI (p = 0.886). Mean infarct size in acute and chronic MI by seg-IR was 24 ± 16 g and 12 ± 8 g respectively with excellent correlation to ss-IR (r = 0.96 and r = 0.98 p < 0.001). Depending on the imaging time for LGE, the transmurality index also changed, and thus, the number of patient with a transmural infarction (>75%) decreased over time (Table). A transmural infarction (>75%) at 25th min better predicted the absence of improvement in the WMSI, a lower number of segments that recovers function, a higher increase in left ventricular volumes and a lower ejection fraction compared to the transmurality assessed 10th minutes after. (Table). Conclusions: There is a change in infarct mass over time in acute but not in chronic MI, with a maximum volume 3 min after contrast injection. Infarct transmurality 25th min after contrast injection better predicts infarct size and functional recovery at follow-up.

Measuring the Effect of Pars Plana Vitrectomy on Vitreous Oxygenation Using Magnetic Resonance Imaging

To study the effect of pars plana vitrectomy (PPV) on vitreous oxygenation (pO2) using magnetic resonance imaging (MRI). Patients due to undergo PPV for either macular hole or epiretinal membrane were recruited. MRI scanning was performed 1 week before and at least 3 months after PPV. MRI T1 mapping was performed using an inversion recovery-true fast imaging with steady-state precession (TrueFISP) sequence at several inversion times, from a single slice positioned through the center of both eyes in the axial oblique plane. Additional phantom data were measured in porcine vitreous, to define the relationships between T1 relaxation times and balanced salt solution (BSS), to simulate human vitreous and aqueous, respectively, for a suitable pO2 range (5-70 mm Hg). Pre-PPV pO2 was also measured intraoperatively using a polarographic oxygen probe. Eleven participants (age range 59-84) were recruited; two declined the post-PPV scan. Corrected T1 times indicated that the mean (±SD) pO2 increased significantly following PPV, from 13.2 ± 5.8 to 34.5 ± 8.0 mm Hg (P < 0.001). In the nonsurgical (control) eye, pO2 did not change significantly from the first to second MRI scan (13.7 ± 7.8 vs. 16.3 ± 8.7 mm Hg, P = 0.239). Mean pO2 measured intraoperatively was 7.2 ± 0.6 mm Hg (n = 10). These results confirm that vitrectomy substantially increases vitreous pO2. MRI is a noninvasive technique that can be used to study vitreous oxygenation in both vitrectomized and nonvitrectomized eyes.

Comparison between magnitude reconstruction and phase-sensitive mR imaging in the detection of myocardial infarction

ObjectiveTo determine the deference between phase sensitive magnetic resonance (MR) imaging and magnitude reconstruction to detect infracted myocardium. MethodsTwenty patients (16 men; 4 women; mean age, 56 years). experienced Q-wave myocardial infarction 2 weeks earlier were examined with a 3.0-T MR system 10 minutes after administration of 0.1 mmol/kg body weight gadobenate dimeglumine. To determine the optimal TI, a TI scout sequence was used. A segmented 2D IR true fast imaging with steady-state precession (trueFISP) sequence that produces both phase-sensitive and magnitude-reconstructed images were used at TI values of 200-600 msec (TI values were varied in 100-msec steps) and at optimal TI (mean value, 330 msec). Contrast-noise ratios (CNRs) of normal and infarcted myocardium and the area of infarcted myocardium were determined. Two-tailed unpaired sample Student t test was used to compare CNRs, and area of infarction. ResultsMMean CNR phase-sensitive and magnitude-reconstructed images at optimal TI (mean value, 330 msec) were 6.2, and 6.1, respectively. For a TI of 200 msec, CNR values were 5.5, and 4.2, respectively; for TI of 600 msec, CNR values were 5.8 and 4.3, respectively. Area of infarcted myocardium was underestimated on magnitude-reconstruction images (P = 0.002-0.03) for short TI values (ie., 200 msec) but not on phase sensitive reconstructed when compared with IR tureFISP images obtained at optimal TI. ConclusionsLPhase-sensitive image reconstruction results in reduced need for precise choice of TI and more consistent image quality.

Quantitative analysis of cardiac left ventricular variables obtained by MRI at 3 T: a pre- and post-contrast comparison

Short-axis cine images are acquired during cardiac MRI in order to determine variables of cardiac left ventricular (LV) function such as ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV) and LV mass. In cardiac perfusion assessments this imaging can be performed in the temporal window between first pass perfusion and the acquisition of delayed enhancement images in order to minimise overall scanning time. The objective of this study was to compare pre- and post-contrast short-axis LV variables of 15 healthy volunteers using a two-dimensional cardiac-gated segmented cine true fast imaging with steady state precession sequence and a 3.0 T MRI unit in order to determine the possible effects of contrast agent on the calculated cardiac function variables. Image analysis was carried out using semi-automated software. The calculated mean LV mass was lower when derived from the post-contrast images, relative to those derived pre-contrast (102 vs 108.1 g, p<0.0001). Small but systematic significant differences were also found between the mean pre- and post-contrast values of EF (69.4% vs 68.7%, p<0.05), EDV (142.4 vs 143.7 ml, p<0.05) and ESV (44.2 vs 45.5 ml, p<0.005), but no significant differences in SV were identified. This study has highlighted that contrast agent delivery can influence the numerical outcome of cardiac variables calculated from MRI and this was particularly noticeable for LV mass. This may have important implications for the correct interpretation of patient data in clinical studies where post-contrast images are used to calculate LV variables, since LV normal ranges have been traditionally derived from pre-contrast data sets.

SU-D-218-02: 4D-MRI Based on Body Area (BA) Surrogate and Sagittal Image Acquisition.

4D-MRI based on body area (BA) surrogate using axial image acquisition has been demonstrated. Since respiratory motion mostly occurs in the superior-inferior (SI) direction, it is expected that sagittal acquisition may provide more robust and accurate breathing signal than axial acquisition. The aim of this study was to investigate the feasibility of extracting breathing signals from sagittal images using BA surrogate and its application in 4D-MRI. 7 human subjects were imaged continuously in a single (n=5) or multiple (n=2) sagittal planes using a steady-state precession sequence. Imaging parameters were: TR/TE, 3.7ms/1.21ms; Matrix, 256×166; FOV, 350×300mm; flip angle, 52°; slice thickness, 5mm; frame rate: ∼3 frames/s. Imaging time per slice is 2 minutes for single slice acquisition and ∼10 seconds for multi-slice acquisition. Breathing signals were generated for all subjects by tracking the change of BA. The multi-slice sagittal acquisition was performed on a MRI- compatible motion phantom with a cylindrical gel target and was simulated on a 4D digital human phantom. Breathing signals were extracted from the sagittal images using the BA surrogate. Respiratory phases were calculated. 4D-MRI of both phantoms were retrospectively reconstructed based on the respiratory phases. Breathing signals extracted from both single slice and multi-slice sagittal acquisitions showed stable and well- characterized patterns. 4D-MRI of the physical phantom showed clear sinusoidal motion of the gel target in all three planes with minimal artifacts. Simulated '4D-MRI' of the 4D digital phantom matched well with original images: the mean absolute difference in motion amplitude of the 'tumor' was 0.4±0.3mm. Small artifacts of discontinuity were observed in the SI direction in certain phases. It is feasible to extract breathing signals from sagittal images for 4D-MRI application. Further investigation is needed to test whether sagittal acquisition is more robust and accurate than axial acquisition for breathing signal extraction.

Assessment of articular cartilage repair tissue after matrix-associated autologous chondrocyte transplantation or the microfracture technique in the ankle joint using diffusion-weighted imaging at 3 Tesla

The objective was to compare patients after matrix-associated autologous chondrocyte transplantation (MACT) and microfracture therapy (MFX) of the talus using diffusion-weighted imaging (DWI), with morphological and clinical scoring. Twenty patients treated with MACT or MFX (10 per group) were examined using 3 T magnetic resonance imaging (MRI) at 48 ± 21.5 and 59.6 ± 23 months after surgery, respectively. For comparability, patients from each group were matched by age, body mass index, and follow-up. American Orthopaedic Foot and Ankle Society (AOFAS) score served as clinical assessment tool pre- and postoperatively. DWI was obtained using a partially balanced, steady-state gradient echo pulse sequence, as well as the Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score, based on a 2D proton density-weighted turbo spin-echo sequence and a 3D isotropic true fast imaging with steady-state precession sequence. Semi-quantitative diffusion quotients were calculated after region of interest analysis of repair tissue (RT) and healthy control cartilage, and compared among both groups. The mean AOFAS score improved significantly (P = 0.001) for both groups (MACT: 48.8 ± 20.4-83.6 ± 9.7; MFX: 44.3 ± 16.5-77.6 ± 13.2). No differences in the AOFAS (P = 0.327) and MOCART (P = 0.720) score were observed between MACT and MFX postoperatively. DWI distinguished between healthy cartilage and cartilage RT in the MFX group (P = 0.016), but not after MACT treatment (P = 0.105). Significant correlations were found between MOCART score and DWI index after MFX (Pearson: -0.648; P = 0.043), and between the diffusivity and longer follow-up interval in MACT group (Pearson: -0.647, P = 0.043). Whereas conventional scores reveal a similar outcome after MACT or MFX treatment in the ankle joint, DWI was able to distinguish between different RT qualities, as reported histologically for these diverse surgical procedures.

Evaluation of bowel peristalsis by dynamic cine MRI: Detection of relevant functional disturbances—initial experience

To investigate the diagnostic performance of a cine magnetic resonance imaging (MRI) sequence in the visualization and detection of impaired bowel peristalsis. In all, 91 consecutive patients (mean age 45 years) were prospectively examined on a 1.5 T system and stratified into a surgery group (n = 22) and a nonsurgery group (n = 69). A coronal fast imaging with steady-state precession (TrueFISP) sequence with 30 acquisitions per slice covered the abdomen in 10-15 slices each 7-12 mm thick (temporal resolution: 6-8 sec per frame). Image evaluation for reduced bowel peristalsis and relevant bowel stenosis was compared to surgical findings or clinical follow-up. Cine MRI reached 96% accuracy (94% sensitivity; 100% specificity) in detecting a relevant reduction in bowel peristalsis and 85% of relevant stenosis was identified in the surgery group. Twenty of 69 patients of the nonsurgery group showed reduced peristalsis on cine MR which was attributed to underlying disease; 49/69 patients in this group had no findings on cine MR and were uneventfully followed up. Cine MRI of the bowel provides functional information of bowel passage. The visualization of a reduction in peristalsis may improve the assessment of the functional impact of suspected bowel adhesions or stenosis. Standard bowel MR protocols can be easily complemented by cine MR, extending scan time by <4 minutes.

Dynamic Magnetic Resonance Imaging of the Cervical Spine with High-Resolution 3-Dimensional T2-Imaging

Imaging of the cervical spine in functional positions has so far been limited to conventional X-ray examinations or the scarcely available open magnetic resonance imaging (MRI). An MRI compatible positioning device allows MRI examinations in various positions and even in motion. In combination with high-resolution T2-weighted MRI it allows detailed functional imaging of the cervical spine and nerve roots. To evaluate the utility of this method a population of patients from a clinical study was examined 5 years after anterior cervical discectomy and fusion (ACDF). A total of 32 patients (median age 51.5 years, 15 female, 17 male) were examined after a median interval of 64.3 months from ACDF including 16 patients with a titanium cage and 16 with autologous bone graft. The prototype of an MR compatible positioning device (NeuroSwing) was used for MRI of the cervical spine in functional positions on a 1.5 T MRI unit (Siemens Avanto). A real-time true fast imaging with steady-state precession (FISP) sequence [6 mm, TR 704, TE 1.3 ms, matrix 256 x 207, field of view (FoV) 22 cm] was used for monitoring of flexion up to 45° and extension up to 40° or until patient discomfort. A sagittal T2 sampling perfection with application optimized contrast using different flip angle evolution sequence (SPACE sequence, 0.9 mm isotropic voxels, TR 1770, TE 186 ms, matrix 320 x 318, FoV 28 cm) and an axial true FISP sequence (3 mm slices, TR 194, TE 1.9 ms, matrix 256 x 256, FoV 22 cm) were used for imaging in the end positions. Using the motorized positioning device and a real-time true FISP sequence, imaging of the cervical spine in flexion and extension motion was possible in a quality suitable to observe changes in the alignment of vertebral bodies, the width of the spinal canal and the spinal cord itself. The 3D T2-weighted SPACE sequence yielded high quality and resolution images in the maximum flexion and extension positions. Compared to primary axial T2 true FISP slices, axial reconstructions of the T2 SPACE sequence were found to be clearly less affected by metal artifacts with the additional benefit of multiplanar and transforaminal reconstructions. The combination of a mechanical positioning device and a high-resolution 3D T2-weighted sequence (SPACE) on a conventional 1.5 T MRI allows kinematic imaging of the cervical spine as well as high-resolution imaging in the end positions, even in the presence of metal implants. In this proof of concept study a good visualization of narrowing of the spinal canal in functional positions could be achieved, showing the potential of MRI in functional positions for clinical and research applications.

Pancreaticobiliary duct changes of periampullary carcinomas: Quantitative analysis at MR imaging

PurposeTo quantitatively analyse the pancreaticobiliary duct changes of periampullary carcinomas with volumetric interpolated breath-hold examination (VIBE) and true fast imaging with steady-state precession (true FISP) sequence, and investigate the value of these findings in differentiation and preoperative evaluation. Materials and methodsMagnetic resonance (MR) images of 71 cases of periampullary carcinomas (34 cases of pancreatic head carcinoma, 16 cases of intrapancreatic bile duct carcinoma and 21 cases of ampullary carcinoma) confirmed histopathologically were analysed. The maximum diameter of the common bile duct (CBD) and main pancreatic duct (MPD), dilated pancreaticobiliary duct angle and the distance from the end of the proximal dilated pancreaticobiliary duct to the major papilla were measured. Analysis of variance and the Chi-squared test were performed. ResultsThese findings showed significant differences among the three subtypes: the distance from the end of proximal dilated pancreaticobiliary duct to the major papilla and pancreaticobiliary duct angle. The distance and the pancreaticobiliary duct angle were least for ampullary carcinoma among the three subtypes. The percentage of dilated CBD was 94.1%, 93.8%, and 100% for pancreatic head carcinoma, intrapancreatic bile duct carcinoma and ampullary carcinoma, respectively. And that for the dilated MPD was 58.8%, 43.8%, and 42.9%, respectively. ConclusionQuantitative analysis of the pancreaticobiliary ductal system can provide accurate and objective assessment of the pancreaticobiliary duct changes. Although benefit in differential diagnosis is limited, these findings are valuable in preoperative evaluation for both radical resection and palliative surgery.

Fast monitoring of T1, T2, and relative proton density (M0) changes in skeletal muscles using an IR‐TrueFISP sequence

To investigate the feasibility of fast and simultaneous assessment of T(1) , T(2) , and M(0) (relative proton density) changes in skeletal muscle studies using an inversion recovery true fast imaging with steady-state precession (TrueFISP) sequence. NMR signal dynamics in calf muscles were analyzed under four different conditions: intravenous injection of a low-molecular weight Gd contrast agent (CA), postarterial occlusion reactive hyperemia, local cooling, and an exercise bout. Experiments were conducted on a clinical 3T whole-body scanner. At rest, average muscle T(1) and T(2) values obtained from the IR-TrueFISP experiments were 1.34 ± 0.13 seconds and 45 ± 5 msec, respectively (median ± standard deviation). 1) Noticeable T(1) decreases (ΔT(1) max ≈-30%) were measured in the calf muscles after CA injection, while no significant changes were observed for T(2) and M(0) . 2) T(2) increased rapidly during reactive hyperemia and reached a peak value (+6%) at about 1 minute postischemia. During ischemia, a significant decrease was observed only in the soleus muscle. No significant paradigm-related changes in M(0) and T(1) were noted in all muscle groups, except in the m. soleus (ΔT(1) ≈+1% during reactive hyperemia). 3) Opposite variations in muscle T(1) (ΔT(1) max ≈-30%) and M(0) (ΔM(0) max ≈+25%) associated with local cooling were detected. 4) Concomitant changes in T(1) (ΔT(1) max ≈+15%), T(2) (ΔT(2) max ≈+35%), and M(0) (ΔM(0) max ≈+16%) were observed in the activated muscles following the exercise bout. IR-TrueFISP was sufficiently fast and sensitive to detect small and transient T(1) , T(2) , and M(0) changes in the calf muscles under different experimental conditions. The sequence offers a time-resolution adequate to track rapid physiological adaptations in skeletal muscle.

MR-compatible Assistance System for Biopsy in a High-Field-Strength System: Initial Results in Patients with Suspicious Prostate Lesions

To examine the feasibility and safety of magnetic resonance (MR)-guided biopsy by using a transgluteal approach in patients with suspicious prostate lesions by using an MR-compatible robotic system and a 1.5-T MR system. The study was approved by the institutional review board of University Frankfurt, and informed consent was obtained from each patient. A total of 20 patients (age range, 57.8-71.9 years; mean age, 65.1 years) underwent biopsy in a closed-bore high-field-strength MR system. Biopsy was performed with an MR-compatible pneumatically driven robotic system. T1-weighted gradient-echo fast low-angle shot and T2-weighted true fast imaging with steady-state precession sequences were used to plan and guide the intervention with a transgluteal access on the external planning computer of the assistance system. The system calculated the trajectory and then moved the guiding arm to the insertion point. The cannula was advanced manually, and biopsies were performed with the coaxial technique by using a 15-gauge pencil tip needle. Intervention time, complications, and biopsy findings were documented. The MR-compatible robotic system did not interfere with image quality, nor did MR imaging cause dysfunction of the robot. In one patient, the interventionist caused a fail-safe system shutdown. This was due to inadvertent displacement of the guiding arm during cannula insertion. This problem was solved by increasing the displacement threshold. Accurate coaxial cannula biopsy could be performed in all subsequent patients. Sufficient histopathologic assessment was performed in 19 patients. Insufficient material was retrieved in the patient who experienced fail-safe system shutdown. The median intervention time was 39 minutes (23-65 minutes). No procedure-related complications were observed. Preliminary results indicate that MR-guided robot-assisted biopsy is feasible and can be performed safely with highly accurate cannula placement.

Real‐time 3D MRI of contrast agents in whole living mice

A specific mouse whole body coil and a dedicated gradient system at 4.7 T were coupled with an ultra-fast 3D gradient echo MRI and keyhole reconstruction technique to obtain 3D whole-body dynamic T(1)-weighted or T(2)*-weighted imaging. The technique was used to visualize the real-time distribution of non-targeting T(1) and T(2)* contrast agent (CA) in a glioma-bearing mouse model. T(1) dynamic contrast-enhancement imaging was performed with a fast imaging with steady-state precession sequence [echo time/repetition time (TE/TR), 1.32/3.7 ms] before and after CA injection (Gd-DOTA and BSA-Gd-DOTA) for 21 min. The temporal resolution was 1 image/6.5 s. T(2)* imaging (TE/TR, 4/8 ms) was performed before and after iron-based (small and ultra-small particles of iron oxide) CA injection for 45 min. The temporal resolution was 1 image/14 s. Signal-to-noise ratio curves were determined in various mouse organs. The whole-body coil and gradient systems made it possible to acquire data with sufficient and homogeneous signal-to-noise ratio on the whole animal. The spatial resolution allowed adequate depiction of the major organs, blood vessels and brain glioma. The distribution and the time-course of T(1) and T(2)* contrasts upon contrast agent injection were also assessed. 3D whole-body mouse MRI is feasible at high spatial resolution in movie mode and can be applied successfully to visualize real-time contrast agent distribution. This method should be effective in future preclinical molecular imaging studies.

Type 1 Perimedullary Arteriovenous Fistula with Subarachnoid Hemorrhage: Utility of Contrast-enhanced 3D Gradient-echo Technique

In patients with perimedullary arteriovenous fistula (AVF) with subarachnoid hemorrhage (SAH), knowledge of lesion location is necessary to select the appropriate approach for catheter spinal angiography. We evaluated the utility of 3-dimensional (3D) fast imaging with steady-state precession (FISP) sequence for detecting type 1 perimedullary AVF with SAH. We evaluated 4 patients (2 men, 2 women, aged 53 to 68 years, mean age, 59.25 years) with type 1 perimedullary AVF who presented with SAH and underwent conventional spin-echo MR and contrast-enhanced 3D FISP imaging. Two neuroradiologists assessed detection of vascular lesions and delineation of their relationships to the adjacent vessels. Catheter angiography was used as the reference standard and compared with the MR findings. Perimedullary AVF was located at the medullocervical junction in 2 patients, cervical spine in one, and thoracic spine in one. For all patients, use of contrast-enhanced 3D FISP in addition to conventional MR imaging improved lesion detection and delineation of the relationship between the lesion and surrounding vessels. Contrast-enhanced 3D FISP imaging was useful for detecting and delineating type 1 perimedullary AVF with SAH.

Focal adhesive arachnoiditis of the spinal cord: Imaging diagnosis and surgical resolution

Background:Although adhesive arachnoiditis of the spinal cord can cause progressive symptoms associated with syringomyelia or myelomalacia, its surgical resolution based on the imaging diagnosis is not well characterized. This study aims to describe the use of imaging for the diagnosis of focal adhesive arachnoiditis of the spinal cord and its surgical resolution using microsurgical arachnoidolysis.Materials and Methods:Four consecutive patients with symptomatic syringomyelia or myelomalacia caused by focal adhesive arachnoiditis underwent microsurgical arachnoidolysis. Comprehensive imaging evaluation using constructive interference in steady-state (CISS) magnetic resonance imaging (MRI) or myelographic MR imaging using true fast imaging with steady-state precession (TrueFISP) sequences was included before surgery to determine the surgical indication.Results:In all four patients a focal adhesion was identified at the cervical or thoracic level of the spinal cord, a consequence of infection or trauma. Three patients showed modest or minor improvement in neurological function, and one patient was unchanged after surgery. The syringomyelia or myelomalacia resolved after surgery and no recurrence was noted within the follow-up period, which ranged from 5 months to 30 months.Conclusions:MRI diagnosis of focal adhesive arachnoiditis is critical to determine the surgical indication. Microsurgical arachnoidolysis appears to be a straightforward method for stabilizing the progressive symptoms, though the procedure is technically demanding.

Three-Dimensional Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) Score Assessed With an Isotropic Three-Dimensional True Fast Imaging With Steady-State Precession Sequence at 3.0 Tesla

Cartilage defects are common pathologies and surgical cartilage repair shows promising results. In its postoperative evaluation, the magnetic resonance observation of cartilage repair tissue (MOCART) score, using different variables to describe the constitution of the cartilage repair tissue and the surrounding structures, is widely used. High-field magnetic resonance imaging (MRI) and 3-dimensional (3D) isotropic sequences may combine ideal preconditions to enhance the diagnostic performance of cartilage imaging.Aim of this study was to introduce an improved 3D MOCART score using the possibilities of an isotropic 3D true fast imaging with steady-state precession (True-FISP) sequence in the postoperative evaluation of patients after matrix-associated autologous chondrocyte transplantation (MACT) as well as to compare the results to the conventional 2D MOCART score using standard MR sequences. The study had approval by the local ethics commission. One hundred consecutive MR scans in 60 patients at standard follow-up intervals of 1, 3, 6, 12, 24, and 60 months after MACT of the knee joint were prospectively included. The mean follow-up interval of this cross-sectional evaluation was 21.4 +/- 20.6 months; the mean age of the patients was 35.8 +/- 9.4 years. MRI was performed at a 3.0 Tesla unit. All variables of the standard 2D MOCART score where part of the new 3D MOCART score. Furthermore, additional variables and options were included with the aims to use the capabilities of isotropic MRI, to include the results of recent studies, and to adapt to the needs of patients and physician in a clinical routine examination. A proton-density turbo spin-echo sequence, a T2-weighted dual fast spin-echo (dual-FSE) sequence, and a T1-weighted turbo inversion recovery magnitude (TIRM) sequence were used to assess the standard 2D MOCART score; an isotropic 3D-TrueFISP sequence was prepared to evaluate the new 3D MOCART score. All 9 variables of the 2D MOCART score were compared with the corresponding variables obtained by the 3D MOCART score using the Pearson correlation coefficient; additionally the subjective quality and possible artifacts of the MR sequences were analyzed. The correlation between the standard 2D MOCART score and the new 3D MOCART showed for the 8 variables "defect fill," "cartilage interface," "surface," "adhesions," "structure," "signal intensity," "subchondral lamina," and "effusion"-a highly significant (P < 0.001) correlation with a Pearson coefficient between 0.566 and 0.932. The variable "bone marrow edema" correlated significantly (P < 0.05; Pearson coefficient: 0.257). The subjective quality of the 3 standard MR sequences was comparable to the isotropic 3D-TrueFISP sequence. Artifacts were more frequently visible within the 3D-TrueFISP sequence. In the clinical routine follow-up after cartilage repair, the 3D MOCART score, assessed by only 1 high-resolution isotropic MR sequence, provides comparable information than the standard 2D MOCART score. Hence, the new 3D MOCART score has the potential to combine the information of the standard 2D MOCART score with the possible advantages of isotropic 3D MRI at high-field. A clear limitation of the 3D-TrueFISP sequence was the high number of artifacts. Future studies have to prove the clinical benefits of a 3D MOCART score.

MR imaging of aortic coarctation

Aortic coarctation accounts for 5%-10% of all congenital heart diseases and represents 7% of critically ill infants with heart disease. Magnetic resonance (MR) imaging allows the study of this disease with several advantages in comparison with conventional angiography, transesophageal echocardiography, and computed tomography. The MR protocol applied at our institution for both diagnosis and follow-up after surgical or endovascular treatment consists of four steps: morphologic study, cine MR study, flow analysis, and MR angiography (MRA). The first three sequences are acquired during breath-hold and with electrocardiographic gating. Anatomy is well depicted with dark-blood half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences. Cine true-fast imaging with steady-state precession (true-FISP) sequences show not only morphologic features but also blood-flow changes inside the aorta. Gradient-echo sequences for phase-velocity mapping allow flow analysis. Application of Bernoulli's equation--here briefly presented and discussed--allows for calculation of the pressure gradient caused by the coarctation. MRA, acquired with a breath-hold three-dimensional T1-weighted gradient-echo sequence and intravenous administration of paramagnetic contrast material, allows for optimal depiction of the aortic lumen, with a panoramic view of the whole aorta, its main branches and possible collateral circulation.

Functional MRI: Evaluation of Chronic Kidney Disease with Perfusion Imaging

To evaluate the functional alterations of chronic kidney disease (CKD) with magnetic resonance dynamic perfusion imaging. Twenty-one healthy subjects (42 kidneys) and 20 CKD patients (40 kidneys) underwent routine scans with fat-saturated T1-weighted fast low angle shot (FLASH) and true-fast imaging with steady-state precession (FISP) sequences followed by dynamic perfusion scans using a turbo-FLASH T1-weighted sequence. Signal intensity (SI) of the cortex and medulla on images was measured and plotted as a function of time. Peak height (P) and time to peak (T) of the cortex and medulla SI were estimated, and P/T ratio and the area under the time-intensity curves were calculated. We also tested the correlation between these data and serum creatinine (sCr) levels in patients. P, P/T ratio, and the area under the curve of patients' cortex and medulla were significantly decreased compared to control subjects, and T was delayed. In patients, P and P/T ratio of the cortex and P of the medulla were negatively correlated with sCr levels (r = -0.469, r = -0.419, and r = -0.423, respectively; P < 0.01). Renal dysfunction in CKD can be evaluated by magnetic resonance dynamic perfusion imaging.