MRI planimetry for diagnosis and follow-up of valve area in mitral stenosis treated with valvuloplasty.

PURPOSE: We sought to determine whether noninvasive planimetry by magnetic resonance imaging (MRI) is suitably sensitive and reliable for visualizing the mitral valve area (MVA) and for detecting increases in the MVA after percutaneous balloon mitral valvuloplasty (PBMV). MATERIALS AND METHODS: In 8 patients with mitral valve stenosis, planimetry of the MVA was performed before and after PBMV with a 1.5 T MR scanner using a breath-hold balanced gradient echo sequence (True FISP). The data was compared to the echocardiographically determined MVA (ECHO-MVA) as well as to the invasively calculated MVA by the Gorlin formula at catheterization (CATH-MVA). RESULTS: PBMV was associated with an increase of 0.79 +/- 0.30 cm (2) in the MVA (Delta MRI-MVA). The correlation between Delta MRI-MVA and Delta CATH-MVA was 0.92 (p < 0.03) and that between Delta MRI-MVA and Delta ECHO-MVA was 0.90 (p < 0.04). The overall correlation between MRI-MVA and CATH-MVA was 0.95 (p < 0.0001) and that between MRI-MVA and ECHO-MVA was 0.98 (p < 0.0001). MRI-MVA slightly overestimated CATH-MVA by 8.0 % (1.64 +/- 0.45 vs. 1.51 +/- 0.49 cm (2), p < 0.01) and ECHO-MVA by 1.8 % (1.64 +/- 0.45 vs. 1.61 +/- 0.43 cm (2), n. s.). CONCLUSION: Magnetic resonance planimetry of the mitral valve orifice is a sensitive and reliable method for the noninvasive quantification of mitral stenosis and visualization of small relative changes in the MVA. This new method is therefore capable of diagnosing as well as following the course of mitral stenosis. It must be taken into consideration that planimetry by MRI slightly overestimates the MVA as compared to cardiac catheterization.

Targeted-HASTE imaging with automated device tracking for MR-guided needle interventions in closed-bore MR systems.

Percutaneous MR-guided interventions with needles require fast pulse sequences to image the needle trajectory with minimal susceptibility artifacts. Spin-echo pulse sequences are well suited for reducing artifact size; however, even with single-shot turbo spin-echo techniques, such as rapid acquisition with relaxation enhancement (RARE) or half-Fourier acquisition single-shot turbo spin-echo (HASTE), fast imaging remains challenging. In this work we present a HASTE pulse sequence that is combined with inner-volume excitation to reduce the scan time and limit the imaging field of view (FOV) to a small strip close to the needle trajectory (targeted-HASTE). To compensate for signal saturation from fast repeated acquisitions, a magnetization restore pulse (driven equilibrium Fourier transform (DEFT)) is used. The sequence is combined with dedicated active marker coils to measure the position and orientation of the needle so that the targeted-HASTE image slice is automatically repositioned. In an animal experiment the coils were attached to an MR-compatible robotic assistance system for MR-guided interventions. Needle insertion and infusion via the needle could be visualized with a temporal resolution of 1 s, and the needle tip could be localized even in the presence of a stainless steel mandrel.

Intra-arterial MR angiography in the iliac system: initial clinical experience with 25 patients.

The aim of this study was to evaluate intra-arterial magnetic resonance angiography (MRA) of the iliac arteries. Therefore, 25 consecutive patients (17 male, 8 female) suffering from symptomatic occlusive disease of the lower limbs were investigated prospectively. Catheter angiography was performed before MRA and served as the standard of reference. Contrast-enhanced intra-arterial MRA was performed using a 1.5 Tesla MRI system. Contrast agent (gadodiamide) was injected by a conventional pigtail-shaped angiography catheter placed in the abdominal aorta. Vascular lesions were assessed by four investigators. The degree of stenosis was compared with the findings of conventional catheter angiography. Additionally, the diagnostic quality of the MR angiograms was assessed by the investigators using a semi quantitative five-point scale. All lesions shown by catheter angiography were detected and correctly localized by intra-arterial MRA. MR angiograms exhibit a specificity of 95% and a sensitivity of 96% for stenoses of 50% or more. The diagnostic quality of the images was judged from good to excellent, on average. Intra-arterial MRA exhibits a specificity and sensitivity comparable with intravenous angiography. The image quality appears to be adequate for supporting MR-guided vascular intervention.

Delayed hyperenhancement in magnetic resonance imaging of left ventricular hypertrophy caused by aortic stenosis and hypertrophic cardiomyopathy: visualisation of focal fibrosis.

OBJECTIVE: To compare the extent and distribution of focal fibrosis by gadolinium contrast-enhanced magnetic resonance imaging (MRI; delayed hyperenhancement) in severe left ventricular (LV) hypertrophy in patients with pressure overload caused by aortic stenosis (AS) and with genetically determined hypertrophic cardiomyopathy (HCM). METHODS: 44 patients with symptomatic valvular AS (n = 22) and HCM (n = 22) were studied. Cine images were acquired with fast imaging with steady-state precession (trueFISP) on a 1.5 T scanner (Sonata, Siemens Medical Solutions). Gadolinium contrast-enhanced MRI was performed with a segmented inversion-recovery sequence. The location, extent and enhancement pattern of hyperenhanced myocardium was analysed in a 12-segment model. RESULTS: Mean LV mass was 238.6 (SD 75.3) g in AS and 205.4 (SD 80.5) g in HCM (p = 0.17). Hyperenhancement was observed in 27% of patients with AS and in 73% of patients with HCM (p < 0.01). In AS, hyperenhancement was observed in 60% of patients with a maximum diastolic wall thickness >or= 18 mm, whereas no patient with a maximum diastolic wall thickness < 18 mm had hyperenhancement (p < 0.05). Patients with hyperenhancement had more severe AS than patients without hyperenhancement (aortic valve area 0.80 (0.09) cm(2)v 0.99 (0.3) cm(2), p < 0.05; maximum gradient 98 (22) mm Hg v 74 (24) mm Hg, p < 0.05). In HCM, hyperenhancement was predominant in the anteroseptal regions and patients with hyperenhancement had higher end diastolic (125.4 (36.9) ml v 98.8 (16.9) ml, p < 0.05) and end systolic volumes (38.9 (18.2) ml v 25.2 (1.7) ml, p < 0.05). The volume of hyperenhancement (percentage of total LV myocardium), where present, was lower in AS than in HCM (4.3 (1.9)% v 8.6 (7.4)%, p< 0.05). Hyperenhancement was observed in 4.5 (3.1) and 4.6 (2.7) segments in AS and HCM, respectively (p = 0.93), and the enhancement pattern was mostly patchy with multiple foci. CONCLUSIONS: Focal scarring can be observed in severe LV hypertrophy caused by AS and HCM, and correlates with the severity of LV remodelling. However, focal scarring is significantly less prevalent in adaptive LV hypertrophy caused by AS than in genetically determined HCM.

In vitro evaluation of stent patency and in-stent stenoses in 10 metallic stents using MR angiography.

In vitro study to investigate the suitability of contrast enhanced magnetic resonance angiography (CEMRA) for determination of stent patency and grading of in-stent stenoses in 10 metallic stents. The Acculink carotid, DynaLink, Easy Wallstent, JostentSelfX XF, Luminexx, Omnilink, sinus-SuperFlex, SMART, Symphony and ZA stent were separately placed in a vascular phantom. Dedicated stenoses inside the stents generated a concentric lumen narrowing of 50%. CEMRA was performed for each stent. Signal loss inside the stents and artificial lumen narrowing were assessed objectively using the evaluation software of the MR imager. Moreover, three blinded observers determined visibility of stent patency and in-stent stenoses subjectively on a 3-point scale and graded in-stent stenoses. Loss of signal intensity within the stent lumen ranged between 90% (Wallstent) and 5% (ZA), artificial lumen narrowing between 56% (Symphony) and 22% (ZA). For the Symphony and Wallstent, visibility of patency and in-stent stenoses was impaired and the observers' grading exaggerated the degree of stenoses (by 23% and 33%, respectively). For the remainder of stents, patency and stenoses were visible and stenoses were graded accurately (less than 10% discrepancy from reference standard). In this in vitro study, eight of 10 stents presented with MRI characteristics which enabled determination of stent patency and accurate grading of clinically relevant in-stent stenoses.

Intra-arterial magnetic resonance angiography of the iliac arteries: clinical experience using two different protocols.

PURPOSE: To assess the feasibility of intra-arterial magnetic resonance angiography (iaMRA) with two different protocols. MATERIAL AND METHODS: Twenty patients were prospectively examined after digital subtraction angiography. Contrast-enhanced iaMRA was performed using a 1.5T magnetic resonance imaging (MRI) system. Contrast agent (gadodiamide) was injected through a conventional angiography catheter placed in the abdominal aorta. The patients were randomized into two groups each comprising 10 patients. Group 1 was examined with a FLASH-3D (fast low-angle shot) sequence, allowing the center of the k-space to be acquired 0.5 s after initiation of the measurement. Group 2 was examined with the identical sequence, but the center of the k-space was acquired after 8.7 s. The increase in the intravascular signal intensity was determined and the diagnostic value of the angiograms was independently scored by 4 investigators using a 5-point scale. RESULTS: Nineteen of 20 MRAs were scored as diagnostic; only 1 was scored as non-diagnostic by 2 observers. The diagnostic value of the angiograms of group 2 was judged superior to that of group 1 owing to a more homogeneous intravascular contrast distribution. CONCLUSION: Intra-arterial MRA is feasible. The diagnostic value of angiograms using a flash sequence with center of the k-space acquisition after 8.7 s ranged from good to excellent. This sequence is appropriate for iaMRA of iliac arteries to support MR guided intervention.

Interventional magnetic resonance imaging: an alternative to image guidance with ionising radiation.

At present, interventional procedures, such as stent placement, are performed under X-ray image guidance. Unfortunately with X-ray imaging, both patient and interventionalist are exposed to ionising radiation. Furthermore, X-ray imaging is lacking soft tissue contrast and is not capable of true 3-D displays of either interventional device or tissue morphology. Magnetic resonance imaging (MRI) offers excellent soft tissue contrast, 3-D acquisition techniques, as well as rapid image acquisition and reconstruction. Despite these advantages, MR-guided interventions are challenging owing to the limited access to the patient, strong magnetic and radio-frequency fields that require special interventional devices, inferior image frame rates and spatial resolution, and high MRI scanner noise. For MR-guided intravascular interventions, where access to the target organ is achieved through catheters, dedicated hardware and automated image slice positioning techniques have been developed. We illustrate that MR-guided renal embolisations can be performed in closed-bore high-field MR scanners.

Feasibility of MR-guided angioplasty of femoral artery stenoses using real-time imaging and intraarterial contrast-enhanced MR angiography.

PURPOSE: To show the feasibility of magnetic resonance (MR) for guided interventional therapy of femoral and popliteal artery stenoses with commercially available materials supported by MR real-time imaging and intraarterial MR angiography. MATERIALS AND METHODS: Three patients (1 female, 2male), suffering from symptomatic arterial occlusive disease with stenoses of the femoral (n = 2) or popliteal (n = 1) arteries were included. Intraarterial digital subtraction angiography was performed in each patient pre- and post-interventionally as standard of reference to quantify stenoses. The degree of the stenoses reached from 71 - 88 %. The MR images were acquired on a 1.5 T MR scanner (Magnetom Sonata; Siemens, Erlangen, Germany). For MR-angiography, a Flash 3D sequence was utilized following injection of 5 mL diluted gadodiamide (Omniscan; Amersham Buchler, Braunschweig, Germany) via the arterial access. Two maximum intensity projections (MIP) were used as road maps and localizer for the interactive positioning of a continuously running 2D-FLASH sequence with a temporal solution of 2 images per second. During the intervention, an MR compatible monitor provided the image display inside the scanner room. Safety guidelines were followed during imaging in the presence of a conductive guidewire. The lesion was crossed by a commercially available balloon catheter (Wanda, Boston Scientific; Ratingen, Germany), which was mounted on a 0.035" guidewire (Terumo; Leuven, Belgium). The visibility was provided by radiopaque markers embedded in the balloon and was improved by injection of 1 mL gadodiamide into the balloon. After dilation, the result was checked by intraarterial MR angiography and catheter angiography. RESULTS: The stenoses could be correctly localized by intraarterial MR angiography. There was complete correlation between intraarterial MR angiography and digital subtraction angiography. The combination of guidewire and balloon was visible and the balloon was placed correctly to cover the entire stenoses. Balloon dilation reduced the degree of stenosis about 45 % on average. A prolonged dilation was necessary in one patient due to a relevant residual stenosis, which was recognized by intraarterial MR angiography. CONCLUSION: MR-guided balloon dilatation of femoral and popliteal artery stenoses supported by real time imaging and intraarterial MR angiography is feasible with commercially available materials in the above mentioned way.

[Influence of sequence type on the extent of the susceptibility artifact in MRI--a shoulder specimen study after suture anchor repair]. / Abhängigkeit der Artefaktgrösse vom Sequenztyp in der MRT--Präparatstudie zur Beurteilung der postoperativen Schulter nach Labrumfixation.

PURPOSE: To compare the extent of susceptibility artifacts after metallic suture anchor implantation by analyzing 14 different MRI sequences. MATERIALS AND METHODS: A metallic suture anchor was implanted in the central area of three glenoid porcine specimens. The specimens were imaged with a 1.5 T scanner using a protocol of 14 standard sequences including gradient echo, spin echo and turbo spin echo sequences with and without fat-saturation. Artifact size was measured for each specimen and sequence. The resulting mean artifact areas were determined for each type of sequence and the mean values of the three specimens compared. RESULTS: Gradient echo-sequences produced significantly larger artifact areas than the spin echo and turbo spin echo sequences, whereby the artifacts of the 3D-gradient echo sequences were smaller than the artifacts of the 2D-gradient echo sequences. A turbo spin echo sequence with a high readout band width and a short effective echo time showed the best results. For the conventional spin echo sequence, a reduction in the echo time did not significantly decrease the artifact size. Spectral fat-saturation did not affect the area of the susceptibility artifact compared to the non-saturated sequence. CONCLUSION: Gradient echo sequences should not be used after metallic suture anchor repair. Turbo spin echo sequences showed a decrease in the artifact size compared to conventional spin echo sequences and should be performed with a short effective echo time and a high band width. Spectral fat- saturation did not increase the artifact size significantly.

[In vitro examination of the visibility of 11 stent catheters with real-time MR imaging]. / In-vitro-Untersuchung der Sichtbarkeit von 11 Stentkathetern unter Echtzeit-MR-Kontrolle.

PURPOSE: To evaluate artifacts of unexpended stents and to determine their exact position for MR-guided percutaneous transluminal angioplasty using real-time sequences. MATERIALS AND METHODS: By using an in vitro model, 11 unexpended stents - 9 nitinol, 1 stainless steel, and 1 cobalt alloy - were investigated by MR. Each stent was studied in a vessel-phantom filled with saline solution. Imaging was performed using five different real-time sequences: fast low angle shot (Flash 2D), fast imaging with steady precession (true FISP, FISP, interactive true FISP) and segmented echo planar imaging (seg. EPI). Artifacts of the introducer system and the stent were calculated by four blinded radiologists (scale: 1 - artifacts, making an excellent contribution to visualization; 2 - artifacts, making mainly a contribution to visualization; 3 - artifacts, making no contribution to visualization). Furthermore, an evaluation of the visibility of the tip of the stent-catheter and the proximal and distal end of the stent was performed using a four-point scale (very good visibility to invisible). RESULTS: The artifacts of the introducer system and stent were rated best for Omnilink (1.3 +/- 0.47), Wallstent (1.6 +/- 0.5), Jostent (1.65 +/- 0.5) and Luminexx (1.65 +/- 0.5). The differences between Omnilink and Jostent as well as Omnilink and Luminexx were significant. A very good to good visibility of the catheter tip was observed with a mean of 1.7 +/- 0.66 for Omnilink followed by the Jostent (1.95 +/- 0.69), by the Wallstent(R) (2.1 +/- 0.72) and by Luminexx (2.5 +/- 1.14). Differences between Omnilink and Luminexx were significant. The visibility of the proximal and distal end of the stent was evaluated as very good to good in 4 stent catheters (Omnilink, Wallstent, Jostent, Luminexx). However, the differences between Omnilink and Jostent as well as between Omnilink and Luminexx, and between Wallstent and Luminexx were significant. For all evaluation criteria, the segmented EPI and the interactive true FISP were rated to be most suitable for visualization. There were no significant differences in the evaluation of these two sequences. CONCLUSION: Omnilink stent, Jostent, Wallstent, and Luminexx stent are suitable for MR-angioplasty due to their good visibility in MR. Segmented EPI- and a newly developed interactive true FISP-sequence enable an effective visualization of these stent-catheters.

[Magnetic resonance imaging. Sequence acronyms and other abbreviations in MR imaging]. / Magnetresonanztomographie. Sequenzakronyme und weitere Kürzel in der MR-Bildgebung.

The role of magnetic resonance imaging in clinical routine is still increasing. The large number of possible MR acquisition schemes reflects the variety of tissue-dependent parameters that may influence the contrast within the image. Those schemes can be categorized into gradient echo and spin echo techniques. Within these groups, further sorting can be done to differentiate between single-echo, multi-echo, and single-shot techniques. Each of these techniques can be combined with preparation schemes for modifying the longitudinal magnetization. Hybrids are found between the groups, which are those techniques that utilize spin echoes as well as gradient echoes. Academic groups as well as vendors often have different sequence acronyms for the same acquisition scheme. This contribution will sort these sequence acronyms into the previously mentioned scheme. The basic principle of the data acquisition is elaborated on and hints are given for potential clinical applications. Besides the sequence-specific acronyms, new abbreviations have surfaced recently in conjunction with parallel acquisition techniques." The latter means the utilization of multiple surface coils where the position and the sensitivity profile of the coils provide additional spatial information, allowing the application of reduced matrixes leading to a shorter measurement time.

Fast and ultrafast non-echo-planar MR imaging techniques.

The topic fast and ultrafast MR imaging commonly includes relatively slow gradient-echo techniques with spoiled transverse magnetization (FLASH, FFE-T1, SPGR), gradient-echo techniques with partially refocused transverse magnetization (FISP, FFE, GRASS), gradient-echo techniques with fully refocused transverse magnetization (trueFISP, balanced FFE, FIESTA), the multi-echo spin-echo techniques (RARE, TSE, FSE), a mixture of multi-echo spin-echo and gradient-echo techniques (GRASE, TGSE), and finally single-shot techniques (HASTE, SS-FSE, EPI). This article gives a description of the sequence structures of non-echo-planar fast imaging techniques and a list of potential clinical applications. Recent advances in faster imaging which are not sequence related, such as simultaneous acquisitions of spatial harmonics (SMASH) and sensitivity encoding (SENSE) for fast MRI, are mentioned as well as some novel techniques such as QUEST and BURST. Due to the recent success with gradient-echo techniques with fully refocused transverse magnetization (trueFISP, balanced FFE, FIESTA), this "faster" gradient-echo technique is discussed in more detail followed by multi-echo spin-echo techniques that present the counterpart to the multi-echo gradient-echo (EPI) technique, which is not discussed in this paper. Three major areas appear to be the domain for EPI: diffusion; perfusion; and blood oxygenation level dependent imaging (BOLD, fMRI). For all other applications there is ample room for utilizing other fast and ultrafast imaging techniques, due to some intrinsic problems with EPI.

[Contrast-enhanced MR angiography in the routine work-up of the lower extremity arteries]. / Kontrastmittelverstärkte MR-Angiographie der Becken- und Beingefässe in der klinischen Routinediagnostik.

PURPOSE: Prospective evaluation of the effectiveness of contrast-enhanced moving-table magnetic resonance angiography (CE-MRA) as the sole routine tool for the diagnosis of peripheral arterial occlusive disease and determination whether it can replace catheter arteriography. SUBJECTS AND METHODS: In a time period of 23 weeks, 100 consecutive patients were evaluated. A total of 112 contrast-enhanced moving-table MR angiograms were performed at 1.5 Tesla. A dedicated vascular coil system was used. It was evaluated in which cases MR angiography was sufficient to determine the treatment plan and in which cases limited quality required additional examinations. RESULTS: In 93.75 % (105/112) of all examinations, the treatment plan was determined by MRA as the sole diagnostic tool. Twenty-two patients underwent surgery or percutaneous angioplasty based on MRA findings. Additional examinations due to impaired quality were performed in seven (6.25 %) cases: two MR angiographies of the pelvic arteries, one MR angiography of the calf, and four selective arteriographies because of venous overlay at the calf. CONCLUSION: Contrast-enhanced MR angiography can take the place of catheter angiography in the routine work-up of patients with peripheral arterial occlusive disease. Further assessment might be necessary in five to ten percent of the cases when the diagnostic quality is inadequate, mostly due to venous overlay in the lower leg.

MR imaging of cranial nerve lesions using six different high-resolution T1- and T2(*)-weighted 3D and 2D sequences.

PURPOSE: To find a suitable high-resolution MR protocol for the visualization of lesions of all 12 cranial nerves. MATERIAL AND METHODS: Thirty-eight pathologically changed cranial nerves (17 patients) were studied with MR imaging at 1.5 T using 3D T2*-weighted CISS, T1-weighted 3D MP-RAGE (without and with i.v. contrast medium), T2-weighted 3D TSE, T2-weighted 2D TSE and T1-weighted fat saturation 2D TSE sequences. Visibility of the 38 lesions of the 12 cranial nerves in each sequence was evaluated by consensus of two radiologists using an evaluation scale from 1 (excellently visible) to 4 (not visible). RESULTS: The 3D CISS sequence provided the best resolution of the cranial nerves and their lesions when surrounded by CSF. In nerves which were not surrounded by CSF, the 2D T1-weighted contrast-enhanced fat suppression technique was the best sequence. CONCLUSIONS: A combination of 3D CISS, the 2D T1-weighted fat suppressed sequence and a 3D contrast-enhanced MP-RAGE proved to be the most useful sequence to visualize all lesions of the cranial nerves. For the determination of enhancement, an additional 3D MP-RAGE sequence without contrast medium is required. This sequence is also very sensitive for the detection of hemorrhage.

Determination of the pressure gradient in children with coarctation of the aorta by low-field magnetic resonance imaging.

During the past few years magnetic resonance imaging (MRI) has gained increasing importance in the noninvasive examination of congenital heart defects. Practically all existing examinations have been carried out with a magnetic field strength exceeding 1 (T high-field MRI). Flow quantification is considered to be an advanced MRI application and, in the past, has been available for high-field systems only. Therefore until recently, functional examinations such as MRI tomographic flow quantification were reported exclusively for high-field MRI units. From December 1998 to December 1999, nine patients (five girls and four boys, mean age 130 plus minus 3.6 months, range 62-185 months) were investigated by means of MRI after a previous surgical repair or interventional balloon dilatation of a coarctation of the aorta (mean postinterventional time period 23 plus minus 0.4 months). The examination was carried out without sedation in an open low-field unit (Siemens Magnetom Open 0.2 T). Cardiac-triggered spin-echo sequences were used with a 3-mm to 7-mm slice thickness in an axial and a double oblique plane. The measurement of the immediate poststenotic flow velocity was done by flow-sensitive sequences developed for the study (phase-sensitive flow measurement sequences: TE, 6-12 msec; TR, 50 msec; flip angle, 60 degrees; Vmax, 200-1200 cm/sec; two acquisitions). All patients were examined on the same day with comparative echocardiographic procedures. In all cases, an excellent anatomical evaluation of the aortic arch was possible. The diameters of the residual stenosis were measured by MRI and correlated well r = 0.95; p ? 0.001; mean difference 0.44 +/- 2.47 mm) with echocardiographic results. No wall damage was observed in any of the cases studied. The pressure gradient of the stenosis calculated from the flow sequence was between 17 and 50 mmHg and corresponded well (r = 0.93; p = 0.001; mean difference 0.67 +/- 11 mmHg) with the results obtained from echocardiography. The study demonstrates that examination of the aortic arch is possible in a low-field MRI system, with its significant advantages (lower patient discomfort and more cost-effective examination). In addition, a quantitative flow measurement in low-field MRI was realized for the first time. Low-field MRI therefore seems to be a good, noninvasive method for examining patients with a poor echocardiographic representation of the aortic arch.

Quantification of blood flow in the carotid arteries: comparison of Doppler ultrasound and three different phase-contrast magnetic resonance imaging sequences.

RATIONALE AND OBJECTIVES: To compare blood flow velocities in the carotid arteries measured with three different magnetic resonance (MR) phase-contrast imaging techniques and with percutaneous Doppler ultrasound. METHODS: Fourteen healthy male volunteers with a mean age of 33 +/- 3.8 years were studied. Ultrasound and MR phase velocity mapping of both common carotid arteries (n = 28) was performed within 5 hours. A two-dimensional fast low-angle shot sequence with retrospective cardiac gating, a sequence with prospective cardiac triggering, and a breath-hold sequence with prospective cardiac triggering were used. Resistance indexes and pulsatility indexes were calculated for all modalities. RESULTS: The comparison of flow velocities obtained with ultrasound and the different MR techniques led to a moderate correlation of the retrospective gated and prospective triggered MR techniques (eg, r = 0.73 for maximum systolic velocity). The worst correlation was found between the breath-hold technique and retrospective cardiac gating (eg, r = 0.004 for pulsatility index). There was a weak correlation of all three MR sequences compared with ultrasound (r = 0.19-0.60) CONCLUSIONS: A moderate correlation was found between velocities and indexes measured with the prospective cardiac-triggered phase-contrast MR technique and the retrospective cardiac-gated phase-contrast MR technique. A weak correlation was found between the three different MR techniques and ultrasound, as well as between the breath-hold prospective cardiac-triggered MR sequence and both of the other MR sequences. The influence of temporal and spatial resolution on MR phase-contrast velocity mapping was confirmed.

Comparison of two-dimensional gradient echo, turbo spin echo and two-dimensional turbo gradient spin echo sequences in MRI of the cervical spinal cord anatomy.

The aim of this study was to assess the detectability and distinguishability of the cervical spinal cord, the anterior and posterior spinal roots and of the internal anatomy of the cord (distinction of grey and white matter). For this purpose 20 healthy volunteers were examined using a 1.5 T MR unit with 20 mT/m gradient strength and a dedicated circular polarized neck array coil. Three T2* weighted (w). 2D gradient echo sequences, two T2 w. 2D turbo spin echo (TSE) sequences and one T2 w. 2D turbo gradient spin echo (TGSE) sequence were compared. The multiecho 2D fast low angle shot (FLASH) sequence with magnetization transfer saturation pulse (me FLASH+MTS) yielded the best results for liquor/compact bone, liquor/spinal cord and grey/white matter contrast, as found with regions of interest (ROI) analysis. The single echo 2D FLASH sequence was significantly poorer than the two me FLASH+/-MTS sequences. Two-dimensional TGSE as well as 2D TSE with a 256 matrix and with a 512 matrix yielded the poorest results. In the visual analysis the contrast between liquor and compact bone, liquor and cord as well as liquor and roots was best with me FLASH+MTS, whereas grey/white matter distinction was best using me FLASH-MTS. In conclusion, we would therefore recommend the inclusion of an axial T2* w. multiecho 2D spoiled gradient echo sequence with magnetization transfer saturation pulse and gradient motion rephasing in a MR imaging protocol of the cervical spine.

MR imaging-guided stent placement in iliac arterial stenoses: a feasibility study.

PURPOSE: To assess the feasibility of magnetic resonance (MR) imaging-guided stent placement in iliac arterial stenoses. MATERIALS AND METHODS: Thirteen patients with 14 iliac arterial stenoses were examined prospectively. Angioplasty was performed through a femoral sheath by using a conventional 1.5-T MR imaging system. Stents and catheters were visualized on the basis of their artifacts. Nitinol stents were placed with gradient-echo MR imaging guidance. Angioplasty balloons were inflated with gadolinium-based contrast material. Results were evaluated clinically and with both digital subtraction angiography (DSA) and contrast material-enhanced MR angiography. RESULTS: Ten of 13 patients were treated with technical success by using MR imaging-guided intervention alone. Three patients were treated with additional fluoroscopic guidance, because complications (ie, panic attack, subintimal recanalization, and stent misplacement) occurred with MR guidance. The quality of the postinterventional contrast-enhanced MR angiograms of three of 12 lesions with stents was limited owing to stent-induced signal loss of the lumen. The mean stenosis degree after stent placement was significantly higher at contrast-enhanced MR angiography than at DSA (24.6% vs 6.2%). The mean MR imaging-guided procedure time was 74 minutes. CONCLUSION: MR imaging-guided stent placement in iliac arteries is feasible in select patients. The presented technique has limitations-that is, long procedure times, lack of real-time monitoring, and stent artifacts-that necessitate further modifications before it can be recommended for clinical use.

Comparison between magnetic resonance phase contrast imaging and transcranial Doppler ultrasound with regard to blood flow velocity in intracranial arteries: work in progress.

OBJECTIVE: The authors evaluate blood flow velocities in the medial cerebral artery (MCA) and the basilar artery using magnetic resonance (MR) phase contrast technique in comparison with transcranial Doppler ultrasound (TCD). Eleven healthy male volunteers were studied. TCD of the MCA (n = 22) and basilar artery (n = 11) was performed. MR phase velocity mapping was done in each vessel at the same location where the TCD signal had been acquired. A 2-dimensional FLASH sequence with retrospective cardiac gating and an average temporal resolution of 45 ms was used. Resistance indices (RIs) and pulsatility indices (PIs) were calculated for both modalities. The TCD insonation angle was measured retrospectively with MR, and TCD velocities were corrected based on these measurements. The comparison of flow velocities obtained with TCD and MR led to a low correlation coefficient with regard to the basilar artery and the MCA: maximum systolic velocity, r = 0.02 and r = 0.50, respectively; enddiastolic velocity, r = 0.47 and r = 0.65, respectively; mean velocity, r = 0.52 and r = 0.66, respectively. The average PIs in the basilar artery and the MCA were 0.80 and 0.81 with MR and 0.65 and 0.85 with TCD, respectively. The average RIs in the basilar artery and the MCA were 0.52 and 0.54 with MR and 0.52 and 0.55 with TCD, respectively. The TCD insonation angle differed significantly from the ideal value in the basilar artery (mean value = 32.6 degrees) and the MCA (mean value = 26.5 degrees). The authors find a low correlation between velocities measured with MRI and TCD but similar results with regard to the PIs and RIs. Several sources of error, such as a nonideal TCD insonation angle, were identified.

Visualization of the IXth to XIIth cranial nerves using 3-dimensional constructive interference in steady state, 3-dimensional magnetization-prepared rapid gradient echo and T2-weighted 2-dimensional turbo spin echo magnetic resonance imaging sequences.

OBJECTIVE: The purpose of this study was to evaluate the visibility of the IXth to XIIth cranial nerves using different magnetic resonance sequences. Thirty healthy volunteers underwent magnetic resonance imaging at 1.5 T using 3-dimensional constructive interference in steady state (CISS) sequence (TR = 17 ms, TE = 8.08 ms, alpha = 70 degrees), 3-dimensional magnetization-prepared rapid gradient echo (MP-RAGE) sequence (TR = 11.08 ms, TE = 4.3 ms, alpha = 15 degrees), and T2-weighted (w) 2-dimensional turbo spin echo (TSE) sequence (TR = 4000 ms, TE = 102 ms, alpha = 180 degrees, slice thickness = 2 mm). Visibility of the IXth to XIIth cranial nerves in each sequence was evaluated by consensus of 2 radiologists using an evaluation scale from 1 (excellently visible) to 5 (not visible). A correlation with anatomic specimens was made. The 3-dimensional CISS sequence provides best resolution of the IXth to XIIth cranial nerves and their relation to surrounding structures. Additional information is given by the 3-dimensional MP-RAGE when nerves are surrounded by soft tissues. Using the T2w 2-dimensional TSE sequence, even whole nerves cannot be visualized due to intersection gap and partial volume effects. However, even in 3-dimensional high-resolution sequences, segments of nerves are not always visualized. A combination of 3-dimensional CISS and 3-dimensional MP-RAGE proved to be useful to visualize the IXth to XIIth cranial nerves, whereas the 2-dimensional technique failed. Further investigations using 3-dimensional MP-RAGE with contrast medium should be performed in the case of abnormality.