Interventional magnetic resonance angiography with no strings attached: wireless active catheter visualization.

Active instrument visualization strategies for interventional MR angiography (MRA) require vascular instruments to be equipped with some type of radiofrequency (RF) coil or dipole RF antenna for MR signal detection. Such visualization strategies traditionally necessitate a connection to the scanner with either coaxial cable or laser fibers. In order to eliminate any wire connection, RF resonators that inductively couple their signal to MR surface coils were implemented into catheters to enable wireless active instrument visualization. Instrument background to contrast-to-noise ratio was systematically investigated as a function of the excitation flip angle. Signal coupling between the catheter RF coil and surface RF coils was evaluated qualitatively and quantitatively as a function of the catheter position and orientation with regard to the static magnetic field B0 and to the surface coils. In vivo evaluation of the instruments was performed in interventional MRA procedures on five pigs under MR guidance. Cartesian and projection reconstruction TrueFISP imaging enabled simultaneous visualization of the instruments and vascular morphology in real time. The implementation of RF resonators enabled robust visualization of the catheter curvature to the very tip. Additionally, the active visualization strategy does not require any wire connection to the scanner and thus does not hamper the interventionalist during the course of an intervention.

Whole-body 3D MR angiography of patients with peripheral arterial occlusive disease.

OBJECTIVE: We assessed the diagnostic performance of whole-body 3D contrast-enhanced MR angiography in comparison with digital subtraction angiography (DSA) of the lower extremities in patients with peripheral arterial occlusive disease. SUBJECTS AND METHODS. Fifty-one patients with clinically documented peripheral arterial occlusive disease referred for DSA of the lower extremity arterial system underwent whole-body MR angiography on a 1.5-T MR scanner. Paramagnetic gadobutrol was administered and five contiguous stations were acquired with 3D T1-weighted gradient-echo sequences in a total scanning time of 72 sec. DSA was available as a reference standard for the peripheral vasculature in all patients. Separate blinded data analyses were performed by two radiologists. Additional vascular disease detected by whole-body MR angiography was subsequently assessed on sonography, dedicated MR angiography, or both. RESULTS: All whole-body MR angiography examinations were feasible and well tolerated. AngioSURF-based whole-body MR angiography had overall sensitivities of 92.3% and 93.1% (both 95% confidence intervals [CIs], 78-100%) with specificities of 89.2% and 87.6% (both CIs, 84-98%) and excellent interobserver agreement (kappa = 0.82) for the detection of high-grade stenoses. Additional vascular disease was detected in 12 patients (23%). CONCLUSION: Whole-body MR angiography permits a rapid, noninvasive, and accurate evaluation of the lower peripheral arterial system in patients with peripheral arterial occlusive disease, and it may allow identification of additional relevant vascular disease that was previously undetected.

Interventional MR angiography with a floating table.

A floating table was integrated into a setup for performance of interventional magnetic resonance (MR) angiography procedures with actively visualized catheters and biplanar real-time image fusion. The setup was evaluated by performing catheterizations in eight pigs. The floating table enabled the authors to follow actively visualized instruments in the pigs' vasculature during MR imaging-guided interventional angiography procedures while performing real-time biplanar MR imaging. Interventional MR angiography with a floating table enables the field of view to be moved along with the instrument tip to the region of interest and thus enhances the usability and flexibility of the interventional MR imaging setup.

Using a 1 M Gd-chelate (gadobutrol) for total-body three-dimensional MR angiography: preliminary experience.

PURPOSE: To determine whether higher concentrated gadolinium chelates are advantageous for the recently introduced concept of total-body magnetic resonance angiography (MRA), allowing whole-body coverage, extending from the carotid arteries to the runoff vessels, in merely 72 seconds. MATERIALS AND METHODS: Total-body three-dimensional (3D) MRA using a 1 M Gd-chelate (gadobutrol, Gadovist, Schering, Berlin, Germany) at a dosage of 0.2 mmol/kg body-weight (biphasic injection protocol: 1.3 mL/second and 0.7 mL/second) was performed on three healthy volunteers and ten consecutive patients with DSA-documented peripheral vascular disease. Separated by at least 72 hours, the three healthy volunteers also underwent the same MRA-protocol, using gadopentetate dimeglumine in equimolar dosages. RESULTS: Compared to equimolar dosages, mean signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) values in the three volunteers were significantly higher (up to 32.5% for the arteries of the thighs and calves) using gadobutrol. In the ten patients, gadobutrol-based total-body MRA accurately assessed significant stenoses (luminal narrowing > 50%) with sensitivities and specificities of 96.2% (95% CI 0.83-0.97) and 95.7% (95% CI 0.84-0.96), respectively, compared to digital subtraction angiography. CONCLUSION: The MRA image quality for total-body MRA provided by the administration of gadobutrol is superior to that obtained following administration of an identical dose of gadopentetate dimeglumine, and therefore shows promise for use as a comprehensive single exam assessing the entire arterial system for the presence of atherosclerotic disease manifestations.

Intraindividual comparison of gadopentetate dimeglumine, gadobenate dimeglumine, and gadobutrol for pelvic 3D magnetic resonance angiography.

RATIONALE AND OBJECTIVES: To compare the effect on image quality of a 1.0 mol/L gadolinium chelate with that of two 0.5 mol/L gadolinium compounds. MATERIALS AND METHODS: Five healthy volunteers underwent a mono-station 3D MRA exam (Siemens SONATA, Erlangen, Germany) four times using four separate gadolinium preparations. All subjects first received a fixed volume of undiluted gadobutrol (1 mol/L), which corresponded to a dose between 0.1 and 0.15 mmol/kg body weight. This gadobutrol dosage was then diluted with saline into twice the volume and administered as a bolus at twice the injection rate. For Gd-DTPA and Gd BOPTA, because these contrast agents are 0.5 mol/L preparations, the volume and flow rate were doubled to match diluted gadobutrol volume and concentration. Quantitative and qualitative analysis of the angiographic data sets was performed on nine arterial segments. RESULTS: Image quality was rated diagnostic for all image data sets without statistically significant differences between any of the compounds (P > 0.3). Quantitative measurements of Gd BOPTA (SNR: 81.15; CNR: 68.91) and both standard and diluted forms of gadobutrol (SNR: 84.33; CNR: 71.62; SNR(diluted): 79,23; CNR(diluted): 66.26) yielded significantly higher results (P < 0.02) in comparison with Gd-DTPA (SNR: 49.55; CNR: 38.24). The difference between either form of gadobutrol and Gd BOPTA was not shown to be statistically significant (P > 0.3), whereas both the SNR and CNR of standard gadobutrol were significantly higher than diluted gadobutrol. CONCLUSION: Gadobutrol- and Gd BOPTA-MRA exams lead to improved delineation of the pelvic arterial morphology compared with MRA exams performed with Gd-DTPA.

Inductively coupled stent antennas in MRI.

The development of intimal hyperplasia following stent deployment can lead to narrowing or even occlusion of the stent lumen. The underlying mechanisms leading to neointimal proliferation within stents remain largely unknown. Long-term evaluation of stent patency requires a noninvasive means for assessing the stent lumen. MR angiography (MRA) has shown potential to provide noninvasive assessment of the vascular system. However, a detailed assessment of the stent lumen with MRI is often hampered by material-dependent susceptibility artifacts, as well as by radiofrequency (RF) eddy currents generated inside the electrically conducting stent mesh. In this study, stent prototypes were designed to act as active resonant structures at the Larmor frequency of the MR system. Employing the principle of inductive coupling, the B(1) fields of the stents were coupled to that of an outside surface coil. The stents thus acted as local RF signal amplifiers. Various stent designs were investigated regarding their coupling to an external coil, signal homogeneity, and suitability for mechanical expansion for implantation purposes. The dependency of flip angle amplification on the quality factor Q of the stents was systematically investigated. Phantom experiments revealed signal amplification in all stent prototypes. Signal enhancement inside and close to the surface of the stents enabled their localization with high contrast in MR images. In vivo imaging experiments in the iliac, renal, and splenic arteries of two pigs confirmed the in vitro findings. Wireless active visualization of stents allows for detailed analysis of the stent lumen with high contrast and spatial resolution. The proposed method could thus provide a powerful diagnostic means for the noninvasive long-term follow-up of stent patency, thereby enhancing our understanding of the mechanisms of restenosis.

Whole-body MRI using a rolling table platform for the detection of bone metastases.

The aim of this study was to compare the results of whole-body MRI using a recently developed rolling table platform with findings of nuclear scintigraphy in patients with bone metastases. Twenty-six patients with known or suspected bone metastases who had undergone radionuclide scintigraphy were examined by MRI. Patients were placed on a rolling table platform with integrated phased-array surface coils [BodySURF (system for unlimited field of view)] capable of pulling the patient through the isocenter of the magnet. Using a five-station approach three different image sets (T1-weighted gradient recalled echo, half-Fourier acquired single-shot turbo spin echo, and short tau inversion recovery) were collected in the coronal plane. In addition, the spine was imaged in the sagittal plane. The MRI findings were compared with the results obtained by scintigraphy. The whole-body MR examination lasting merely 40 min was feasible in all 26 patients. The MRI revealed excellent correlation with scintigraphy regarding metastatic lesions. A total of 60 regions with metastatic lesions were identified on bone scintigraphy. Fifty-three regions were detected on identical locations by MRI. The regions missed by MRI were located mainly in ribs and skull. The MRI could identify additional bone metastases in spine, pelvis, and femur. The MRI screening for bone metastases correlated well with bone scintigraphy. Use of the rolling table platform permits rapid imaging based on three different contrast mechanisms of the entire skeletal system.

Real-time MRI of joint movement with trueFISP.

PURPOSE: To develop a technique for dynamic magnetic resonance imaging (MRI) of joint motion based on a combination of real-time TrueFISP (fast imaging with steady state precession) imaging with surface radiofrequency (RF) coils. MATERIALS AND METHODS: The metacarpal, elbow, tarsal, and knee joint of five volunteers and the knees of four patients were examined with a real-time TrueFISP sequence during movement of the joints. RESULTS: All examined joints could be assessed under dynamic conditions with high image contrast and high temporal resolution. CONCLUSION: Dynamic MRI of joints with TrueFISP is feasible and can provide information supplemental to static joint examinations.

Whole-body three-dimensional MR angiography with a rolling table platform: initial clinical experience.

A technique for performing whole-body magnetic resonance (MR) angiography with multi-station three-dimensional MR angiography by using a self-developed rolling table platform that integrates the surface coil was evaluated in three volunteers and 10 patients. Use of the surface coil resulted in high signal-to-noise and contrast-to-noise ratios, which translated into sensitivity and specificity of 95.3% and 95.2%, respectively, for detection of significant stenoses (luminal narrowing, >50%) in lower extremity peripheral vascular disease.

Optimization of contrast dosage for gadobenate dimeglumine-enhanced high-resolution whole-body 3D magnetic resonance angiography.

RATIONALE AND OBJECTIVES: To determine the optimal dose of gadobenate dimeglumine for diagnostic high-resolution whole-body 3D-MR angiography. METHODS: Ten healthy volunteers were examined three times with an ascending dose of Gd-BOPTA (0.1/0.2/0.3 mmol/kg BW). Three-dimensional data sets were collected with a rolling table platform (AngioSURF; MR-Innovation GmbH, Essen, Germany) which integrates the torso surface coil, using a 3D FLASH sequence at five stations from carotid arteries to the trifurcation vessels in 72 seconds. SNR- and contrast-to-noise-values were calculated for 30 segments per patient. For qualitative evaluation a 4-point-visualization scale was used. RESULTS: Overall, significantly (P < 0.05) higher signal-to-noise values and CNR values were determined for Gd-BOPTA at a dose of 0.2 and 0.3 mmol/kg compared with 0.1 mmol/kg. Similarly, the qualitative analysis demonstrated image quality to be superior with 0.2 and 0.3 mmol/kg compared with 0.1 mmol/kg (P < 0.05). Qualitative and quantitative assessment failed to demonstrate a statistically significant difference between 0.2 and 0.3 mmol/kg BW (P > 0.05). CONCLUSION: A dose of 0.2 mmol/kg BW Gd-BOPTA rendered diagnostic image quality in all vascular segments of all volunteers.

Right-lobe living related liver transplantation: evaluation of a comprehensive magnetic resonance imaging protocol for assessing potential donors.

The purpose of this study was to determine the practicability and diagnostic accuracy of a magnetic resonance (MR) protocol capable of replacing computed tomography, catheter angiography, and endoscopic retrograde cholangiopancreatography for the presurgical evaluation of potential liver donors before right hepatectomy. MR imaging (MRI) was performed on a 1.5 T scanner using a phased-array torso surface coil for signal reception. The following image sets were collected: axial two-dimensional (2D) T1-weighted fast low angle shot (FLASH), axial 2D T2-weighted half-Fourier acquisition single-shot turbo-spin-echo (HASTE) with fat saturation, coronal MR cholangio-pancreatography (MRCP) based on 2D multisection HASTE and single-section single-shot rapid acquisition with relaxation enhancement (RARE) imaging, dynamic contrast-enhanced three-dimensional (3D) FLASH, and contrast-enhanced T1-weighted FLASH. 3D FLASH data sets were collected before and after an intravenous administration of Multihance (gadobenate dimeglumine, Gd-BOPTA; Bracco, Milano, Italy), 0.2 mmol/kg of body weight. Thirty-eight potential liver donors were assessed by means of MRI. Twenty patients also underwent digital subtraction angiography (DSA). Of these, 16 patients underwent liver harvesting. MR angiography (MRA) data sets correlated with DSA results, and MRCP results correlated with intraoperative findings. Patients were excluded as potential donors based on insufficient liver mass of the left hepatic lobe (n = 5) or presence of hepatic pathological states (n = 9) seen at MRI, such as hemangiomas, focal nodular hyperplasias, or hepatic steatosis. MRCP showed the biliary system to the level of the first hepatic side branch. Dilated ducts were present in 4 patients. MRA depiction of hepatic arterial morphological characteristics correlated with catheter angiography results in all 20 patients: Three left hepatic arteries originating from the left gastric artery, three aberrant right hepatic arteries originating from the superior mesenteric artery, and two aberrant origins of both hepatic arteries and one common hepatic artery originating from the superior mesenteric artery were correctly identified on MRA. Similarly, the portal venous system was fully assessed on MRA. A comprehensive assessment of the hepatic parenchyma, biliary and pancreatic ductal system, and hepatic arterial, portal, and venous systems can be accomplished using the outlined protocol.