Interactive MR imaging-guided biopsy and aspiration with a modified clinical C-arm system.

OBJECTIVE: This investigation was performed to test the hypotheses that interactive guidance of MR image acquisition during needle-directed procedures using a clinical 0.2-T C-arm open MR imaging system integrated with a frameless optically linked stereotaxy system is feasible, and that procedure times can be sufficiently short to be well tolerated by the patient. SUBJECTS AND METHODS: One hundred six MR-guided procedures were performed in 86 patients (ranging in age from 5 months to 88 years) using a clinical C-arm imaging system supplemented with an in-room RF-shielded liquid crystal display monitor, a frameless stereotaxy system, rapid gradient-echo sequences for needle guidance, and MR-compatible monitoring and surgical lighting equipment. We performed 50 biopsies and aspirations of the head and neck in 37 patients, 23 biopsies of musculoskeletal lesions in 22 patients, 16 biopsies of abdominal sites in 10 patients, six biopsies of the thoracolumbar spine or sacrum in six patients, and 11 shoulder joint injections for MR arthrography in 11 patients, in addition to 38 MR arthrographic injections on the same imaging system described in a previous report. Tissue sampling included fine-needle aspiration (n = 90) and cutting needle core biopsy (n = 41). Thirty-five patients underwent both procedures. Procedures were evaluated for success of needle placement, procedure time, and complications. RESULTS: Needle placement was successful in all cases, and no complications occurred. Tissue was sufficient for pathologic diagnosis for all but eight patients. Passes per patient averaged 2.1. For fine-needle aspiration, instrument time averaged 7 min 42 sec per pass, cutting needle core biopsy averaged 6 min 24 sec, and shoulder injection averaged 8 min. CONCLUSION: MR imaging guidance for needle procedures on a clinical 0.2-T C-arm system with supplemental interventional accessories is feasible, with relatively rapid needle placement.

MR monitoring of MR-guided radiofrequency thermal ablation of normal liver in an animal model.

The purpose of this study was to determine the suitability of MRI to accurately detect radiofrequency (RF) thermoablative lesions created under MR guidance. In vivo RF lesions were created in the livers of six New Zealand White rabbits using a 2-mm-diameter titanium alloy RF electrode with a 20-mm exposed tip and a 50-W RF generator. This was performed using a 0.2T clinical C-arm MR imager for guidance and monitoring. Each animal was sacrificed and gross evaluation was performed. Histologic correlation was performed on the first two animals. The MR-compatible RF electrode was easily identified on rapid gradient-echo images used to guide electrode placement. A single lesion was created in each rabbit liver. Lesions ranged from approximately 10 to 17 mm in diameter (mean, 13.5 mm). T2-weighted and short T1 inversion recovery (STIR) images demonstrated lesions ranging in diameter from 12 to 18 mm (mean, 14.6 mm). Lesion dimensions determined from images closely correlated with those determined at gross examination with the discrepancy never exceeding 2 mm, for an r2 value of .87. MRI performed at the time of MR-guided RF ablation accurately demonstrated created lesions. This modality may provide a new option for the treatment of local and regional neoplastic disease.

Interactive MRI-guided radiofrequency interstitial thermal ablation of abdominal tumors: clinical trial for evaluation of safety and feasibility.

This clinical trial was performed to evaluate the safety and feasibility of interactive MR-guided radiofrequency (RF) interstitial thermal ablation (ITA) performed entirely within the MR imager. RF-ITA was performed on 11 intra-abdominal metastatic tumors during 13 sessions. The RF electrode was placed under MR guidance on a .2-T system using rapid fast imaging with steady state precession (FISP) and true FISP images. A custom 17-gauge electrode was used and was modified in four sessions to allow circulation of iced saline for cooling during ablation. Tissue necrosis monitoring and electrode repositioning were based on rapid T2-weighted and short-inversion-time inversion recovery (STIR) sequences. Morbidity and toxicity were assessed by clinical and imaging criteria. The region of tissue destruction was visible in all 11 tumors treated, as confirmed on subsequent contrast-enhanced images. No significant morbidity was noted, and patient discomfort was minimal. In conclusion, interactive MR-guided RF-ITA is feasible on a clinical .2-T C-arm system with supplemental interventional accessories with only minor patient morbidity. The ability to completely ablate tumors with RF-ITA depends on tumor size and vascularity.

Gadolinium-enhanced high-resolution MR angiography with adaptive vessel tracking: preliminary results in the intracranial circulation.

To overcome problems associated with poor contrast between vessels and background tissue in time-of-flight magnetic resonance angiography, the role of intravenous gadopentetate dimeglumine in conjunction with a postprocessing adaptive vessel tracking scheme was studied. Vessel tracking makes it possible to discriminate arteries from veins, to prevent problems associated with other bright tissues on maximum-intensity projections, and to increase the signal-to-noise ratio. Short, asymmetric, velocity-compensated field echoes were used in conjunction with high-resolution imaging techniques to spatially discriminate between adjacent vessels and stationary background tissue. Gadopentetate dimeglumine was shown to be useful for visualization of small vessels, aneurysms, and regions of slow flow, when used with this post-processing scheme.

Electrocardiograph-independent, "wireless" cardiovascular cine MR imaging.

A new electrocardiograph (ECG)-independent, "wireless" gating technique for cine magnetic resonance (MR) imaging was evaluated in 23 cases of cardiovascular disease; in each case, standard ECG-dependent image loops were available for comparison. The ECG-independent strategy references cine MR imaging data retrospectively to inherent periodic changes in MR signal related to the cardiac cycle. With a "double-section" method, both timing data reflecting such changes and imaging data can be acquired simultaneously. "Artificial R waves" are extracted from the timing data acquired with a projection approach. The ECG-independent image loops were diagnostic in 91% of cases. Their overall image quality was at least equal to that of available ECG-dependent versions in only 39% of cases, but this proportion increased to 53% if cases with suboptimal imaging orientations for monitoring of the motion-dependent signal changes were excluded. Orientation appeared to be the primary technical limitation associated with this ECG-independent technique; however, poor ventricular function also significantly impaired performance. Improvement in the performance of the ECG-independent strategy is anticipated with technical advances.

The effect of motion on two-dimensional Fourier transformation magnetic resonance images.

The effect of motion on two-dimensional Fourier transformation magnetic resonance (MR) images was investigated using phantoms, animals, and normal volunteers. All images were obtained with a 0.30-Tesla superconducting magnet using spin echo pulse sequences. Respiratory motion was simulated while imaging the phantoms. In addition to image blurring, motion produced ghost images, or image harmonics. These ghost images were copies of the static image that was produced at periodic intervals. Canine images, which were obtained during respiration and after the administration of curare, showed significant improvement after respiratory motion was eliminated. Images of normal volunteers were improved with respiratory and cardiac gating, but data acquisition time was significantly increased. These results indicate that MR image quality could be improved with a system that acquires all necessary data within a single breathhold .

Head trauma evaluated by magnetic resonance and computed tomography: a comparison.

Magnetic resonance (MR) images and computed tomograms of 25 patients with head trauma were compared. MR proved to be superior in many ways for demonstrating extracerebral as well as intracerebral traumatic lesions. Isodense subdural hematomas, which present a diagnostic dilemma on CT images were clearly seen on MR, regardless of their varying CT densities. In a case of epidural hematoma, the dura mater was shown directly as nearly devoid of signal on MR. Direct coronal images provided excellent visualization of extracerebral collections along the peritentorial space and subtemporal area. In a patient with intracerebral hematoma, CT failed to demonstrate residual parenchymal changes in a 3-month follow-up study, but MR clearly depicted the abnormalities. The superiority of MR over CT was also well illustrated in a patient with post-traumatic osteomyelitis of the calvarium.