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The purpose of this paper was to investigate the feasibility of MR-guided insertion of a temporary vena cava filter on an open low-field imager. In vivo procedures were performed on four anesthetized pigs using a common nonferromagnetic temporary vena cava filter and a special prototype guidewire developed for vascular interventions guided by low-field MRI. Breath-hold spoiled gradient-echo sequences (fast low-angle shot [FLASH]) with flow compensation were used for position monitoring of the passively visualized intravascular devices. Using the described technique and equipment, all steps of the procedure were feasible in the MR unit. Practicability of the procedure seems to be sufficient for clinical purposes but was inferior compared to the conventional technique of filter placement.

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PURPOSE: To optimise and evaluate fast "inflow"-based contrast-prepared gradient-echo magnetic resonance angiography (MRA) of blood vessels with pulsatile flow. MATERIAL AND METHOD: We used a standard 2-D Turbo-FLASH sequence with an acquisition time of 0.9 s and a slice-selective hyperbolic secant inversion (SSIR) pulse for contrast preparation. Trigger delay and inversion time were systematically varied. RESULTS: Abdominal blood vessels of volunteers showed high signal intensity compared to stationary tissue without pulsatile artifacts. However, depending on cardiac cycle and inversion time, venous vessels in particular exhibited a periodic signal drop by maximum 70% of the peak value. Using optimised parameters SSIR turbo-FLASH images of patients could be obtained with high flow contrast between normal and pathological structures. CONCLUSION: With ECG triggering SSIR Turbo-FLASH MRA enables fast imaging of pulsatile vessels with optimised flow contrast.

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We assessed the value of high temporal resolution in the dynamic characterization of hepatic hemangioma with use of magnetization-prepared gradient-echo (MP-GRE) imaging. Single-level inversion recovery incremental flip angle MP-GRE images were obtained in 26 patients with 34 hemangiomas before and at a repetition rate of 30 images/min after injection of Gd-DTPA without breath-holding. Enhancement patterns and temporal changes thereof were analyzed. Hemangiomas were categorized as small ( < 2.0 cm), medium (2.0-5.0 cm), and large ( > 5 cm) lesions. Classic early peripheral nodular enhancement (PNE) with progressive hyperintense fill-in was observed in 31 lesions (91%). Two of 10 small and 1 of 20 medium lesions showed complete fill-in within 10 s, and three small and one medium lesions within 45 s after the onset of PNE. In no cases of hemangioma was immediate homogenous hyperintensity observed without preceding PNE. In conclusion, temporal resolution of less than 10 s is a prerequisite for confident dynamic characterization of some hemangiomas, predominantly small hemangiomas.

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For optimizing MR imaging of the joints, a sophisticated knowledge of MR system hard- and software conditions and coil technologies, sequence and contrast preparation techniques, and the use of paramagnetic contrast agents is necessary. This review article discusses the basic principles of the appropriate use of surface coils as well as the different conventional and fast imaging sequences, including three-dimensional (3D) MR imaging. In addition, the applications of contrast agents as well as the most important contrast preparation techniques are reviewed.

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11 lesions of focal nodular hyperplasia (FNH) in 6 patients were studied by means of dynamic snapshot-FLASH MRI before and after bolus injection of Gd-DTPA. In addition, plain snapshot-FLASH images were compared with T1- and T2-weighted spin-echo (SE) images and with T1-weighted breathhold-FLASH images. Highest FNH-liver signal-difference-to-noise ratios were obtained with snapshot-FLASH followed by T2-SE. In all patients contrast-enhanced serial snapshot-FLASH demonstrated reliably the typical haemodynamic appearance of FNH known from dynamic computed tomography. Because of its high intrinsic lesion-liver contrast and high time-resolution dynamic snapshot-FLASH MRI may facilitate differential diagnosis of hepatic tumours.

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Incremental flip angle (IFA) snapshot fast low angle shot (FLASH) is a new modification of inversion recovery snapshot FLASH MR imaging. The method changes the flip angle incrementally from low to high during data acquisition and was applied in the evaluation of 16 focal hepatic lesions in 10 patients. Sequence comparisons were performed with a fixed flip angle inversion recovery snapshot FLASH sequence (standard), a T1- and T2-weighted spin-echo (SE) sequence, and a T1-weighted breath-hold FLASH sequence. Whereas snapshot FLASH images in both pulse sequences were free from physiological motion artifacts, SE and FLASH images showed respiratory artifacts in some patients. Quantitative analysis of IFA snapshot FLASH images at low hepatic and low lesion signal revealed both superior lesion-liver signal-difference-to-noise ratio (SD/N) and superior contrast compared with standard snapshot FLASH without additional artifacts. Unless motion artifacts were evident, SE and FLASH images showed a higher anatomic resolution but lower SD/N and lower contrast than IFA snapshot images. Because of its superior SD/N and contrast, IFA snapshot FLASH will likely widen the application of fast MR imaging techniques.

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Pelvimetry by means of snapshot-FLASH-MRI was carried out during the last trimester in 20 pregnant women. In 10 cases the results were compared with conventional spin-echo and FLASH-MRI. Snapshot-FLASH-MRI resulted in identical measurements but in addition provided images free from motion artifacts with good contrast of bone and soft tissue structures. The reduction in acquisition time resulted in pelvimetry in a few seconds. The total examination time and comfort for the patient were thereby improved.

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The utility of gadolinium-enhanced ultrafast MR imaging in the diagnosis of focal nodular hyperplasia (FNH) of the liver was assessed in one patient. Contrast-enhanced serial snapshot-FLASH with a frequency of 30 images/min demonstrated the typical hemodynamic appearance of FNH known from CT studies.

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Magnetic resonance imaging was used to analyze functional positions of the tongue and soft palate in 10 patients and 10 healthy volunteers. The patients had velopharyngeal insufficiency and/or dysfunction of the tongue. With snapshot FLASH (fast low-angle shot) sequences (data acquisition time, less than 1 second), malpositions of the articulatory apparatus were imaged and recorded for follow-up documentation.

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The use of MRI for demonstrating the articulators during phonation by means of a snapshot-FLASH technique has been studied in ten healthy subjects. Unlike ultrasound, which can only demonstrate movement of the tongue during articulation, MRI with snapshot-flash technique provides significant information on all articulators during phonation.

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A new examination protocol for patients with suspected meniscal or hyaline cartilage disorders is presented. Knees were imaged with a fast gradient echo imaging sequence with subsequent three-dimensional transformation. Data were transferred to an image processing system that allows reconstruction in any plane desired. Approximately 200 interactively positioned reconstructions are displayed and reviewed in approximately 10 min. Thirty-five patients with suspected meniscal or hyaline cartilage disorders were examined prospectively. All underwent subsequent arthroscopy. The magnetic resonance (MR) diagnosis showed an accuracy of 91.4% compared with arthroscopic findings. Owing to the short imaging time, the proposed procedure permits screening of knee joint disorders with MR.

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MRI is of increasing importance as a noninvasive method for the investigation of abnormalities in the knee. 2-D spin-echo sequences were compared with 3-D gradient-echo sequence using normal and cadaver knee joints. 3-D imaging using a fast computer was found to provide significantly improved diagnostic information concerning the cartilage when compared with a 2-D spin-echo techniques. The important advantages are: sections of less than 1 mm., reconstruction in any required plane, which can be related to the complex anatomy of the knee joint, and very good distinction between intra-articular fluid, fibrocartilage and hyaline cartilage.

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From the knees of healthy persons and cadavers 2D-spin-echo-sequences were compared to 3D-gradient-echo-sequences (FLASH, FISP). We were able to show that 3D-volume-imaging, combined with image processing on a fast computer, is superior to 2D-spin-echo-imaging. The advantages are: slice thickness lower than 1 mm, secondary reconstruction in any desired plane, good contrast between intraarticular fluid, the meniscus and the hyaline cartilage. For the practical application of 3D-volume-imaging resulting in multiple images the secondary reconstruction and post processing of the large numbers of images with an image processing computer is necessary.

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