Proton Density-weighted Spin-echo Sequences Research Articles

Evaluation of Magnetic Resonance Imaging-Compatible Needles and Interactive Sequences for Musculoskeletal Interventions Using an Open High-Field Magnetic Resonance Imaging Scanner

In this article, we study in vitro evaluation of needle artefacts and image quality for musculoskeletal laser-interventions in an open high-field magnetic resonance imaging (MRI) scanner at 1.0T with vertical field orientation. Five commercially available MRI-compatible puncture needles were assessed based on artefact characteristics in a CuSO4 phantom (0.1%) and in human cadaveric lumbar spines. First, six different interventional sequences were evaluated with varying needle orientation to the main magnetic field B0 (0 degrees to 90 degrees ) in a sequence test. Artefact width, needle-tip error, and contrast-to-noise ratio (CNR) were calculated. Second, a gradient-echo sequence used for thermometric monitoring was assessed and in varying echo times, artefact width, tip error, and signal-to-noise ratio (SNR) were measured. Artefact width and needle-tip error correlated with needle material, instrument orientation to B0, and sequence type. Fast spin-echo sequences produced the smallest needle artefacts for all needles, except for the carbon fibre needle (width <3.5 mm, tip error <2 mm) at 45 degrees to B0. Overall, the proton density-weighted spin-echo sequences had the best CNR (CNR(Muscle/Needle) >16.8). Concerning the thermometric gradient echo sequence, artefacts remained <5 mm, and the SNR reached its maximum at an echo time of 15 ms. If needle materials and sequences are accordingly combined, guidance and monitoring of musculoskeletal laser interventions may be feasible in a vertical magnetic field at 1.0T.

Comparative study of the lower uterine segment after Cesarean section using ultrasound and magnetic resonance tomography

To determine whether ultrasound (US) or magnetic resonance imaging (MRI) gave more accurate and objective information about the thickness and continuity of scarred isthmical myometrium following previous Caesarean section (CS), US and MRI assessments of the scarred myometrium in 10 pregnant women (37-41 weeks gestation) after 1-8 CS were compared with each other and with findings at subsequent elective CS. Vaginal ultrasound gave more accurate information about the condition of the scarred isthmical myometrium than MRI, since US always allowed precise differentiation of isthmical myometrium from the urinary bladder wall and thus measurements of the scar thickness; there was a good correlation to intraoperative observations. MRI achieved better contrast resolution with T2- than T1-weighted and proton density-weighted spin-echo sequences. However, differentiation of the various tissues was either impossible (T1- and protondensity-weighted sequences) or less informative than with US. Image quality of body and posterior wall of the uterus was better with MRI (T2-weighted sequence) than with US.

Fast Fluid-Attenuated Inversion-Recovery MR of Intracranial Infections

PURPOSE To assess the usefulness of fast fluid-attenuated inversion-recovery (FLAIR) MR sequences in the diagnosis of intracranial infectious diseases. METHODS We compared fast FLAIR images with conventional spin-echo images (T1- and T2-weighted) obtained in 20 patients with infectious diseases (six with encephalitis, five with brain abscesses, three with meningitis, two with meningoencephalitis, two with Creutzfeldt-Jakob disease, one with epidural empyema, and one with cysticercosis). Two neuroradiologists independently reviewed the FLAIR images and compared them with the conventional spin-echo images, obtaining agreement in all patients. RESULTS FLAIR images of diagnostic quality were obtained in 18 patients. In two patients, FLAIR images were degraded by motion. Lesions in the patients with encephalitis and meningoencephalitis were better delineated on FLAIR images than on spin-echo images. FLAIR images clearly depicted lesions in the basal ganglia in both patients with Creutzfeldt-Jakob disease. In patients with brain abscess, meningitis, cysticercosis, and epidural empyema, FLAIR images provided no more information than conventional spin-echo images, and the lesions were seen better on postcontrast T1-weighted spin-echo images. CONCLUSION Fast FLAIR images showed pathologic changes in intracranial infectious diseases better than or as well as conventional T2- and proton density-weighted spin-echo sequences. However, postcontrast T1-weighted spin-echo sequences resulted in better visibility of abscess, meningitis, cysticercosis, and epidural empyema than did FLAIR images.

EVALUATION OF MAGNETIC RESONANCE IMAGING TECHNIQUES IN THE EQUINE DIGIT

An anatomic study of the equine digit using magnetic resonance imaging (MRI) was performed. Seventeen isolated forelimbs and one hindleg of nine warmblood horses were imaged in transverse, sagittal, and dorsal planes with a 1.5 Tesla magnet using T1-, T2- proton density-weighted spin echo sequences as well as T2 gradient echo sequences. One scan plane in each horse was compared with corresponding anatomic and histologic sections. The best imaging planes to visualize various anatomic structures were determined. Fibrocartilage was visualized in the insertion of the deep digital flexor tendon and the suspensory ligament as well as in the distal sesamoidean ligaments. The correlation of MRI images with anatomic and histologic sections confirmed that all of the anatomic structures in the equine digit could be evaluated in PD and T2 studies.

Tomographic abdominal anatomy with magnetic resonance color composites

Magnetic resonance imaging (MRI) is an excellent modality for tomographically visualizing abdominal structures, particularly the liver, In an effort to simulate the natural color scheme of the living abdomen using MRI, we have generated color composites from sets of gray tone MR images obtained at corresponding anatomic slice positions from two healthy individuals. Pulse sequences used for our image sets included T1-, T2-, and proton density-weighted spin echo sequences as well as an angiographic FISP gradient echo sequence. A PC/AT-compatible computer with 24-bit graphics display capbilites, along with commerical and customized image-processing software, was used for composite generation. The applied colors were selected based on quantitative characteristics tissue intensity patterns so that tissue contrast could be optimized in the final image. The generated composites were correlated with cadaver sections to evaluate the color scheme of these false-colored images. With our composite generation techniques, it was possible to generated near-natural appearing color images of the abdomen. Color composites may be useful for teaching human cross-sectional anatomy and may also have diagnostic applications in abdominal MRI studies. © 1992 Wiley-Liss, Inc.