B. S. Worthington

PREVALENCE OF LUMBAR DISC DEGENERATION OBSERVED BY MAGNETIC RESONANCE IN SYMPTOMLESS WOMEN

302 women aged 16-80 without symptoms of spinal disease had their lumbar intervertebral discs examined by magnetic resonance. The prevalence of one or more degenerate discs increased linearly with age but disc degeneration was already present in over one-third of women aged 21-40; these young women may prove to be at special risk of disc prolapse later in life. The high prevalence of symptomless disc degeneration must be taken into account when magnetic resonance is used for assessment of spinal symptoms.

Correction of spatial distortion in EPI due to inhomogeneous static magnetic fields using the reversed gradient method

To derive and implement a method for correcting spatial distortion caused by in vivo inhomogeneous static magnetic fields in echo‐planar imaging (EPI).

Fetal weight estimation by echo-planar magnetic resonance imaging.

Fetal weight was estimated in utero in eleven singleton pregnancies by measurement of fetal volume with echo-planar imaging (EPI), a form of magnetic resonance imaging, and by ultrasound measurements. EPI estimates of fetal volume were closely correlated with actual birthweight (R = 0.97). The median difference (expressed as a percentage of actual birthweight) between actual and EPI-estimated birthweights was 3.0% (range 0.6-9.9); this discrepancy was significantly smaller than that found for ultrasonographic estimates (6.5% [1.7-17.8]; p < 0.01).

Measurement of fetal liver, brain and placental volumes with echo–planar magnetic resonance imaging

Objective To quantify accurately in utero fetal liver, brain and placental volumes using echo planar imaging, and to assess whether the technique has the potential to enhance intrauterine fetal assessment.

ECHO PLANAR IMAGING OF THE HUMAN FETUS IN UTERO AT 0.5 T

The snap-shot capability of the echo-planar imaging technique is used to freeze motion effectively in human fetal studies in utero. These first results obtained at 0.5 T demonstrate diagnostic quality images without the need for averaging. Although averaging improves the image signal to noise ratio, it is shown that significant image blurring is produced even when only eight separate images are averaged over a period of a few seconds. Results are presented showing anatomical detail of the internal organs of the fetus. Some pathology is also demonstrated. These results were obtained using the modulus blipped echo-planar single-pulse technique (MBEST). Running at 10 frames/second, the modulus version of the fast low-angle excitation echo-planar technique (FLEET) is used to produce ungated fetal cardiac movies.

Magnetic resonance imaging of spinal trauma

A retrospective series of 118 magnetic resonance examinations of 110 patients who had sustained previous spinal trauma is reported. Examinations performed within 3 weeks of trauma showed extraspinal soft tissue (including ligamentous) injury in 48% and intraspinal lesions in 61% (mostly consisting of extradural haematoma and spinal cord contusion). In examinations performed more than 3 weeks after injury intraspinal abnormalities were shown in 51% and these represented spinal cord compression, atrophy, myelomalacia and syringohydromyelia. Magnetic resonance imaging has the unique capability of displaying non-invasively the late sequelae of spinal trauma permitting simultaneous evaluation of the extra-spinal soft tissues, vertebral column and spinal cord. It is therefore recommended as the technique of choice in the investigation of patients who have sustained previous spinal injury, particularly those with neurological deficit. In the acute phase potentially remediable causes of neurological impairment such as disc herniation or extradural haematoma can be identified. Signal changes in the cord may allow the prognosis for neurological recovery to be established. In the later stages sequelae such as cord atrophy, myelomalacia and syringohydromyelia are accurately identified and surgical therapy may be guided, where appropriate.

Comparison of Magnetic Resonance Angiography With Conventional Angiography in the Detection of Intracranial Aneurysms in Patients Presenting With Subarachnoid Haemorrhage

Thirty-nine patients admitted with proven subarachnoid haemorrhage were imaged both with 3-D time of flight (TOF) magnetic resonance angiography (MRA) and conventional angiography. As the definitive examination, catheter angiography demonstrated 37 aneurysms; ten patients had no aneurysm, the remaining 29 patients had 37 aneurysms. We found the sensitivity of 3-D TOF MRA for the detection of aneurysms to be 81% and specificity to be 100% when the reporting radiologist inspects not only the MIP reconstructions but also the MRA source data and the axial spin-echo images. The investigation is less accurate if all the available imaging data is not considered.

In vivo intravoxel incoherent motion measurements in the human placenta using echo-planar imaging at 0.5 T

This paper presents the first in vivo measurements of intravoxel incoherent motion in the human placenta, obtained using the pulsed gradient spin echo (PGSE) sequence. The aims of this study were two‐fold. The first was to provide an initial estimate of the values of the IVIM parameters in this organ, which are currently unknown. The second aim was then to use these results to optimize the sequence timings for future studies. The moving blood fraction (f), diffusion coefficient (D), and pseudo‐diffusion coefficient (D*) were measured. The average value of f was 26 ± 6 % (mean ± SD), D was 1.7 ± 0.5 × 10−3 mm2/sec, and D* was 57 ± 41 × 10−3 mm2/sec. For the optimized values of b, the expected percentage uncertainty in the fitted values of f, D, and D* for the placenta were σf/f = 14.9%, σD/D = 14.3%, σD*/D* = 44.9%, for an image signal‐to‐noise of 20:1, and a total imaging time of 800 sec. Magn Reson Med 43:295–302, 2000.

Problems and pitfalls of 3-D TOF Magnetic resonance angiography of the intracranial circulation

3-D Time of flight (TOF) Magnetic resonance angiography (MRA) is being increasingly adopted as a technique for assessment of the intracranial circulation in neuroradiological practice. We describe our recent experience of 3-D time of flight Magnetic resonance angiography. We describe some of the problems and potential pitfalls that we have experienced employing 3-D TOF MRA in these circumstances, and the diagnostic dilemmas that have arisen. A range of problems have been encountered. When performing 3-D TOF MRA, other phenomena such as sub-acute thrombus and high signal structures may be incorporated into the Maximal Intensity Projection (MIP) reconstruction and masquerade as vascular abnormalities. Interpretation of MIP reconstructions can also be difficult or impossible in the presence of sizeable haematoma. Conversely, vascular structures may not be appreciated because of loss of signal from saturation effects or dephasing due to slow or complex flow. Local susceptibility artefacts, from aneurysm clips or coils, may reduce the signal from vascular structures. Interpretation of 3-D TOF MRA must take account of potential pitfalls which can be minimized by adoption of appropriate imaging and review strategies. This requires careful consideration of MRA source data, the spin-echo axial images as well as the MIP reconstructions.

Neuro-endoscopic third ventriculostomy: Evaluation with magnetic resonance imaging

We have performed a prospective study of the use of magnetic resonance (MR) imaging in 14 patients undergoing neuro-endoscopic third ventriculostomy. MR imaging was undertaken prior to the endoscopy and serial studies were carried out after the procedure. MR imaging provides important information concerning the morphology of the third ventricle and allows the identification of an appropriate puncture site in the floor of the third ventricle. In particular, the relationship of the third ventricular floor to the basilar artery is well demonstrated. Following an endoscopic septostomy, MR imaging allows visualisation of any change in ventricular size. A cerebro-spinal fluid (CSF) flow void in the anterior inferior third ventricle, sometimes extending into the suprasellar cisterns was frequently demonstrated and this was found to be a more constant feature than reduction in ventricular size. MR imaging provides an indispensable tool for both planning and follow-up of endoscopic third ventriculostomy.