In utero perfusing fraction maps in normal and growth restricted pregnancy measured using IVIM echo-planar MRI.

The aim of this study was to measure and portray blood movement in the placenta in vivo in normal and growth restricted pregnancies, using Intra Voxel Incoherent Motion (IVIM) magnetic resonance imaging. Thirteen patients with apparently normal healthy pregnancies were scanned at 31+/-7 (mean+/-s.d.) weeks gestation and seven patients with intrauterine growth restriction (IUGR) were scanned at 31+/-4 weeks. A region of interest (ROI) was defined encompassing the placenta between the decidual and chorionic plates. The volume of moving blood within each imaging voxel of the ROI was then calculated as a percentage of the total voxel volume (f per cent). This information was colour coded to produce maps of moving blood volume. The placenta was segmented length ways into two zones of approximately equal area, termed inner and outer, the latter being adjacent to the uterine wall. f was fitted for the average in the outer zone (f(out)) and inner zone (f(in)). The parameter (f(out)-f(in)) was then calculated for each subject. This was positive in 12/13 of the normal cases and zero for one case (+10 per cent+10, mean+/-s.d.). For pregnancy affected by IUGR this value was negative in all cases (-4 per cent+/-3). Perfusion fraction mapping identified differences in function within the normal placenta in vivo, and between the placentae of normal and IUGR pregnancies. The technique has potential applications in managing, and investigating the aetiology of, pregnancy compromise.

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 x 10(-3) mm2/sec, and D* was 57 +/- 41 x 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 sigmaf/f = 14.9%, sigmaD/D = 14.3%, sigmaD*/D* = 44.9%, for an image signal-to-noise of 20:1, and a total imaging time of 800 sec.

In vivo perfusion measurements in the human placenta using echo planar imaging at 0.5 T.

This paper presents the first in vivo measurements of perfusion in the human placenta from 20 weeks gestational age until term, using the non-selective/selective inversion recovery echo-planar imaging sequence, in which data is alternately acquired following a selective and non-selective inversion pulse. Twenty pairs of images were collected, two each at the following inversion times: 20, 310, 610, 910, 1110, 1410, 1910, 2810, 3310, and 4510 ms with the sequence being repeated with a repetition time (TR) of 10 s. The results of these measurements were used to suggest the optimum sequence for future work in terms of the signal to noise ratio in the measured perfusion rate in a given measurement time. The sequence was also analyzed to determine the expected variability in the measurements. In normal pregnancies the average value of perfusion rate was found to be 176 (standard error = +/-24) ml/100 mg/min. (n = 16, standard deviation = 96 ml/100 mg/min). The expected variability in the measured parameters due to signal to noise ratio considerations alone was calculated to be 71%. For a maximum scanning time of 400 s, the optimum sequence for measuring placental perfusion was found to require 8 repetitions at each of 10 inversion times which were geometrically spaced (given by a(o), a(o)r, a(o)r2, a(o)r3, . . .), with a(o) = 850 ms, r = 1.073 and TR = 5 s, giving a pixel variability of 38%. Other timing schemes are recommended for measuring perfusion in other anatomical regions with different values of perfusion rate and longitudinal relaxation time.

In vivo relaxation time measurements in the human placenta using echo planar imaging at 0.5 T.

This paper presents the first in vivo measurements of the nuclear magnetic resonance relaxation times T1 and T2 at 0.5 T in the human placenta from 20 weeks gestational age until term, in both normal and compromised pregnancies. T1 measurements were performed by using both an inversion recovery sequence and the Look-Locher echo planar imaging (EPI) sequence on a total of 41 women with normal pregnancies and 11 women with compromised pregnancies. T2 measurements were performed by using a spin-echo EPI sequence on 36 women with normal pregnancies and 14 women with compromised pregnancies. In normal pregnancies, both the T1 values measured with the inversion recovery sequence and the T2 values were found to decrease with gestational age, the linear regression results gave T1 = -9.1t + 1538 r2 = 0.23 p = 0.03. T2 = -4.0t + 338 r2=0.47 p =410(-6) where t is the gestational age in weeks, and T1 and T2 are the relaxation times in milliseconds. T1 values measured very rapidly with the Look-Locher EPI sequence, but, therefore, with a much lower signal-to-noise ratio, showed no significant trends. The T1 values measured in the abnormal group were significantly lower than those measured in the normal group. Four out of eight patients with compromised pregnancies had placental T1 values lying outside the 90% confidence limits for the normal population based about the regression line, significantly more than expected by chance (p = 0.005). Ten out of fourteen of the T2 measurements in the abnormal group were below the regression line established for the normal group, with 4 lying below the 90% confidence interval, although these trends were only just significant (p = 0.06 and p = 0.03).

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.

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.

The value of MRI in the assessment of traumatic intra-uterine adhesions (Asherman's syndrome).

Since the publication titled Amenorrhea Traumatica (atretica) by Asherman in 1948, this syndrome has been considered a well defined clinical entity. It is typically manifested by the formation of fibrous adhesions involving the uterine cavity, sometimes involving the internal cervical os. The major causes are surgical intervention of the post-partum uterus and elective termination of early pregnancy. The diagnosis is usually suggested by hysterography and confirmed by hysteroscopy. The MRI appearances are reported in four cases of Asherman's Syndrome in which the diagnosis was confirmed by hysteroscopy. The full range of MRI appearances in Asherman's Syndrome has not been established and to our knowledge there has been only one case reported in the literature.

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. DESIGN: Thirty-two singleton, complicated pregnancies were scanned using echo planar imaging, a form of magnetic resonance imaging. Pregnancies were subdivided on the basis of whether the fetus was found subsequently to have an individualised birthweight ratio above (n = 21) or below (n = 11) the 10th centile. Comparisons of the organ volumes of these two groups were made. RESULTS: The first quantitative in utero measurement of fetal liver volume showed a linear relation between liver volume and gestational age in fetuses where the individualised birthweight ratio was above the 10th centile (the normal growth group). Ten of the 11 liver volume measurements of fetuses subsequently found to have an individualised birthweight ratio below the 10th centile fell on or outside the 95% confidence limits established for the normal growth group. In contrast, no such differences were demonstrated when the brain and placental volumes were considered, with 10 of the 11 brain measurements and all of the 11 placental measurements falling within the 95% confidence limits of the normal growth group. CONCLUSIONS: A single measurement of fetal liver volume using echo planar imaging enabled accurate identification of fetuses subsequently found to have individualised birthweight ratios below the 10th centile. If these findings are repeated in larger, more representative studies, this suggests that the technique has the potential to contribute to intrauterine fetal assessment.

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).

Review article: computed tomography and magnetic resonance in the diagnosis of intraventricular cerebral masses.

We describe a series of 60 cases of patients with masses arising within the cerebral ventricles. The site and relative frequency is noted for each histological type. The differential diagnosis depends on patient age and sex, site, morphology and number of masses, presence and type of hydrocephalus and the characteristics of the mass on computed tomography (CT) and magnetic resonance (MR) images. A review of the literature has been performed and this information collated with our own experience to give detailed descriptions of the typical features of each intraventricular mass. Attention is drawn to intraventricular neurocytoma, a recently described tumour that may be mistaken histologically for intraventricular oligodendroglioma or ependymoma. A comparison is made of the value of CT and MR in the diagnosis of intraventricular masses.

Case report: CT and MRI of the cauda equina syndrome in ankylosing spondylitis.

The clinical and radiological findings in a patient with long-standing ankylosing spondylitis who developed the clinical features of a cauda equina syndrome are presented. CT and MRI revealed characteristic expansion of the lumbar spinal canal with scalloping of the laminae and spinous processes related to the presence of dorsal dural diverticulae. MRI permitted confident exclusion of other intradural pathology without recourse to invasive investigations.

Clinical experience with contrast enhanced echo-planar imaging of the brain.

The overall effects of intravenous Gd-DTPA on tissue signal in intracranial tumors are complex depending on dose, time of administration, pulse sequence, and tissue structure. Ultrahigh speed EPI permits the kinetics of tissue enhancement in intracranial tumors to be studied during the "wash-in" equilibrium and "wash-out" phases. Ongoing studies employing dynamic scanning have shown it to be a valuable adjunct to a morphological study of tumors, providing an assessment of vascularity which is important in planning resection; and demonstrating areas with maximal breakdown of the blood-brain barrier which are most suitable for stereotactic biopsy. There are grounds for anticipating that the analysis of the temporal profile of enhancement may allow discrimination between different tumor types and provide information on factors which relate to the malignant potential of a single type.

Dynamic imaging of contrast enhancement in brain tumors.

Gadolinium-DTPA has been shown to be a good probe for demonstrating defects in the blood-brain barrier, but it has a rapid rate of elimination so that peak circulating levels are short-lived. In this study ultrafast echo-planar imaging has been used in combination with a bolus injection of gadolinium-DTPA to evaluate perfusion within brain tumors and to assess the degree of disruption of the blood-brain barrier. The temporal profile of enhancement may allow discrimination between different tumor types.

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.

Observation of cerebrospinal fluid flow with echo-planar magnetic resonance imaging.

Using echo-planar (EP) magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) flow patterns have been demonstrated in the normal subject and patients with pathological conditions including communicating hydrocephalus, aqueduct stenosis and syringohydromyelia. Snap-shot imaging times of 128 ms allow detailed demonstration of transient intraventricular CSF flow patterns, which is not possible with conventional MRI. The potential of EPI as a method for qualitative and quantitative assessment of CSF dynamics is illustrated.