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To determine the feasibility of using MR microscopy to characterize the root ligaments of the human knee at both ultra-high-field (11.7 T) and high-field (3 T) strengths. Seven fresh cadaveric knees were used for this study. Six specimens were imaged at 11.7 T and one specimen at 3 T using isotropic or near-isotropic voxels. Histologic correlation was performed on the posteromedial root ligament of one specimen. Meniscal root ligament shape, signal intensity, and ultrastructure were characterized. High-resolution, high-contrast volumetric images were generated from both MR systems. Meniscal root ligaments were predominantly oval in shape. Increased signal intensity was most evident at the posteromedial and posterolateral root ligaments. On the specimen that underwent histologic preparation, increased signal intensity corresponded to regions of enthesis fibrocartilage. Collagen fascicles were continuous between the menisci and root ligaments. Predominantly horizontal meniscal radial tie fibers continued into the root ligaments as vertical endoligaments. MR microscopy can be used to characterize and delineate the distinct ultrastructure of the root ligaments on both ultra-high-field- and high-field-strength MR systems.

One of the unusual features of magnetic resonance (MR) imaging of the musculoskeletal system is the fact that many of the tissues of most interest such as tendons, ligaments, menisci, periosteum, and cortical bone have short T2s and produce no signal when imaged with conventional pulse sequences. They have been described as MR “invisible.” The lack of signal from the invisible tissues provides a useful dark background against which abnormalities that have an increase in signal can be recognized, but it also creates problems because the absence of signal means that it is not possible to characterize these tissues by measuring their mobile proton densities, T1s or T2s, actively manipulate their image contrast, differentiate adjacent tissues with short T2s, visualize short T2 internal structures within them, or observe effects due to contrast enhancement. These problems have meant that from a technical point of view, study of the MRinvisible tissues has lagged far behind that of visible tissues. The T2 which represents the cut-off between visible and invisible tissues was about 10 ms using spin echo sequences on older MR systems [1] but with conventional gradient echo sequences and modern clinical machines, the cut-off has become shorter and is probably 1–2 ms for images with clinically useful spatial resolution. Of particular interest have been ultrashort echo time (UTE) pulse sequences with TEs as short as 8 μs. These were originally described in the 1990s [2, 3] but improved machine performance has led to images using these sequences with signal detectable from previously MRinvisible tissues at spatial resolutions comparable to those obtainable with conventional sequences in clinically acceptable scan times.

The objective of this study was to assess the feasibility of using ultrashort TE (UTE) pulse sequences to image the lumbar spine. Pulse sequences of TE=0.08 ms were used to image the lumbar spine in 5 normal subjects and 14 patients with degenerative disease. Contrast enhancement was administered in 11 cases. The sequences showed high signal in the anterior and posterior longitudinal ligaments, the cartilaginous end plate, the annulus fibrosus, the ligamentum flavum, interspinous ligaments and insertions of ligaments. Normal contrast enhancement was seen in these structures. Enhancement of hypertrophied ligaments and scar tissue was readily identified. Long T2 suppression techniques were useful in distinguishing enhancement of scar tissue from veins. Enhancement in discs was more obvious than with conventional sequences. In a case of thalassaemia bands of high signal were seen in the intervertebral discs parallel to the end plates. The UTE sequences offer new options for visualizing discs, scar tissue, ligaments and other structures of the lumbar spine in health and disease.

To demonstrate the surgical-anatomical relationship of the neonatal conjunctival fornices to the globe in order to ascertain whether adequate cryotherapy is possible in infants with stage 3 retinopathy of prematurity using a trans-scleral approach without opening the conjunctiva.Magnetic resonance (MR) scans of the orbit were performed on an adult and an infant of 38 weeks post-conceptual age with maximal posterior placement of a MR-compatible replica of the Schulenburg cryoprobe in the nasal and temporal aspects of the globe.In the infant MR scan, the scleral indentation produced by the probe was anterior to the equator on the nasal side and at, or just anterior to, the equator on the temporal side. Nasally, the scleral indentation reached only the more anterior part and not the posterior part of zone 2 and none of zone 1. Temporally, the scleral indentation reached the central part of zone 2 but not the posterior part of zone 2 or zone 1.The findings suggest that adequate cryotherapy with a trans-scleral approach without opening the conjunctiva is unlikely to be achieved in the more immature neonate with posteriorly located retinopathy of prematurity. To permit access of the cryoprobe to the more posterior part of the globe, one radial conjunctival incision from the corneal limbus in each quadrant may be required to achieve adequate ablation of the posterior non-vascularised retina in these high-risk infants.

Diffusion-weighted imaging (DWI) can readily be performed in the neonate, although currently studies remain a few years behind-those carried out on adults. DWI relies on the random diffusion of water molecules. As for the adult population, a pulsed gradient spin echo sequence (PGSE) with cardiac gating can be used to exploit the effect of diffusion on image contrast and to determine the apparent diffusion coefficient (D*) for tissues or fluids. Anisotropic properties caused by the restriction of the movement of water molecules may be demonstrated. In the neonatal brain restricted motion can be detected in both myelinated and unmyelinated white matter tracts. DWI has been used to study changes in global and focal ischaemic injury to the neonatal brain. A decreased D* may be documented after an ischaemic insult followed by a gradual increase. These changes are consistent with animal data but show a slower time course. Intervention following perinatal ischaemic injury must be started within hours. DWI detects early ischaemic injury and may therefore be a useful tool for identifying those infants who could benefit from intervention.

We wished to determine the pattern of cerebellar disease in children with a history of premature birth and early ultrasound evidence of intraventricular haemorrhage and/or parenchymal lesions of the cerebral hemispheres.MRI findings for all premature infants examined in a 3-year period (73 patients) were reviewed to determine the nature and frequency of lesions of the cerebellum and the results were correlated with clinical data.Six cases of unilateral cerebellar infarction were identified. These involved the posterior inferior cerebellar territory in each case (as well as other territories in two cases). A case of generalised cerebellar atrophy and three cases of unilateral cerebellar hemisphere atrophy were identified as well. In nine of these ten cases abnormalities were also seen elsewhere in the brain.The literature describes cerebellar infarction in infants and children as rare, but this study shows that it is not unusual following perinatal haemorrhagic/ischaemic anoxic injury. It is suggested that cerebellar atrophy may also occur as a result of vascular disease.

The application of diffusion-weighted imaging to the early diagnosis of neonatal cerebral infarction and hypoxic ischemic encephalopathy is illustrated. Diffusion-weighted images showed early infarction before conventional imaging in both cases. These were subsequently seen with conventional imaging on follow-up. In four cases of grades I and II hypoxic-ischemic encephalopathy (HIE) no abnormality was seen with either diffusion-weighted or conventional imaging. In four other cases of grades II and III HIE, much more extensive changes were seen with diffusion-weighted imaging than with conventional imaging. Follow-up scans with conventional imaging confirmed the abnormalities in the two surviving infants. Diffusion-weighted imaging may be particularly useful for the early diagnosis of ischemic-anoxic injury in infants.

Heavily T2-weighted fluid-attenuated inversion recovery (FLAIR) sequences with inversion times of 2000-2500 ms and echo times of 130-200 ms were used to image the brain stem of a normal adult and five patients. These sequences produce high signal from many white matter tracts and display high lesion contrast. The corticospinal and parietopontine tracts, lateral and medial lemnisci, superior and inferior cerebellar peduncles, medial longitudinal fasciculi, thalamo-olivary tracts and the cuneate and gracile fasciculi gave high signal and were directly visualised. The oculomotor and trigeminal nerves were demonstrated within the brain stem. Lesions not seen with conventional T2-weighted spin echo sequences were seen with high contrast in patients with infarction, multiple sclerosis, sarcoidosis, shunt obstruction and metastatic tumour. The anatomical detail and high lesion contrast given by the FLAIR pulse sequence appear likely to be of value in diagnosis of disease in the brain stem.

Hereditary haemochromatosis is a recessive disease in which primary hepatocellular carcinoma, complicating cirrhosis, is responsible for about one-third of deaths in affected homozygotes. We describe a unique HLA haplo-identical pedigree showing parent-to-off-spring transmission of hereditary haemochromatosis in whom HLA typing studies, including class I and class II allogenotype analysis, were of no benefit in identifying affected homozygotes. However, affected siblings in the pre-cirrhotic stage of haemochromatosis, with apparent discordance between the haemochromatosis allele and class I loci on chromosome 6, were detected by undertaking a family study, using analysis of serum parameters of iron status in combination with magnetic resonance imaging (MRI). This pedigree emphasises the critical importance of genetic and non-invasive methods for the identification of asymptomatic homozygotes before cirrhosis develops.

Magnetic Resonance Imaging of the Posterior Limb of the Internal Capsule and Neurodevelopmental Impairment After Hypoxic-Ischaemic Encephalopathy. 35

Natural abundance carbon 13 magnetic resonance spectroscopy (13C MRS) allows the proportion of saturated and unsaturated fatty acids in adipose tissue to be measured repeatedly and non-invasively. Eleven infants and two of their mothers underwent 13C MRS. Ten infants were studied in the first week of life, one also at 6 weeks and one at 10 weeks only. Using an enveloping transmitter coil and a surface receiver coil, coupled 13C spectra were obtained with repetition times of 0.3 seconds and 30 seconds. These were analysed by the NMRI curve fitting program and the percentages of saturated and unsaturated fatty acids calculated1. The results are shown either individually or as the median and range in the table

Recent developments in MRI of the brain are reviewed. Over the past year there has been a general improvement in image quality, a paramagnetic contrast agent has been used in clinical practice, and surface coils have been used more generally in imaging. A wider range of disease has been studied, and there has been considerable agreement about the advantages and disadvantages of MRI at a basic level. As the technique moves into routine clinical use, questions about the economics of the technique are becoming more pressing.

The basic features of an NMR imaging system are outlined and three pulse sequences which produce images with varying dependence on proton density T1 and T2 are described. The first of these sequences, Repeated Free Induction Decay produces images which demonstrate changes in proton density as well as flow effects. The second sequence, Inversion-recovery, produces images which are dependent on T1 and show a high level of grey, white matter contrast giving considerable anatomical detail. In addition pathological processes such as infarction, haemorrhages, demyelination and malignancy, produce changes in T1 enabling lesions to be localised. The third sequence, Spin-echo, produces images which are dependent on T2. These show very little grey, white matter contrast but demonstrate acute and space occupying lesions as well as cerebral oedema. The high level of grey, white matter contrast, lack of bone artefact, variety of sequences, capacity for multiplanar imaging, sensitivity to pathological change and lack of known hazard make NMR an important addition to existing techniques of neurological diagnosis.

A prospective magnetic resonance imaging (MRI) study was carried out in 13 patients (19 examinations) with primary bone tumours to assess the relative value of each of four pulse sequences in showing the extent and nature of the lesion. The four pulse sequences used were a T1-weighted spin-echo (SE544/44), a T2-weighted spin echo (SE1500/80), a short TI inversion recovery (STIR) (IR500/100/44), and a partial saturation (PS) (PS500/22) with field echo data collection. For soft tissue disease the combination of PS and STIR gave better definition of the boundary of the tumour than the more conventional T1 and T2-weighted spin echo sequences. For the demonstration of bone cortex, periosteal change and calcification, T1 and T2-weighted spin echo sequences were better. However, for calcified tissues, plain radiographs were better than either MRI combination. On the assumption that plain films will be available in all cases, PS and STIR sequences could therefore be substituted for T1 and T2-weighted spin echo sequences allowing an increase in soft tissue detectability for lesions in both red and yellow marrow.