Glyn A. Coutts

Use of multicoil arrays for separation of signal from multiple slices simultaneously excited

Increased acquisition efficiency has been achieved by exciting several slices simultaneously. The mixed data were unfolded to produce separate slices using the spatial encoding information inherent in a multicoil receiver system. Each coil yields a linear combination of signals from all excited slices weighted by the sensitivity of each coil. A matrix inversion provides a solution to unfold these images. J. Magn. Reson. Imaging 2001;13:313–317.

Proton MR spectroscopy of intracranial tumours: in vivo and in vitro studies.

Proton magnetic resonance spectroscopy (1H MRS) was used to investigate intracranial tumours in vitro and in vivo. Biopsy specimens were studied from 47 patients, 11 of whom were also examined in vivo. Analysis was based on the signals from N-acetylaspartate (NAA), phosphocreatine plus creatine (Cr), choline-containing compounds (Cho), alanine (Ala), and lactate. Biopsy data from 26 astrocytomas showed that the NAA/Cr ratio differs significantly in all grades from its value in normal white matter and that the Cho/Cr ratio differs significantly in grade IV tumours from its value in the other grades. Meningiomas have an unusually high Ala/Cr ratio. Spectra obtained in vivo are consistent with in vitro results from the same patients, and their lactate signal provides additional information about abnormal metabolism. We conclude that 1H MRS has a clear role in the diagnosis and biochemical assessment of intracranial tumours and in the evaluation and monitoring of therapy.

Proton MR Spectroscopy of the Brain in AIDS Dementia Complex

Proton MR spectroscopy of the brain has been undertaken in 8 healthy volunteers and in 11 patients with human immunodeficiency virus infection and varying stages of AIDS dementia complex (ADC). Spectral appearances in patients with no ADC or early ADC were not significantly different from normal volunteers. Spectra from patients with moderate to severe ADC exhibited significant reductions in levels of N-acetyl aspartate (NAA) relative to creatine (Cr) and also showed elevations in choline containing compounds (relative to Cr). Because NAA is thought to be a metabolic marker for normally functioning neurons, these findings suggest the presence of neuronal injury or loss in moderate to severe ADC. The significance of these findings is discussed.

MRI of fistula-in-ano : A comparison of Endoanal coil with external phased array coil techniques

PURPOSE The objective of our study was to compare MRI of fistulas-in-ano using an endoanal coil with that using a pelvic phased array coil and to assess the value of a combined approach by correlating the findings with those at surgery. METHOD Twenty consecutive patients with clinical suspicion of perianal sepsis were studied using an endoanal coil immediately followed by a phased array coil. T1 weighted and STIR images in transverse and coronal planes were made with each coil and analysed by noting the presence and site of a collection and primary track, the position of any internal opening, and subcutaneous or supralevator extension. Operative findings were similarly recorded. RESULTS Of 20 patients with suspected fistulas, 8 had simple fistulas, 8 had complex fistulas, and 4 had no current evidence of infection. The concordance between MR and surgery for identifying the presence and site of the collection, the primary track, and the internal opening in both simple and complex cases was superior using the endoanal coil as compared with the phased array. Both coils together reflected the findings of the endoanal coil used alone. However, for supralevator/subcutaneous extension, concordance was superior using the phased array compared with the endoanal coil, and a combined approach reflected the values of the phased array coil used alone. CONCLUSION Endoanal MRI is highly sensitive in the delineation of fistulas-in-ano. In combination with phased array techniques, it provides valuable preoperative assessment in both simple and complex cases.

Phosphorus-31 magnetic resonance spectroscopy of the human liver using chemical shift imaging techniques

Phosphorus-31 magnetic resonance spectroscopy of the human liver was undertaken in 28 healthy adult individuals and in 49 patients with liver disease of varying aetiology. Data localised to the liver were obtained using chemical shift imaging techniques. The mean (+/- 1 S.D.) of the peak area ratio phosphomonoesters (PME)/phosphodiesters (PDE) in healthy adult individuals, from spectra obtained with pulse angle 45 degrees and repetition time 1 s, was 0.24 +/- 0.07. The intra-examination variability of this ratio was 20%, the intra-subject variability 27% and the inter-subject variability 32%. An increase in the PME/PDE was observed in the 31P hepatic MR spectrum from primary or secondary tumours in all 17 patients studied, which invariably represented an increase in PME/ATP and, in some cases, a reduction in PDE/ATP. The spectra did not show aetiological characteristics. A non-specific elevation in PME/PDE was also observed in the 31P hepatic MR spectra of 10 (40%) of 25 patients studied who had diffuse liver diseases, such as cirrhosis and infiltrating malignancies. The spectral pattern did not distinguish between diseases of varying aetiologies, but there was a linear correlation between increasing PME/PDE and a reduction in plasma albumin concentrations (p = 0.03). In three patients with hepatic malignancy and abnormal hepatic 31P-MRS, marked spectral changes were observed after successful treatment to debulk the tumour. Only minor changes were observed in the abnormal spectrum of a fourth patient in whom treatment was unsuccessful. Hepatic 31P-MR spectroscopy may prove useful for monitoring disease processes and treatment effects in well characterised patient populations.

Proton MR spectroscopy in herpes simplex encephalitis: assessment of neuronal loss.

We present here the case of an 11-year-old boy with herpes simplex encephalitis diagnosed on the basis of clinical features, serology, and response to acyclovir, who relapsed after 3 weeks of therapy. In vivo proton magnetic resonance spectroscopy (1H MRS) of the brain, at 8 and 16 weeks after the onset of symptoms, showed abnormalities, most prominently a reduction in the N-acetylaspartate/choline ratio. The role of 1H MRS in assessing disease activity is discussed.

Fast and Reproducible Method for the Direct Quantitation of Adipose Tissue in Newborn Infants

The role of body fat content and distribution in infants is becoming an area of increasing interest, especially as perception of its function appears to be rapidly evolving. Although a number of methods are available to estimate body fat content in adults, many are of limited use in infants, especially in the context of regional distribution and internal depots. In this study we developed and implemented a whole-body magnetic resonance imaging (MRI)-based protocol that allows fast and reproducible measurements of adipose tissue content in newborn infants, with an intra-observer variability of<2.4% and an inter-observed variability of<7%. The percentage total body fat for this cohort of infants ranged from 13.3–22.6% (mean and standard deviation: 16.6±2.9%), which agrees closely with published data. Subcutaneous fat accounted for just over 89% of the total body fat, whereas internal fat corresponded to almost 11%, most of which was nonabdominal fat. There were no gender differences in total or regional body fat content. These results show that whole-body MRI can be readily applied to the study of adipose tissue content and distribution in newborn infants. Furthermore, its noninvasive nature makes it an ideal method for longitudinal and interventional studies in newborn infants.

Characterization of Cerebral White Matter Damage in Preterm Infants Using 1H and 31P Magnetic Resonance Spectroscopy

The biochemical characteristics of white matter damage (WMD) in preterm infants were assessed using magnetic resonance spectroscopy (MRS). The authors hypothesized that preterm infants with WMD at term had a persisting cerebral lactic alkalosis and reduced N-acetyl aspartate (NAA)/creatine plus phosphocreatine (Cr), similar to that previously documented in term infants weeks after perinatal hypoxia–ischemia (HI). Thirty infants (gestational age 27.9 ± 3.1 weeks, birth weight 1122 ± 445 g) were studied at postnatal age of 9.8 ± 4.1 weeks (corrected age 40.3 ± 3.9 weeks). Infants were grouped according to the presence or absence of WMD on magnetic resonance (MR) images. The peak area ratios of lactate/Cr, NAA/Cr, myo-inositol/Cr, and choline (Cho)/Cr were measured from an 8-cm3 voxel in the posterior periventricular white matter (WM) using proton MRS. Intracellular pH (pHi) was calculated using phosphorus MRS. Eighteen infants had normal WM on MR imaging; 12 had WMD. For infants with WMD, lactate/Cr and myo-inositol/Cr were related (P < 0.01); lactate/Cr and pHi were not (P = 0.8). In the WMD group, mean lactate/Cr and myo-inositol/Cr were higher (P < 0.001, P < 0.05, respectively) than the normal WM group. There was no difference in the NAA/Cr, Cho/Cr, or pHi between the two groups, although pHi was not measured in all infants. These findings suggest that WMD in the preterm infant at term has a different biochemical profile compared with the term infant after perinatal HI.

Hepatic phosphorus-31 magnetic resonance spectroscopy in primary biliary cirrhosis and its relation to prognostic models.

BACKGROUND: In vivo hepatic phosphorus-31 magnetic resonance spectroscopy (31P MRS) provides biochemical information about phosphorus metabolism. AIM: To assess 31P MRS as a prognostic marker in patients with primary biliary cirrhosis (PBC) in relation to the current clinical prognostic models. PATIENTS AND METHODS: Twenty three patients with PBC of varying functional severity and 16 matched healthy volunteers were studied using in vivo 31P MRS. Spectra were acquired using a 1.5 T spectroscopy system. Peak area ratios of phosphomonoesters (PME), inorganic phosphate (Pi), and phosphodiesters (PDE) and nucleotide triphosphate (NTP) were calculated. Pugh score, Christensen prognostic index, and R value according to the Mayo model were calculated from the clinical data. RESULTS: The PME/NTP, Pi/NTP, PME/PDE, and PME/Pi ratios and the PME signal height ratio (SHR) were significantly higher, while the PDE/NTP and PDE/SHR were significantly lower in PBC patients compared with healthy volunteers (p < 0.01). Significant correlations were seen between PME/Pi ratio and the prognostic index according to Christensen (r = 0.63, p < 0.001), R value according to the Mayo model (r = 0.45, p < 0.03), and with the Pugh score (r = 0.55, p < 0.007). CONCLUSIONS: This study shows that PME/Pi ratio obtained from 31P MRS correlates well with all three of the commonly used models of prognosis in patients with PBC. A longitudinal study with larger number of patients is required to confirm these findings and elucidate the biochemical changes underlying this phenomenon.

Twisted-pair RF coil suitable for locating the track of a catheter †

An RF coil, made by twisting a conventional wire loop, was tuned to form an extended sensor to provide an effective method of showing the track of a catheter. A twisted‐pair coil can be made small enough in diameter to pass through needles in common clinical use. The coil has a very small field of view and in transmit/receive operation has minimal effect on the magnetization of the surrounding tissue. Magn Reson Med 41:636–638, 1999.