Depth-resolved Surface Coil Spectroscopy Research Articles

Routine addition of diffusion-weighted imaging to pediatric brain imaging with acute presentation: An initial experience

Context: A number of disorders affecting the pediatric brain pose a diagnostic challenge. Magnetic resonance imaging (MRI) is widely accepted as a sensitive technique for the diagnosis of ischemia, encephalitis, and leukodystrophies. Conventional MR sequences used in routine practice include T1-weighted (T1-W), T2-weighted, and fluid-attenuation inversion recovery (FLAIR) sequences. However usually, the presentation in small children is confusing and presents a diagnostic challenge even after the use of these various MR sequences requiring repeated MRI examinations. Detecting pathological changes occurring at microenvironment level is vital for early diagnosis, effective treatment, and obviating the need of repeated MRI. Aims: The purpose of our study was to assess the additional role of diffusion-weighted imaging (DWI) in better detection of these various pathologies of brain. Settings and Design: This was a prospective study. Subjects and Methods: Thirty children of ages ranging from neonate to 12 years of age with various complaints of central nervous system involvement were evaluated with MRI brain within 72 h of initial clinical presentation. T1 and T2 spin-echo sequences FLAIR and postcontrast T1-W imaging were done. DWI was performed with echoplanar imaging using depth-resolved surface coil spectroscopy sequence. The lesions were evaluated on DWI and conventional sequences. The final diagnosis was established on the basis of clinical evaluation, electroencephalographic findings, imaging, cerebrospinal fluid analysis, serologic tests, and fatty acid evaluation in plasma assay. Statistical Analysis Used: This was a descriptive study. Results: The patients were divided into three groups. Group A included patients in whom DWI detected more lesions or showed a greater extent of lesions on apparent diffusion coefficient (ADC) map than conventional MRI. This group had 11 cases including 7 cases of ischemic encephalopathy, one case of adrenoleukodystrophy (ADL) showing increased extent of lesion with restricted diffusion at the advancing edge and 3 cases of viral encephalitis. In Group B, 12 cases had similar results in both DWI and conventional MRI imaging. Of these, 7 cases with no specific diagnosis and subsequent spontaneous recovery showed no lesion on both conventional and DWI; 5 cases showed equal extent and number of lesions on DWI; 1 case was diagnosed as ADL, 2 as viral encephalitis, and 2 as ischemic encephalopathy on final workup. In Group C, T2 and FLAIR showed more lesions than DWI and had 7 cases. 5 had normal ADC maps but 1–2 small hyperintense lesions on T2 and FLAIR imaging, while the remaining two diagnosed with ischemic encephalopathy had hyperintense areas on T2 and FLAIR sequences with associated ventricular enlargement and cortical atrophy while DWI revealed them to be T2 shine through areas with increased ADC value focally. The 5 cases with hyperintensity on T2 and FLAIR, but normal ADC maps were labeled as nonspecific white matter hyperintensities. These children showed neither any progress of lesion nor any further clinical symptoms during the duration of study. Conclusions: We concluded that DWI was more sensitive than the other MR sequences in detecting early pathological changes even in cases of viral encephalitis and leukodystrophy apart from ischemia. It was also helpful in delineating the area more accurately at the microscopic level. We were also able to rule out actual pathology from nonspecific hyperintensities on T2 and FLAIR in some cases on DWI.

1H- and 31P-magnetic resonance spectroscopy and imaging as a new diagnostic tool to evaluate neuropathic foot ulcers in Type II diabetic patients.

We studied 36 Type II (non-insulin-dependent) diabetic patients without occlusive arterial diseases in the lower extremities and 12 age-matched and sex-matched non-diabetic subjects to clarify the association between diabetic polyneuropathy and foot ulcers using 1H- and 31P-magnetic resonance spectroscopy and imaging. The 36 diabetic patients consisted of 12 patients with superficial foot ulcers and 24 patients free from this disease. We measured fat to water and phosphocreatine to inorganic phosphate (PCr:Pi) ratios and calculated the intracellular pH of resting plantar muscles by depth-resolved surface-coil spectroscopy using an 1H-31P double tuned coil. Furthermore, foot vasculature, fat and PCr contents of plantar muscles were visualised by phase-contrast angiography, T1-weighted spin-echo imaging and 31P-chemical shift imaging. The 12 foot ulcer patients showed a reduced PCr to Pi ratio (p < 0.001) and peripheral nerve functions (p < 0.01-0.001) but an increased fat to water ratio (p < 0.001) and intracellular pH (p < 0.001) compared with the 24 patients without ulcers. From stepwise multiple regression analyses, motor nerve function as well as severity of nephropathy was associated with both fat to water and PCr to Pi ratios. When these patients were categorised into three groups based on their level of motor nerve function, the frequency of foot ulcers of the lowest group was higher than that of the highest group. Our findings indicated that motor nerve dysfunction in diabetic patients was closely associated with impaired energy metabolism, fatty infiltration and increased intracellular pH of plantar muscles and high frequency of foot ulcers. These new techniques could contribute to help clarify the predisposing factors for foot ulcers.

Influence of aging or left ventricular hypertrophy on the human heart: contents of phosphorus metabolites measured by 31P MRS.

Although both aging and hypertrophy are extremely important factors for cardiac performance, their influence on cardiac metabolism, especially that of high-energy phosphates, has not been fully elucidated as yet. Quantitative measurements of high-energy phosphates were attempted by comparing myocardial 31P NMR spectra with an external reference using depth-resolved surface-coil spectroscopy. The voxel size of the region of interest (ROI) was disk-shaped with 15-cm diameter and 25-mm thickness, but the left ventricular weight actually involved in the ROI was estimated to be between 22 and 66 g using MRI. Myocardial phosphocreatine (PCr) content and adenosine triphosphate (ATP) content for the 30 normal volunteers showed significant age dependence since both decreased in relation to increasing age. Myocardial PCr content and ATP content in patients with hypertension did not differ significantly from the age-matched control group. PCr content (6.1 +/- 2.2 micromol/g wet tissue, n = 10) and ATP content (4.1 +/- 1.3 micromol/g wet tissue) in patients with hypertrophic cardiomyopathy were less than the age-matched control group (n = 15; PCr: 9.7 +/- 2.5 micromol/g wet tissue, P < 0.01; ATP: 6.4 +/- 1.8 micromol/g wet tissue, P < 0.05), respectively. These results indicate that quantitative 31P MRS may be valuable in the assessment of changes in high-energy phosphate metabolism caused by aging or hypertrophy.

Relationship of 31P MR Spectroscopy to the Histopathological Grading of Chronic Hepatitis and Response to Therapy

In vivo phosphorus-31 MR spectroscopy (31P MRS) was performed in the human liver in order to investigate the relation between: the ratios of phosphorus metabolites in the liver; the histopathological grading of chronic hepatitis; and the response to therapy. Hepatic 31P MRS using the DRESS method (depth-resolved surface-coil spectroscopy) was carried out in 45 patients with chronic viral hepatitis or autoimmune hepatitis, and in 16 control subjects. We measured the ratios of the peak areas of phosphomonoesters (PME), inorganic phosphate (Pi), or phosphodiesters (PDE) to the peak area of beta-adenosine triphosphate (ATP). The PDE/ATP ratio of patients with chronic hepatitis or liver cirrhosis was lower than that of control subjects (liver cirrhosis = 0.74; chronic active hepatitis = 1.13-1.21; normal = 1.43); only a small difference was found in the PME/ATP and Pi/ATP ratios. There was no correlation between the spectra and histopathological grading or response to therapy, but the response to therapy was poor when a reduced PDE/ATP ratio was present. The PDE/ATP ratio measured by 31P MRS makes it possible to identify the transition of chronic active hepatitis into liver cirrhosis with a poor response to therapy.

31P MR spectroscopy in hypertrophic cardiomyopathy: Comparison with Tl-201 myocardial perfusion imaging

Abnormal phosphate metabolism of the myocardium was evaluated in patients with hypertrophic cardiomyopathy (HCM) using 31P magnetic resonance (MR) spectroscopy. The results were compared with those from left ventricular function and thallium 201 (Tl-201) perfusion scintigraphy. Six normal volunteers and 19 patients with HCM were studied with a 1.5 T MR system. The spectra were localized to the myocardium using volume selection with the depth-resolved surface coil spectroscopy (DRESS) technique. Peak areas of 2,3-diphosphoglycerate (DPG), phosphodiesters (PDE), phosphocreatine (PCr), and β-ATP were determined by fitting Gaussian functions to the phased spectra. The peak areas were corrected for contamination of blood adenosine triphosphate (ATP) and PDE. The corrected PCr β- ATP ratio in patients (1.07 ± 0.10, mean ± SE) was significantly lower compared with that in normal volunteers (1.71 ± 0.13, p < .01). The PCr β- ATP ratio showed an abnormal decrease (< mean − 2 SD of the controls) in 11 (58%) of 19 patients. The averaged PCr β- ATP ratio in 15 patients with normal left ventricular ejection fraction (LVEF) was 1.14 ± 0.10, significantly lower than in healthy subjects. By contrast, the corrected PDE/PCr ratio in HCM did not differ significantly compared with that in healthy subjects (0.46 ± 0.09 vs 0.36 ± 0.09). The PDE/PCr ratio was abnormally elevated (> mean + 2 SD of the controls) in only four (21%) of the patients. On Tl-201 myocardial single-photon emission computed tomography (SPECT) imaging, the perfusion of the left ventricular wall looked normal in 6 and abnormal in 5 of 11 HCM patients. The averaged PCr β- ATP ratio did not differ between the two groups (0.99 ± 0.18 vs 1.10 ± 0.21). This study suggests that the PCr β- ATP ratio may be a more reliable parameter for assessing the abnormal phosphorous metabolism in HCM than the PDE/PCr ratio. The metabolic changes in the myocardium of patients with HCM did not always correlate with perfusion abnormalities on the Tl-201 myocardial scintigram.

In vivo 31P nuclear magnetic resonance spectroscopy in patients with old myocardial infarction.

To assess the usefulness of in vivo 31P nuclear magnetic resonance (NMR) spectroscopy, we investigated spectra from the myocardium in 6 patients with old Q-wave infarction (QMI), 6 with old non-Q-wave infarction (NQMI) and 9 controls by ECG-gated depth-resolved surface-coil spectroscopy. External hexamethylphosphoric triamide (HMPT) was used to quantify the signal intensities. Left ventricular weight in the region of interest (LVW) was estimated from 1H magnetic resonance images. The extent score by 201Tl scintigraphy was determined in 3 QMI and 4 NQMI patients. No significant differences were found among the 3 groups in peak area ratios of 31P NMR spectra to phosphocreatine (PCr) or adenosine triphosphate (ATP). Compared with controls, significant reductions were observed in values for the peak areas of PCr normalized by the standard HMPT (PCr/HMPT) or by both HMPT and LVW (PCr/HMPT/LVW) for QMI patients (p less than 0.05), and in ATP/HMPT and ATP/HMPT/LVW for QMI and NQMI patients (p less than 0.01). There was a significant negative correlation between ATP/HMPT and the 201Tl scintigraphy extent score (p less than 0.05). These findings suggest that in vivo 31P NMR spectroscopy can detect high-energy phosphate reduction in the infarcted myocardium and may be useful in evaluating myocardial viability.

Clinical Application of Proton Magnetic Resonance Spectroscopy to Cerebral Ischemia

Proton magnetic resonance spectroscopy (MRS) with the depth resolved surface coil spectroscopy technique and the 1331-2662 water suppression method was used to examine two cerebral ischemia patients and 10 normal volunteers. In all cases, N-acetyl-aspartate, creatine, phosphocreatine, and residual lipid were clearly observed. No lactic acid peak was observed in normal volunteers, but a large lactic acid peak appeared in the early stage of cerebral ischemia. This MRS abnormality was observed before abnormalities appeared in conventional imaging such as computed tomographic scanning and magnetic resonance imaging.

Depletion of high‐energy phosphates in the central nervous system of patients with systemic lupus erythematosus, as determined by phosphorus‐31 nuclear magnetic resonance spectroscopy

Systemic lupus erythematosus (SLE) can produce profound disturbances in the central nervous system, characterized by encephalopathy, focal neurologic deficits, cerebral infarction, psychosis, and seizures. We used 31P nuclear magnetic resonance (NMR) spectroscopy to determine the in vivo levels of high-energy phosphates in the central nervous system of 10 patients with SLE and 10 age-matched normal controls. 31P NMR spectroscopy was performed on a 1.5-Tesla unit equipped with a dual-tuned 1H-31P surface coil and a software-directed DRESS (depth resolved surface coil spectroscopy) pulse sequence. This procedure detected ADP, ATP, sugar phosphates, phosphocreatine (PCr), inorganic phosphate, phosphomonoesters, and phosphodiesters in the brain tissue of all study subjects. Levels of ATP in the deep white matter of 10 SLE patients were significantly decreased compared with the levels in 10 normal controls, as quantitated by the ratio of ATP:ATP + ADP (mean +/- SD 0.81 +/- 0.11 versus 0.91 +/- 0.05; P less than 0.02). In a subgroup of 4 patients, PCr levels were decreased to a greater extent than the ATP levels. NMR spectroscopic alterations were not related to obvious anatomic lesions, as determined by standard cranial proton magnetic resonance imaging. In 4 SLE patients with markedly abnormal 31P NMR spectra, treatment with prednisone (80 mg/day) normalized the levels of ATP and PCr. Restoration of a normal 31P profile was accompanied by an obvious improvement in the patients' mental status and clinical symptoms. 31P NMR spectroscopy is a powerful new technique for monitoring high-energy phosphate metabolism, and may be particularly useful for characterizing central nervous system disease in patients with neuropsychiatric SLE.

Problems and expediencies in human 31P spectroscopy. The definition of localized volumes, dealing with saturation and the technique-dependence of quantification.

Several technological problems in in vivo localized spectroscopy of metabolism are discussed in the context of comparing data obtained by different means. Deficiencies in spectroscopy localization methods can produce spectra that are dominated by artefactual signals derived from outside of selected volumes. Such artefacts are not usually correctly accounted for by representations of the profiles of the transverse magnetization alone. Selected sensitive volumes should be defined in terms of the size of tissue contributing the major fraction of signal to an observed spectrum, which is the integrated response from the sample including any phase cancellation effects. Phase cancellation in one-dimensional localization techniques employing excitation by an RF field with uniform phase distribution and surface coil detection such as depth resolved surface coil spectroscopy, chemical shift imaging (CSI) and rotating frame zeugmatography (RFZ) can significantly alter the effective radius of the sensitive volumes depending on the sample distribution and the extent of the homogeneous region of the magnet. Also, discrete spatial sampling in RFZ and CSI can radiate signal artefacts of around 25% into adjacent elements depending on the location and distribution of signal sources. Acquisition delays between excitation and detection and partial saturation are other major sources of systematic error. Saturation factors for metabolites are not easily obtainable on localized volumes during clinical exams on an individual basis, but may be expediently obtained as larger-volume tissue-averages. Better documentation of saturation effects, acquisition delays and localized volume sizes is needed to compare and validate clinical results and performance.

Proton‐decoupled, overhauser‐enhanced, spatially localized carbon‐13 spectroscopy in humans

Spatially localized, natural abundance, carbon (13C) NMR spectroscopy has been combined with proton (1H) decoupling and nuclear Overhauser enhancement to improve 13C sensitivity up to five-fold in the human leg, liver, and heart. Broadhand-decoupled 13C spectra were acquired in 1 s to 17 min with a conventional 1.5-T imaging/spectroscopy system, an auxiliary 1H decoupler, an air-cooled dual-coil coplanar surface probe, and both depth-resolved surface coil spectroscopy (DRESS) and one-dimensional phase-encoding gradient NMR pulse sequences. The surface coil probe comprised circular and figure-eight-shaped coils to eliminate problems with mutual coupling of coils at high decoupling power levels applied during 13C reception. Peak decoupler RF power deposition in tissue was computed numerically from electromagnetic theory assuming a semi-infinite plane of uniform biological conductor. Peak values at the surface were calculated at 4 to 6 W/kg in any gram of tissue for each watt of decoupler power input excluding all coil and cable losses, warning of potential local RF heating problems in these and related experiments. The average power deposition was about 9 mW/kg per watt input, which should present no systemic hazard. At 3 W input, human 13C spectra were decoupled to a depth of about 5 cm while some Overhauser enhancement was sustained up to about 3 cm depth, without ill effect. The observation of glycogen in localized natural abundance 13C spectra of heart and muscle suggests that metabolites in the citric acid cycle should be observable noninvasively using 13C-labeled substrates.

Cardiovascular applications of nuclear magnetic resonance spectroscopy

Nuclear magnetic resonance spectroscopy has great potential for defining noninvasively the metabolic status of the heart and skeletal muscle. This technique uses the spin properties of certain nuclei (such as phosphorus-31, hydrogen-1 and carbon-13) to measure high energy phosphates, intracellular pH, lactate and glycogen. Animal studies have formed the basis for human investigations and have demonstrated well-defined changes in high energy phosphates during myocardial ischemia and reperfusion, as well as in cardiomyopathies. Human studies have been limited by issues of sensitivity and localization, although techniques such as rotating frame, depth-resolved surface coil spectroscopy, image-selected in vivo spectroscopy and spectroscopic imaging have been used to acquire phosphorus-31 spectra from the human heart. The few human studies of patients with disease have demonstrated elevated inorganic phosphate peaks after myocardial infarction and abnormal phosphodiester peaks in patients with hypertrophic cardiomyopathy. Studies of patients with heart failure have shown that these patients acidify their peripheral muscles with exercise more easily than do control subjects. Clinical application of nuclear magnetic resonance spectroscopy will depend on technical advances and the demonstration of sensitivity of metabolic changes with disease.

Application of image-guided surface coil P-31 MR spectroscopy to human liver, heart, and kidney.

Localized phosphorus-31 magnetic resonance (MR) spectroscopy in humans has previously been accomplished with surface coils by means of depth-resolved surface coil spectroscopy or rotating frame experiments, in which the extent of tissue sampled critically depends on surface coil placement. The authors' goal was to modify the surface coil image-selected in vivo spectroscopy (ISIS) experiment to accomplish three-dimensional volume selection through application of selective pulses in the presence of B0 gradients. Advantages of ISIS include the ability to use proton images to define the volume of interest (VOI) and reduced dependence on exact positioning of the surface coil. However, rapid replication of the surface coil ISIS experiment can cause spectral contamination from signals originating outside the VOI. A modified version of the ISIS experiment was developed to alleviate contamination under conditions of rapid replication. Applications of localized P-31 MR spectroscopy for observation of high-energy phosphorus metabolites are presented in human liver, heart, and transplanted and normal kidney.

The fate of inorganic phosphate and pH in regional myocardial ischemia and infarction: a noninvasive 31P NMR study.

To determine the characteristic appearance of phosphorus (31P) nuclear magnetic resonance spectra in acute and chronic myocardial infarction in situ, cardiac-gated depth-resolved surface coil spectroscopy (DRESS) at 1.5 T was used to monitor 31P NMR spectra from localized volumes in the left anterior canine myocardium for up to 5 days following permanent occlusion of the left anterior descending coronary artery. Coronary occlusion initially produced regional ischemia manifested as significant reductions in the phosphocreatine (PCr) to inorganic phosphate (Pi) ratios and intracellular pH (P less than 0.05, Student's t test) in endocardially displaced spectra acquired in periods as short as 50 to 150 s postocclusion. Spectra acquired subsequently revealed either (i) restoration of near-normal phosphate metabolism sometime between 10 and about 50 min postocclusion or (ii) advancing ischemic phosphate metabolism at about an hour postocclusion, and/or (iii) maintenance of depressed PCr/Pi ratios for up to 5 days postocclusion with a return of the apparent pH to near normal values between 6 and 15 h postocclusion. Postmortem examination of animals exhibiting the first type of behavior revealed the existence of coronary collateral vessels. The last type of behavior indicates that Pi remains substantially localized in damaged myocardium for days following infarction. The location and size of infarctions were determined postmortem by staining excised hearts. The smallest infarctions detected by 31P DRESS weighed 4.9 and 7.5 g. The most acidic pH measured in vivo was 5.9 +/- 0.2. Infarctions aged 1/2 day to 5 days were characterized by elevated but broad Pi resonances at 5.1 +/- 0.2 ppm relative to PCr and significantly depressed PCr/Pi ratios (P less than 0.002, Student's t test) relative to preocclusion values. Contamination of Pi resonances by phosphomonoester (PM) components is a significant problem for preocclusion Pi and pH measurements. These results should be applicable to the detection and identification of human myocardial infarction using 31P NMR and DRESS.

Noninvasive detection and monitoring of regional myocardial ischemia in situ using depth-resolved 31P NMR spectroscopy.

Phosphorus (31P) NMR spectra showing the relative concentrations of phosphocreatine, ATP, and Pi were recorded noninvasively from localized regions in the left ventricles of dog hearts in situ by using depth-resolved surface-coil spectroscopy at 1.5 T. Proton (1H) NMR surface-coil imaging was used to position 31P NMR coils and to determine the location of depth-resolved volumes immediately prior to 31P examination. Occlusion of the left anterior descending coronary artery produced regional ischemia detected as changes in the ratios of phosphocreatine, ATP, and Pi and by changes in the pH measured from the spectra. Spectral changes were not typically observed in regions adjacent to ischemic myocardium. Reperfusion produced some recovery, and ventricular fibrillation resulted in deterioration in high-energy metabolites. The location and size of ischemic tissue was measured by single-photon-emission computed tomography (SPECT) and gamma-ray counting or by staining excised hearts. The technique should permit the long-term noninvasive monitoring of the metabolic response of the heart to pathologic processes and allow assessment of interventions.

Slice-interleaved depth-resolved surface-coil spectroscopy (SLIT DRESS) for rapid 31P NMR in Vivo

Slice-interleaved depth-resolved surface-coil spectroscopy (SLIT DRESS) for rapid 31P NMR in Vivo

Depth-resolved surface-coil spectroscopy (DRESS) for in Vivo1H, 31P, and 13C NMR

Depth-resolved surface-coil spectroscopy (DRESS) for in Vivo1H, 31P, and 13C NMR