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The objective of this study to determine a suitable scan timing scheme in contrast enhanced MRA for the depiction of the arterial. the portal and the systemic venous system in the abdomen with maximum signal intensity in healthy subjects and in patients with cirrhosis. The signal intensity in the aorta, hepatic artery. portal vein, left renal vein and the supra- and infrarenal IVC were measured in 40 consecutive orthotopic liver transplantation candidates with cirrhosis and 20 healthy renal donors in a bolus triggered arterial scan and after 30, 60, 90 and 150 s respectively. The aorta and hepatic artery showed the highest signal intensity on the arterial scan. The portal and left renal vein showed the highest signal intensity after 30 s, the suprarenal IVC after 60 s and the infrarenal IVC after 90 s. No significant differences were found between healthy subjects and patients with cirrhosis. The arterial, portal and systemic venous system in the abdomen can be visualized selectively with maximum signal intensity by proper timing of the scans, hereby reducing redundant scans. Scanning at just the right time to achieve optimal vessel opacification can he promoted by using data from this study. The proposed scan scheme is suitable for subjects with and without cirrhosis. (C) 2001 Elsevier Science Inc. All rights reserved.

We monitored 10 patients with unresected (9) or partially resected (1) supratentorial gliomas with 11C-tyrosine position emission tomography (TYR-PET) before and after radiotherapy. TYR-PET tumour volumes were measured using a threshold technique. In seven patients the tumour volume decreased after radiotherapy, although all gliomas persisted on TYR-PET images. In eight patients the tumour protein synthesis rate (PSR) was calculated using a dynamic study protocol in combination with a PATLAK analysis. There were no changes in PSR after radiotherapy, but the PSR was calculated on the remaining tumour volume using the same threshold technique as before therapy, i.e. the decrease in tumour volume was not taken into account. In eight patients the PET data were compared with magnetic resonance spectroscopic imaging (1H-MRSI) performed simultaneously. Although there was no statistically significant correlation between TYR-PET volume changes and 1H-MRSI choline level we observed a simultaneous decrease in volume and choline in four patients.

Background. The purpose of this study was to investigate whether phosphorus-31 magnetic resonance spectroscopy (P-31-MRS) of the isolated donor liver can serve as a viability indicator with prognostic value for transplantation outcome. Methods. Forty human donor livers preserved with University of Wisconsin solution were studied shortly before transplantation. The respective spectral peak areas of the isolated donor liver were correlated with the amount of hepatocellular graft damage and liver metabolic function shortly after implantation. Results. The individual phosphomonoesters, inorganic phosphate, phosphodiesters, and nicotine adenine dinucleotide peaks were not prognostic for postoperative hepatocellular damage or liver metabolic capacity. The presence of adenosine triphosphate, however, predicts a significantly better metabolic capacity to eliminate bilirubin, to synthesize fibrinogen and antithrombin III, and to maintain a better prothrombin time after transplantation. Furthermore, this study is probably the first P-31-MRS demonstration in the human liver of phosphocreatine, Conclusions. In the clinical setting described, metabolic assessment using P-31-MRS did not result in a reliable noninvasive test to predict primary graft dysfunction. Study of the role of phosphocreatine in liver metabolism during cold storage is needed.

During cold preservation for transplantation the tissue hydration state changes, It is not known whether such changes lead to altered relaxation times of P-31 nuclei with potential consequences for the quantification of tissue metabolites, Therefore, P-31 spectroscopic and proton T-1 relaxometric measurements were performed on 42 isolated human donor livers shortly before implantation, The results demonstrate that P-31 T-1 relaxation times change during preservation for clinical transplantation, thus quantification of tissue metabolites in cold stored donor livers may be in part dependent on the tissue hydration state, Furthermore, it appeared that changes in tissue hydration state especially affect the physico-chemical characteristics of the intracellular fluid compartment. This study indicates that reliable spectroscopic quantification of tissue metabolites, particularly during sequential spectroscopic measurements in cold stored donor organs is best warranted under fully relaxed conditions. (C) 1997 Elsevier Science Inc.

It is not known whether the tissue acidosis that accompanies cold storage is the beginning of irreversible cell injury, ultimately leading to cell death, or whether it is a natural ''protective'' mechanism for cells to survive hypoxic periods. To answer this question, the tissue pH of 45 cold-stored human donor livers preserved in University of Wisconsin solution (UW) was assessed shortly before implantation using noninvasive P-31 magnetic resonance spectroscopy. We conclude that tissue pH during cold storage may be partly dependent upon hepatic glycogen stores and donor age. The wide range of tissue pH values that was observed at the time of implantation does not result in significant effects on cellular damage after transplantation. This indicates that tissue pH is not a major determinant for the viability of UW solution-preserved human donor livers, as indicated by postoperative hepatocellular damage and liver synthesis function. The membrane stabilizing and buffering capacity of UW solution appears to protect liver viability against tissue acidosis. Our results also indicate that liver tissue pH can be lower than has been previously assumed in the literature without significant adverse effects on liver viability.

In 32 patients with gliomas, one- and two-dimensional proton magnetic resonance spectroscopy (H-1-MRS) has been conducted, the latter allowing reconstruction of spectroscopic data into a spectroscopic image (MRSI), showing the distribution of the various metabolite concentrations over the cross-sectional plane. For lack of absolute concentrations, the measured concentrations of phosphocholine (CHOL), N-acetyl-L-aspartate (NAA), and lactate (LAG) were conventionally expressed in ratios relative to that of creatine (CREAT). Compared to normal brain tissue, an increased CHOL/CREAT ratio was found in all groups of tumours, in glioblastomas, high-, middle- and low-grade astrocytomas both at the margin and the core of the tumours, but in oligodendrogliomas only at the margin. This is consistent with an increased phosphocholine turnover in relation to membrane biosynthesis by the proliferating cells. The NAA/CREAT ratio was decreased in all groups of tumours, both in the centre and at the margin, reflecting replacement of functioning neurons by neoplastic cells. The LAG/CREAT ratio was elevated in the core of malignant gliomas, which may be the result of a prevailing glycolysis, characteristic of tumours, possibly in conjunction with hypoxia/ischaemia. In the perifocal oedema, there was neither elevation of the CHOL/CREAT ratio nor decrease of the NAA/CREAT ratio; an increased LAC/CREAT ratio therefore rather reflected ischaemia/hypoxia probably due to locally elevated pressure and compromised regional perfusion. In the normal brain, the metabolite ratios of grey matter did not differ from those of white matter. The frontal lobe and basal ganglia showed lower NAA/CREAT ratios than the other cerebral areas. In 7 patients positron emission tomography was also performed with [F-18] fluoro-2-deoxy-D-glucose ((18)FDG) or L-[1-C-11]-tyrosine (C-11-TYR); the latter demonstrated a pattern of C-11-TYR uptake similar to that of CHOL elevation in the MRSI.

Extracorporeal resection of hepatic tumors that were considered inoperable in the past is now possible in selected cases, Such procedures require high-quality preoperative images for the exact delineation of the tumor extent and for an optimal planning of the line of parenchymal division, In-vivo CT and MRI can not always depict the tumor adequately, In such cases, ex-vivo MRI may be a useful additional technique. It combines a high spatial resolution with the best possible soft tissue contrast, as was learned from previous studies on donor livers destined for transplantation. Ex-vivo MRI favours both a sufficiently radical resection as well as sufficient hepatic functional reserve to be present for reimplantation. A case history is reported together with details on the technical procedure.

Proton magnetic resonance spectroscopic imaging (1H-MRSI) and positron emission tomography with the tracer L-[1-11C]tyrosine (11C-TYR) were used to localize gliomas for biopsy or resection. This is especially helpful in cases of low-grade gliomas, if these lesions are not visualized by contrast-enhanced computed tomographic and magnetic resonance imaging scans. The clues to improved localization are provided by changes in tissue metabolite contents, such as elevation of phosphocholine, indicating cellular proliferation; decrease of N-acetylaspartate, denoting loss of neurons (as these are replaced by tumor cells); and elevation of lactate, pointing to the prevalence of glycolysis, as observed in many tumors. These data on tissue metabolite content have been obtained in vivo in the patient by proton magnetic resonance spectroscopy; metabolite maps derived from these data then visualize the distribution of the various metabolites over the section of the brain under investigation. Alternatively, localization of a tumor may be achieved by means of positron emission tomography depicting the pattern of uptake of the amino acid tracer 11C-TYR, as it tends to be incorporated in the process of cellular proliferation and protein biosynthesis. Five cases are presented as examples.

To determine the relation between tissue hydration state-as indicated by tissue proton magnetic resonance relaxation times-in UW-preserved human donor livers and viability parameters of the donor and early graft function, ''ex vivo'' magnetic resonance relaxometry was performed with a clinical MR imaging system. Relaxometric data were obtained from MR images in which signal intensities were directly proportional to T-1 and T-2. Forty three subsequently transplanted livers and five discarded livers were studied. The donor serum concentrations of direct and total bilirubin had a positive correlation with T-1 (P

There is a great variability in the amount of peritumoural brain oedema accompanying meningiomas. In a previous study it was found that the degree of brain oedema in the white matter around meningiomas correlated with disruption of the layers (especially the cerebral cortex), which separate the tumour from the white matter, as well as with the size and histological subtype of the tumour. In the present study comprising 9 meningiomas, the volume of oedema was calculated by integration of the cross-sectional oedematous areas on serial MRI slices. The volume of oedema was zero in 3 cases and ranged from 11 to 176.4 ml in the other 6 cases. The MRI-scans also showed disruption of the cortex in all cases, ranging from slight to severe. T1 and T2 measurements were made at the level of maximum extension, using a mixed sequence at a field strength of 1.5 T. From the T2 values tissue water content in % was calculated using the equations: WC = 39.36/(R2 + 37.2) for cortex, and WC = 29.63/(R2 + 27.8) for white matter. These had been obtained by correlating water content with relaxation rates, measured in vitro on human brain autopsy specimens which were subjected to hydration with distilled water or dehydration by hyperosmolar solutions. Mean water content amounted to 82.53% for normal cortex, 74.72% for normal white matter, and 84.59% for oedematous white matter around the tumour.(ABSTRACT TRUNCATED AT 250 WORDS)

With in vivo 1H-MRS resonances of several metabolites were simultaneously measured in cerebral gliomas and adjacent normal brain. 15 patients with inoperable brain gliomas all histologically verified were monitored with 1H-MRS and MRI before and after radiotherapy. 11 patients were evaluable. 1H-MRS technique evolved from single volume measurements to one dimensional and two dimensional 1H spectroscopic imaging. In all patients N-acetyl-aspartate signals were decreased in tumour areas compared to the normal brain hemisphere. No recovery was seen after radiotherapy. Choline signals were increased in tumour margins of high grade gliomas and more diffusely in low grade gliomas. In 5 patients the choline resonance decreased after radiotherapy, accompanied by a shrinkage of tumour diameter on MRI. Lactate signals were present in high grade and unspecified astrocytomas and absent in most low grade gliomas. In 3 patients the lactate signal disappeared after radiotherapy. These observations indicate the feasibility of 1H-MRS in monitoring metabolic responses on radiotherapy of brain gliomas.

31P Magnetic Resonance-Spectroscopy was performed at the site of tender points in the trapezius muscle of patients with primary fibromyalgia syndrome. Earlier, in vitro studies have reported changes in the high energy phosphate-metabolism in biopsies taken from tender points of fibromyalgia patients. The observed alterations could not be confirmed with in vivo Magnetic Resonance-Spectroscopy.

To evaluate the diagnostic value of combined contrast enhanced MRA (ce-MRA) and MRI compared to that of intra-arterial DSA (i.a.DSA) in liver transplantation, transjugular porto-systemic (TIPSS) and spleno-renal shunt candidates. 50 patients in the workup for liver transplantation underwent ce-MRA/MRI and i.a.DSA within a three days interval. Both examinations were assessed with respect to vessel anatomy and patency of the arterial, portal venous, porto-systemic collateral and systemic venous system. The results were compared with the intra-operative findings when available. Malignancy detection in ce-MRA/MRI and i.a.DSA were compared. There are no significant differences for the arterial part of the vascular supply to the liver that is important for transplantation. Although the differences for the portal system are not significant, the difference between the two techniques is of clinical importance because i.a.DSA failed to detect portal vein occlusion in 4 patients. Ce-MRA is significantly better for the detection of collaterals (p

To evaluate whether combined contrast enhanced MRA and MRI (ce-MRA-MRI) has the potential to replace intra-arterial DSA (i.a.DSA) in patients with impaired graft function or suspected of vascular complications after pancreas and/or kidney transplantation. 7 patients after combined pancreas-kidney and 22 patients after kidney transplantation underwent ce-MRA-MRI and i.a.DSA within a 3 days interval. Qualitative and quantitative comparison of the arterial and venous supply, the parenchyma and urinary collecting system was made. Both ce-MRA and i.a.DSA showed good results in the detection of arterial stenoses. However, ce-MRA falsely suggested stenoses if vascular clips were used; on the other hand, i.a.DSA was less informative if the graft arteries were very tortuous. Ce-MRA was superior in depicting the venous anatomy (p

Using in vivo proton-magnetic resonance spectroscopy (1H-MRS), which allows the measurement of metabolites of adequate tissue concentration, the origin of lactate in peritumoral edema has been assessed by comparison with lactate levels in the central and marginal areas of the tumor in 18 patients with cerebral gliomas. In the majority of cases lactate content in the area of peritumoral edema was lower than that in the tumor margin or tumor center, which is consistent with the assumption that the tumor is the source of lactate, which then reaches the surrounding area of edema by diffusion. In 3 of the 18 cases the amount of lactate in the peritumoral edematous tissue was higher than in the tumor, indicating that the lactate is locally produced on account of ischemia due to regional elevation of tissue pressure in the edematous area.

Cold preservation of donor organs induces hypothermia-related tissue edema as a result of a reduced activity of the ATP-dependent sodium pump at low temperatures. Hypothermia-induced tissue edema occurs in kidney preservation and is a significant risk factor for delayed graft function (DGF) after transplantation. DGF remains a major problem in kidney transplantation and is significantly associated with preservation injury. The state of hydration of cold-stored organs can be assessed from a biopsy for determination of the wet/dry weight ratio. As a non-invasive method to determine tissue hydration MRI T1 and T2 relaxometry can be used. In this study we have compared changes in tissue hydration in UW-preserved porcine kidneys with increasing cold ischemia times (CIT) using wet/dry weight ratio and MR ralaxometry. The results of the two techniques were correlated to evaluate the use of MR relaxometry. Wet/dry weight ratios of the renal cortex decreased with prolonged CIT (P < 0.01) whereas these of the medulla did not change significantly. T1 values of the cortex decreased with prolonged CIT (P < 0.01). T2 values of the cortex showed a non-significant decline with increased CIT. No significant changes in T1 and T2 were found in the medulla. The correlation between T1 and the wet/dry weight ratio of the cortex was significant (P = 0.05, linear correlation coefficient 0.8698). We conclude that MR relaxometry can be a valuable non-invasive technique to assess tissue hydration in cadaveric donor kidneys before transplantation.

It is not known whether the tissue acidosis that accompanies cold storage is the beginning of irreversible cell injury, ultimately leading to cell death, or whether it is a natural "protective" mechanism for cells to survive hypoxic periods. To answer this question, the tissue pH of 45 cold-stored human donor livers preserved in University of Wisconsin solution (UW) was assessed shortly before implantation using noninvasive 31P magnetic resonance spectroscopy. We conclude that tissue pH during cold storage may be partly dependent upon hepatic glycogen stores and donor age. The wide range of tissue pH values that was observed at the time of implantation does not result in significant effects on cellular damage after transplantation. This indicates that tissue pH is not a major determinant for the viability of UW solution-preserved human donor livers, as indicated by postoperative hepatocellular damage and liver synthesis function. The membrane stabilizing and buffering capacity of UW solution appears to protect liver viability against tissue acidosis. Our results also indicate that liver tissue pH can be lower than has been previously assumed in the literature without significant adverse effects on liver viability.

Cold preservation of donor organs induces hypothermia-related tissue edema as a result of a reduced activity of the ATP-dependent sodium pump at low temperatures. Hypothermia-induced tissue edema occurs in kidney preservation and is a significant risk factor for delayed graft function (DGF) after transplantation. DGF remains a major problem in kidney transplantation and is significantly associated with preservation injury. The state of hydration of cold-stored organs can be assessed from a biopsy for determination of the wet/dry weight ratio. As a non-invasive method to determine tissue hydration MRI T1 and T2 relaxometry can be used. In this study we have compared changes in tissue hydration in UW-preserved porcine kidneys with increasing cold ischemia times (CIT) using wet/dry weight ratio and MR ralaxometry. The results of the two techniques were correlated to evaluate the use of MR relaxometry. Wet/dry weight ratios of the renal cortex decreased with prolonged CIT (P0.01) whereas those of the medulla did not change significantly. T1 values of the cortex decreased with prolonged CIT (P0.01). T2 values of the cortex showed a non-significant decline with increased CIT. No significant changes in T1 and T2 were found in the medulla. The correlation between T1 and the wet/dry weight ratio of the cortex was significant (P = 0.05, linear correlation coefficient 0.8698). We conclude that MR relaxometry can be a valuable noninvasive technique to assess tissue hydration in cadaveric donor kidneys before transplantation.

Cold preservation of donor organs induces hypothermia-related tissue edema as a result of a reduced activity of the ATP-dependent sodium pump at low temperatures. Hypothermia-induced tissue edema occurs in kidney preservation and is a significant risk factor for delayed graft function (DGF) after transplantation. DGF remains a major problem in kidney transplantation and is significantly associated with preservation injury. The state of hydration of cold-stored organs can be assessed from a biopsy for determination of the wet/dry weight ratio. As a non-invasive method to determine tissue hydration MRI T1 and T2 relaxometry can be used. In this study we have compared changes in tissue hydration in UW-preserved porcine kidneys with increasing cold ischemia times (CIT) using wet/dry weight ratio and MR ralaxometry. The results of the two techniques were correlated to evaluate the use of MR relaxometry. Wet/dry weight ratios of the renal cortex decreased with prolonged CIT (P < 0.01) whereas those of the medulla did not change significantly. T1 values of the cortex decreased with prolonged CIT (P < 0.01). T2 values of the cortex showed a non-significant decline with increased CIT. No significant changes in T1 and T2 were found in the medulla. The correlation between T1 and the wet/dry weight ratio of the cortex was significant (P = 0.05, linear correlation coefficient 0.8698). We conclude that MR relaxometry can be a valuable noninvasive technique to assess tissue hydration in cadaveric donor kidneys before transplantation.

A survey is given of the principles underlying the diagnosis of brain tumours. Traditionally diagnosis and localization of brain tumours have been based upon morphological criteria. Currently unsurpassed levels in imaging of anatomical details and topographical relations by the techniques of computed tomography (CT) and magnetic resonance imaging (MRI) have been achieved. The techniques of positron emission tomography (PET) and of magnetic resonance spectroscopy (MRS), which depict also metabolic and blood flow aspects, provide a refinement of our knowledge on the metabolism, structure and pathophysiological relations of a tumour to the surrounding parenchyma. Recent advances in the recording of function-related changes of the cerebral electro-magnetic field allow a better definition of critical functional areas.

Magnetic resonance imaging (MRI) is of restricted value for the in vivo characterization of tumor types. The applicability of phosphorus-31 (31P) magnetic resonance spectroscopy (MRS) in the diagnosis of bone and soft tissue tumors is unknown.A total of 191 consecutive patients (85 females and 106 males; mean age 41 years, range 1-80) with a well-defined bone or soft tissue tumor on MRI were analyzed for additional 31P spectroscopy. Histology and/or cytology was obtained from all tumors. Because of low sensitivity of the 31P nucleus and the contamination of surrounding tissue, only large, superficially located tumors accessible to the surface coil could be accepted for MRS.Twenty-one patients (11%) could be included in the study. From this remaining group only 12 studies (57%) produced spectra with well resolved phosphorus peaks and an acceptable signal-to-noise ratio. However, these spectra did not allow differentiation between the benign and malignant nature of the lesions. The other 9 studies showed spectra with poor signal intensities and/or poorly defined peaks, making tumor differentiation impossible.Only 6% of the bone and soft tissue tumors produced well defined spectra, which implies that localized 31P MRS cannot be considered as a routine technique in the diagnostic and treatment evaluation of bone and soft tissue tumors.

To determine the relation between tissue hydration state--as indicated by tissue proton magnetic resonance relaxation times--in UW-preserved human donor livers and viability parameters of the donor and early graft function, "ex vivo" magnetic resonance relaxometry was performed with a clinical MR imaging system. Relaxometric data were obtained from MR images in which signal intensities were directly proportional to T1 and T2. Forty-three subsequently transplanted livers and five discarded livers were studied. The donor serum concentrations of direct and total bilirubin had a positive correlation with T1 (P0.05 and P0.01, respectively). Sequential measurements in 7 livers demonstrated a firm time relation between the cold storage time and the length of the relaxation times. As cold storage time lengthened, T1 and T2 shortened. T1 of the donor liver showed a significant negative correlation with recipient ASAT and ALAT values on days 1, 2, and 3 after transplantation. T1 in the discarded group was significantly higher than T1 in the accepted group. T2 was not different in the two groups. It is concluded that in UW-preserved human donor livers, the tissue hydration state, as indicated by the tissue MR relaxation times, is largely independent of the clinical condition of the organ donor and the preservation procedure. An optimum tissue hydration state, in UW-preserved donors liver might have protective properties against parenchymal damage, although the clinical consequences appear to be of minor importance. The capacity of relaxometry as a discriminative instrument to accept or to discard donor livers is poor.

Imaging of blood-brain barrier damage by magnetic resonance was currently studied as to the potential of dextran-magnetite particles (DMP) for contrast enhancement. For that purpose, dextran-T10 (average molecular weight: 10.9 Kilodalton) was complexed with magnetite (Fe3O4) in ammonia. Experimental testing of the agent was made in vivo using Wistar rats with a freezing injury to the brain. DMP was i.v. injected at a dose of 90 microM Fe/kg b.w. followed by 2% Evans blue (0.6 ml). Control animals with trauma were studied without administration of DMP. Histochemical assessments were made to analyze the tissue distribution of DMP in the brain, kidney and liver after fixation in 4% formalin. MR imaging was conducted with 1.5 Tesla field strength with a circular coil 15 min after the freezing insult and administration of DMP. T1- and T2-weighted images were obtained using spin echo sequences among others. Regression analyses indicated a 50% reduction of T1 at a DMP concentration of 48 microM Fe, while for T2 only 4 microM/Fe(DMP) were sufficient for a 50% reduction. DMP was also accumulating in other organs, particularly in the Kupffer cells of the liver. Administration of DMP led to recognition of the freezing lesion as black area in agreement with macroscopical findings obtained by autopsy. In animals with a freezing lesion without administration of DMP, only T2-weighted images demonstrated a somewhat higher intensity attributable to the disruption of the blood-brain barrier. The present findings demonstrate the usefulness of DMP for contrast enhancement of lesions following disruption of the blood-brain barrier.

Imaging of blood-brain barrier damage by magnetic resonance was currently studied as to the potential of dextran-magnetite particles (DMP) for contrast enhancement. For that purpose, dextran T10 (average molecular weight: 10.9 Kilodalton) was complexed with magnetite (Fe3O4) in ammonia. Experimental testing of the agent was made in vivo using Wistar rats with a freezing injury to the brain. DMP was i.v. injected at a dose of 90 µM Fe/kg b.w. followed by 2% Evans blue (0.6 ml). Control animals with trauma were studied without administration of DMP. Histochemical assessments were made to analyze the tissue distribution of DMP in the brain, kidney and liver after fixation in 4% formalin. MR imaging was conducted with 1.5 Tesla field strength with a circular coil 15 min after the freezing insult and administration of DMP. T1- and T2-weighted images were obtained using spin echo sequences among others. Regression analyses indicated a 50% reduction of Ti at a DMP concentration of 48 µM Fe, while for T2 only 4 µM/ Fe(DMP) were sufficient for a 50% reduction. DMP was also accumulating in other organs, particularly in the Kupffer cells of the liver. Administration of DMP led to recognition of the freezing lesion as black area in agreement with macroscopical findings obtained by autopsy. In animals with a freezing lesion without administration of DMP, only T2-weighted images demonstrated a somewhat higher intensity attributable to the disruption of the blood-brain barrier. The present findings demonstrate the usefulness of DMP for contrast enhancement of lesions following disruption of the blood-brain barrier.

Characterization of tumor processes and studying their metabolism is one of the main challenges in diagnostic clinical oncology. Magnetic resonance spectroscopy (MRS) provides a noninvasive method to monitor tissue metabolism. Since the early work of Griffiths [1], an increasing number of papers have been published on in vivo measurement of tumor metabolism using MRS. Detailed accounts of the methods of NMR spectroscopy and NMR imaging have been published [2,3] and are beyond the scope of this review.

Localized phosphorus magnetic resonance spectroscopy at 1.5 T was performed in 39 patients with multiple sclerosis and in 15 healthy controls. The multiple sclerosis spectra showed increased creatine phosphate levels. This increase was correlated with the severity of the handicap and was greater in patients with a progressive course of the disease than in patients with relapsing-remitting disease. No clear abnormalities were observed in the spectra of patients with multiple sclerosis regarding the phosphomonoesters, phosphodiesters, inorganic phosphate, and beta-adenosine triphosphate or with respect to pH values. There was an increased creatine phosphate level in the spectra in relation to a low metabolic state of the brain.

In general, patients with fibromyalgia suffer from non-articular chronic pain and stiffness. A typical feature is the finding of so-called tender points on physical examination [1].

To study the possible application of monoclonal antibody/dextran-magnetite conjugates in specific MR imaging of brain metastases, both components of these conjugates were tested for their ability to penetrate the endothelium during conditions of local blood-brain barrier (BBB) impairment. The passage of dextran-magnetite particles (DMP) across a disrupted blood-brain barrier was studied in a freezing lesion model using electron microscopy (EM) and MR imaging. One hour after i.v. injection, focal accumulation of DMP in capillary endothelial cells within the freezing lesion was shown by EM. In parallel with this, MR imaging indicated a strong contrast enhancement in the lesion. EM observations showed that the particles were still present in the endothelial cells four and eight hours after injection. The passage of an anti-small cell lung cancer (SCLC) monoclonal antibody across the endothelium of intracerebrally xenografted human SCLC was studied using immunohistological techniques. It was found that passage across endothelial cell occurred in the tumor within four hours after injection.

Proton relaxation times of protein solutions, bovine brain, and edematous feline brain tissue were studied as a function of water concentration, protein concentration, and temperature. In accordance with the fast proton exchange model for relaxation, a linear relation could be established between R1 and the inverse of the weight fraction of tissue water. This relation also applied to R2 of gray matter and of protein solutions. No straightforward relation with water content was found for R2 of white matter. Temperature-dependent studies indicated that in this case, the slow exchange model for relaxation had to be applied. The effect of macromolecules in physiological relevant concentrations on the total relaxation behavior of edematous tissue was weak. Total water content changes predominantly affected the relaxation rates. The linear relation may have high clinical potential for assessment of the status of cerebral edema on the basis of T1 and T2 readings from MR images.

To study the possible application of monoclonal antibody/dextranmagnetite conjugates in specific MR imaging of brain metastases, both components of these conjugates were tested for their ability to penetrate the endothelium during conditions of local blood-brain barrier (BBB) impairment.

Proton relaxation times T1 and T2 of macromolecular solutions, bovine brain tissues, and experimental cat brain edema tissues were studied as a function of water concentration, protein concentration, and temperature. A linear relation was found between the inverse of the weight fraction of tissue water and the spin-lattice relaxation rate, R1, based on a fast proton exchange model for relaxation. This correlation was also found for the spin-spin relaxation rate, R2, of gray matter samples and macromolecular solutions at low concentrations. Concentrated solutions of protein-water samples showed an enhanced relaxation due to viscosity effects. The T2 of white matter was considerably lengthened with elevated water concentration, but showed no straightforward relation with the total tissue water content. The relaxation times of all samples increased with temperature, supporting the assumption of fast proton exchange in the model for relaxation. This was not found for white matter, in which T2 decreased with increasing temperature, which indicated that intermediate or even slow exchange was present. The relation found between relaxation times and tissue water content can be used to predict the amount of and/or increase in tissue water due to water-elevating processes such as edema. © 1988 Academic Press, Inc.

Proton spin longitudinal (T1) and transverse (T2) relaxation and proton density studies were carried out on human fatty tissue and bovine white matter, both in the native state and after immersion in D2O. It is concluded that nuclear magnetic resonance signals from fatty tissue result mainly from methyl and methylene protons of hydrocarbons. No contribution from lipid protons could be detected for white matter, although it contains a high percentage of lipids. Imaging experiments, resulting in T1, T2, and proton density maps, support the results obtained with spectroscopic relaxation studies.

A display method is proposed in which the spin‐lattice relaxation time T 1, the spinspin relaxation time T 2, and the proton density ρ of each pixel in a MR image are simultaneously expressed in color features in a unified way that allows international standardization. MR images were made from a phantom, a healthy volunteer, and patients in such a way that T 1 and T 2 and proton density images could be derived. T 1 and T 2 data were compared with accurate relaxation time measurements of the phantom content. Color images were computed from the acquired T 1 and T 2 images using matrix multiplication on a pixel base. In this way the color combination in each pixel represents the properties of that particular pixel by a unique mixing of the elementary colors red, green, and blue. Color resolution could be modified using different choices of the reference triangle in which the color combinations were defined. This method of representation offers a means for displaying multiple features as T 1, and T 2 in one directly interpretable image, independent of instrumental settings. © 1989 Academic Press, Inc

This study was undertaken to evaluate the feasibility of multiexponential relaxation data analysis to MR imaging techniques. The first part of this study contains accurate relaxation time measurements performed on a conventional spectrometer. In the second part, essentially the same measuring techniques were applied but now on standard whole body MR imaging equipment. T2 relaxation was measured using multi-echo techniques, T1 relaxation using multiple inversion recovery measurements. Manganese chloride solutions were used for verification of the single exponential model. Water and fat mixtures were considered for multi-exponentiality. Pure fat showed an intrinsic two-exponentiality in T1 and T2 relaxation. Mixtures of fat and water were analyzed and could at best be characterized by two exponentials, although at least three exponentials were known to be present. From the two-exponential fit the relative amounts of fat and water were calculated and compared with the mixture composition. Statistical criteria are discussed to discriminate between single and double exponential behavior in relaxation curves. It is concluded that the time consuming IR measurements for the determination of multiple T1 relaxation are not applicable in a clinical environment. Multiple T2 relaxation can be determined in a reasonable amount of time using multiple echo measurements in one image acquisition. It is shown that the observed values of T1 and T2 from tissues with intrinsic multiexponential relaxation behavior, measured with MR imaging or MR relaxation techniques on a whole-body imager or a conventional spectrometer, depend strongly on the way the experiments are set up and on the model accepted for data analysis.

NMR spectroscopical measurements of relaxation times were conducted on muscle, intestine, fatty tissue and cerebral cortex and white matter of the rat at various time intervals following removal of the tissue. It appeared that most tissues can be stored at 4 degrees C up to 24 hours without noticeable effects on NMR relaxation parameters. Exceptions are the T2 of muscle and the T1 and T2 of intestine, which tended to change in the first hour after biopsy. Relaxation parameters change considerably after fixation of the tissues. Therefore the effects of fixation have to be taken into account when carrying out NMR measurements on fixed tissues.

Magnetic resonance imaging (MRI) has been reported to be a promising method in diagnosing head and neck masses [1–4]. In general, T1- and T2-weighted pulse sequences are used for the study of the nature and extension of the abnormal tissue. When using conventional spin echo (SE) techniques, a compromise has to be made between signal-to-noise ratio, spatial resolution, and acquisition time. For T2-weighted pulse sequences, acquisition time usually ranges between 10 and 20 min.

A display method is proposed in which the relaxation times T1 and T2, and the proton density of tissue in each pixel in an MR image are simultaneously expressed in color features in a unified way. MR images were made from phantoms, volunteers and patients in such a way that T1 and T2 and proton density images could be calculated. Color images were computed from these images using matrix multiplication on a pixel base. In this way the color combination in each pixel represents the properties of that particular pixel by a unique mixing of the elementary colors red, green and blue. Color resolution could be modified using different choices of a reference color triangle in which the color combinations were defined. This method of representation offers a means for displaying multiple features as T1 and T2 in one directly interpretable image, independent of instrumental settings.

Fast gradient echo (GE) MR imaging during breathhold was performed in 73 abdominal MR examinations in order to determine the value of GE technique in the reduction of movement artefacts and improvement of image quality. The results were compared with conventional spin-echo (SE) technique. T 1 -weighted SE images consistently demonstrated normal anatomy and pathology. T 2 ∗ -weighted and intermediate GE technique proved to be superior to T 2 -weighted SE technique in a considerable number of cases providing not only better delineation of normal structures but also better lesion detection. At this stage GE technique should be considered as an adjunct to T 1 -weighted SE technique. If the artefacts presently inherent to GE imaging could be reduced or compensated for, this technique of rapid MR imaging during suspended respiration could become an important tool being one of the fastest techniques for abdominal MR imaging.

In cat brain with a freezing injury, the uptake of 1-11C-acetoacetate (11C-ACAC), 2-18F-fluorodeoxy-D-glucose (18FDG), and L-1-11C-tyrosine (11C-TYR) was monitored by positron emission tomography following intravenous administration of the tracers, at 1 day, and 1-3 weeks after the injury. The development and further course of the cold-induced oedema was monitored by magnetic resonance imaging. In the fresh (1 day old) lesion there was increased uptake of 11C-ACAC, probably due to release of the restrictive influence of the blood-brain barrier upon passage of the substance into brain. The uptake of 18FDG, which normally occurs by carrier-mediated transport at the barrier, was decreased in the fresh lesion, probably as a result of damage of the carrier mechanism. In the 3 week old lesion 18FDG uptake was still reduced, and 11C-ACAC uptake was still increased, although barrier function to Evans blue had recovered. It is suggested, that the increased 11C-ACAC uptake in the chronic lesion bears upon the proliferation of macrophages and reactive glial cells in the lesion. This is supported by the increased uptake of 11C-TYR in the 2 weeks old lesion, while in the fresh lesion 11C-TYR uptake was unchanged.

✓ Nuclear magnetic resonance tomography is an imaging method based on the magnetic resonance behavior of protons, as they occur predominantly in tissue water or in fatty acids. This behavior, as characterized by the relaxation times T1 and T2, is determined by the chemical and physical environment of the protons. The relaxation properties of the tissue can be accentuated by selection of the appropriate pulse sequence. Interpretation of the images requires an understanding of the principles of the technique with which the relaxation times are expressed in the images, and acquaintance with the composition of the tissue in terms of relaxation properties (as in computerized tomography, tissue composition is expressed as attenuation coefficients).

T1 and T2 relaxation times were determined in vitro at 21 MHz (0.5 T) for a variety of spinal and paraspinal tissues. Intensity formulas for spin echo and inversion recovery sequences were derived and used to calculate the intensities of these tissues as they would appear in magnetic resonance images. The intensity was calculated as a function of various repetition, echo, and inversion times. It is shown that the combination of acquiring in vitro relaxation time values and calculating intensity as a function of pulse timings is useful to predict the parameter setting for optimal contrast between certain tissues without applying series of magnetic resonance images.

Cine MR is a new technique using a movie loop of sequential gradient reversal echo images obtained during various points of the cardiac cycle, thus allowing cinegraphic display of structures and substances demonstrating movements related to cardiac function. Although the application of the method has until recently focused on cardiovascular studies, pulsatile movements synchronous with the arterial pulse have been described and studied by fluoroscopic filming and videodensitometry of movements of contrast media introduced into the CSF spaces 1,2 .

When relaxation parameters of tissues are known, selection of adequate instrumental parameters in magnetic resonance imaging is possible. The signal strength of various tissues is defined by proton density, T1 and T2. The calculation of this signal strength is given. The advantages of multiple echoes and the reason why they are used, are mentioned.