Comparison of contrast enhanced MR-angiography-MRI and digital subtraction angiography in the evaluation of pancreas and/or kidney transplantation patients: initial experience.

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 < 0.001) and the parenchymal enhancement of the pancreatic grafts. For the assessment of the contrast excretion, the pyelocalyceal system and the ureter of the renal graft ce-MRA-MRI was superior (p < 0.001), for small caliber arteries in the renal grafts i.a.DSA was of greater value (p < 0.001). The combination of ce-MRA and MRI is reliable for evaluating the vascular anatomy and has several advantages over i.a.DSA after pancreas and/or kidney transplantation. It can replace i.a.DSA in patients with impaired graft function or suspected of vascular complications after pancreas and/or kidney transplantation.

Superior diagnostic strength of combined contrast enhanced MR-angiography and MR-imaging compared to intra-arterial DSA in liver transplantation candidates.

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 < 0.001) and the assessment of the inferior vena cava, the hepatic and the renal veins (p < 0.001). Although the detection of liver malignancy is poor in both techniques, ce-MRA/MRI is superior to i.a.DSA. This study shows that a one step diagnostic approach with a combination of ce-MRA and MRI is a valuable radiological tool with a superior diagnostic strength compared to i.a.DSA in the liver transplantation and shunt candidate. Therefore, ce-MRA/MRI should replace i.a.DSA in these patients groups.

Optimization of scantiming in abdominal breathhold contrast-enhanced MRA: an empirical guideline.

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 be promoted by using data from this study. The proposed scan scheme is suitable for subjects with and without cirrhosis.

11C-tyrosine position emission tomography and 1H magnetic resonance spectroscopy of the response of brain gliomas to radiotherapy.

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.

Noninvasive metabolic assessment of human donor livers: prognostic value of 31P-magnetic resonance spectroscopy for early graft function.

BACKGROUND: The purpose of this study was to investigate whether phosphorus-31 magnetic resonance spectroscopy (31P-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 31P-MRS demonstration in the human liver of phosphocreatine. CONCLUSIONS: In the clinical setting described, metabolic assessment using 31P-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.

Changes in 31P-relaxation times during organ preservation: observations on cold stored human donor livers.

During cold preservation for transplantation the tissue hydration state changes. It is not known whether such changes lead to altered relaxation times of 31P nuclei with potential consequences for the quantification of tissue metabolites. Therefore, 31P spectroscopic and proton T1 relaxometric measurements were performed on 42 isolated human donor livers shortly before implantation. The results demonstrate that 31P T1 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.

The origin of lactate in peritumoral edema as measured by proton-magnetic resonance spectroscopic imaging.

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.

Tissue hydration in kidneys during preservation: a relaxometric analysis of time-dependent differences between cortex and medulla.

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.

Tissue pH in cold-stored human donor livers preserved in University of Wisconsin solution. A noninavasive clinical study with 31P-magnetic resonance spectroscopy.

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.

Localised proton spectroscopy and spectroscopic imaging in cerebral gliomas, with comparison to positron emission tomography.

In 32 patients with gliomas, one- and two-dimensional proton magnetic resonance spectroscopy (1H-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 (LAC) 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 LAC/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.(ABSTRACT TRUNCATED AT 250 WORDS)

Ex vivo MRI in extracorporeal liver surgery.

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.

On the principles underlying the diagnosis of brain tumours--a survey article.

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.

Clinical applicability of human in vivo localized phosphorus-31 magnetic resonance spectroscopy of bone and soft tissue tumors.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Ex vivo magnetic resonance imaging of pretransplant human donor liver. Clinical experience in 66 cases.

Magnetic resonance imaging (MRI) was performed on 66 cold-stored human donor livers. Spin echo images were obtained with a clinical whole body MRI system. Various parenchymal and vascular abnormalities were found. An unexpected finding was the abundant presence of intrahepatic air. Although the majority of parenchymal abnormalities that were found would not have precluded transplantation, the rationale of pretransplant MRI was to prevent the introduction of unidentified pathology into the recipient. Guided by the MR images, lesions in the isolated organ can be easily located for biopsy and resection. Unnecessary or inadequate therapeutic interventions after transplantation can thus be avoided. In addition, the visualization of the hepatic veins with their confluence appears to be useful in split-liver procedures.

Contribution of magnetic resonance spectroscopic imaging and L-[1-11C]tyrosine positron emission tomography to localization of cerebral gliomas for biopsy.

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.

The tissue hydration state in UW-preserved human donor livers. A clinical study of the relation between proton magnetic resonance relaxation times, donor condition, preservation procedure, and early graft function.

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 (P < 0.05 and P < 0.01, 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.

A study on peritumoral brain edema around meningiomas by MRI and contrast CT.

In the present study upon 9 meningiomas, the volume of peritumoral brain edema was calculated by integration of the cross-sectional edematous areas on serial MRI slices. It was zero in 3 cases and ranged from 11 to 176.4 ml in the other cases. There was disruption of the cortex in all cases, ranging from slight to severe. T1 and T2 measurements were made at the level of maximum edema extension (at 1.5 T), using a mixed sequence. From the T2 values tissue water content in % was calculated using equations, which had been obtained by correlating water content with relaxation rates. These had been measured on human brain autopsy specimens subjected to hydration or dehydration. Assuming that spread of contrast agent marks the advancement of the front of edema produced by the tumor, calculation of the excess of edema production per unit tumor volume Veff/VN was performed on the basis of CT-studies made before, and at 1.5, 3 and 6 hr after contrast infusion. Of 6 tumors with edema (mean water content of peritumoral white matter of 91% and mean edema volume of 69.2 ml) the Veff/VN was 0.18-1.08 ml/h/cm3 tumor volume, whereas 3 tumors without associated edema had a Veff/VN of 0.03-0.12 ml/h/cm3. In meningiomas cortex penetration seemed to be a separate factor determining the spread of edema.

Cystic lesions of the brain. A classification based on pathogenesis, with consideration of histological and radiological features.

A classification of the existing multitude of cystic lesions of the brain is proposed, which allows an understanding of their genesis and consequent therapeutic implications, as well as their diagnostic characteristics. Essentially, cerebral cystic lesions may be classified into the following categories: Cysts containing CSF-like fluid, which include ex vacuo type cysts, such as leptomeningeal cysts, and cysts following surgical resection; cysts with fluid secreting walls and CSF-like content, such as arachnoid cysts; cysts associated with dysgenesis, for example Dandy-Walker cysts. The ex vacuo cysts increase craniospinal compliance, whereas the other cysts with CSF-like content do not; they are not per se expansive, however, although their occasional location along CSF pathways may cause obstruction and hydrocephalus. Another category includes cysts with a lining of non-neural epithelium like colloid cysts, epidermoid cysts, or craniopharyngiomas. They may increase in size and cause symptoms by compression, although not at the rate of tumour-associated cysts. The cysts associated with gliomas and other tumours have a pathogenesis bearing upon blood-brain barrier impairment and formation of vasogenic oedema. Finally, one may distinguish a category of cysts with infectious origin, such as brain abscesses and hydatid cysts. The cysts with CSF-like contents may be recognised by their magnetic resonance characteristics resembling those of CSF, whereas cysts containing proteinaceous fluid are associated with blood-brain barrier impairment and consequent contrast enhancement. The cysts with a lining of non-neural epithelium exhibit diverse properties of attenuation on computed tomography (CT) and magnetic resonance imaging (MRI), depending on the nature of their cyst contents.

Localized proton spectroscopy of inoperable brain gliomas. Response to radiation therapy.

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.