Pattern recognition of MRSI data shows regions of glioma growth that agree with DTI markers of brain tumor infiltration.

Gliomas are the most common primary brain tumors and the majority are highly malignant, with one of the worst prognoses for patients. Gliomas are characterized by invasive growth into normal brain tissue that makes complete surgical resection and accurate radiotherapy planning extremely difficult. We have performed independent component analysis of magnetic resonance spectroscopy imaging data from human gliomas to segment brain tissue into tumor core, tumor infiltration, and normal brain, with confirmation by diffusion tensor imaging analysis. Our data are consistent with previous studies that compared anomalies in isotropic and anisotropic diffusion images to determine regions of potential glioma infiltration. We show that coefficients of independent components can be used to create colored images for easy visual identification of regions of infiltrative tumor growth.

The relationship between white matter brain metabolites and cognition in normal aging: the GENIE study.

Magnetic resonance spectroscopy (MRS) has demonstrated age-related changes in brain metabolites that may underlie micro-structural brain changes, but few studies have examined their relationship with cognitive decline. We performed a cross-sectional study of brain metabolism and cognitive function in 82 healthy adults (aged 50-90) participating in the GENIE (St GEorge's Neuropsychology and Imaging in the Elderly) study. Absolute metabolite concentrations were measured by proton chemical shift imaging within voxels placed in the centrum semiovale white matter. Cognitive abilities assessed were executive function, working memory, information processing speed, long-term memory and fluid intelligence. Correlations showed that all cognitive domains declined with age. Total creatine (tCr) concentration increased with age (r=0.495, p<0.001). Regression analyses were performed for each cognitive variable, including estimated intelligence and the metabolites, with age then added as a final step. A significant relationship was observed between tCr and executive function, long-term memory, and fluid intelligence, although these relationships did not remain significant after age was added as a final step in the regression. The regression analysis also demonstrated a significant relationship between N-acetylaspartate (NAA) and executive function. As there was no age-related decline in NAA, this argues against axonal loss with age; however the relationship between NAA and executive function independent of age and estimated intelligence is consistent with white matter axonal integrity having an important role in executive function in normal individuals.

White matter damage on diffusion tensor imaging correlates with age-related cognitive decline.

BACKGROUND: Damage to white matter tracts, resulting in "cerebral disconnection," may underlie age-related cognitive decline. METHODS: Using diffusion tensor MRI (DTI) to investigate white matter damage, and magnetic resonance spectroscopy (MRS) to look at its underlying pathologic basis, the authors investigated the relationship between white matter structure and cognition in 106 healthy middle-aged and elderly adults. Fractional anisotropy (FA) and mean diffusivity (MD) values, whole brain white matter histograms, and regions of interest placed in the white matter of the centrum semiovale were analyzed. Correlations with executive function, working memory, and information-processing speed were performed. RESULTS: There was a progressive reduction in FA and increase in diffusivity with age in both region of interest (r = 0.551, p < 0.001), and whole brain histograms (r = 0.625, p < 0.001). DTI values correlated with performance in all three cognitive domains. After controlling for age, DTI parameters correlated with working memory but not with the other two cognitive domains. MRS studies found a correlation of N-acetyl aspartate, a neuronal marker, with DTI parameters (r = 0.253, p < 0.05). CONCLUSION: The results are consistent with white matter damage due to axonal loss, causing age- related cognitive decline. Working memory may be particularly dependent on complex networks dependent on white matter connections.

Tumour dose response to the antivascular agent ZD6126 assessed by magnetic resonance imaging.

ZD6126 is a vascular targeting agent that disrupts the tubulin cytoskeleton of proliferating neo-endothelial cells. This leads to the selective destruction and congestion of tumour blood vessels in experimental tumours, resulting in extensive haemorrhagic necrosis. In this study, the dose-dependent activity of ZD6126 in rat GH3 prolactinomas and murine RIF-1 fibrosarcomas was assessed using two magnetic resonance imaging (MRI) methods. Dynamic contrast-enhanced (DCE) MRI, quantified by an initial area under the time-concentration product curve (IAUC) method, gives values related to tumour perfusion and vascular permeability. Multigradient recalled echo MRI measures the transverse relaxation rate T(2)*, which is sensitive to tissue (deoxyhaemoglobin). Tumour IAUC and R(2)* (=1/T(2)*) decreased post-treatment with ZD6126 in a dose-dependent manner. In the rat model, lower doses of ZD6126 reduced the IAUC close to zero within restricted areas of the tumour, typically in the centre, while the highest dose reduced the IAUC to zero over the majority of the tumour. A decrease in both MRI end points was associated with the induction of massive central tumour necrosis measured histologically, which increased in a dose-dependent manner. Magnetic resonance imaging may be of value in evaluation of the acute clinical effects of ZD6126 in solid tumours. In particular, measurement of IAUC by DCE MRI should provide an unambiguous measure of biological activity of antivascular therapies for clinical trial.

Why are cancers acidic? A carrier-mediated diffusion model for H+ transport in the interstitial fluid.

31P MRS studies have shown that the intracellular compartment ot tumours is kept near neutrality, whereas the interstitial fluid is acidic (pH 6.5-6.8). Why is this compartment acidic? Balance studies confirm that tumours produce excessive lactic acid, although less than usually supposed, but this cannot be the whole story, since Tannock and co-workers have shown interstitial acidity in glycolysis-deficient tumours. Another major acid load is caused by hydration of CO2 molecules to carbonic acid, catalysed by carbonic anhydrase. The distance that H+ must diffuse from cancer cells to capillaries is further than in normal tissue and this will increase acidification near the cells. We show that previous quantitative models based on simple H+ diffusion are unsatisfactory. This is because most H+ ions cross the interstitial space bound to buffers such as inorganic phosphate. Although these protonated buffers (i.e. conjugate acids) diffuse much more slowly than H+ ions they carry most of the protons, so the pH predicted by this model is closer to neutrality for a given proton production rate than that predicted by the dissolved H+ model. We have developed a mathematical model of this carrier-mediated system that predicts pHe values as low as those observed in some tumours.

Issues in flow and oxygenation dependent contrast (FLOOD) imaging of tumours.

The sensitivity of blood oxygenation level dependent (BOLD) contrast techniques to changes to tumour deoxyhaemoglobin concentration is of relevance to many strategies in cancer treatments. In the context of tumour studies, which frequently involve the use of agents to modify blood flow, there are underlying physiological changes different to those of BOLD in the brain. Hence we use the term, flow and oxygenation dependent (FLOOD) contrast, to emphasize this difference and the importance of flow effects. We have measured the R(2)* changes in a prolactinoma tumour model for a variety of vasoactive challenges [carbogen, 100% oxygen and 100% nitrogen as different breathing gases, and administration of tumour blood flow modifiers such as calcitonin gene related peptide (CGRP), hydralazine and nicotinamide]. In addition we have measured other relevant physiological parameters, such as bioenergetic status from (31)P MRS, and blood pH and glucose, that may change during a vasoactive challenge. Here we discuss how they relate to our understanding of FLOOD contrast in tumours. We frequently observe R(2)* changes that match the expected action of the vascular stimulus: R(2)* decreases with agents expected to improve tumour oxygenation and blood flow, and increases with agents designed to increase tumour hypoxia. Unlike most normal tissues, tumours have a chaotic and poorly regulated blood supply, and a mix of glycolytic and oxidative metabolism; thus the response to a vasoactive challenge is not predictable. Changes in blood volume can counteract the effect of blood oxygenation changes, and changes in blood pH and glucose levels can alter oxygen extraction. This can lead to R(2)* changes that are smaller or the reverse of those expected. To properly interpret FLOOD contrast changes these effects must be accounted for.

Issues of normal tissue toxicity in patient and animal studies--effect of carbogen breathing in rats after 5-fluorouracil treatment.

Non-invasive magnetic resonance spectroscopy (MRS) can be used in the clinic to monitor the pharmacokinetics of the chemotherapeutic drug 5-fluorouracil (5-FU) and the effects of modifiers. We report two studies of 5-FU toxicity in normal tissue--one with patients and the other an animal study. 1) 19F MRS signals from fluoronucleotides, cytotoxic anabolites of 5-FU metabolism, were observed in the livers of two patients treated with 5-FU for colorectal cancer, shown by computed tomography (CT) and ultrasound (US) to have no liver metastases. This is the first report of non-invasive monitoring of toxic 5-FU metabolites in normal human tissues. 2) In animals, carbogen-breathing enhances tumour uptake and the efficacy of 5-FU, and the method is under trial in patients. This study demonstrates that there were no significant effects of carbogen breathing on the levels of 5-FU and its metabolites in normal rat tissues, or on the histology of the tissues assessed after treatment.

In vivo hyperpolarized 129Xe NMR spectroscopy in tumors.

The first in vivo hyperpolarized 129Xe NMR study in experimental tumors is presented. Hyperpolarized 129Xe was dissolved in solutions, and was injected intratumorally in GH-3 prolactinomas in rats and RIF-1 fibrosarcomas in mice. The 129Xe NMR spectra and apparent spin-lattice relaxation times in the two tumor types present characteristic differences. These differences are discussed in terms of xenon exchange between the carrier medium and the tissue compartments.

In-vivo intracellular pH at rest and during exercise in patients with essential hypertension.

BACKGROUND: Several studies in isolated cells have reported that intracellular pH (pHi) in individuals with essential hypertension may be relatively alkaline compared to normotensive individuals. Such an abnormality of pHi in hypertension would be consistent with enhanced sodium-hydrogen exchanger activity and may provide potential mechanisms by which hypertension and its complications could develop. OBJECTIVES: To determine in-vivo intracellular pH of skeletal muscle at rest and during recovery from exercise-induced acidosis in hypertensive and normotensive subjects. METHODS: Using 31-phosphorus magnetic resonance spectroscopy, pHi of the dominant flexor digitorum superficialis was measured in 20 Caucasian subjects (14 male) with essential hypertension and 20 normotensive controls matched for gender, age, race and body mass index. Measurements were made at rest and during the exercise and recovery periods of a stepped incremental maximal exercise protocol. The rate of pHi recovery from exercise-induced acidosis was calculated by linear regression over the first 210 s of recovery from the pHi time plots of respective subjects. RESULTS: Mean resting pHi in the hypertensive (7.05 +/- 0.04) and normotensive groups (7.06 +/- 0.04) were not significantly different. There was a significant effect of gender on pHi: mean pHi was 7.07 +/- 0.03 in males and 7.02 +/- 0.03 in females, respectively (P < 0.0005). The mean intracellular pH achieved by exercise was 6.74 +/- 0.31 in hypertensive individuals and not significantly different in normotensive individuals (6.68 +/- 0.19; P = 0.4). The mean rate of pHi recovery in the hypertensives was 0.08 +/- 0.03 pH units/min and not significantly different in normotensives (0.08 +/- 0.02; P = 0.4). CONCLUSIONS: These results contrast with previously documented abnormalities in the control of pHi in hypertension and demonstrate the absence of major in-vivo disturbances of pHi in skeletal muscle, both at rest and during recovery from exercise-induced acidosis, in essential hypertension. Therefore, it is possible that previously documented abnormalities of pHi and activity of the exchanger may be either specific to cell type or not present under in-vivo conditions.

Measurement of the extracellular pH of solid tumours in mice by magnetic resonance spectroscopy: a comparison of exogenous (19)F and (31)P probes.

Precise measurement of pH(e) in vivo may be of clinical value for both diagnosis and selection of therapy. pH(e) measurements made by the (31)P probe 3-aminopropylphosphonate (3-APP) were compared with those made by the (19)F probe, 3-[N-(4-fluor-2-trifluoromethylphenyl)-sulphamoyl]-propionic acid (ZK-150471) in three solid tumour types, human HT29 xenografts, murine RIF-1 fibrosarcomas and Lettre tumours grown subcutaneously in mice. No significant differences were observed when probe measurements of pH(e) were compared at 20-60 min post-administration, although very low pH(e) values (ca. 6.0) were recorded in two out of eight Lettre tumours by ZK-150471. The more rapid pH(e) measurements possible using ZK-150471 showed that during the first 20 min post-administration significant increases occurred in pH(e) which were greatest in the more necrotic tumours. Since isolated cell experiments showed that ZK-150471 was non-toxic and did not enter the cells, this early increase in pH(e) may reflect gradual penetration by ZK-150471 of the reportedly alkaline necrotic space in the tumours. The wide chemical shift range, improved signal-to-noise and absence of signal overlap allowed a more rapid and precise measurement of pH(e) by ZK-150471 compared to 3-APP. These characteristics suggest that ZK-150471 is currently the preferred pH(e) probe for non-invasive MRS.

SPARE: A robust method for magnetic resonance imaging in inhomogeneous fields.

An imaging sequence based on a spin-echo train has been developed which is free from geometric distortions in the imaging plane due to main field inhomogeneity. Such inhomogeneities, and chemical shifts, cause only a displacement in the selected slice, which is minimized by the use of high gradient strengths and short radiofrequency pulses. Additionally, variations in the radiofrequency field strength cause variations in the image amplitude but cause no other artifacts. This allows the use of low-flip-angle refocusing pulses, reducing the power deposition to levels which are safe in vivo at high field strengths. The sequence was implemented on a Bruker whole-body 3T system. Example images from a perfluorocarbon phantom and a human head are presented.

Magnetic resonance spectroscopy and imaging methods for measuring tumour and tissue oxygenation.

It is well known that low levels of tissue oxygen (pO2) protect tumour cells from ionising radiation and some chemotherapeutic agents. Thus, numerous studies have been aimed at developing methods to measure tissue oxygenation. An initial discussion of some of the traditional methods for measuring oxygenation is included, followed by a discussion of magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) methods for measuring tumour and normal tissue oxygenation. The latter methods are of interest because of the non-invasive nature of magnetic resonance (MR). Some of the MR methods described herein include: 31P MRS, 1H MRS and MRI, and 19F MRS and MRI. Each method is detailed, including a brief assessment of its ability to measure tumour oxygenation and its potential for clinical application.

The design of practical selective pulses for magnetic resonance imaging and spectroscopy using SPINCALC.

Recently, we introduced a new numerical approach to the design and optimization of NMR selective pulses, which we have christened "SPINCALC" (J. T. Ngo and P. G. Morris, Biochem. Soc. Trans. 14, 1271 (1986); J. T. Ngo and P. G. Morris, Magn. Reson. Med. 5, 217 (1987]. The first practical application of pulses generated by SPINCALC is demonstrated on a standard 0.5-T clinical MRI system. Results are shown for single phase pi pulses suitable both for selective inversion and for selective refocusing. The extension of SPINCALC to multidimensional pulses is illustrated by the design of a two-dimensional pi pulse.

Rational approaches to the design of NMR selective pulses.

The need for NMR selective pulses in magnetic resonance imaging and spectroscopy is reviewed. The shortcomings of the current generation of pulses are discussed and the need for new categories of pulse identified. Strategies for selective pulse design are outlined and two numerical optimization methods, simulated annealing and SPINCALC (a method recently introduced by us: J. T. Ngo and P. G. Morris, Magn. Reson. Med. 5, 217 (1987], are discussed in detail. Their use is illustrated and compared for the design of pi/2 phase-compensated pulses. Both methods require substantial amounts of CPU time, with simulated annealing the more demanding. Unconstrained, simulated annealing also tends to produce pulses with discontinuous waveforms. A crude two-dimensional pulse derived from a low flip angle approximation is illustrated.