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The nuclear spin polarization of 129 Xe can be enhanced by several orders of magnitude by using optical pumping techniques. The increased sensitivity of xenon NMR has allowed imaging of lungs as well as other in vivo applications. The most critical parameter for efficient delivery of laser-polarized xenon to blood and tissues is the spin-lattice relaxation time (T 1 ) of xenon in blood. In this work, the relaxation of laser-polarized xenon in human blood is measured in vitro as a function of blood oxygenation. Interactions with dissolved oxygen and with deoxyhemoglobin are found to contribute to the spin-lattice relaxation time of 129 Xe in blood, the latter interaction having greater effect. Consequently, relaxation times of 129 Xe in deoxygenated blood are shorter than in oxygenated blood. In samples with oxygenation equivalent to arterial and venous blood, the 129 Xe T 1 s at 37°C and a magnetic field of 1.5 T were 6.4 s ؎ 0.5 s and 4.0 s ؎ 0.4 s, respectively. The 129 Xe spin-lattice relaxation time in blood decreases at lower temperatures, but the ratio of T 1 in oxygenated blood to that in deoxygenated blood is the same at 37°C and 25°C. A competing ligand has been used to show that xenon binding to albumin contributes to the 129 Xe spin-lattice relaxation in blood plasma. This technique is promising for the study of xenon interactions with macromolecules.

Decreases in tumor size and nodal downstaging can be seen on MRI after chemoradiation therapy in approximately two thirds of patients. The surgically more relevant parameter--distance between tumor and circumferential resection margin--can be accurately predicted. Errors were caused by the presence of considerable tumor, rectal wall fibrosis, and mucinous tumors.

Proton (hydrogen 1) magnetic resonance (MR) spectroscopy was used to study model and porcine bile in vitro. The method was subsequently developed to facilitate the acquisition of in vivo 1H MR spectra from the gallbladder bile of 10 human volunteers. Signals attributable to phosphotidylcholine and conjugated bile acid protons were observed in eight of the 10 volunteers. Phosphotidylcholine concentrations were estimated, and five values (mean = 35.8 mmol/L, SD = 9.8) were within the expected range of levels in human bile. Findings in this preliminary investigation indicate that human gallbladder bile can be qualitatively and quantitatively studied noninvasively with 1H MR spectroscopy.

The aim of this study was to evaluate the MR findings of anal carcinoma using an external pelvic phased-array coil before and after chemoradiation treatment. 15 patients with carcinoma of the anal canal underwent T(2) weighted and short-tau inversion recovery (STIR) imaging before and after chemoradiation. Images were reviewed in consensus by two radiologists. At pre-treatment imaging, the tumour size and stage, signal intensity and infiltration of adjacent structures were recorded. MR imaging was repeated immediately after chemoradiation, every 6 months for the first year and then yearly. Tumour response was assessed by recording change in tumour size and signal intensity. Prior to treatment, the mean tumour size was 3.9 cm (range, 1.8-6.4 cm). Tumours appeared mildly hyperintense at T(2) weighted and STIR imaging. There was good agreement in T staging between clinical examination and MR imaging (kappa = 0.68). In 12 responders with long disease remission, a greater percentage reduction in the size of MR signal abnormality in the tumour area was observed at 6 months (mean 54.7%; 46-62%) than immediately after treatment (mean 38.6%; 30-46%) (p = 0.002, t-test). 7/12 showed stabilization of T(2) signal reduction in the tumour area after 1 year, and 5/12 showed complete resolution of signal alterations at 2 years. Pelvic phased-array MR imaging is useful for local staging of anal carcinoma and assessing treatment response. After treatment, a decrease in tumour size accompanied by reduction and stability of the MR T(2) signal characteristics at 1 year after chemoradiation treatment was associated with favourable outcome.

Assessment of low-grade glioma treatment response remains as much of a challenge as the treatment itself. Proton magnetic resonance spectroscopy ( 1 H-MRS) and imaging were incorporated into a study of patients receiving temozolomide therapy for lowgrade glioma in order to evaluate and monitor tumour metabolite and volume changes during treatment. Patients (n ¼ 12) received oral temozolomide (200 mg m À2 day À1 ) over 5 days on a 28-day cycle for 12 cycles. Response assessment included baseline and three-monthly magnetic resonance imaging studies (pretreatment, 3, 6, 9 and 12 months) assessing the tumour size. Short (TE (echo time) ¼ 20 ms) and long (TE ¼ 135 ms) echo time single voxel spectroscopy was performed in parallel to determine metabolite profiles. The mean tumour volume change at the end of treatment was À33% (s.d. ¼ 20). The dominant metabolite in long echo time spectra was choline. At 12 months, a significant reduction in the mean choline signal was observed compared with the pretreatment (P ¼ 0.035) and 3-month scan (P ¼ 0.021). The reduction in the tumour choline/water signal paralleled tumour volume change and may reflect the therapeutic effect of temozolomide.

When summing the spectra acquired with phased array coils, signals with low signal-to-noise ratio or wrongly corrected phase may degrade the overall signal-to-noise ratio (SNR). Here we present a mathematical expression predicting the dependence of combined SNR on the signal-to-noise ratios and errors in phase correction of composite signals. Based on this equation, signals that do not lead to an overall increase in signal-to-noise ratio can be identified and excluded from the weighted sum of signals. This tool is particularly useful for the combination of large numbers of signals. Additionally, a simple and robust algorithm for calculating the complex weighting factors necessary for the signal-to-noise weighted combination of spectroscopic data is presented. Errors in the calculation and correction of relative phase differences between composite spectra are analysed. The errors have a negligible effect on the overall spectral SNR for typical clinical magnetic resonance spectroscopy (MRS). The signal combination routine developed here has been applied to the first in vivo MRS study of human rectal adenocarcinomas at 1.5 T (Dzik-Jurasz A S K, Murphy P S, George M, Prock T, Collins D J, Swift I and Leach M O 2001 Magn. Reson. Med. at press), showing improvements of combined spectral SNR of up to 34% over the maximum SNR from a single element.

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