I J Rowland

Monitoring temozolomide treatment of low-grade glioma with proton magnetic resonance spectroscopy

Assessment of low-grade glioma treatment response remains as much of a challenge as the treatment itself. Proton magnetic resonance spectroscopy (1H-MRS) and imaging were incorporated into a study of patients receiving temozolomide therapy for low-grade glioma in order to evaluate and monitor tumour metabolite and volume changes during treatment. Patients (n=12) received oral temozolomide (200u2009mgu2009m−2u2009day−1) 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)=20u2009ms) and long (TE=135u2009ms) echo time single voxel spectroscopy was performed in parallel to determine metabolite profiles. The mean tumour volume change at the end of treatment was −33% (s.d.=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=0.035) and 3-month scan (P=0.021). The reduction in the tumour choline/water signal paralleled tumour volume change and may reflect the therapeutic effect of temozolomide.

Vascular occlusion using focused ultrasound surgery for use in fetal medicine

OBJECTIVEnFocused ultrasound surgery (FUS) is being developed clinically for the non-invasive treatment of soft tissue tumours of the prostate, bladder, liver, kidney, muscle and breast. In the work described in this paper, the application of FUS is extended to investigate the potential to induce vascular occlusion, with the aim of applying the technique to problems in fetal medicine and oncology.nnnMETHODSnIn this feasibility study the occlusion of femoral blood flow in vivo is demonstrated using an array of multiple single exposures of 1.7 MHz focused ultrasound. These were placed in two rows of four lesions at a focal depth of 5 mm. The 4660-W cm-2 (free field spatial peak intensity) 2-s exposures were placed 2 mm apart. Vascular patency was assessed using a Siemens Vision (1.5T) magnetic resonance (MR) imaging scanner with an extremity coil, and intravenous gadolinium contrast agent. FLASH and FISP MR sequences were used to obtain full 3D data sets providing information on soft tissue damage and perfusion.nnnRESULTS AND CONCLUSIONnTotal vascular occlusion was achieved in four of nine cases and significant vascular disruption in five of nine cases. Refinement of the FUS technique and long-term studies are now indicated prior to initial clinical application in fetal medicine.

Preclinical development of noninvasive vascular occlusion with focused ultrasonic surgery for fetal therapy

OBJECTIVEnThis study was undertaken to investigate the ability of focused ultrasonic surgery to occlude blood flow in vivo.nnnSTUDY DESIGNnA 5-mm linear track exposure of 1.7-MHz focused ultrasound was applied across the femoral vessels for 5 seconds. Free field spatial peak intensities in the range of 1,000 to 4,660 W x cm(-2) were used. Vascular occlusion was confirmed after demonstration of an absent distal arterial pulse and an absent flow signal on magnetic resonance angiography and subtracted (after minus before) contrast-enhanced dual-echo steady-state sequences.nnnRESULTSnThe minimum intensity for consistent vascular occlusion was 1,690 W x cm(-2) at a focal depth of 5 mm when the transducer was moved at 1 mm x s(-1) orthogonal to the direction of blood flow.nnnCONCLUSIONSnThis study demonstrates that focused ultrasonic surgery can achieve reproducible vascular occlusion in vivo. Potential obstetric applications include noninvasive ultrasonographically guided occlusion of placental vessels mediating interfetal transfusion in monochorionic twins.

Gallbladder localization of 19F MRS catabolite signals in patients receiving bolus and protracted venous infusional 5-fluorouracil

The hepatobiliary distribution of 5‐fluorouracil (5FU) catabolites was investigated in nine patients. Using fluorine 3D‐chemical shift imaging, four patients receiving protracted venous infusion of 5FU demonstrated catabolite localized to the gallbladder. No hepatobiliary fluorine signals were detected in three patients whose gallbladders were absent or abnormal. Signals from the gallbladder showed a 2.2–2.4 ppm high‐frequency shift from α‐fluoro‐β‐alanine, suggesting the presence of α‐fluoro‐β‐alanine‐bile‐acid conjugates. 3D‐chemical shift imaging of two patients receiving bolus 5FU revealed α‐fluoro‐β‐alanine to be localized to the liver within 1 hr of administration. In one patient examined 4 hr after bolus administration, catabolite signal was detected only in the gallbladder. Magn Reson Med 44:516–520, 2000.

The quantitative 19F-imaging of albumin at 1.5 T: a potential in-vivo tool.

19F-MR-imaging has been used to quantitate albumin concentration in a phantom at 1.5 T. The experimentally derived relationship between albumin concentration and the T1 relaxation time of a fluorinated marker, tetrafluorosuccinic acid (TFSA) was used to calculate the albumin concentration from a quantitative 19F T1 map acquired using a gradient echo sequence. There was close correlation between calculated and actual BSA concentrations (r = 0.99, SE = 0.15). The potentially interfering effect of paramagnetic species on T1 relaxation times was also investigated. Relaxivity data show that albumin concentration measurements should be performed prior to any contrast agent administration.

Focused ultrasound surgery-induced vascular occlusion in fetal medicine

Aim: This study investigates whether it is possible to occlude blood flow in vivo using high intensity focused ultrasound surgery (FUS). Such an effect could be used in the non-invasive treatment of fetal dysfunctions. Conclusion: Our ability to curtail blood flow using FUS allows the possibility of non-invasively treating feto-fetal transfusion syndrome by occluding the placental shunt vessels responsible for the vascular imbalance in twins sharing a placenta. This would have advantages over currently available interventional treatments (surgery or intrauterine lasers), which have significant related mortality and morbidity.

Intravascular delivery of hyperpolarized129Xenon forin vivo MRI

The nuclear polarization of129Xe and3He can be enhanced by several orders of magnitude by using optical pumping techniques, thus allowing NMR detection of xenon and helium in very low concentrations. The benefits of optically enhanced magnetic resonance (MR) are already exploited in MR imaging of the lungs using optically polarized3He. The high solubility of xenon in blood and lipids suggests a variety ofin vivo MR applications, for instance perfusion measurements or functional MR studies. This article reviews some current work directed towards delivery of optically polarized xenon forin vivo MR applications.

Occlusion of blood flow by high‐intensity focused ultrasound

This work investigates the possiblity of occluding blood flow (in vivo) using high‐intensity focused ultrasound surgery (FUS). Such an effect could be used, for example, in the noninvasive treatment of foetal dysfunctions. A high‐power 1.7‐MHz, 150‐mm focal length, piezoelectric transducer was used to expose rat femoral vessels to a free field I−SP=4660 W cm−2 for 2 s under terminal anaesthesia. Initially, eight separate exposures were used. Later experiments were aimed at determining an optimal single exposure to produce flow occlusion. Before and after exposure, magnetic resonance FISP 3‐D angiograms (MRA) with submillimeter spatial resolution were acquired using a Siemens Vision MR System (1.5T) and extremity coil. In all animals, MRA showed reduced blood flow both in the treated region and distal to it. The results of single‐dose optimization will be discussed. The ability to curtail blood flow using FUS allows the possibility of treating Foeto‐Foetal Transfusion Syndrome by occluding the placental sh...