WE-G-217A-09: Phase Imaging Measurement of Static Magnetic Field Homogeneity

PURPOSE

The ACR MRI accreditation program requires measurement of the magnetic field homogeneity (MFH) in the annual QA. Full implementation of vendor methods can be very time consuming and incorporates techniques not available to clinical physicists. Conversely, many of the less involved techniques proposed tend to be less inaccurate and/or precise. Here, we propose a robust approach to MFH analysis using a simple phase mapping acquisition which is a time efficient compromise.

METHODS

The root mean square (r.m.s.) for MFH measurement is commonly used over multiple slices (∼24). In regions with high SNR, the MR signal can be reasonably assumed Gaussian distributed. Therefore, the standard deviation of phase values in ROI is equivalent to the r.m.s. of those. The standard deviations of phases in x, y and z are assumed uncorrelated. Thus, only axial, sagittal and coronal planes need to be acquired to approximate the MFH as opposed to a full 3D acquisition. To investigate this concept, phase images were acquired on four 1.5T clinical scanners and one 3.0 clinical scanner (MAGNETOM Espree, Siemens Medical Systems, Signa Excite HD 1.5T, and 3.0T GE Healthcare Technologies). The manufacturer phantoms were scanned using two echo times (delta_TE=TE2-TE1<5ms) using a simple 2D gradient echo acquisition to produce phase images. After acquiring phase difference images in three orthogonal planes, the standard deviation was calculated in three circular ROIs (Diameter=10, 20 and 30cm) in each plane, respectively, to estimate the MFH for the effective DSV.

RESULTS

The MFH values in five scanners using this method were within vendor specifications for the DSV. Additionally, the measured MFH values compared favorably with vendor planned maintenance records with <0.1 ppm discrepancy.

CONCLUSIONS

This proposed method may be a reliable and practical for regular MFH measurement in QA programs and providing an independent check of the vendor measurement.

Role of matrix metalloproteinase-8 in the modulation of systemic 5-fluorouracil pharmacokinetics by local irradiation

466

Background: Concurrent chemoradiation with 5-fluorouracil (5-FU) is widely accepted for cancer treatment. However, the interactions between radiation and 5-FU remain unclear. We evaluated the influence of local irradiation on the pharmacokinetics of 5-FU in rats.

Methods: The single-fraction radiation was delivered to the whole pelvic fields of Sprague-Dawley rats from a linear accelerator after computerized tomography-based planning. 5-FU at 100 mg/kg was intravenously infused 24 hours after radiation. A high-performance liquid chromatography system equipped with a UV detector was used to measure 5-FU in the blood. Matrix metalloproteinase-8 (MMP-8) inhibitor I was administered to the rats to examine whether or not RT modulation of 5-FU pharmacokinetic parameters could be blocked.

Results: Compared with sham-irradiated controls, whole pelvic irradiation reduced the area under the concentration versus time curve (AUC) of 5-FU in plasma and, in contrast, increased the AUC in bile in a radiation dose-dependent manner. Based on protein array analysis, the amount of plasma MMP-8 was increased by whole pelvic irradiation (2.8-fold by 0.5 Gy and 5.3-fold by 2 Gy) in comparison with controls. Pretreatment with MMP-8 inhibitor reversed the effect of irradiation on AUC of 5-FU in plasma.

Conclusions: Local irradiation may modulate the systemic pharmacokinetics of 5-FU through stimulating the release of MMP-8. This unexpected influence is worthy of further investigation and for consideration in clinical practice of radiotherapy for cancer.

No significant financial relationships to disclose.

Effect of interfacial shallow traps on polaron transport at the surface of organic semiconductors

The photo-induced electron and hole transfer across the semiconductor-dielectric interface in trap-dominated p-type organic field-effect transistors has been investigated. It has been observed that the transfer of electrons into the dielectric results in a decrease of the field-effect mobility of polarons, suggesting that additional shallow traps are generated in the conduction channel. Using this effect, the dependence of the field-effect mobility on the density of shallow traps, mu(N), has been measured, which allowed us to estimate the average polaron trapping time, tau_{tr}=50+/-10 ps, and the density of shallow traps, N0=(3+/-0.5) x 10(11) cm(-2), in the channel of single-crystal tetracene devices.

Pegylated liposomal doxorubicin and platinum in patients with advanced ovarian cancer in late relapse (>6 months)

15035

Background: Platinum and doxorubicin have different mechanisms of action, show no cross-resistance, and their toxicities do not overlap. Because pegylated liposomaI doxorubicin (Lipo-Dox was manufactured by TTY Biopharm Company Ltd. in Taiwan) appears to be a promising form of delivering doxorubicin with decrease of some of the most problematic toxicities, a combination with platinum should be assessed. Methods: An open-label, non-comparative, single center phase II clinical trial. Eligible patients must have histologically proven advance ovarian cancer with two-dimensioned measurable disease or evaluable disease (defined as CA-125 ≥ 40 U/ml), who have been treated with one or two previous platinum- and taxane-based regimen. All patients will hospitalize for 24 hours for treatment. The dose of platinum is fixed (cisplatin at 75 mg/m2 or carboplatin at AUC=5) on D1 and the initial dose of pegylated liposomaI doxorubicin (Lipo-Dox) is 35 mg/m2 on D2 at a 4-week interval. Results: Twenty patients were enrolled from July 2002 to January 2004 and follow up until June 2004. All eligible patients are assessable for response and toxicity. The overall response rate was 80%. Of the 20 patients eligible for response evaluation, 10 (50%) patients had a complete response, 6 (30%) had partial response, 3 (15%) were with stable disease, and 1 (5%) showed progressive disease. An overall response (OR) was achieved in 80% of patients. In patients achieving an OR based on WHO criteria, median CA125 levels declined from 142 U/ml (range, 13–3670 U/ml) during the baseline to 26.5 U/ml (range, 5–375 U/ml) during the last cycle. Median time to response was 65 days (range, 12–188 days). Median duration of response was 471 days (range 146–1085 days). Furthermore, the median time to progression was 481 days (range, 138–1136 days). The main toxicity was myelosuppression, with grade 3 and 4 neutropenia in 3 patients, anemia in 4 patients, and leukopenia in 2 patients. Conclusions: Based on effectiveness and toxicity advantages, the combination of pegylated liposomaI doxorubicin (Lipo-Dox) and platinum should be considered in patients with advanced ovarian cancer in late relapse.

No significant financial relationships to disclose.

Focused ion beam milling of vitreous water: prospects for an alternative to cryo-ultramicrotomy of frozen-hydrated biological samples

The feasibility of using a focused ion beam (FIB) for the purpose of thinning vitreously frozen biological specimens for transmission electron microscopy (TEM) was explored. A concern was whether heat transfer beyond the direct ion interaction layer might devitrify the ice. To test this possibility, we milled vitreously frozen water on a standard TEM grid with a 30-keV Ga(+) beam, and cryo-transferred the grid to a TEM for examination. Following FIB milling of the vitreous ice from a thickness of approximately 1200 nm to 200-150 nm, changes characteristic of heat-induced devitrification were not observed by TEM, in either images or diffraction patterns. Although numerous technical challenges remain, it is anticipated that 'cryo-FIB thinning' of bulk frozen-hydratred material will be capable of producing specimens for TEM cryo-tomography with much greater efficiency than cryo-ultramicrotomy, and without the specimen distortions and handling difficulties of the latter.