Breast MRI is frequently performed prior to breast conserving surgery in order to assess the location and extent of the lesion. Ideally, the surgeon should also be able to use the image information during surgery to guide the excision and this requires that the MR image is co-registered to conform to the patient's position on the operating table. Recent progress in MR imaging techniques has made it possible to obtain high quality images of the patient in the supine position which significantly reduces the complexity of the registration task. Surface markers placed on the breast during imaging can be located during surgery using an external tracking device and this information can be used to co-register the images to the patient. There remains the problem that in most clinical MR scanners the arm of the patient has to be placed parallel to the body whereas the arm is placed perpendicular to the patient during surgery. The aim of this study is to determine the accuracy of co-registration based on a surface marker approach and, in particular, to determine what effect the difference in a patient's arm position makes on the accuracy of tumour localization. Obtaining a second MRI of the patient where the patient's arm is perpendicular to body axes (operating room position) is not possible. Instead we obtain a secondary MRI scan where the patient's arm is above the patient's head to validate the registration. Five patients with enhancing lesions ranging from 1.5 to 80 cm3 in size were imaged using contrast enhanced MRI with their arms in two positions. A thin-plate spline registration scheme was used to match these two configurations. The registration algorithm uses the surface markers only and does not employ the image intensities. Tumour outlines were segmented and centre of mass (COM) displacement and Dice measures of lesion overlap were calculated. The relationship between the number of markers used and the COM-displacement was also studied. The lesion COM-displacements ranged from 0.9 to 9.3 mm and the Dice overlap score ranged from 20% to 80%. The registration procedure took less than 1 min to run on a standard PC. Alignment of pre-surgical supine MR images to the patient using surface markers on the breast for co-registration therefore appears to be feasible.

Dynamic contrast enhanced (DCE) MRI has high sensitivity for the detection of breast cancer [1–3] and provides accurate assessment of the extent and presence of multi-focal disease [4–6]. DCE breast MRI is an attractive and powerful three-dimensional tool for the breast surgeon, because it results in excellent selection of patients for breast conserving surgery and low rates of positive histologic margins [7]. Usually, breast MRI is performed in the prone position to overcome motion artifacts from respiration thereby providing high resolution imaging. However in this configuration, the breast shape and tumor location are significantly altered when compared to the actual configuration found in the surgical setting where the patient is supine on the operating room table. In order to match the breast configuration to the surgical setting, breast MRI with supine positioning of the patient has been suggested [8,9]. In studies performed on patients with known breast abnormalities, supine breast MRI is able to depict the lesion of interest and the corresponding contrast enhancement dynamic [9]. Supine positioning simplifies the registration of supine MR images to the operating room and therefore aids breast conserving surgery using MRI. The biggest change of the breast conformation between a supine breast MRI and the later situation in the OR is expected to be caused by the different arm positions in the two settings. While the arm of the patient is parallel to the body during the supine MRI, it is commonly positioned perpendicular to the body axis during the surgery. Any registration algorithm should correct for the corresponding positional changes of the breast which may occur. Because the breast is highly deformable, this could be a challenging task. In this preliminary study, supine MRI images were acquired with the arm of the patient adjacent to the body and the arm placed above the head. Since the arm position during surgery is an intermediate of these positions, the result of the registration between these two data-sets provides a first measure of the tumour localization accuracy during surgery using image-guidance based on supine breast MRI.

PURPOSE:To achieve high-quality unilateral supine breast magnetic resonance imaging (MRI) as a step to facilitate image aiding of clinical applications, which are often performed in the supine position. Contrast-enhanced breast MRI is a powerful tool for the diagnosis of cancer. However, prone patient positioning typically used for breast MRI hinders its use for image aiding.MATERIALS AND METHODS:A fixture and a flexible four-element receive coil were designed for patient-specific shaping and placement of the coil in close conformity to the supine breast. A 3D spoiled gradient sequence was modified to incorporate compensation of respiratory motion. The entire setup was tested in volunteer experiments and in a pilot patient study.RESULTS:The flexible coil design and the motion compensation produced supine breast MR images of high diagnostic value. Variations in breast shape and in tissue morphology within the breast were observed between a supine and a diagnostic prone MRI of a patient.CONCLUSION:The presented supine breast MRI achieved an image quality comparable to diagnostic breast MRI. Since supine positioning is common in many clinical applications such as ultrasound-guided breast biopsy or breast-conserving surgery, the registration of the supine images will aid these applications.

Purpose: To evaluate three multicoil breast arrays for both conventional and SENSE-accelerated imaging. Materials and Methods: Two commercially available 8-element coils and a prototype 16-element coil were compared. One 8-element array had adjustable coils located next to the breast tissue and the other had a fixed coil arrangement; both were designed to allow parallel imaging in the left-right direction. The 16-element coil was designed to have coil sensitivity variation in both the left-right and superior-inferior directions, and also had adjustable coils. Their performance was assessed in terms of signal-to-noise ratio (SNR). g-factor. and uniformity with a custom-built phantom. Results: The 16-element array with adjustable coils provided the highest SNR, while the 8-element coil with a fixed coil arrangement had the best uniformity. All coils performed well for SENSE acceleration in the left-right direction. The 8-element coils did not have the capability for acceleration in the superior-inferior direction across the whole volume. The 16-element coil enabled acceleration in the superior-inferior direction in addition to the left-right direction. Conclusion: Smaller, adjustable coil elements located next to breast tissue can provide greater SNR than larger, fixed coil elements. A multicoil breast array with high intrinsic SNR and low g-factors enables high-quality parallel imaging.

Abstract A new method to produce covariance or dispersion matrices for the resonance parameters of neutron cross sections was developed. The technique uses resonance shape analysis in association with Monte Carlo treatment of the uncertainties. The method was implemented in the error propagation tool MCFIT. This program provides a user-friendly textual interface for the shape analysis code REFIT. It was designed to take into account the main sources of uncertainties involved in time-of-flight measurements. Its capability is illustrated with the simultaneous analysis of 237Np capture and transmission data. The covariance matrix obtained in this work was used to interpret oscillation measurements of 237Np samples carried out in the Minerve reactor located at Cadarache.

In static magnetic resonance elastography, the elasticity of an object is determined by measuring the internal displacement between two compression states. To reduce signal loss during the long time delay between application of external deformation and the static compression state, a STEAM sequence with a long mixing time is used This results in long scan times. The aim of this work was the development of a STEAM sequence with a multi-echo-readout, which allows the reduction of scan time and number of necessary external deformations. This new sequence was compared to the standard STEAM sequence on an agarose gel phantom with a hard inclusion. In addition, the elasticity of thermal tissue lesions was investigated, which were induced using high-intensity focused ultrasound (HIFU). During a given measurement time, more acquisitions per image can be taken using the multi-echo-readout. As a result the signal-to-noise ratio is increased and errors in the data become clearly smaller. Drawbacks of. the new sequence are its higher signal loss due to T2-decay and its greater sensitivity against ghosting artefacts caused by k-space segmentation. During the investigation of the thermally-induced lesions, a clear contrast in elasticity between normal tissue and the treated region was observed. Taking advantage of the greater accuracy of the new STEAM sequence, it was shown, that this contrast is significantly larger than the one in conventional MR parameters.

Therapy with high intensity focused ultrasound (HIFU) has been shown to be both safe and clinically practical in a growing number of patient studies for a variety of different target organs. Especially in cancer therapy there are comparable ablation methods like radio frequency (RFA) or laser (LITT) ablation, which are clinically more accepted. In an ongoing study we compare HIFU with RF- and laser ablation under MRI guidance in a perfused organ model. All evaluated techniques were appropriate to induce defined and localized ablation necrosis in the renal cortex. Our HIFU system and the laser system were completely MRI compatible. The tested RF- system showed local needle artefacts and disturbed the MR images during operation. The ablation rate of HIFU using a spot scanning technique was clearly lower compared to the other ablation techniques. However, advanced HIFU scanning methods might overcome this limitation. In addition HIFU is the only complete non-invasive ablation technique.

Dynamic, contrast-enhanced breast MRI (DCE-MRI) has been shown to be more accurate than mammography, ultrasound and clinical breast exam for the identification of tumour extent in the breast. However, DCE breast MRI is not currently utilized for the guidance of breast conservation surgery, primarily due to the differences in breast positioning during the MR imaging compared to the positioning in the surgical theatre. Therefore a supine positioning of the patient during MR imaging is preferred, which should result in a better matching of the images of the preoperative MRI and the later positioning in the operating room.

In static magnetic resonance elastography, the elasticity of an object is determined by measuring the internal displacement between two compression states. To reduce signal loss during the long time delay between application of external deformation and the static compression state, a STEAM sequence with a long mixing time is used. This results in long scan times. The aim of this work was the development of a STEAM sequence with a multi-echo-readout, which allows the reduction of scan time and number of necessary external deformations. This new sequence was compared to the standard STEAM sequence on an agarose gel phantom with a hard inclusion. In addition, the elasticity of thermal tissue lesions was investigated, which were induced using high-intensity focused ultrasound (HIFU). During a given measurement time, more acquisitions per image can be taken using the multi-echo-readout. As a result the signal-to-noise ratio is increased and errors in the data become clearly smaller. Drawbacks of the new sequence are its higher signal loss due to T-2-decay and its greater sensitivity against ghosting artefacts caused by k-space segmentation. During the investigation of the thermally-induced lesions, a clear contrast in elasticity between normal tissue and the treated region was observed. Taking advantage of the greater accuracy of the new STEAM sequence, it was shown, that this contrast is significantly larger than the one in conventional MR parameters.

The aim of this work was to visualize the HIFU (high intensity focused ultrasound) induced lesion formation. For that purpose a tissue mimicking transparent egg white phantom was used. Investigation on lesion growth was conducted with different parameters. The ultrasonic exposure time, the applied power and the pause time between two consecutive sonications were varied. Additionally magnet resonance imaging (MRI) was employed to monitor the temperature during sonication and to verify the formed lesions. Moreover HIFU ablation was compared to radio frequency ablation (RFA) technique with identical phantoms. Using the transparent egg white phantoms allows the direct observation of lesion formation during HIFU. These phantoms offer the possibility to study the influence of various ultrasound parameters on lesion growth.

Objectives: Exogenous magnetic resonance (MR) contrast media (CM) are used to improve detection and delineation of physiological and pathologic structures. Temporary binding between CM and proteins such as human serum albumin (HSA) may alter the relaxation-enhancing properties of specific contrast agents. In this study, the presence and strength of HSA interaction with different CM was investigated.Material and Methods: Three contrast agents were chosen: GdDTPA, Gd-BT-DO3A, and Gd-BOPTA, each of which is known to have a different protein interaction. Samples were prepared using 7 different HSA concentrations, all at a constant CM concentration of 0.5 mmol/L. The relaxation rates, R1 and R2, of each sample were measured at 1.5 T. Virtual docking studies were performed to estimate the number of high affinity-binding sites of Gd-BOPTA and the surface of the HSA dimer.Results: Gd-BOPTA caused the greatest increase in R1 and R2, which followed an exponential dependency with increasing HSA concentration. Between the range of 0 and 7 g/dL of HSA, GdDTPA and Gd-BT-DO3A showed a relative change in both relaxation rates of approximately 13% and 22% for R1 and 26% and 30% for R2, respectively. In contrast, Gd-BOPTA demonstrated a relative increase of approximately 108% and 363% for R1 and R2, respectively. Changes of HSA concentration within physiological range (3.5-5.5 g/dL) resulted in an increase of RI and R2 of approximately 40% when using Gd-BOPTA. The docking study revealed that approximately 10 small hydrophobic pockets exist on the HSA surface where the aromatic tail of Gd-BOPTA can fit in and a stronger noncovalent binding can occur compared with Gd-DTPA and Gd-BT-DO3A.Conclusion: Relaxation rates of Gd-BOPTA showed a strong dependency on HSA. In contrast, Gd-DTPA and Gd-BT-DO3A demonstrated little or no relevant dependency. On the basis of these results, the influence of serum protein concentration should be considered in both research studies and in clinical use.

High intensity focused ultrasound (HIFU) is a method for non-invasive tumor therapy. The high energy density in the focal spot leads to local tissue heating and finally to thermal coagulation in the focal area (Fig.1) [1]. To monitor this treatment, the focus position can be detected online with temperature sensitive MR imaging. However characterization of the induced lesion is difficult. It has been shown that HIFU lesions have a decreased elasticity and that the change in elasticity is larger than change in relaxation times [2]. This new parameter for characterization of the lesions can be measured with MR elastography (MRE). In dynamic MRE [3], images of mechanical wave propagation are acquired using oscillating bipolar gradients. Determination of the local wavelength allows reconstruction of the local elasticity. The problem to generate mechanical waves inside samples can be solved using HIFU itself: The ultrasound absorption in the tissue causes a small but continuous radiation force in the direction of wave propagation. The radiation force has its maximum in the focus of the sound field. Thus a pulsed HIFU sonication induces shear waves with a propagation perpendicular to the sound direction and with the ultrasound focus as the origin point (Fig. 1) [4]. The aim of this work is to improve the significance of the HIFU therapy control by visualization of the generated shear waves using dynamic MRE.

During the last decade there has been a growing interest in Partitioning and Transmutation technologies as a means of strongly reducing the long-term radiotoxic inventory of nuclear waste. Main emphasis has been placed on the burning of minor actinides (MA) and of long-lived fission products (LLFP). In order to contribute building a sound data base for the neutron induced reactions of the concerned isotopes, a collaboration has been started in 1995 between the Service de Physique Nuclaire of CEA France and the Institute for Reference Materials and Measurements of Geel, Belgium. In the frame of this co-operation, a mixed group of scientists carries out measurements and analysis of neutron capture and transmission cross sections at the GELINAtime-of-flight facility of the IRMM. An important preparatory activity is also the procurement of such radioactive isotopes and the production of gram-quantity samples, a work that is also carried out at the IRMM, Geel. The isotopes investigated so far are 99Tc, 129I and 237Np. Work on 99Tc, which is considered the most offending LLFP, is practically completed: a total of 659 resonances have been analyzed up to 10 keV neutron energy making use of both capture and transmission data. Spin has also been assigned to 51 s-wave levels. Quantities such as the average level spacing, the average capture width and the strength function for s- and p-wave levels have been derived from such a large sample of resonances. Average capture and transmission cross sections have also been determined in the unresolved region from 10 to 150 keV. The analysis of 237Np transmission data has allowed to determine the neutron widths, and at low energy also the capture widths, of some 570 resonances below 500 eV and preliminary data up to 1 keV are available. Preliminary results of 129I transmission measurements below 1 keV energy are presented at this conference in a separate contribution. 1)

Transmission time-of-flight measurements (TOF) for natural hafnium were performed in the energy range from 2 eV to 50 keV at the white neutron source GELINA of the Institute for Reference Materials and Measurements (IRMM) in Geel, Belgium. Experimental transmission data for 77 K and 300 K and for 3 different sample thicknesses are compared to theoretical transmission values. These were obtained using the code CALENDF with input from ENDF/B6.3, JENDL3.2 and JEF2.2.

Within the framework of a collaboration between the Institute for Reference Materials and Measurements (IRMM) and the Commissariat à l’Énergie Atomique (CEA), a project has been started to study neutron cross sections for nuclear waste transmutation purposes. We describe the measurements of the total neutron cross section of Np, performed at the pulsed white neutron source GELINA of the IRMM. We used the time of flight method to obtain neutron spectra in the energy range from 0.3 eV to 2 keV. A preliminary list of new resonances under 120 eV is presented here. Besides these measurements, the Doppler effect has also been investigated for NpO2. We will show how the use of an harmonic crystal model for Doppler broadening can explain some unexpected effects in the fit of the resonances.

Within the framework of a collaboration between the Institute for Reference Materials and Measurements (IRMM) and the Commissariat à l'Energie Atomique (CEA), a project has been started to measure neutron cross sections for nuclear waste transmutation purposes. We describe the measurements of the neutron total and capture cross section of 237Np, performed at the pulsed white neutron source GELINA of the IRMM in Geel (Belgium). We used the time of flight method to obtain neutron spectra in the energy range from 0.3 eV to 2 keV. Preliminary resonance parameters obtained from transmission experiments below 112 eV and comparison with previous measurements are presented here. Besides these measurements, the Doppler effect has also been investigated for NpO 2. We show that the use of a harmonic crystal model gives a better fit of the resonances.