Improve Image Contrast Research Articles

SU‐E‐T‐325: Dosimetric Impact Due to FlexiShield in Electronic Brachytherapy (eBx) of Breast IORT: A Phantom Study

Purpose:To evaluate dosimetric change of eBx plan due to Flexishield.Methods:To simulate a clinically difficult case (skin spacing < 1 cm and touching chest wall), prostheses breast tissue phantom overlaid Xoft spherical balloon applicator. To minimize significant metal streak artifact, megavoltage CT (MVCT) scan was acquired using helical TomoTherapy HiART. Two sets of MVCT images were taken with/without FlexiShield for 15 cases: 4 for small (3–4 cm), 4 for medium (4–5 cm) and 7 for large (5–6 cm) balloon. Total 30 MVCT scans were obtained with 50 % contrast to improve image contrast of balloon relative to breast tissue phantom. Balloon deformation was measured in anterior‐posterior (AP) and lateral (LAT) dimensions in the middle of balloon. Skin spacing was also evaluated. Treatment plan was made based on each MVCT scan and two balloon surface doses (AP and LAT directions) and skin dose were compared between plans with/without FlexiShield.Results:The balloon was deformed due to pressure from both FlexiShield (skin side) and FlexiShield mini (chest wall side). Mean ± standard deviation (maximum) value was 1.5 ± 1.0 mm (3.3 mm) for AP compression and 0.4 ± 0.3 mm (1.1 mm) for LAT expansion. Balloon surface dose was increased by 1.8 ± 1.2 Gy (4.9 Gy) at AP point and decreased by 0.4 ± 0.4 Gy (1.3 Gy) at LAT point. Skin spacing was constantly reduced by 1.1 ± 0.8 mm (3 mm). Skin surface dose was increased by 1.5 ± 0.8 Gy (3.3 Gy) and its relative increase was 17.9 ± 9.3% (39.6%).Conclusion:FlexiShield deforms the balloon and reduces skin spacing, thereby resulting in higher dose in AP direction, lower dose in LAT direction, and elevated skin dose compared to the plan without FlexiShield. In the clinic, this balloon deformation and corresponding dose variation should be considered.

TH‐CD‐210‐00: Nuclear Medicine 102

There have been significant recent advances in SPECT/CT and PET/CT for Oncology and Cardiology. In oncologic imaging, some commercial SPECT/CT systems now output quantitative uptake values; calibration and calculation of these quantitative uptake values will be discussed. Advances in PET detector design and PET data acquisition modes that have implemented in commercial PET/CT systems will be presented. Innovations in iterative reconstruction of SPECT/CT and PET/CT will also be described.In cardiac imaging, novel collimator designs, such as multi‐pinhole and locally focusing collimators arranged in geometries that are optimized for cardiac imaging have been implemented to reduce imaging time and radiation dose. These new collimators have been coupled with solid‐state photon detectors. The new SPECT scanners demonstrate up to a 7‐fold increase in photon sensitivity and up to 2 times improvement in image resolution. Although PET scanners are used primarily for oncological imaging, cardiac imaging can benefit from the improved PET sensitivity of 3D systems without inter‐plane septa and implementation of the time‐of‐flight reconstruction. Additionally, all major PET vendors now implement resolution recovery techniques. These new methods improve image contrast, image resolution, and reduce image noise for cardiac imaging. New quantification techniques have been proposed for analysis of cardiac SPECT and PET images. These include direct change analysis, motion‐frozen analysis, hybrid quantification of SPECT and anatomical CT angiography data, and integration of several quantitative parameters in composite scores.Learning Objectives: To discuss clinical implementation of commercial quantitative SPECT/CT systems To describe advances in PET detector design and data acquisition To report on innovations in iterative reconstruction of SPECT/CT and PET/CT 4 Describe novel hardware designed for cardiac SPECT Understand how recent hardware advances in PET/CT are relevant to cardiology Describe new software techniques for quantification of cardiac SPECT and PET

TH‐CD‐210‐02: Advances in SPECT, SPECT/CT and PET/CT for Cardiology

There have been significant recent advances in SPECT/CT and PET/CT for Oncology and Cardiology. In oncologic imaging, some commercial SPECT/CT systems now output quantitative uptake values; calibration and calculation of these quantitative uptake values will be discussed. Advances in PET detector design and PET data acquisition modes that have implemented in commercial PET/CT systems will be presented. Innovations in iterative reconstruction of SPECT/CT and PET/CT will also be described.In cardiac imaging, novel collimator designs, such as multi‐pinhole and locally focusing collimators arranged in geometries that are optimized for cardiac imaging have been implemented to reduce imaging time and radiation dose. These new collimators have been coupled with solid‐state photon detectors. The new SPECT scanners demonstrate up to a 7‐fold increase in photon sensitivity and up to 2 times improvement in image resolution. Although PET scanners are used primarily for oncological imaging, cardiac imaging can benefit from the improved PET sensitivity of 3D systems without inter‐plane septa and implementation of the time‐of‐flight reconstruction. Additionally, all major PET vendors now implement resolution recovery techniques. These new methods improve image contrast, image resolution, and reduce image noise for cardiac imaging. New quantification techniques have been proposed for analysis of cardiac SPECT and PET images. These include direct change analysis, motion‐frozen analysis, hybrid quantification of SPECT and anatomical CT angiography data, and integration of several quantitative parameters in composite scores.Learning Objectives: To discuss clinical implementation of commercial quantitative SPECT/CT systems To describe advances in PET detector design and data acquisition To report on innovations in iterative reconstruction of SPECT/CT and PET/CT 4 Describe novel hardware designed for cardiac SPECT Understand how recent hardware advances in PET/CT are relevant to cardiology Describe new software techniques for quantification of cardiac SPECT and PET

TH‐CD‐210‐01: Recent Advances in SPECT/CT and PET/CT for Oncology

There have been significant recent advances in SPECT/CT and PET/CT for Oncology and Cardiology. In oncologic imaging, some commercial SPECT/CT systems now output quantitative uptake values; calibration and calculation of these quantitative uptake values will be discussed. Advances in PET detector design and PET data acquisition modes that have implemented in commercial PET/CT systems will be presented. Innovations in iterative reconstruction of SPECT/CT and PET/CT will also be described.In cardiac imaging, novel collimator designs, such as multi‐pinhole and locally focusing collimators arranged in geometries that are optimized for cardiac imaging have been implemented to reduce imaging time and radiation dose. These new collimators have been coupled with solid‐state photon detectors. The new SPECT scanners demonstrate up to a 7‐fold increase in photon sensitivity and up to 2 times improvement in image resolution. Although PET scanners are used primarily for oncological imaging, cardiac imaging can benefit from the improved PET sensitivity of 3D systems without inter‐plane septa and implementation of the time‐of‐flight reconstruction. Additionally, all major PET vendors now implement resolution recovery techniques. These new methods improve image contrast, image resolution, and reduce image noise for cardiac imaging. New quantification techniques have been proposed for analysis of cardiac SPECT and PET images. These include direct change analysis, motion‐frozen analysis, hybrid quantification of SPECT and anatomical CT angiography data, and integration of several quantitative parameters in composite scores.Learning Objectives: To discuss clinical implementation of commercial quantitative SPECT/CT systems To describe advances in PET detector design and data acquisition To report on innovations in iterative reconstruction of SPECT/CT and PET/CT 4 Describe novel hardware designed for cardiac SPECT Understand how recent hardware advances in PET/CT are relevant to cardiology Describe new software techniques for quantification of cardiac SPECT and PET

SU-C-201-05: Imaging 212Pb-TCMC-Trastuzumab for Alpha Radioimmunotherapy for Ovarian Cancer

Purpose: To support the phase I trial for toxicity, biodistribution and pharmacokinetics of intra-peritoneal (IP) 212Pb-TCMC-trastuzumab in patients with HER-2 expressing malignancy. A whole body gamma camera imaging method was developed for estimating amount of 212Pb-TCMC-trastuzumab left in the peritoneal cavity. Methods: 212Pb decays to 212Bi via beta emission. 212Bi emits an alpha particle at an average of 6.1 MeV. The 238.6 keV gamma ray with a 43.6% yield can be exploited for imaging. Initial phantom was made of saline bags with 212Pb. Images were collected for 238.6 keV with a medium energy general purpose collimator. There are other high energy gamma emissions (e.g. 511keV, 8%; 583 keV, 31%) that penetrate the septae of the collimator and contribute scatter into 238.6 keV. An upper scatter window was used for scatter correction for these high energy gammas. Results: A small source containing 212Pb can be easily visualized. Scatter correction on images of a small 212Pb source resulted in a ∼50% reduction in the full width at tenth maximum (FWTM), while change in full width at half maximum (FWHM) was <10%. For photopeak images, substantial scatter around phantom source extended to > 5 cm outside; scatter correction improved image contrast by removing this scatter around the sources. Patient imaging, in the 1st cohort (n=3) showed little redistribution of 212Pb-TCMC-trastuzumab out of the peritoneal cavity. Compared to the early post-treatment images, the 18-hour post-injection images illustrated the shift to more uniform anterior/posterior abdominal distribution and the loss of intensity due to radioactive decay. Conclusion: Use of medium energy collimator, 15% width of 238.6 keV photopeak, and a 7.5% upper scatter window is adequate for quantification of 212Pb radioactivity inside peritoneal cavity for alpha radioimmunotherapy of ovarian cancer. Research Support: AREVA Med, NIH 1UL1RR025777-01

Enhancement of Corneal Visibility in Optical Coherence Tomography Images Using Corneal Adaptive Compensation.

To improve the contrast of optical coherence tomography (OCT) images of the cornea (post processing). We have recently developed standard compensation (SC) algorithms to remove light attenuation artifacts. A more recent approach, namely adaptive compensation (AC), further limited noise overamplification within deep tissue regions. AC was shown to work efficiently when all A-scan signals were fully attenuated at high depth. But in many imaging applications (e.g., OCT imaging of the cornea), such an assumption is not satisfied, which can result in strong noise overamplification. A corneal adaptive compensation (CAC) algorithm was therefore developed to overcome such limitation. CAC benefited from local A-scan processing (rather than global as in AC) and its performance was compared with that of SC and AC using Fourier-domain OCT images of four human corneas. CAC provided considerably superior image contrast improvement than SC or AC did, with excellent visibility of the corneal stroma, low noise overamplification, homogeneous signal amplification, and high contrast. Specifically, CAC provided mean interlayer contrasts (a measure of high stromal visibility and low noise) greater than 0.97, while SC and AC provided lower values ranging from 0.38 to 1.00. CAC provided considerable improvement compared with SC and AC by eliminating noise overamplification, while maintaining all benefits of compensation, thus making the corneal endothelium and corneal thickness easily identifiable. CAC may find wide applicability in clinical practice and could contribute to improved morphometric and biomechanical understanding of the cornea.

Fast imaging of live organisms with sculpted light sheets.

Light-sheet microscopy is an increasingly popular technique in the life sciences due to its fast 3D imaging capability of fluorescent samples with low photo toxicity compared to confocal methods. In this work we present a new, fast, flexible and simple to implement method to optimize the illumination light-sheet to the requirement at hand. A telescope composed of two electrically tuneable lenses enables us to define thickness and position of the light-sheet independently but accurately within milliseconds, and therefore optimize image quality of the features of interest interactively. We demonstrated the practical benefit of this technique by 1) assembling large field of views from tiled single exposure each with individually optimized illumination settings; 2) sculpting the light-sheet to trace complex sample shapes within single exposures. This technique proved compatible with confocal line scanning detection, further improving image contrast and resolution. Finally, we determined the effect of light-sheet optimization in the context of scattering tissue, devising procedures for balancing image quality, field of view and acquisition speed.

A NEW COLOR CORRECTION METHOD FOR UNDERWATER IMAGING

Abstract. Recovering correct or at least realistic colors of underwater scenes is a very challenging issue for imaging techniques, since illumination conditions in a refractive and turbid medium as the sea are seriously altered. The need to correct colors of underwater images or videos is an important task required in all image-based applications like 3D imaging, navigation, documentation, etc. Many imaging enhancement methods have been proposed in literature for these purposes. The advantage of these methods is that they do not require the knowledge of the medium physical parameters while some image adjustments can be performed manually (as histogram stretching) or automatically by algorithms based on some criteria as suggested from computational color constancy methods. One of the most popular criterion is based on gray-world hypothesis, which assumes that the average of the captured image should be gray. An interesting application of this assumption is performed in the Ruderman opponent color space lαβ, used in a previous work for hue correction of images captured under colored light sources, which allows to separate the luminance component of the scene from its chromatic components. In this work, we present the first proposal for color correction of underwater images by using lαβ color space. In particular, the chromatic components are changed moving their distributions around the white point (white balancing) and histogram cutoff and stretching of the luminance component is performed to improve image contrast. The experimental results demonstrate the effectiveness of this method under gray-world assumption and supposing uniform illumination of the scene. Moreover, due to its low computational cost it is suitable for real-time implementation.

Lung dynamic MRI deblurring using low-rank decomposition and dictionary learning.

Lung dynamic MRI (dMRI) has emerged to be an appealing tool to quantify lung motion for both planning and treatment guidance purposes. However, this modality can result in blurry images due to intrinsically low signal-to-noise ratio in the lung and spatial/temporal interpolation. The image blurring could adversely affect the image processing that depends on the availability of fine landmarks. The purpose of this study is to reduce dMRI blurring using image postprocessing. To enhance the image quality and exploit the spatiotemporal continuity of dMRI sequences, a low-rank decomposition and dictionary learning (LDDL) method was employed to deblur lung dMRI and enhance the conspicuity of lung blood vessels. Fifty frames of continuous 2D coronal dMRI frames using a steady state free precession sequence were obtained from five subjects including two healthy volunteer and three lung cancer patients. In LDDL, the lung dMRI was decomposed into sparse and low-rank components. Dictionary learning was employed to estimate the blurring kernel based on the whole image, low-rank or sparse component of the first image in the lung MRI sequence. Deblurring was performed on the whole image sequences using deconvolution based on the estimated blur kernel. The deblurring results were quantified using an automated blood vessel extraction method based on the classification of Hessian matrix filtered images. Accuracy of automated extraction was calculated using manual segmentation of the blood vessels as the ground truth. In the pilot study, LDDL based on the blurring kernel estimated from the sparse component led to performance superior to the other ways of kernel estimation. LDDL consistently improved image contrast and fine feature conspicuity of the original MRI without introducing artifacts. The accuracy of automated blood vessel extraction was on average increased by 16% using manual segmentation as the ground truth. Image blurring in dMRI images can be effectively reduced using a low-rank decomposition and dictionary learning method using kernels estimated by the sparse component.

Nonlinear fluorescence imaging by photoinduced charge separation

Manipulation of the optical property of fluorescent probes has been a powerful strategy to establish super-resolution microscopy. We describe a new strategy to realize a probe with a nonlinear fluorescence response by using photoinduced charge separation. In this scheme, the first photon is used for the generation of the charge-separated state and the second photon is for fluorescence excitation. This stepwise two-photon absorption was confirmed by detection of a second-order nonlinear fluorescence response. Transient absorption spectra studies and simulation indicate that fluorescence is emitted through the photophysical pathways we proposed. Fluorescence imaging of biological cells showed marked improvements in image contrast and resolution, demonstrating the usefulness of the fluorescent probe in laser scanning confocal microscopy.

Exposure-based Weighted Dynamic Histogram Equalization for Image Contrast Enhancement

Global histogram equalization (GHE) [1] is a common method used for improving image contrast. However, this technique tends to introduce unnecessary visual artifacts and cannot preserve overall brightness. To overcome these problems, many ssudies have been conducted based on partitioned-histogram (i.e., sub-histogram) equalization. An input image is first divided into sub-images, individual histograms of the sub-images are equalized independently, and all of the sub-images are ultimately integrated into one complete image. For example, exposure-based sub-image histogram equalization (ESIHE) [2] uses an exposure-related threshold to divide the original image into different intensity ranges (horizontal partitioning) and also uses the mean brightness as a threshold to clip the histogram (vertical partitioning). In this paper, a novel method, called exposure-based weighted dynamic histogram equalization (EWDHE), which is an extension of ESIHE, is proposed. This study makes three major contributions to the literature. First, an Otsu-based approach and a clustering performance measure are integrated to determine the optimal number of sub-histograms and the separating points. Second, an exposure-related parameter is used to automatically adapt the contrast limitation, to avoid over-enhancement in some portions of the image. Third, a new weighted scale factor is proposed to resize the sub-histograms, which accounts for sub-histogram ranges and individual pixel numbers of these ranges. The simulation results indicated that the proposed method outperformed state-of-the-art approaches in terms of contrast enhancement, brightness preservation, and entropy preservation.

Photoacoustic radar phase-filtered spatial resolution and co-registered ultrasound image enhancement for tumor detection.

Co-registered ultrasound (US) and frequency-domain photoacoustic radar (FD-PAR) imaging is reported for the first time in this paper. The merits of ultrasound and cross-correlation (radar) frequency-domain photoacoustic imaging are leveraged for accurate tumor detection. Commercial US imagers possess sophisticated, optimized software for rapid image acquisition that could dramatically speed-up PA imaging. The PAR image generated from the amplitude of the cross-correlation between detected and input signals was filtered by the standard deviation (SD) of the phase of the correlation signal, resulting in strong improvement of image spatial resolution, signal-to-noise ratio (SNR) and contrast. Application of phase-mediated image improvement is illustrated by imaging a cancer cell-injected mouse. A 14-15 dB SNR gain was recorded for the phase-filtered image compared to the amplitude and phase independently, while ~340 μm spatial resolution was seen for the phase PAR image compared to ~840 μm for the amplitude image.

Advances in SPECT and PET Hardware

There have been significant recent advances in single photon emission computed tomography (SPECT) and positron emission tomography (PET) hardware. Novel collimator designs, such as multi-pinhole and locally focusing collimators arranged in geometries that are optimized for cardiac imaging have been implemented to reduce imaging time and radiation dose. These new collimators have been coupled with solid state photon detectors to further improve image quality and reduce scanner size. The new SPECT scanners demonstrate up to a 7-fold increase in photon sensitivity and up to 2 times improvement in image resolution. Although PET scanners are used primarily for oncological imaging, cardiac imaging can benefit from the improved PET sensitivity of 3D systems without inter-plane septa and implementation of the time-of-flight reconstruction. Additionally, resolution recovery techniques are now implemented by all major PET vendors. These new methods improve image contrast, image resolution, and reduce image noise. Simultaneous PET/magnetic resonance (MR) hybrid systems have been developed. Solid state detectors with avalanche photodiodes or digital silicon photomultipliers have also been utilized in PET. These new detectors allow improved image resolution, higher count rate, as well as a reduced sensitivity to electromagnetic MR fields.

On image quality metrics and the usefulness of grids in digital mammography.

Antiscatter grids are used in digital mammography to reduce the scattered radiation from the breast and improve image contrast. They are, however, imperfect and lead to partial absorption of primary radiation, as well as failing to absorb all scattered radiation. Nevertheless, the general consensus has been that antiscatter grids improve image quality for the majority of breast types and sizes. There is, however, inconsistency in the literature, and recent results show that a substantial image quality improvement can be achieved even for thick breasts if the grid is disposed of. The purpose of this study was to investigate if differences in the considered imaging task and experimental setup could explain the different outcomes. We estimated the dose reduction that can be achieved if the grid were to be removed as a function of breast thickness with varying geometries and experimental conditions. Image quality was quantified by the signal-difference-to-noise ratio (SDNR) measured using an aluminum (Al) filter on blocks of poly(methyl methacrylate) (PMMA), and images were acquired with and without grid at a constant exposure. We also used a theoretical model validated with Monte Carlo simulations. Both theoretically and experimentally, the main finding was that when a large [Formula: see text] Al filter was used, the SDNR values for the gridless images were overestimated up to 25% compared to the values for the small [Formula: see text] filter, and gridless imaging was superior for any PMMA thickness. For the small Al filter, gridless imaging was only superior for PMMAs thinner than 4cm. This discrepancy can be explained by a different sensitivity to and sampling of the angular scatter spread function, depending on the size of the contrast object. The experimental differences were eliminated either by using a smaller region of interest close to the edge of the large filter or by applying a technique of scatter correction by subtracting the estimated scatter image. These results explain the different conclusions reported in the literature and show the importance of the selection of measurement methods. Since the interesting structures in mammography are below the 1-cm scale, we advocate the use of smaller contrast objects for assessment of antiscatter grid performance.

Improving image contrast and material discrimination with nonlinear response in bimodal atomic force microscopy.

Atomic force microscopy has recently been extented to bimodal operation, where increased image contrast is achieved through excitation and measurement of two cantilever eigenmodes. This enhanced material contrast is advantageous in analysis of complex heterogeneous materials with phase separation on the micro or nanometre scale. Here we show that much greater image contrast results from analysis of nonlinear response to the bimodal drive, at harmonics and mixing frequencies. The amplitude and phase of up to 17 frequencies are simultaneously measured in a single scan. Using a machine-learning algorithm we demonstrate almost threefold improvement in the ability to separate material components of a polymer blend when including this nonlinear response. Beyond the statistical analysis performed here, analysis of nonlinear response could be used to obtain quantitative material properties at high speeds and with enhanced resolution.

Differential magnetic force microscope imaging.

This paper presents a method for differential magnetic force microscope imaging based on a two-pass scanning procedure to extract differential magnetic forces and eliminate or significantly reduce background forces with reversed tip magnetization. In the work, the difference of two scanned images with reversed tip magnetization was used to express the local magnetic forces. The magnetic sample was first scanned with a low lift distance between the MFM tip and the sample surface, and the magnetization direction of the probe was then changed after the first scan to perform the second scan. The differential magnetic force image was obtained through the subtraction of the two images from the two scans. The theoretical and experimental results have shown that the proposed method for differential magnetic force microscope imaging is able to reduce the effect of background or environment interference forces, and offers an improved image contrast and signal to noise ratio (SNR).

A joint Richardson—Lucy deconvolution algorithm for the reconstruction of multifocal structured illumination microscopy data

We demonstrate the reconstruction of images obtained by multifocal structured illumination microscopy, MSIM, using a joint Richardson–Lucy, jRL-MSIM, deconvolution algorithm, which is based on an underlying widefield image-formation model. The method is efficient in the suppression of out-of-focus light and greatly improves image contrast and resolution. Furthermore, it is particularly well suited for the processing of noise corrupted data. The principle is verified on simulated as well as experimental data and a comparison of the jRL-MSIM approach with the standard reconstruction procedure, which is based on image scanning microscopy, ISM, is made. Our algorithm is efficient and freely available in a user friendly software package.

Reception pattern influence on magnetoacoustic tomography with magnetic induction**Project supported by the National Basic Research Program of China (Grant No. 2011CB707900), the National Natural Science Foundation of China (Grant Nos 11274176 and 11474166), and the Priority Academic Program Development of Jiangsu Higher Education Institutions, China.

Based on the acoustic radiation theory of a dipole source, the influence of the transducer reception pattern is studied for magnetoacoustic tomography with magnetic induction (MAT-MI). Numerical studies are conducted to simulate acoustic pressures, waveforms, and reconstructed images with unidirectional, omnidirectional, and strong directional transducers. With the analyses of equivalent and projection sources, the influences of the model dimension and the layer effect are qualitatively analyzed to evaluate the performance of MAT-MI. Three-dimensional simulation studies show that the strong directional transducer with a large radius can reduce the influences of equivalent sources, projection sources, and the layer effect effectively, resulting in enhanced pressure and improved image contrast, which is beneficial for boundary pressure extraction in conductivity reconstruction. The reconstructed conductivity contrast images present the conductivity boundaries as stripes with different contrasts and polarities, representing the values and directions of the conductivity changes of the scanned layer. The favorable results provide solid evidence for transducer selection and suggest potential practical applications of MAT-MI in biomedical imaging.

Ultrasound modulated optical tomography contrast enhancement with non-linear oscillation of microbubbles.

Ultrasound modulated optical tomography (USMOT) is an imaging technique used to provide optical functional information inside highly scattering biological tissue. One of the challenges facing this technique is the low image contrast. A contrast enhancement imaging technique based on the non-linear oscillation of microbubbles is demonstrated to improve image contrast. The ultrasound modulated signal was detected using a laser pulse based speckle contrast detection system. Better understanding of the effects of microbubbles on the optical signals was achieved through simultaneous measurement of the ultrasound scattered by the microbubbles. The length of the laser pulse was found to affect the system response of the speckle contrast method with shorter pulses suppressing the fundamental ultrasound modulated optical signal. Using this property, image contrast can be enhanced by detection of the higher harmonic ultrasound modulated optical signals due to nonlinear oscillation and destruction of the microbubbles. Experimental investigations were carried out to demonstrate a doubling in contrast by imaging a scattering phantom containing an embedded silicone tube with microbubbles flowing through it. The contrast enhancement in USMOT resulting from the use of ultrasound microbubbles has been demonstrated. Destruction of the microbubbles was shown to be the dominant effect leading to contrast improvement as shown by simultaneously detecting the ultrasound and speckle contrast signals. Line scans of a microbubble filled silicone tube embedded in a scattering phantom demonstrated experimentally the significant image contrast improvement that can be achieved using microbubbles and demonstrates the potential as a future clinical imaging tool.

Targetting of the ventro-intermediate nucleus using ultra-high field (7 T) MRI for gamma knife surgery purposes: A pilot in vivo study on healthy subjects

Introduction Gamma Knife surgery (GKS) is a non-invasive neurosurgical stereotactic procedure, increasingly used as an alternative to open functional procedures. This includes targeting of the ventro-intermediate nucleus of the thalamus (e.g. Vim) for tremor. We currently perform an indirect targeting, as the Vim is not visible on current 3 Tesla MRI acquisitions. Our objective was to enhance anatomic imaging (aiming at refining the precision of anatomic target selection by direct visualisation) in patients treated for tremor with Vim GKS, by using high field 7 T MRI. Materials and methodsh Five young healthy subjects were scanned on 3 (T1-w and diffusion tensor imaging) and 7 T (high-resolution susceptibility weighted images (SWI)) MRI in Lausanne. All images were further integrated for the first time into the Gamma Plan Software® (Elekta Instruments, AB, Sweden) and co-registered (with T1 was a reference). A simulation of targeting of the Vim was done using various methods on the 3 T images. Furthermore, a correlation with the position of the found target with the 7 T SWI was performed. The atlas of Morel et al. (Zurich, CH) was used to confirm the findings on a detailed analysis inside/outside the Gamma Plan. Results The use of SWI provided us with a superior resolution and an improved image contrast within the basal ganglia. This allowed visualization and direct delineation of some subgroups of thalamic nuclei in vivo, including the Vim. The position of the target, as assessed on 3 T, perfectly matched with the supposed one of the Vim on the SWI. Furthermore, a 3-dimensional model of the Vim-target area was created on the basis of the obtained images. Conclusion This is the first report of the integration of SWI high field MRI into the LGP, aiming at the improvement of targeting validation of the Vim in tremor. The anatomical correlation between the direct visualization on 7 T and the current targeting methods on 3 T (e.g. quadrilatere of Guyot, histological atlases) seems to show a very good anatomical matching. Further studies are needed to validate this technique, both by improving the accuracy of the targeting of the Vim (potentially also other thalamic nuclei) and to perform clinical assessment.