In the present study, we evaluated the applicability of ex vivo photoacoustic imaging (PAI) on small animal organs. We used photoacoustic tomography (PAT) to visualize infarcted areas within murine hearts and compared these data to other imaging techniques [magnetic resonance imaging (MRI), micro-computed tomography] and histological slices. In order to induce ischemia, an in vivo ligation of the left anterior descending artery was performed on nine wild-type mice. After varying survival periods, the hearts were excised and fixed in formaldehyde. Samples were illuminated with nanosecond laser pulses delivered by a Nd:YAG pumped optical parametric oscillator. Ultrasound detection was achieved using a Mach-Zehnder interferometer (MZI) working as an integrating line detector. The voxel data were computed using a Fourier-domain based reconstruction algorithm, followed by inverse Radon transforms. The results clearly showed the capability of PAI to visualize myocardial infarction and to produce three-dimensional images with a spatial resolution of approximately 120 μm. Regions of affected muscle tissue in PAI corresponded well with the results of MRI and histology. Photoacoustic tomography utilizing a MZI for ultrasound detection allows for imaging of small tissue samples. Due to its high spatial resolution, good soft tissue contrast and comparatively low cost, PAT offers great potentials for imaging.
A device for three-dimensional (3-D) photoacoustic tomography with resolution in the range of tens of micrometers is presented that uses a light beam for interferometric detection of acoustic waves. Reconstruction of the 3-D initial pressure distribution from the signals representing line integrals of the acoustic field is a two-step process. It uses an inversion of 2-D wave propagation to obtain line projections of the initial pressure distribution and the inverse Radon transform. The light beam, propagating freely in a water bath, is scanned either in an arc- or box-shaped curve around the object. Simulations are performed to compare the two scanning procedures. The projection images are obtained either using the filtered back projection algorithm for the -arc scanning mode or the frequency domain algorithm for the box scanning mode. While the former algorithm provides slightly better image quality, the latter is about 20 times faster. The ability of the photoacoustic tomography device to create 3-D images with constant resolution throughout the reconstruction volume is demonstrated experimentally using a human hair phantom. These measurements revealed a 3-D resolution below 100 µm. In a second experiment, 3-D imaging of an isolated mouse heart is demonstrated to show the applicability for preclinical and biological research.
In the present study, we evaluate the applicability of ex-vivo photoacoustic imaging (PAI) in organs of small animals.
We used photoacoustic tomography (PAT) to visualize infarcted areas within mouse hearts and compared it to other
imaging techniques (MRI and μCT).
In order to induce ischemia an in-vivo ligation of the Ramus interventricularis anterior (RIVA, left anterior descending,
LAD) was performed on nine wild type C41 mice. After varying survival periods the mice were sacrificed. The hearts
were excised and immediately transferred into a formaldehyde solution for conservation.
Various wavelengths in the visible and near infrared region (500 nm - 1000 nm) had been tested to find the best
representation of the ischemic regions. Samples were illuminated with nanosecond laser pulses delivered by an Nd:YAG
pumped optical parametric oscillator. Ultrasound detection was achieved by an optical Mach-Zehnder interferometer
working as an integrating line detector. For acoustic coupling the samples were located inside a water tank. The voxel
data are computed from the measurement data by a Fourier-domain based reconstruction algorithm, followed by a
sequence of inverse Radon transforms.
Results clearly show the capability of PAI to detect pathological tissue and the possibility to produce three-dimensional
images with resolutions well below 100 μm. Different wavelengths allow the representation of structure inside an organ
or on the surface even without contrast enhancing tracers.
We present two approaches for reconstructing a patient’s atrial myocardium from morphological image data.
Both approaches are based on a segmentation of the left and right atrial blood masses which mark the inner
border of the atrial myocardium. The outer border of the atrial myocardium is reconstructed differently by the
two approaches. The surface manipulation approach is based on a triangle manipulation procedure while the
label-voxel-field approach adds or deletes label-voxels of the segmented blood mass labelset. Both approaches
yield models of a patient’s atrial myocardium that qualify for further applications. The obtained atrial models
have been implemented many times in the construction of a patient’s volume conductor model needed for solving
the electrocardiographic inverse problem. The label-voxel-field approach has to be favored because of its superior
performance and ability of implementation in a segmentation pipeline.
Robert Modre, Bernhard Tilg, Gerald Fischer, Friedrich Hanser, Bernd Messnarz, Michael Schocke, Christian Kremser, Florian Hintringer, Franz Roithinger
Noninvasive imaging of electrical function in the human atria is attained by the combination of data from electrocardiographic (ECG) mapping and magnetic resonance imaging (MRI). An anatomical computer model of the individual patient is the basis for our computer-aided diagnosis of cardiac arrhythmias. Three patients suffering from Wolff-Parkinson-White syndrome, from paroxymal atrial fibrillation, and from atrial flutter underwent an electrophysiological study. After successful treatment of the cardiac arrhythmia with invasive catheter technique, pacing protocols with stimuli at several anatomical sites (coronary sinus, left and right pulmonary vein, posterior site of the right atrium, right atrial appendage) were performed. Reconstructed activation time (AT) maps were validated with catheter-based electroanatomical data, with invasively determined pacing sites, and with pacing at anatomical markers. The individual complex anatomical model of the atria of each patient in combination with a high-quality mesh optimization enables accurate AT imaging, resulting in a localization error for the estimated pacing sites within 1 cm. Our findings may have implications for imaging of atrial activity in patients with focal arrhythmias.
A recently introduced dynamic T1 mapping technique was used to investigate changes of tumor microcirculatory parameters in 16 patients with clinically staged T3) primary rectal carcinoma during a course of preoperative combined chemoradiation. For dynamic T1 mapping an ultra-fast snapshot FLASH T1 mapping sequence was implemented on a 1.5T whole body MR scanner. Acquiring a series of T1 maps contrast media (CM) uptake and washout over an examination time of 40 min was monitored. From the obtained series of T1-maps perfusion-indices (PI) were calculated as the ratio of maximum slope of the tumor CM curve and the maximum of the arterial CM curve. Using pathologic classification of the resected tumors after therapy the patient group could be divided into patients with and without response to therapy. It was found that mean pre-therapy PI values of tumors showing therapy-response were significantly lower than for tumors without no therapy-response. In addition a different behavior of PI distributions within tumors for both groups was observed. The presented study indicates that PI values and their distributions within a tumor seem to be of predictive value for therapy outcome of preoperative therapy in patients with primary rectal carcinoma.
Inverse electrocardiography has been developing for several years. By coupling electrocardiographic mapping and 3D+time anatomical data, the electrical excitation sequence can be imaged completely noninvasively in the human heart. In this study, a bidomain theory based surface heart model activation time imaging approach was applied to single beat data of atrial and ventricular depolarization. For sinus and paced rhythms, the sites of early activation and the areas with late activation were estimated with sufficient accuracy. In particular for focal arrhythmias, this model-based imaging approach might allow the guidance and evaluation of antiarrhythmic interventions, for instance, in case of catheter ablation or drug therapy.
Magnetic Resonance Imaging is the accepted method of choice for the diagnosis of central nervous system disorders.' Present neurosurgical planning depends on two-dimensional information obtained from MRI and CT cross-sections.2' 3After sequential reading of a series of two-dimensional images, the information has to be mentally transformed into a virtual threedimensional image of the complex three-dimensional anatomy by the neurosurgeon. These mental transformations are difficult or sometimes even impossible. Nowadays the challenge to the neurosurgeon has changed from the primary succesfull removal of a tumor to a minimal iniasive approach without distruction of normal brain tissue. These minimal invasive strategies need meticulous preoperative planning and often the support of intraoperative navigation.4 For the approach of subcortical lesions the precise pre-operative defmition not only of the target but also of the cortical entrance point is crucial. Therefore exact knowledge about the gyral and sulcal anatomy of the cerebral cortex in relation to the cortical veins is 567,8 We evaluated the impact of a 3D-display of the brain, vasculature and tumor on surgical decisions during planning and executions of operations for intracranial tumors in or near the central region. The 3D reconstruction and display is based on 3D MR data sets and a semiautomatic segmentation technique. Tumors as well as the surrounding or overlying neuronal and neurovascular anatomy are displayed on the 3D computer screen.
The red boundary has been found for an integral power detector based on PbSnTe(In). It was possible by using a new kind of FIR semiconductor lasers based on p-Ge crystal.
The basic principles for achieving population inversion and stimulated emission between light hole Landau levels in p-Germanium are discussed. An inversion between the Landau levels of the light hole subband of germanium is achieved when the crystal is subject to crossed electric and magnetic fields. This leads to stimulated far-infrared emission at the cyclotron resonance frequency. The emission spectrum consists of a single line which is linearly tunable with magnetic field between 65 cm-1 and 85 cm-1. The linewidth of the observed spectrum is about 0.2 cm-1 with an estimated output power of 200 mW. Lasing is found to depend critically on the orientation of the electric and magnetic field in respect to the crystallographic axis. By a comparison of absorption and emission spectra with band structure calculations including nonparabolicity corrections, the lasing transition was identified to be the n equals 2 to n equals 1 Landau level transition of the b-set light holes. Applications of the p-Ge cyclotron resonance lasers are discussed.
An Inversion between Landau levels (LL's) of the light hole (lh) subband of germanium is achieved when the crystal is subjected to crossed electric and magnetic fields /1,2/. This leads to stimulated far infrared (FIR) emission at the cyclotron resonance (CR) frequency. The emission spectrum consists of a single line linearly tunable with magnetic field /3/. Lasing was found to depend critically on the orientation of the electric and magnetic field with respect to the crystallographic axes. Characteristically the laser emission is observed in two field regimes - which we call here low field (1) and high field (2) - depending on conditions of sample doping and external stress. In general, low concentration samples (NA − ND = 8 × 1012 cm-3) oscillate in region (1) giving frequencies between 30 cm-1 and 50 cm-1, and high concentration samples (NA − ND = 6 × 1013 cm-3) oscillate in region (2) with frequencies between 65 cm-1 and 85 cm-1. The latter samples howerver can be made to oscillate also in range (1) by applying uniaxial stress /4/.
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