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.
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.
The purpose of this study was to compare the radiologist`s performance in detecting small low-contrast objects with hardcopy and softcopy reading of digital mammograms. 12 images of a contrast-detail (CD) phantom without and with 25.4 mm, 50.8 mm, and 76.2 mm additional polymethylmetacrylate (PMMA) attenuation were acquired with a caesium iodid/amorphous silicon flat panel detector under standard exposure conditions. The phantom images were read by three independent observers, by conducting a four-alternative forced-choice experiment. Reading of the hardcopy was done on a mammography viewbox under standardized reading conditions. For soft copy reading, a dedicated workstation with two 2K monitors was used. CD-curves and image quality figure (IQF) values were calculated from the correct detection rates of randomly located gold disks in the phantom. The figures were compared for both reading conditions and for different PMMA layers. For all types of exposures, soft copy reading resulted in significantly better contrast-detail characteristics and IQF values, as compared to hard copy reading of laser printouts. (p< 0.01). The authors conclude that the threshold contrast characteristics of digital mammograms displayed on high-resolution monitors are sufficient to make soft copy reading of digital mammograms feasible.