Passive element enriched photoacoustic computed tomography (PER PACT) for simultaneous imaging of acoustic propagation properties and light absorption\ud

We present a ‘hybrid’ imaging approach which can image both light absorption properties and acoustic transmission properties of an object in a two-dimensional slice using a computed tomography (CT) photoacoustic imager. The ultrasound transmission measurement method uses a strong optical absorber of small cross-section placed in the path of the light illuminating the sample. This absorber, which we call a passive element acts as a source of ultrasound. The interaction of ultrasound with the sample can be measured in transmission, using the same ultrasound detector used for photoacoustics. Such measurements are made at various angles around the sample in a CT approach. Images of the ultrasound propagation parameters, attenuation and speed of sound, can be reconstructed by inversion of a measurement model. We validate the method on specially designed phantoms and biological specimens. The obtained images are quantitative in terms of the shape, size, location, and acoustic properties of the examined heterogeneitie

Whole field laser Doppler imaging of the microcirculation in psoriasis and clinically unaffected skin

Contains fulltext : 137211.pdf (publisher's version ) (Closed access)BACKGROUND: Angiogenesis represents a key phenomenon in psoriasis. Insights in the microcirculation within psoriatic lesions in a whole field are lacking. Recently, the Twente Optical Perfusion Camera (TOPCam) was developed, which provides the possibility of evaluating the superficial cutaneous microcirculation in a whole field. OBJECTIVES: This pilot study aims to examine whether the TOPCam can be used to visualize the microcirculation within and around psoriatic lesions, and whether it is capable of revealing vascular changes during topical treatment. METHODS: Five patients with chronic plaque psoriasis were included. The superficial microcirculation and clinical local scores (SUM score) were analyzed in two comparable lesions within one patient. At baseline and after 2, 4, 6, and 8 weeks the disease's natural course was evaluated in one plaque versus topical treatment in the other. RESULTS: The TOPCam was able to visualize an increased microcirculation within psoriatic lesions and perfusion variability due to the heartbeat. Whole field images demonstrated heterogeneity in perfusion intensity (hot and cold spots) within clinically homogeneous-looking plaques. Topical therapy induced a decrease in overall perfusion and a significant decrease in SUM score. CONCLUSION: The TOPCam is the first noninvasive technique to visualize the microcirculation of psoriatic lesions in a whole field, to correct images for the heartbeat, and to reveal heterogeneity in perfusion intensity

Design and evaluation of a laboratory prototype system for 3D photoacoustic full breast tomography

Photoacoustic imaging can visualize vascularization-driven optical absorption contrast with great potential for breast cancer detection and diagnosis. State-of-the-art photoacoustic breast imaging systems are promising but are limited either by only a 2D imaging capability or by an insufficient imaging field-of-view (FOV). We present a laboratory prototype system designed for 3D photoacoustic full breast tomography, and comprehensively characterize it and evaluate its performance in imaging phantoms. The heart of the system is an ultrasound detector array specifically developed for breast imaging and optimized for high sensitivity. Each detector element has an acoustic lens to enlarge the acceptance angle of the large surface area detector elements to ensure a wide system FOV. We characterized the ultrasound detector array performance in terms of frequency response, directional sensitivity, minimum detectable pressure and inter-element electrical and mechanical cross-talk. Further we evaluated the system performance of the laboratory prototype imager using well-defined breast mimicking phantoms. The system possesses a 2 mm XY plane resolution and a 6 mm vertical resolution. A vasculature mimicking object was successfully visualized down to a depth of 40 mm in the breast phantom. Further, tumor mimicking spherical objects with 5 and 10 mm diameter at 20 mm and 40 mm depths are recovered, indicating high system sensitivity. The system has a 170 × 170 × 170 mm3 FOV, which is well suited for full breast imaging. Various recommendations are provided for performance improvement and to guide this laboratory prototype to a clinical version in future

An optimized ultrasound detector for photoacoustic breast tomography

Purpose: \ud Photoacoustic imaging has proven to be able to detect vascularization-driven optical absorption contrast associated with tumors. In order to detect breast tumors located a few centimeter deep in tissue, a sensitive ultrasound detector is of crucial importance for photoacoustic mammography. Further, because the expected photoacoustic frequency bandwidth (a few MHz to tens of kHz) is inversely proportional to the dimensions of light absorbing structures (0.5–10+ mm), proper choices of materials and their geometries and proper considerations in design have to be made to implement optimal photoacoustic detectors. In this study, we design and evaluate a specialized ultrasound detector for photoacoustic mammography.\ud \ud Methods: \ud Based on the required detector sensitivity and its frequency response, a selection of active material and matching layers and their geometries is made leading to functional detector models. By iteration between simulation of detector performances, fabrication and experimental characterization of functional models an optimized implementation is made and evaluated. For computer simulation, we use 1D Krimholtz–Leedom–Matthaei and 3D finite-element based models.\ud \ud Results: \ud The experimental results of the designed first and second functional detectors matched with the simulations. In subsequent bare piezoelectric samples the effect of lateral resonances was addressed and their influence minimized by subdicing the samples. Consequently, using simulations, a final optimized detector was designed, with a center frequency of 1 MHz and a −6 dB bandwidth of 0.4–1.25 MHz (fractional bandwidth of ∼80%). The minimum detectable pressure was measured to be 0.5 Pa.\ud \ud Conclusions: \ud A single-element, large-aperture, sensitive, and broadband detector is designed and developed for photoacoustic tomography of the breast. The detector should be capable of detecting vascularized tumors with 1–2 mm resolution. The minimum detectable pressure is 0.5 Pa, which will facilitate deeper imaging compared to the current systems. Further improvements by proper electrical grounding and shielding and implementation of this design into an arrayed detector will pave the way for clinical applications of photoacoustic mammograph

Imaging breast lesions using the Twente Photoacoustic Mammoscope: ongoing clinical experience

Current imaging modalities are often not able to detect early stages of breast cancer with high imaging contrast. Visualizing malignancy-associated increased hemoglobin concentrations might improve breast cancer diagnosis. Photoacoustic imaging can visualize hemoglobin in tissue with optical contrast and ultrasound resolution, which makes it potentially ideal for breast imaging. The Twente Photoacoustic Mammoscope (PAM) has been designed specifically for this purpose. Based on a successful pilot study in 2007, a large clinical study using PAM has been started in December 2010. PAM uses a pulsed Q-switched Nd:YAG laser at 1064 nm to illuminate a region of interest on the breast. Photoacoustic signals are detected with a 1MHz, unfocused ultrasound detector array. Three dimensional data are reconstructed using an acoustic backprojection algorithm. Those reconstructed images are compared with conventional imaging and histopathology. In the first phase of the study, the goal was to optimize the visualization of malignancies. We performed sixteen technically acceptable measurements on confined breast malignancies. In the reconstructed volumes of all malignancies, a confined high contrast region could be identified at the expected lesion depth. After ten successful measurements, the illumination area was increased and the fluence was substantially decreased. This caused a further significant increase in PAM lesion contrast

Visualizing breast cancer using the Twente photoacoustic mammoscope: What do we learn from twelve new patient measurements?

We acquired images of breast malignancies using the Twente photoacoustic mammoscope (PAM), to obtain more information about the clinical feasibility and limitations of photoacoustic mammography. Results were compared with conventional imaging and histopathology. Ten technically acceptable measurements on patients with malignancies and two measurements on patients with cysts were performed. In the reconstructed volumes of all ten malignant lesions, a confined region with high contrast with respect to the background could be seen. In all malignant cases, the PA contrast of the abnormality was higher than the contrast on x-ray mammography. The PA contrast appeared to be independent of the mammographically estimated breast density and was absent in the case of cysts. Technological improvements to the instrument and further studies on less suspicious lesions are planned to further investigate the potential of PAM