Accurate reconstruction of 3D photoacoustic (PA) images requires detection of photoacoustic signals from many angles. Several groups have adopted staring ultrasound arrays, but assessment of array performance has been limited. We previously reported on a method to calibrate a 3D PA tomography (PAT) staring array system and analyze system performance using singular value decomposition (SVD). The developed SVD metric, however, was impractical for large system matrices, which are typical of 3D PAT problems. The present study consisted of two main objectives. The first objective aimed to introduce the crosstalk matrix concept to the field of PAT for system design. Figures-of-merit utilized in this study were root mean square error, peak signal-to-noise ratio, mean absolute error, and a three dimensional structural similarity index, which were derived between the normalized spatial crosstalk matrix and the identity matrix. The applicability of this approach for 3D PAT was validated by observing the response of the figures-of-merit in relation to well-understood PAT sampling characteristics (i.e. spatial and temporal sampling rate). The second objective aimed to utilize the figures-of-merit to characterize and improve the performance of a near-spherical staring array design. Transducer arrangement, array radius, and array angular coverage were the design parameters examined. We observed that the performance of a 129-element staring transducer array for 3D PAT could be improved by selection of optimal values of the design parameters. The results suggested that this formulation could be used to objectively characterize 3D PAT system performance and would enable the development of efficient strategies for system design optimization.
We present a two-dimensional (2D) snapshot multispectral imager that utilizes the optical transmission characteristics of nanohole arrays (NHAs) in a gold film to resolve a mixture of input colors into multiple spectral bands. The multispectral device consists of blocks of NHAs, wherein each NHA has a unique periodicity that results in transmission resonances and minima in the visible and near-infrared regions. The multispectral device was illuminated over a wide spectral range and the transmission was spectrally unmixed using a least-squares estimation algorithm. A NHA-based multispectral imaging system was built and tested in both reflection and transmission modes. The NHA-based multispectral imager was capable of extracting 2D multispectral images representative of four independent bands within the spectral range of 662 nm to 832 nm for a variety of targets. The multispectral device can potentially be integrated into a variety of imaging sensor systems.
Abstract Spatial resolution in three-dimensional fringe projection profilometry is determined in large part by the number and spacing of fringes projected onto an object. Due to the intensity-based nature of fringe projection profilometry, fringe patterns must be generated in succession, which is time-consuming. As a result, the surface features of highly dynamic objects are difficult to measure. Here, we introduce multispectral fringe projection profilometry, a novel method that utilizes multispectral illumination to project a multispectral fringe pattern onto an object combined with a multispectral camera to detect the deformation of the fringe patterns due to the object. The multispectral camera enables the detection of 8 unique monochrome fringe patterns representing 4 distinct directions in a single snapshot. Furthermore, for each direction, the camera detects two π-phase shifted fringe patterns. Each pair of fringe patterns can be differenced to generate a differential fringe pattern that corrects for illumination offsets and mitigates the effects of glare from highly reflective surfaces. The new multispectral method solves many practical problems related to conventional fringe projection profilometry and doubles the effective spatial resolution. The method is suitable for high-quality fast 3D profilometry at video frame rates.
Abstract Breast shapes are affected by gravitational loads and deformities. Measurements obtained in the standing position may not correlate well with measurements in the supine position, which is more representative of patient position during breast surgery. A dual color 3D surface imaging system capable of scanning patients in both supine and standing positions was developed to evaluate the effect of changes in body posture on breast morphology. The system was evaluated with breast phantoms to assess accuracy, then tested on ten subjects in three body postures to assess its effectiveness as a clinical tool. The accuracy of the system was within 0.4 mm on average across the model. For the human study, there was no effect of body posture on breast volumes ( p value > 0.05), but we observed an effect of completeness of breast scans on body posture ( p value < 0.05). Post-hoc tests showed that the supine position and the standing position with hands at the waist differed significantly ( p value < 0.05). This study shows that the system can quantitatively evaluate the effect of subject postures, and thereby has the potential to be used to investigate peri-operative changes in breast morphology.
Multispectral imaging is a highly desirable modality for material-based analysis in diverse areas such as food production and processing, satellite-based reconnaissance and biomedical imaging. Here, we present nanofilter-based multispectral videography (nMSV) in the 700 to 950 nm range made possible by the tunable extraordinary-optical-transmission properties of 3D metallic nanostructures. Measurements made with nMSV during a bolus injection of an intravascular tracer in the ear of a piglet resulted in spectral videos of the microvasculature. Analysis of the multispectral videos generated contrast measurements representative of arterial pulsation, the distribution of microvascular transit times, as well as a separation of the venous and arterial signals arising from within the tissue. Therefore, nMSV is capable of acquiring serial multispectral images relevant to tissue hemodynamics, which may have application to the detection and identification of skin cancer.
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