Noninvasive visualization of electrical conductivity in tissues at the micrometer scale.

Despite its importance in regulating cellular or tissue function, electrical conductivity can only be visualized in tissue indirectly as voltage potentials using fluorescent techniques, or directly with radio waves. These either requires invasive procedures like genetic modification or suffers from limited resolution. Here, we introduce radio-frequency thermoacoustic mesoscopy (RThAM) for the noninvasive imaging of conductivity by exploiting the direct absorption of near-field ultrashort radio-frequency pulses to stimulate the emission of broadband ultrasound waves.

Sensitivity Enhanced Photoacoustic Imaging Using a High-Frequency PZT Transducer with an Integrated Front-End Amplifier.

Photoacoustic (PA) imaging is a hybrid imaging technique that can provide both structural and functional information of biological tissues. Due to limited permissible laser energy deposited on tissues, highly sensitive PA imaging is required. Here, we developed a 20 MHz lead zirconium titanate (PZT) transducer (1.

Spatial and Spectral Mapping and Decomposition of Neural Dynamics and Organization of the Mouse Brain with Multispectral Optoacoustic Tomography.

In traditional optical imaging, limited light penetration constrains high-resolution interrogation to tissue surfaces. Optoacoustic imaging combines the superb contrast of optical imaging with deep penetration of ultrasound, enabling a range of new applications. We used multispectral optoacoustic tomography (MSOT) for functional and structural neuroimaging in mice at resolution, depth, and specificity unattainable by other neuroimaging modalities.

Blood vessel imaging using radiofrequency-induced second harmonic acoustic response.

We introduce a contrast mechanism for visualizing blood vessels based on radiofrequency-induced second harmonic acoustic (RISHA) signals sensing blood conductivity. We develop a novel imaging system using commonly available inexpensive components, and demonstrate in vivo RISHA visualization of blood vessels based on low-power quasi-continuous radiofrequency excitation of tissue at frequencies of a few MHz. We show how the novel approach also implicitly enables radiofrequency-induced passive ultrasound imaging and can be readily applied to non-invasive imaging of blood vessels ex vivo and in vivo.

Continuous wave laser diodes enable fast optoacoustic imaging.

Pulsed laser diodes may offer a smaller, less expensive alternative to conventional optoacoustic laser sources; however they do not provide pulse rates faster than a few tens of kHz and emit at wavelengths only within the near-infrared region. We investigated whether continuous wave (CW) laser diodes, which are available in visible and near-infrared regions, can be good optoacoustic light sources when overdriven with a peak current >40-fold higher than the CW absolute maximum. We found that overdriven CW diodes provided ∼10 ns pulses of ∼200 nJ/pulse and repetition rates higher than 600 kHz without being damaged, outperforming many pulsed laser diodes.

Ionoacoustic tomography of the proton Bragg peak in combination with ultrasound and optoacoustic imaging.

Ions provide a more advantageous dose distribution than photons for external beam radiotherapy, due to their so-called inverse depth dose deposition and, in particular a characteristic dose maximum at their end-of-range (Bragg peak). The favorable physical interaction properties enable selective treatment of tumors while sparing surrounding healthy tissue, but optimal clinical use requires accurate monitoring of Bragg peak positioning inside tissue. We introduce ionoacoustic tomography based on detection of ion induced ultrasound waves as a technique to provide feedback on the ion beam profile.

Magnetoacoustic Sensing of Magnetic Nanoparticles.

The interaction of magnetic nanoparticles and electromagnetic fields can be determined through electrical signal induction in coils due to magnetization. However, the direct measurement of instant electromagnetic energy absorption by magnetic nanoparticles, as it relates to particle characterization or magnetic hyperthermia studies, has not been possible so far. We introduce the theory of magnetoacoustics, predicting the existence of second harmonic pressure waves from magnetic nanoparticles due to energy absorption from continuously modulated alternating magnetic fields.

In vivo frequency domain optoacoustic tomography.

Optoacoustic imaging has been primarily implemented in the time domain, i.e., using ultrashort nanosecond laser pulses for illumination.

Near-field thermoacoustic imaging with transmission line pulsers.

Purpose: Near-field radiofrequency thermoacoustic (NRT) tomography has been recently introduced for imaging electromagnetic (EM) properties of tissues using ultrawideband, high-energy impulses, which induce thermoacoustic responses. Operation in the near-field allows for more effective energy coupling into tissue, compared to using radiating sources, which in turn enables the use of shorter excitation pulses and leads to higher image resolution. This work aimed at investigating transmission lines as a method to generate excitation pulses to improve the NRT resolution over previous implementations without compromising the energy coupled into tissue.

Capsule endoscopy image analysis using texture information from various colour models.

Wireless capsule endoscopy (WCE) is a novel imaging technique that is gradually gaining ground as it enables the non-invasive and efficacious visualization of the digestive track, and especially the entire small bowel including its middle part. However, the task of reviewing the vast amount of images produced by a WCE examination is a burden for the physicians. To tackle this major drawback, an innovative scheme for discriminating endoscopic images related to one of the most common intestinal diseases, ulceration, is presented here.

Diffuse reflectance spectroscopic mapping imaging applied to art objects materials determination from 200 up to 5000 nm.

The microsampling destructions caused by the sampling of analytical spectroscopic methods are generally not permitted to art objects. Consequently, the development of nondestructive analysis techniques is a necessity. In this work we present a set of signal processing and artificial intelligence techniques which support the operation of a novel device developed for the nondestructive identification of art objects.

Abnormal pattern detection in Wireless Capsule Endoscopy images using nonlinear analysis in RGB color space.

In recent years, an innovative method has been developed for the non-invasive observation of the gastrointestinal tract (GT), namely Wireless Capsule Endoscopy (WCE). WCE especially enables a detailed inspection of the entire small bowel and identification of its clinical lesions. However, the foremost disadvantage of this technological breakthrough is the time consuming task of reviewing the vast amount of images produced.

Estimation of motions in color image sequences using hypercomplex fourier transforms.

Although the motion estimation problem has been extensively studied, most of the proposed estimation approaches deal mainly with monochrome videos. The most usual way to apply them also in color image sequences is to process each color channel separately. A different, more sophisticated approach is to process the color channels in a "holistic" manner using quaternions, as proposed by Ell and Sangwine.

Estimation of multiple, time-varying motions using time-frequency representations and moving-objects segmentation.

We extend existing spatiotemporal approaches to handle time-varying motions estimation of multiple objects. It is shown that multiple, time-varying motions estimation is equivalent to the instantaneous frequency estimation of superpositioned FM sinusoids. Therefore, we apply established signal processing tools, such as time-frequency representations to show that for each time instant, the energy is concentrated along planes in the 3-D space: spatial frequencies-instantaneous frequency.

Nondestructive multispectral reflectoscopy between 800 and 1900 nm: An instrument for the investigation of the stratigraphy in paintings.

In the present work, a powerful tool for the investigation of paintings is presented. This permits the tuneable multispectral real time imaging between 200 and 5000 nm and the simultaneous multispectral acquisition of spectroscopic data from the same region. We propose the term infrared reflectoscopy for tuneable infrared imaging in paintings (Chryssonlakis and Chassery, The Application of Physicochemical Methods of Analysis and Image Processing Techniques to Painted Works of Art, Erasmus Project ICP-88-006-6, Athens, June, 1989) for a technique that is effective especially when the spectroscopic data acquisition is performed between 800 and 1900 nm.

Estimation of multiple accelerated motions using chirp-Fourier transform and clustering.

Motion estimation in the spatiotemporal domain has been extensively studied and many methodologies have been proposed, which, however, cannot handle both time-varying and multiple motions. Extending previously published ideas, we present an efficient method for estimating multiple, linearly time-varying motions. It is shown that the estimation of accelerated motions is equivalent to the parameter estimation of superpositioned chirp signals.

Multirate SPAMM tagging.

Many magnetic resonance tagging sequences rely on periodicity in order to produce a uniform tagging grid that covers the whole image plane. This, however, is not always desirable, since motion may be restricted to specific parts of the image, and also different motion characteristics may call for different tagging grid densities. In this paper, we present a combination of the spatial modulation of magnetization 1-1 method with selective excitation pulses that can be used in order to restrict the tagging grid only to regions of interest and produce tagging grid of different density in each region.

A rotational approach to localized SPAMM 1-1 tagging.

Magnetic resonance tagging usually relies on controlling the phase dispersion of the transverse magnetization component. Phase dispersion is, however, affected by the inherent phase of selective excitation pulses, thus limiting their combination with tagging sequences to the application of refocusable pulses, as in the localized spatial modulation of magnetization (L-SPAMM) technique. In this study, we examine the effect of selective excitation pulses on a L-SPAMM 1-1 sequence, showing that in the case of two identical pulses the phase component is canceled out, and thus preemphasis and refocus gradients are not needed, allowing us to take advantage of a constant gradient throughout the tagging sequence, and also that one might choose nonrefocusable maximum and minimum phase pulses.

Improved Shinnar-Le Roux algorithm.

Selective excitation pulses are widely used in magnetic resonance imaging in order to excite predetermined slices of the body under examination. Such pulses are optimally designed by means of the Shinnar-Le Roux algorithm. In this paper, we show that under minimal assumptions, the complexity and computing cost of the original Shinnar-Le Roux algorithm can be drastically reduced.

Reconstruction of magnetic resonance images using one-dimensional techniques.

Whenever DFT (discrete Fourier transform) processing of a multidimensional discrete signal is required, one can apply either a multidimensional FFT (fast Fourier transform) algorithm, or a single-dimension FFT algorithm, both using the same number of points. That is, the dimensions of a "multidimensional" signal, and of its spectrum, are a matter of choice. Every multidimensional sequence is completely equivalent to a one-dimensional function in both "time" and "frequency" domains.

Single-channel demodulator and Hartley transform in MRI.

A single-channel alternative detection system for magnetic resonance imaging and spectroscopy experiments is presented. After the phase error identification, which is realized through a simple method, one can correct the reconstructed image and discriminate between positive and negative frequencies without any loss of the S/N ratio. Since there is only one channel, that is a real signal, it is possible to use the Hartley instead of the Fourier transform.

A simple high-frequency antenna for NMR imaging.

The classic whole-body or head antennas for NMR imaging do not resonate properly at higher frequencies. The high-frequency antenna presented is constructed from segments of transmission lines and is treated as a distributed parameter system. It has an RF magnetic response similar to that of the classic saddle-shaped antenna, has low exposed impedance to avoid dielectric losses in the patient, and does not disturb the magnetic field gradients.

Electromagnetic field distribution and developed losses inside a finite cylinder and sphere under MRI conditions.

The control of the thermal losses dissipated inside the human body during magnetic resonance imaging (MRI) is very important, since it is directly related to patient safety. The authors give the exact solution to the problem of the electromagnetic energy dissipation and distribution inside a conductive sphere and a finite conductive cylinder, considered as the closest models to the human anatomy. The high-frequency alternating magnetic field is produced by a current loop.

Performance evaluation of whole-body NMR scanner antenna systems.

Whole-body NMR imaging antennas (probes) are strongly affected by the inevitable magnetic and controllable dielectric losses. Using a convenient parallelepiped model, the magnetic losses are evaluated. By introducing the "ideal power gain," the best possible antenna performance is delimited as a function of the frequency and the patient examined.