Holly S. Lay

2C-4 A 64-Channel Beamformer for 50 MHz Linear Arrays

This paper describes the design and implementation of a 64-channel beamformer for a 50 MHz linear array for use in medical imaging. The results for a series of theoretical models comparing various beamforming algorithms are given. The final algorithm is a compromise solution, applying a simple linear interpolation algorithm to a data set acquired using 4x interleaved sampling. This allows for 12 bit, 200 MS/s performance with a 50 MS/s ADC. This algorithm has been implemented on a Virtex 4 FPGA using a commercially available applications board featuring onboard SDRAM, oscillator, and parallel and serial communications. This board was tested with ideal data, as well as with an 8-channel analog board. There was excellent agreement between the hardware and computer simulation results.

Increased variability in Apc Min/+ intestinal tissue can be measured with microultrasound

Altered tissue structure is a feature of many disease states and is usually measured by microscopic methods, limiting analysis to small areas. Means to rapidly and quantitatively measure the structure and organisation of large tissue areas would represent a major advance not just for research but also in the clinic. Here, changes in tissue organisation that result from heterozygosity in Apc, a precancerous situation, are comprehensively measured using microultrasound and three-dimensional high-resolution microscopy. Despite its normal appearance in conventionally examined cross-sections, both approaches revealed a significant increase in the variability of tissue organisation in Apc heterozygous tissue. These changes preceded the formation of aberrant crypt foci or adenoma. Measuring these premalignant changes using microultrasound provides a potential means to detect microscopically abnormal regions in large tissue samples, independent of visual examination or biopsies. Not only does this provide a powerful tool for studying tissue structure in experimental settings, the ability to detect and monitor tissue changes by microultrasound could be developed into a powerful adjunct to screening endoscopy in the clinic.

Microultrasound characterisation of ex vivo porcine tissue for ultrasound capsule endoscopy

Gastrointestinal (GI) disease development and progression is often characterised by cellular and tissue architectural changes within the mucosa and sub-mucosa layers. Current clinical capsule endoscopy and other approaches are heavily reliant on optical techniques which cannot detect disease progression below the surface layer of the tissue. To enhance the ability of clinicians to detect cellular changes earlier and more confidently, both quantitative and qualitative microultrasound (μUS) techniques are investigated in healthy ex vivo porcine GI tissue. This work is based on the use of single-element, focussed μUS transducers made with micromoulded piezocomposite operating at around 48 MHz. To explore the possibility that μUS can detect Crohns disease and other inflammatory bowel diseases, ex vivo porcine small bowel tissue samples were cannulised and perfused with phosphate-buffered saline followed by various dilutions of polystyrene microspheres. Comparison with fluorescent imaging showed that the microspheres had infiltrated the microvasculature of the samples and that μUS was able to successfully detect this as a mimic of inflammation. Samples without microspheres were analysed using quantitative ultrasound to assess mechanical properties. Attenuation coefficients of 1.78 ± 0.66 dB/mm and 1.92 ± 0.77 dB/mm were obtained from reference samples which were surgically separated from the muscle layer. Six intact samples were segmented using a software algorithm and the acoustic impedance, Z, for varying tissue thicknesses, and backscattering coefficient, BSC, were calculated using the reference attenuation values and tabulated.

Design and simulation of a high-frequency ring-shaped linear array for capsule ultrasound endoscopy

Current research into endoscopy and colonoscopy has significantly advanced visualization of the gastrointestinal tract (GIT). The Sonopill project seeks to combine the imaging capabilities of endoscopic ultrasound with the full GIT transit of capsule endoscopy through the development of a capsule capable of ultrasonic imaging of the GIT, focusing on the small intestine. However, due to the small volume of the proposed capsule and the need to transmit received data wirelessly, the Sonopill system is limited both in data bandwidth and power. This paper presents a MATLAB-based simulation to allow testing of transducer topologies and imaging methodologies to achieve optimum results within the physical limitations of the system. To allow rapid evaluation of possible transducer configurations and circuit elements, a hybrid MATLAB simulation was created, incorporating both KLM circuit elements for analog analysis and digitizing and beamforming elements to render a final grey-scale image for imaging quality analysis. This was used in conjunction with a theoretical acoustic propagation model to image ideal point scatterers. The proposed transducers consist of a single, unfocused transmit ring of radius 5 mm separated into eight segments for impedance control, and a 512-element receive linear array curved into a matching ring. Because of the high element count and pad limitations on the intended electronics, the design requires the use of 32 integrated 16:1 multiplexers which will be bonded directly to the connecting flex circuit before the ASIC. Simulating the loading effects of these multiplexers as well as the proposed transducer configuration was critical to the analysis of the design. The MATLAB model was used to simulate a standard pulser transmitting over a 2.5 m cable to a 0.25 mm × 8 mm × 85 μm PMN-PT piezocrystal transmit transducer with a centre frequency of 25 MHz. B-scan images were then modelled for three imaging phantoms, one containing three point target resolution phantoms, a resolution phantom containing two virtual walls, and a tissue mimicking phantom containing particles with two levels of reflectivity to represent a three layer gut phantom with a high-reflectivity front surface.

Acoustic Sensing and Ultrasonic Drug Delivery in Multimodal Theranostic Capsule Endoscopy

Video capsule endoscopy (VCE) is now a clinically accepted diagnostic modality in which miniaturized technology, an on-board power supply and wireless telemetry stand as technological foundations for other capsule endoscopy (CE) devices. However, VCE does not provide therapeutic functionality, and research towards therapeutic CE (TCE) has been limited. In this paper, a route towards viable TCE is proposed, based on multiple CE devices including important acoustic sensing and drug delivery components. In this approach, an initial multimodal diagnostic device with high-frequency quantitative microultrasound that complements video imaging allows surface and subsurface visualization and computer-assisted diagnosis. Using focused ultrasound (US) to mark sites of pathology with exogenous fluorescent agents permits follow-up with another device to provide therapy. This is based on an US-mediated targeted drug delivery system with fluorescence imaging guidance. An additional device may then be utilized for treatment verification and monitoring, exploiting the minimally invasive nature of CE. While such a theranostic patient pathway for gastrointestinal treatment is presently incomplete, the description in this paper of previous research and work under way to realize further components for the proposed pathway suggests it is feasible and provides a framework around which to structure further work.

Progress towards a multi-modal capsule endoscopy device featuring microultrasound imaging

Current clinical standards for endoscopy in the gastrointestinal (GI) tract combine high definition optics and ultrasound imaging to view the lumen superficially and through its thickness. However, these instruments are limited to the length of an endoscope and the only clinically available, autonomous devices able to travel the full length of the GI tract easily offer only video capsule endoscopy (VCE). Our work seeks to overcome this limitation with a device (“Sonopill”) for multimodal capsule endoscopy, providing optical and microultrasound (μUS) imaging and supporting sensors1.μUS transducers have been developed with multiple piezoelectric materials operating across a range of centre frequencies to study viability in the GI tract. Because of the combined constraints of μUS imaging and the low power / heat tolerance of autonomous devices, a hybrid approach has been taken to the transducer design, with separate transmit and receive arrays allowing multiple manufacturing approaches to maximise system efficiency. To explore these approaches fully, prototype devices have been developed with PVDF, high-frequency PZT and PMN-PT composites, and piezoelectric micromachined ultrasonic transducer arrays. Test capsules have been developed using 3D printing to investigate issues including power consumption, heat generation / dissipation, acoustic coupling, signal strength and capsule integrity. Because of the high functional density of the electronics in our proposed system, application specific integrated circuits (ASICs) have been developed to realise the ultrasound transmit and receive circuitry along with white-light and autofluorescence imaging with singlephoton avalanche detectors (SPADs). The ultrasound ASIC has been developed and the SPAD electronics and optical subsystem have been validated experimentally. The functionality of various transducer materials.

Novel interconnection and fabrication method for high-frequency ultrasound arrays

A 9-element annular array is presented that employs a newly-proposed interconnection scheme that simplifies the fabrication process. The fabricated array is a hybrid transducer structure incorporating both a piezoelectric layer and a silicon substrate in the same device. The interconnection scheme consists of a set of 9 equal area Cr/Au electrodes with a 2 mm aperture and 17 μm kerfs patterned on the surface of the silicon substrate using photolithography. A grid of Cr/Au electrodes was patterned on the surface of the piezoelectric layer, and the two layers were connected using an anisotropic conductive adhesive. To avoid the severe alignment restrictions that would result if the two electrode patterns were identical, a grid-pattern of square electrodes was substituted on the piezoelectric layer with a smaller diagonal dimension than the spaces between the silicon electrodes. A Tungsten-loaded epoxy backing layer was added to the acoustic stack and an impedance plot was measured for a single array element. Both 22 MHz and 40 MHz arrays were manufactured and the impedance plots show good correspondence with KLM modeling. A pulse-echo response was generated for the 22 MHz array, showing no degradation due to the silicon layer.

Ultrasound capsule endoscopy: sounding out the future

Video capsule endoscopy (VCE) has been of immense benefit in the diagnosis and management of gastrointestinal (GI) disorders since its introduction in 2001. However, it suffers from a number of well recognized deficiencies. Amongst these is the limited capability of white light imaging, which is restricted to analysis of the mucosal surface. Current capsule endoscopes are dependent on visual manifestation of disease and limited in regards to transmural imaging and detection of deeper pathology. Ultrasound capsule endoscopy (USCE) has the potential to overcome surface only imaging and provide transmural scans of the GI tract. The integration of high frequency microultrasound (µUS) into capsule endoscopy would allow high resolution transmural images and provide a means of both qualitative and quantitative assessment of the bowel wall. Quantitative ultrasound (QUS) can provide data in an objective and measurable manner, potentially reducing lengthy interpretation times by incorporation into an automated diagnostic process. The research described here is focused on the development of USCE and other complementary diagnostic and therapeutic modalities. Presently investigations have entered a preclinical phase with laboratory investigations running concurrently.

High-Frequency Annular Array Fabrication Using a Flex Circuit Matching Layer

Fabricating arrays for high-frequency image applications such as ophthalmic imaging, intravascular imaging, and small animal imaging is challenging. For example, an array for intravascular imaging must be small enough to fit within the lumen of a catheter and inexpensive enough to be discarded after a single use. This article presents a new method for fabricating high-frequency annular arrays that is simple and inexpensive. The annular array elements are defined by the electrode pattern on a back surface of a polyimide quarter-wavelength matching layer that is glued to the front face of a ceramic transducer substrate (PZT5H). Electrical losses associated with bonding the matching layer to the transducer substrate are reduced by fabricating a second set of electrodes on the transducer substrate and then bonding the substrates using an anisotropic conductive epoxy. The feasibility of this technique was established by fabricating a seven-element, 20-MHz, 5-mm diameter annular array. The prototype array produced a pulse with a −6-dB factional bandwidth of 50%, an insertion loss of 22 dB, and secondary lobes in the radiation pattern at f/2 that decreased to −65 dB with respect to the main lobe with a peak amplitude of −53 dB.

A low cost receive beamformer for a high frequency annular array

High-frequency ultrasound imaging systems can be costly to develop due to the more stringent analog design requirements and higher sampling rates. Advances in consumer electronics and computer processors, however, have allowed the development of beamformers which are lower-cost and easily adapted to custom applications. We have developed a software beamformer which uses a new interpolation scheme to reduce the sampling rate while maintaining secondary lobes that are suppressed by approximately 60 dB with respect to the main lobe. A 7-channel, 20 MHz array beamformer was implemented using an Analog Devices AD9272 octal ADC evaluation board and ADC-HSC-EVALC FPGA acquisition board costing <;