High Frequency Annular Array Research Articles

Inkjet-printed P(VDF-TrFE) film for high-frequency annular array.

An innovative processing to deposit P(VDF-TrFE) film on silicon wafers by an inkjet printing method was used to fabricate high-frequency annular array prototype. This prototype has a total aperture of 7.3 mm and 8 active elements. A polymer-based lens with low acoustic attenuation was added to the flat deposition on the wafer, setting the geometric focus to 13.8 mm. With a thickness of around 11 μm, the electromechanical performance of P(VDF-TrFE) films was evaluated with an effective thickness coupling factor of 22%. Electronics allowing all elements to simultaneously emit as a single element transducer was developed. In reception, a dynamic focusing, based on eight independent amplifying channels, was preferred. The center frequency of the prototype was 21.3 MHz, the insertion loss was 48.5 dB and the -6 dB fractional bandwidth was 143%. The trade-off sensitivity/bandwidth has rather favored the large bandwidth. Dynamic focusing on reception was applied and allowed to improvements in the lateral-full width at half maximum as shown on images obtained with a wire phantom at several depths. The next step, for a fully operational multi-element transducer, will be to achieve a significant increase of the acoustic attenuation in the silicon wafer.

1Pa5-7 Evaluation of Backscattering Properties in Skin Tissue by High-frequency Annular Array

1Pa5-7 Evaluation of Backscattering Properties in Skin Tissue by High-frequency Annular Array

Technical notes on high-frequency ultrasound duodenography and colonography imaging of giardial lesions

Background: Worldwide G. lamblia is the third most common agent of diarrheal disease with over 300 million cases annually. Simple technical notes for clinicians are presented on use of high-frequency ultrasound imaging for duodenography and colonography in patients with Giardia lamblia infection. Methods: Ultrasound images were obtained from 100 consecutive patients with symptomatic giardiasis and 40 healthy controls. High-frequency annular array transducer of 7.5 MHz was used to obtain B-mode ultrasound grayscale and color images of the duodenum and colon with and without water contrast. The diagnosis of G. lamblia was based on clinical presentation, serial stool microscopy, and finding of flagellates in duodenal aspirates. Results: We demonstrated normal duodenum and colon echoanatomy in control subjects. In patients with giardiasis, the lesions of the duodenum and colon were associated with increased dimensions and wall thickness compared to healthy controls (P < 0.05). The ultrasound features of giardial lesions were characterized by increased wall echogenicity, flattening or loss of duodenal folds and/or colonic haustration, hyperechoic floating foci demonstrating chaotic motility, increased perilesional tissue echogenicity, and altered colonic peristalsis. Conclusion: In conclusion, high-frequency B-mode ultrasound imaging with and without water contrast demonstrated the details of duodenal and colonic echoanatomy in normal subjects and patients with giardiasis. The technique could be applied in the clinical setting of rural practitioners.

High-frequency annular array with coaxial illumination for dual-modality ultrasonic and photoacoustic imaging

This paper presents a combined ultrasound and photoacoustic (PA) imaging (PAI) system used to obtain high-quality, co-registered images of mouse-embryo anatomy and vasculature. High-frequency ultrasound (HFU, >20 MHz) is utilized to obtain high-resolution anatomical images of small animals while PAI provides high-contrast images of the vascular network. The imaging system is based on a 40 MHz, 5-element, 6 mm aperture annular-array transducer with a 800 μm diameter hole through its central element. The transducer was integrated in a cage-plate assembly allowing for a collimated laser beam to pass through the hole so that the optical and acoustic beams were collinear. The assembly was mounted on a two-axis, motorized stage to enable the simultaneous acquisition of co-registered HFU and PA volumetric data. Data were collected from all five elements in receive and a synthetic-focusing algorithm was applied in post-processing to beamform the data and increase the spatial resolution and depth-of-field (DOF) of the HFU and PA images. Phantom measurements showed that the system could achieve high-resolution images (down to 90 μm for HFU and 150 μm for PAI) and a large DOF of >8 mm. Volume renderings of a mouse embryo showed that the scanner allowed for visualizing morphologically precise anatomy of the entire embryo along with corresponding co-registered vasculature. Major head vessels, such as the superior sagittal sinus or rostral vein, were clearly identified as well as limb bud vasculature.

Design and fabrication of a high frequency annular array for medical ultrasound systems

Most high frequency (&amp;gt;15MHz) medical ultrasound systems are based on single element transducers mechanically scanned. These systems can provide images with excellent resolution. However, single element transducers are often limited by the fixed focal point and small depth of field. High frequency medical ultrasound annular arrays consisting of concentric rings of elements are focused electronically. These arrays are desirable to avoid the fixed focal point of the single element transducers and improve the depth of field. This paper demonstrate an over 10MHz annular array transducer with novel piezoelectric single crystal. This transducer exhibits good energy conversion performance with a very low insertion loss at the center frequency. The transducer is promising for intravascular ultrasonic imaging and other applications. This work was supported by the National Natural Science Foundation of China (Grant Nos. 10904093 and 61031003), the Science and Technology Grant Scheme funds from Shenzhen Government (No. 08CXY-23).

Development of high frequency annular array with a novel structure for medical imaging

High frequency annular arrays offer a number of advantages in medical imaging. A novel 2 mm diameter, 7-element, 40 MHz array using equal width elements, instead of the more conventional equal area ones, has been designed and evaluated. It showed an excellent lateral resolution (LR) with a good secondary lobe (SL) response, comparable to conventional arrays operating in excess of 70 MHz, which the frequency range causes troubles in annular arrays. The novel array with strong-focusing opens a new way to improve the image quality at relatively low operating frequencies.

Pathologic wall changes in the gallbladder in patients with gallstones and in healthy probands. Imaging using high frequency annular array sector transducers

2154 computerized ultrasound diagnoses of 1623 patients were evaluated retrospectively from January 1st to October 31st 1987. The frequency of pathologic gallbladder wall changes in patients with stones and normal controls was examined applying 5 MHz annular array sector transducer. The occurrence of polyps, septae, sludge, kinking, carcinoma and adenomyomatosis was noted separately. The prevalence of polyps and septae in gallstone patients was increased fourfold if compared to the total number of examined patients. Sludge was found in 5.9% of gallstone patients compared to 2.2% in normal controls. Carcinoma and adenomyomatosis were present only in cases of cholelithiasis; the prevalence of these pathologic wall changes is obviously rare. The importance of polyps and septae in biliary lithogenicity is discussed.

High-frequency ultrasound annular array imaging. Part II: digital beamformer design and imaging

This is the second part of a two-paper series reporting a recent effort in the development of a high-frequency annular array ultrasound imaging system. In this paper an imaging system composed of a six-element, 43 MHz annular array transducer, a six-channel analog front-end, a field programmable gate array (FPGA)-based beamformer, and a digital signal processor (DSP) microprocessor-based scan converter will be described. A computer is used as the interface for image display. The beamformer that applies delays to the echoes for each channel is implemented with the strategy of combining the coarse and fine delays. The coarse delays that are integer multiples of the clock periods are achieved by using a first-in-first-out (FIFO) structure, and the fine delays are obtained with a fractional delay (FD) filter. Using this principle, dynamic receiving focusing is achieved. The image from a wire phantom obtained with the imaging system was compared to that from a prototype ultrasonic backscatter microscope with a 45 MHz single-element transducer. The improved lateral resolution and depth of field from the wire phantom image were observed. Images from an excised rabbit eye sample also were obtained, and fine anatomical structures were discerned.