1922
IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. 36, NO. 9, SEPTEMBER 2017
Development of a Mechanical Scanning Device With High-Frequency Ultrasound Transducer for Ultrasonic Capsule Endoscopy Xingying Wang, Vipin Seetohul, Ruimin Chen, Zhiqiang Zhang, Ming Qian, Zhehao Shi, Ge Yang, Peitian Mu, Congzhi Wang, Zhihong Huang, Qifa Zhou, Hairong Zheng, Sandy Cochran, and Weibao Qiu Abstract — Wireless capsule endoscopy has opened a new era by enabling remote diagnostic assessment of the gastrointestinal tract in a painless procedure. Video capsule endoscopy is currently commercially available worldwide. However, it is limited to visualization of superficial tissue. Ultrasound (US) imaging is a complementary solution as it is capable of acquiring transmural information from the tissue wall. This paper presents a mechanical scanning device incorporating a high-frequency transducer specifically as a proof of concept for US capsule endoscopy (USCE), providing information that may usefully assist future research. A rotary solenoid-coil-based motor was employed to rotate the US transducer with sectional electronic control. A set of gears was used to convert the sectional rotation to circular rotation. A single-element focused US transducer with 39-MHz center frequency was used for high-resolution US imaging, connected to an imaging platform for pulse Manuscript received March 7, 2017; revised April 25, 2017; accepted April 25, 2017. Date of publication May 2, 2017; date of current version August 31, 2017. This work was supported in part by Shenzhen International Collaboration under Grant GJHZ20140417113430615, in part by Research Project of CAS under Grant QYZDB-SSW-JSC018 and Grant YZ201507, in part by the National Science Foundation Grants of China under Grant 11325420, Grant 81527901, Grant 61571431, Grant 11272329, Grant 11574342, and Grant 11534013, in part by the National Basic Research Program of China under Grant 2015CB755500, in part by the Guangdong Innovative and Entrepreneurial Research Team Program under Grant 2013S046, in part by the Natural Science Foundation of Guangdong Province under Grant 2015A030306018, Grant 2014A030313686, and Grant 2014A030312006, in part by the Foundation Grants of Shenzhen under Grant JCYJ20140610151856707, and in part by the Shenzhen Peacock Plan under Grant 20130409162728468. The work of V. Seetohul, Z. Huang, and S. Cochran was supported by the U.K. EPSRC Sonopill Programme under Grant EP/K034537/1. (Corresponding author: Weibao Qiu.) X. Wang, Z. Zhang, M. Qian, Z. Shi, G. Yang, P. Mu, C. Wang, and H. Zheng are with the Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China. V. Seetohul and S. Cochran are with the School of Engineering, University of Glasgow, Glasgow G12 8QQ, U.K. R. Chen is with the Department of Biomedical Engineering, University of Southern California, Los Angeles, CA 90089 USA. Z. Huang is with Institute for Medical Science and Technology, University of Dundee, Dundee DD2 1FD, U.K. Q. Zhou is with the Department of Biomedical Engineering, University of Southern California, Los Angeles, CA 90089 USA, and also with Roski Eye Institute, Keck school of Medicine, University of Southern California, Los Angeles, CA 90033 USA. W. Qiu is with the Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China (e-mail:
[email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMI.2017.2699973
generation and image processing. Key parameters of US imaging for USCE applications were evaluated. Wire phantom imaging and tissue phantom imaging have been conducted to evaluate the performance of the proposed method. A porcine small intestine specimen was also used for imaging evaluation in vitro. Test results demonstrate that the proposed device and rotation mechanism are able to offer good image resolution ( ∼60 µm) of the lumen wall, and they, therefore, offer a viable basis for the fabrication of a USCE device.
Index Terms — Capsule endoscopy, ultrasound capsule endoscopy, mechanical scanning device, highFREQUENCY ultrasound, imaging of GI tract.
I. I NTRODUCTION ISUALIZATION of the gastrointestinal (GI) tract was enabled by the invention of endoscopy with fiber-optic light transmission [1]–[2]. Its clinical potential became clear with video capture, flexible tip control, biopsy capability, and interventional treatment [3]. Novel strategies such as miniature scanning mechanisms and specific molecular probes are being developed to obtain biological information from the targeted tissue, including metabolic and molecular function [4]. By combining ultrasonography and endoscopy technology, endoscopic ultrasound (EUS) launched a new dimension for GI imaging and diagnosis [5]. EUS provides visualization not only of lesions inside the gut wall but also of organs beyond it, including lymph nodes, lung, pancreas and liver [6]–[7]. EUS has a role in the detection of cancer as a routine procedure in patients who are suspected to have a mass or cancer in proximity to the GI tract [8]. Moreover, it allows characterization and US-guided biopsy of deep structures. However, traditional fibre optic-based endoscopy is relatively uncomfortable for the patient even though sedation is usually applied during the process and requires a clinician with a high degree of training and skill to apply it, in turn requiring the patient to visit a hospital. Additionally, the small bowel is difficult to probe since it is out of the reach of normal endoscopy [9]. Development of wireless capsule endoscopy is thus essential to complement the current imaging modalities for diagnosis and monitoring of the whole GI tract. Wireless video capsule endoscopy (VCE) opened a new era by enabling remote diagnostic assessment of the GI tract in a painless procedure [10]–[13]. A VCE device is small enough to be swallowed to gain access to the GI tract, eliminating many procedural aspects of endoscopy i.e. the need for a clinical team, sedation and recovery. The integrated miniature
V
0278-0062 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
WANG et al.: DEVELOPMENT OF A MECHANICAL SCANNING DEVICE WITH HIGH-FREQUENCY US TRANSDUCER
camera acquires images of the GI tract and transmits them through the human body wirelessly to an external data recorder from where they can be transferred to a workstation for image processing and clinical diagnosis [14]. VCE devices have the ability to travel through the entire GI tract including the small intestine [15], [16] and are currently commercially available worldwide. However, it is limited to visualization of the tissue surface: information within the lumen wall cannot be acquired by VCE and ultrasound capsule endoscopy (USCE) is thus a complementary solution. The possibility of USCE by incorporating US imaging into a capsule has been recognized for several years. Previously, in separate research: the concept was explored and demonstrated with an imaging platform [17] but no capsule device was fabricated; a rotating mirror was proposed to reflect the US wave to gain a sectional view of the tissue [18]; and an unfocused US transducer with 10 MHz center frequency was evaluated for capsule applications [19], though with image resolution limited by the use of a conventional ultrasound frequency. As an alternative, array-based USCE technology has been proposed to improve the imaging frame rate [20]–[21] and reduce mechanical complexity. The mechanical parts are replaced by a radial array transducer able to scan electronically for circular imaging. However, it is presently challenging to fabricate an array transducer and the necessary circuits in the limited space within a capsule. Capacitive micromachined ultrasonic transducers (CMUTs) have also been subject to extensive research for the last two decades [22] with a CMUT array also proposed for capsule ultrasound applications, using a 5 MHz ultrasound frequency [23]–[24]. Nevertheless, high frequency US (HFUS) is able to provide high resolution images [25]–[27] with the possibility to view the lumen wall in detail and mechanical scanning is therefore of immediate interest. Although the concept of USCE has been proposed previously [18]–[20], this paper represents the first time that high frequency ultrasound (HFUS), at 39 MHz, has been demonstrated in an ultrasonic capsule format to produce a high resolution ultrasound image. HFUS was employed to provide the necessary imaging resolution, which was found to have a best value of 57.8 μm and was demonstrated to be suitable for delineation of the lumen wall and identification of layers within it. A rotary solenoid-coil based motor is employed to obtain a circular images of tissue while eliminating the difficulties associated with other solutions including a rotating mirror and slip rings. An imaging platform is employed for pulse generation and imaging processing. This has allowed key parameters of US imaging for USCE applications to be evaluated, with wire phantom imaging, tissue-mimicking phantom imaging, and ex vivo tissue imaging used to demonstrate the performance of the proposed method. II. M ETHODS
A. Design of Capsule with Gears The USCE scheme proposed in this study is shown in Fig. 1(a). A single-element HFUS transducer is used for US
1923
Fig. 1. The proposed device with motor and gears for USCE applications. (a) The potential application with the proposed mechanical device. (b) The rotation mode of the device.
imaging. A motor with a rotary solenoid-coil (RSR7/10-T010, Takano Co., Ltd, Japan) is used for the sectional scan with an inner cylindrical permanent magnet applied as the rotor. Rotary motion is achieved by mutual attraction of the magnetic poles generated by the rotor and yoke. The rotor is driven to rotate by magnetic force with a fixed stator and the direction of the magnetic force is changed by changing the direction of current in the coil. Metal plates fixed on two sides physically limit the rotation of motor to 120 ° and a set of gears is employed to transfer rotation from the motor to the transducer. 360° rotation is achieved with an internal spur gear, which the motor rotates, and two external spur gears which are fixed in place, with the transducer on a common drive shaft with the central external gear, Fig. 1(b). The transducer was rotated in an oscillatory manner rather that a continuous rotation to gain a circular view of the tissue. The modulus of the gears is set to 0.3. The gears, the mounting board, and the shell of the capsule were fabricated with 3D printing technology (Stratasys, Connex350, Eden Prairie, MN) using photosensitive resin material. In this study, the integrated circuit (IC) and battery shown in Fig. 1(a) were replaced by an external imaging platform for imaging evaluation and this paper focuses on the mechanical scanning and the HFUS transducer. A major advantage of our mechanical scanning scheme is that it avoids the need for miniature slip rings and their deleterious effect on low amplitude, high frequency electrical signals. It also simplifies control and has the potential to reduce power consumption since the motor does not need to run continuously.
B. Ultrasonic Transducer A customized press-focused ultrasonic transducer was fabricated and utilized in this study (Fig. 2). 36° -rotated Y-cut lithium niobate (LNO) single crystal (Boston Piezo-Optics,
1924
IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. 36, NO. 9, SEPTEMBER 2017
Fig. 3. System block diagram of electronics potentially for USCE applications. A dedicated imaging platform was implemented according to this diagram for evaluation of key imaging parameters.
Fig. 2. (a) Structure of single-element based HFUS transducer; (b) Diagram of the setting for USCE applications.
Bellingham, MA) was selected as the piezoelectric material of the transducer. The center frequency of the transducer was designed to be 39 MHz. A double matching-layer scheme was employed to improve transducer performance. The 1st matching layer was made by mixing Ag particles in the size range 2-3 μm (Aldrich Chemical Co., Milwaukee, WI, USA) with Insulcast 501 and Insulcure 9 (American Safety Technologies, Roseland, NJ, USA). The mixture was cast over the LNO plate and then lapped to the desired thickness after curing. Conductive epoxy (E-Solder 3022, VonRoll Isola, New Haven, CT, USA) was cast onto the back of the LNO. The acoustic stack was then turned down to a circular shape with a precise diameter of 2.6 mm on a lathe and then housed in a 3.0 mm diameter cylindrical brass tube with a 150 μm wall thickness. Press-focusing [28] was used to generate a focal distance of 7 mm. A Cr-Au electrode was sputtered on the front surface of the transducer to make aground connection between the transducer and the brass housing. For the 2nd matching layer, a parylene-C layer of thickness 10 μm was vapor-deposited onto the entire outer surface of the transducers using a commercial deposition system (PDS2010, Specialty Coating Systems Inc., Indianapolis, IN, USA). A micro-coaxial cable (5461-115, Hitachi Cable America Inc., Harrison, NY) provided the electrical connection to the finished transducer which had diameter 3.0 mm and height 4.0 mm
C. USCE Electronics System Fig. 3 is a system block diagram for USCE with a single-element transducer. High switching speed metal-oxidesemiconductor field effect transistors (MOSFETs) are used for US pulse excitation. The low noise amplifier and band-pass
filter are needed to process the received echo signals. The processor could be either a microcontroller unit (MCU) or field programmable gate array (FPGA). The power regulator (LT3958, Linear Technology, Milpitas, CA) is used to boost the low supply voltage (∼5 V) from the lithium battery to high voltage (∼ ±48 V) for pulse generation. The antenna is employed for wireless communication with an external workstation. In this study, key parameters of electronics for USCE were tested with a dedicated imaging platform. A microcoaxial cable connects the scanning device and the imaging platform, which is implemented on a 10-layer printed circuit board, including pulse generation and data acquisition circuits. A MOSFET pair (TC6320, Supertex Inc., Sunnyvale, CA) is used to generate a bipolar high voltage pulse for US imaging. A field programmable gate array (FPGA) (Cyclone IV, EP4CE115F29, Altera Corporation, San Jose, CA) is employed to control the workflow of the whole platform. The amplitude and center frequency of the excitation pulse are adjustable to optimize performance (Peak to peak voltage: 24 - 96 Vpp ; Center frequency: 15 - 50 MHz) [29]. Low noise amplifiers (LNAs) (SMA231, Tyco Electronics Co., Berwyn, PA; THS4509, Texas Instruments Inc., Dallas, TX) and a high-speed ADC (ADS5517, Texas Instruments Inc., Dallas, TX) are employed, respectively, for amplification and digitization of the received US echo signals. Radio frequency (RF) signals input to the ADC after the LNAs are processed directly by the FPGA for fast imaging within a small physical volume including digital filtering and envelope detection. The processed image data are transferred to a computer through a WiFi interface implemented with a module based on a commercial wireless transceiver (CC3200, Texas Instruments Inc., Dallas, TX). The image processing algorithm in this USCE study is similar to one previously developed for intravascular ultrasound [30]. In the present case, the image frame rate was set to 0.5 frame per second (fps), consistent with the relatively slow motion of a capsule through the gut.
D. Motor Control Circuit The motor rotates back and forth at a rate corresponding to 1 fps under the control of the circuit shown in Fig 4. This is a transistor-based-switching circuit (S9014 and S9013, Fairchild
WANG et al.: DEVELOPMENT OF A MECHANICAL SCANNING DEVICE WITH HIGH-FREQUENCY US TRANSDUCER
1925
Fig. 4. Driving circuit for the motor with direction control based on switching of transistors.
Semiconductor Corp., San Jose, CA) which would be easy to integrate into a specialized IC. The direction of current flowing into the motor is used to control the direction of rotation. The control signals are 3.3 V TTL, provided by the FPGA in this study. A ± 5 V DC power supply was used to drive the motor as a higher voltage supply provides more torque. A positive voltage (+5 V) provided clockwise rotation and a negative voltage (−5 V) counterclockwise rotation. The motor worked on a “pulsed-mode” to reduce power consumption, with the power supply not required when each rotation is finished.
Fig. 5. Three phantoms for evaluation of the proposed device. (a) Circular tungsten wire phantom with twelve 20 µm diameter wires. The radius at which the wires are located is 11 mm; (b) Line wire phantom with 1 mm equal distance; (c) Tissue phantom with three anechoic cylindrical features, diameters 0.9, 1.4 and 3.0 mm.
simultaneously [33]. CNR was calculated as: CNR =
E. Imaging Evaluation Three US phantoms were fabricated for imaging evaluation, two wire phantoms, A and B, and a tissue-mimicking phantom. Wire phantom A, Fig. 5(a), is a circular arrangement with 12 tungsten wires of 15 μm diameter (Qingyuan Metal Material, Inc., Xingtai, Hebei Province, China) mounted in a hollow cylinder equidistantly in the circumferential direction at a radius of 11 mm. It was used to validate the distribution around the capsule device to make sure a 360° view of the images could be achieved. Wire phantom B, Fig. 5(b), consists of five tungsten wires arranged 1 mm apart equidistantly in the radial direction at a mean radius of 9 mm. The highest resolution of the images was expected at 1.5 mm distance outside the capsule shell, so the third wire of the phantom was located at 9 mm. Quantitative measurements of the axial and lateral resolution were made with these phantoms, measuring the full width at half maximum (FWHM) [31]. The third phantom was a cylindrical agar-based tissuemimicking phantom [32] with three anechoic features. This phantom generates tissue mimicking attenuation of about 32 dB/cm for ultrasound at 39 MHz and backscattering to test resolution and penetration depth. The anechoic features were cylindrical holes with diameters 0.9, 1.4 and 3.0 mm, distributed at 120 °intervals around the phantom at radial positions 9.2, 9.5 and 10.3 mm respectively. The contrastto-noise ratio (CNR) of the anechoic holes provides indirect characterization of device spatial resolution in all directions
|mean t − mean n | stat2 + stan2
(1)
where meant and meann represent the mean backscatter magnitude of the cylindrical tissue-mimicking phantom and the anechoic hole. stat and stan represent the corresponding standard deviations. The CNR was calculated three times for the three different diameter anechoic holes. III. R ESULTS The proof-of-concept prototype of the proposed mechanical scanning device incorporating the HFUS transducer and the imaging platform are depicted in Fig. 6. The prototype device is 15 mm in diameter, 25 mm in length, and has mass 4 g.
A. Transducer Test The pulse-echo response of the HFUS transducer was measured to evaluate its performance. It was mounted on a holder and immersed in a tank filled with deionized water. A flat quartz reflector was placed 7 mm from the transducer, the distance corresponding with its focal length. The transducer was excited with a commercial ultrasonic pulser-receiver (Panametrics 5900PR, Olympus NDT Inc., Waltham, MA) with a 1 μJ electrical impulse, 200 Hz repetition rate, and 50 damping factors. Fig. 7 presents the measured pulseecho waveform and frequency spectrum, indicating center frequency, f c = 39 MHz and −6 dB bandwidth, BW−6dB = 62.5%.
1926
IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. 36, NO. 9, SEPTEMBER 2017
Fig. 6. The proposed mechanical scanning device and the high frequency US imaging platform.
Fig. 7. Measured pulse-echo response and its FFT spectrum of the fabricated US transducer.
B. Imaging of Wire Phantom The image quality was evaluated first with the two tungsten wire phantoms. Fig. 8(a) shows the circular wire phantom image with average axial and lateral resolutions of 67.4 μm and 221.9 μm, respectively. Fig. 8(b) demonstrates the line wire phantom image. The axial and lateral resolutions in the third wire are 57.8 μm and 181.6 μm, respectively, in reasonable agreement with those from the other phantom. The dynamic range of the images is set to 50 dB. C. Imaging of Tissue Phantom Fig. 9 shows an US image and the averaged backscatter as a function of depth of the tissue-mimicking phantom. The focus is located at 1 mm beneath the surface of the tissue phantom. The device provides a certain imaging depth and hole visualization when dynamic range is set to 50 dB. 100 A-lines were averaged (chosen in an area without an anechoic hole) to obtain averaged backscatter data to determine the penetration depth. Defining the penetration depth as the depth in the phantom at which the signal amplitude is 6 dB higher than the background noise, this can be seen to be 6 mm in Fig. 9(b). Average CNRs were 6.5, 4.3, and 3.3 for the
Fig. 8. Images of (a) a circular wire phantom, and (b) a line wire phantom captured by the proposed device. The images are displayed with 50 dB dynamic range.
anechoic hole diameters of 3.0, 1.4 and 0.9 mm, respectively. No time gain compensation was applied and the gain was kept consistent throughout the acquisition.
D. In vitro Measurement of Swine Small Intestine Sample A porcine small intestine specimen was used for imaging evaluation in vitro. The specimen was gently opened by a cylindrical holder. The proposed device was inserted into the specimen immersed in a water tank for cross-sectional imaging, with the resulting US image shown in Fig. 10. This measurement was made with dynamic range 46 dB. Different layers of the lumen wall can be clearly identified. IV. D ISCUSSION The mechanical scanning device incorporating HFUS imaging presented in this paper was designed to explore the potential for wireless USCE. The center frequency of ultrasound could be controlled to match the characteristics of a specific patient by choosing a specific transducer to balance the penetration depth and resolution. This corresponds with contemporary trends in precision medicine. In addition, the
WANG et al.: DEVELOPMENT OF A MECHANICAL SCANNING DEVICE WITH HIGH-FREQUENCY US TRANSDUCER
1927
Fig. 9. The sectional image of the tissue phantom acquired by the proposed device, acquired with 50 dB dynamic range.
TABLE I S UMMARY OF THE DEVICE CHARACTERISTICS
Fig. 10. The sectional image of (a) porcine small intestine in vitro, and (b) enlarged area of interest, shown with 46 dB dynamic range.
proposed motor scheme eliminates the mirror and slip ring. This is a new method for capsule implementation which may be very important to establish reliable capsule operation with high quality imaging. Moreover, the platform provides an effective way to evaluate the key parameters of imaging, which will be useful in the designing of an application-specific IC. Chirp waveform excitation is conceptually a very good method to increase the penetration depth [34]. However, the excitation circuit is more complicated and thus was deemed unsuitable for capsule device development at its present stage.
Since capsule endoscopy devices are usually singleuse/disposable, their cost is important. The approach proposed in this paper is aimed at low-cost USCE as the motor and mechanical gears are inexpensive and easy to fabricate or purchase. A rotary solenoid-coil motor was used to generate rotational motion as the control unit is simpler than for a linear step motor. Similarly, a single-element HFUS transducer was chosen as it is much simpler to fabricate than an array transducer and requires much less complicated control circuitry. The diameter of the fabricated prototype is still too large for human use but highly appropriate for preclinical testing in animals. The principal reason for the present dimensions is the fabrication process for the gears; smaller gears could be achieved by applying high precision engineering. However, to demonstrate full investigation of the imaging resolution, the nearest wire was moved just within the capsule diameter. Variations in brightness in Fig. 8(a) are attributed to variations in alignment of the very small wires. Impedance mismatch and electronic noise are other factors which may degrade the imaging results.
1928
IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. 36, NO. 9, SEPTEMBER 2017
The circuitry demonstrated in this study, Fig. 1(a) and Fig. 3, was implemented with separate components on a PCB allowing the essential electronics for USCE applications to be demonstrated. An application specific integrated circuit (ASIC) for single-channel US imaging could be designed using the summary of USCE requirements presented in Table 1. US image data are transmitted wirelessly in VCE applications. RF technology already available for operation at 2.4 GHz and 433 MHz frequencies can be used for wireless connection. All the electronic requirements are therefore amenable to integration into one ASIC, as with VCE, since the application scenario demonstrated by this study is so similar to VCE [35]. Knowledge of the energy consumption is very important in the design of such an ASIC. Low power design should be taken into consideration [36]–[39]. In the system described here, the frame rate was set to 0.5 fps for ultrasonic imaging as the capsule moves along the lumen at a very low speed, median 0.23 mm/s [40]. High frame rate imaging could be achieved but this is a trade-off with power consumption and is difficult to justify given the rate of passage of capsules through the GI tract, particularly as higher power consumption directly reduces the capsules operating time and thus the length of the gut which can be imaged. Power supply for an ultrasonic capsule in this study is needed for at least four functions: (1) to excite the transducer, (2) to rotate the motor, (3) to acquire and process the echo signal, and (4) to run the wireless transmitter. Our device demonstrated operation in a switched ON/OFF mode to reduce power consumption. We tested the first two functions of the proposed circuit with a current probe (Tektronix DPO 4104B, Beaverton, OR) which showed that the peak current was 0.248 A for 0.025 s for one image. Since the evaluation system in this study did not include an application specific IC, we took a highly-integrated analog front-end chip (AFE5818, Texas Instruments Inc., Dallas, TX) as an example to determine that a single channel ultrasound data path consumes 140 mW. The processor (CC3200, embedded ARM cortex-M4 core) was evaluated for the fourth item, wireless transmission, with average current and voltage of 166 mA and 2.5 V respectively. Hence, the total energy consumption of these four parts is 0.6709 J. Assuming a high performance battery (3V, 1000 mAh) is employed, the theoretical number of images that could be acquired is 16097 images in a period of 8.9 hr, similar to an optical capsule [41]. However, it must be noted that this is a theoretical estimation of the power consumption and this topic should be considered carefully when ASIC design is applied. VCE is currently in clinical use worldwide and problems are being overcome. For example, the time for evaluation of a full series of images can now be reduced to 10 minutes through techniques such as adaptive frame rate recording. However, other problems remain, such as tumbling of the device [42], and new solution are needed to make further progress. Combining ultrasound imaging with optical imaging in one capsule would thus have a very strong impact. Fig. 1(a) demonstrates a basic configuration for dual-modality imaging with an optical imaging circuit placed at one end
of the capsule. Moreover, real time location monitoring and compensation [40]–[42] will also be important when combined into a capsule. V. C ONCLUSION In this study, a mechanical scanning device incorporating HFUS imaging was presented as a means to explore the possibilities of USCE. A solenoid-coil motor and a gear set were employed to rotate a HFUS transducer to acquire a circular view of the lumen wall. The test results that have been presented demonstrate that it is able to offer image resolution better than 60 μm and that the layers within porcine small intestine, closely matching those of the human gut, can be resolved. It therefore offers a viable basis for fabrication of a USCE device. ACKNOWLEDGEMENT The authors are grateful for the critical review of the MS by Dr B. F. Cox, Clinical Research Fellow, Sonopill Programme, and University of Dundee, UK. R EFERENCES [1] H. H. Hopkins and N. S. Kapany, “A flexible fibrescope, using static scanning,” Nature, vol. 173, pp. 39–41, Jan. 1954. [2] B. Hirschowitz et al., “Demonstration of a new gastroscope, the fiberscope,” Gastroenterology, vol. 35, no. 1, pp. 50–51, 1958. [3] M. V. Sivak, “Gastrointestinal endoscopy: Past and future,” Gut, vol. 55, no. 8, pp. 1061–1064, 2006. [4] S. F. Elahi and T. D. Wang, “Future and advances in endoscopy,” J. Biophotonics, vol. 4, nos. 1–8, pp. 471–481, Aug. 2011. [5] E. P. DiMagno et al., “Ultrasonic endoscope,” Lancet, vol. 315, no. 8169, pp. 629–631, Mar. 1980. [6] C. J. Kenneth, G. L. John, F. H. Randall, K. Jeffrey, M. Raman, and L. W. Mark, “Endoscopic ultrasound delivery of an antitumor agent to treat a case of pancreatic cancer,” Nature Rev. Gastroenterol. Hepatol., vol. 5, no. 2, pp. 107–111, 2008. [7] A. Larghi, E. C. Verna, P. G. Lecca, and G. Costamagna, “Screening for pancreatic cancer in high-risk individuals: A call for endoscopic ultrasound,” Clin. Cancer Res., vol. 15, no. 6, pp. 1907–1914, 2009. [8] J. Iglesias–Garcia, J. Larino–Noia, I. Abdulkader, J. Forteza, and J. E. Dominguez–Munoz, “Quantitative endoscopic ultrasound elastography: An accurate method for the differentiation of solid pancreatic masses,” Gastroenterology, vol. 139, no. 4, pp. 1172–1180, 2010. [9] G. Ciuti, A. Menciassi, and P. Dario, “Capsule endoscopy: From current achievements to open challenges,” IEEE Rev. Biomed. Eng., vol. 4, no. 10, pp. 59–72, Oct. 2011. [10] G. Iddan, G. Meron, A. Glukhovsky, and P. Swain, “Wireless capsule endoscopy,” Nature, vol. 405, pp. 405–417, May 2000. [11] A. Moglia, A. Menciassi, P. Dario, and A. Cuschieri, “Capsule endoscopy: Progress update and challenges ahead,” Nature. Rev. Gastroenterol. Hepatol., vol. 6, no. 6, pp. 353–361, Jun. 2009. [12] S. L. Triester et al., “A meta-analysis of the yield of capsule endoscopy compared to other diagnostic modalities in patients with obscure gastrointestinal bleeding,” Amer. J. Gastroenterol., vol. 100, no. 11, pp. 2018–2047, 2005. [13] J. L. Goldstein, G. M. Eisen, B. Lewis, I. M. Gralnek, S. Zlotnick, and J. G. Fort, “Video capsule endoscopy to prospectively assess small bowel injury with celecoxib, naproxen plus omeprazole, and placebo,” Clin. Gastroenterol. Hepatol., vol. 3, no. 2, pp. 133–141, Feb. 2005. [14] S. Paul, I. J. Gavriel, M. Gavriel, and G. Arkady, “Wireless capsule endoscopy of the small bowel: Development, testing, and first human trials,” Proc. SPIE, vol. 4158, pp. 19–23, Jan. 2001. [15] Z. Fireman and Y. Kopelman, “New frontiers in capsule endoscopy,” J. Gastroenterol. Hepatol., vol. 22, no. 8, pp. 1174–1177, Aug. 2007. [16] Z. Fireman et al., “Diagnosing small bowel Crohn’s disease with wireless capsule endoscopy,” Gut, vol. 52, no. 3, p. 390, 2003. [17] C. João et al., Final Report Summary—TROY (Endoscope Capsule Using Ultrasound Technology), Project ID: 33110, Funded under: FP6-SME, Portugal 2009.
WANG et al.: DEVELOPMENT OF A MECHANICAL SCANNING DEVICE WITH HIGH-FREQUENCY US TRANSDUCER
[18] G. Iddan, Ultrasonic Capsule With Rotatable Reflector, document PCT/IB2010/052459. [19] J. H. Lee et al., “Towards wireless capsule endoscopic ultrasound (WCEU),” in Proc. IEEE Int. Ultrason. Symp. (IUS), Sep. 2014, pp. 734–737. [20] H. S. Lay, V. Seetohul, B. Cox, C. E. M. Démoré, and S. Cochran, “Design and simulation of a high-frequency ring-shaped linear array for capsule ultrasound endoscopy,” in Proc. IEEE Int. Ultrason. Symp. (IUS), Sep. 2014, pp. 683–686. [21] A. Michael, W. Bandy, and W. Shanks, “Ultrasound scanning capsule endoscope (USCE),” U.S. Patent 8 647 259 B2, Feb. 11, 2014. [22] B. T. Khuri-Yakub and Ö. Oralkan, “Capacitive micromachined ultrasonic transducers for medical imaging and therapy,” J. Micromech. Microeng., vol. 21, no. 5, p. 054004, 2011. [23] F. Memon et al., “Capsule ultrasound device,” in Proc. IEEE Int. Ultrason. Symp. (IUS), Oct. 2015, pp. 1–4. [24] F. Memon et al., “Capsule ultrasound device: Further developments,” in Proc. IEEE Int. Ultrason. Symp. (IUS), Sep. 2016, pp. 1–4. [25] W. Qiu, Y. Yu, F. K. Tsang, and L. Sun, “An FPGA-based open platform for ultrasound biomicroscopy,” IEEE Trans. Ultrason., Ferroelect., Freq. Control, vol. 59, no. 7, pp. 1558–1567, Jul. 2012. [26] B. Zhu et al., “(100)-Textured KNN-based thick film with enhanced piezoelectric property for intravascular ultrasound imaging,” Appl. Phys. Lett., vol. 106, no. 7, p. 173504, 2015. [27] J. Ma et al., “Design factors of intravascular dual frequency transducers for super-harmonic contrast imaging and acoustic angiography,” Phys. Med. Biol., vol. 60, no. 9, pp. 3441–3457, 2015. [28] J. M. Cannata, T. A. Ritter, W.-H. Chen, R. H. Silverman, and K. K. Shung, “Design of efficient, broadband single-element (20-80 MHz) ultrasonic transducers for medical imaging applications,” IEEE Trans. Ultrason., Ferroelect., Freq. Control, vol. 50, no. 11, pp. 1548–1557, Nov. 2003. [29] W. Qiu, Y. Yu, F. K. Tsang, and L. Sun, “A multifunctional, reconfigurable pulse generator for high-frequency ultrasound imaging,” IEEE Trans. Ultrason., Ferroelect., Freq. Control, vol. 59, no. 7, pp. 1432–1442, Jul. 2012. [30] W. Qiu et al., “An open system for intravascular ultrasound imaging,” IEEE Trans. Ultrason., Ferroelect., Freq. Control, vol. 59, no. 10, pp. 2201–2209, Oct. 2012.
1929
[31] J. M. Thijssen, G. Weijers, and C. L. de Korte, “Objective performance testing and quality assurance of medical ultrasound equipment,” Ultrasound Med. Biol., vol. 33, no. 3, pp. 460–471, Mar. 2007. [32] J. Fromageau, J. L. Gennisson, C. Schmitt, R. L. Maurice, R. Mongrain, and G. Cloutier, “Estimation of polyvinyl alcohol cryogel mechanical properties with four ultrasound elastography methods and comparison with gold standard testings,” IEEE Trans. Ultrason., Ferroelect., Freq. Control, vol. 54, no. 3, pp. 498–509, Mar. 2007. [33] M. A. Lediju, G. E. Trahey, B. C. Byram, and J. J. Dahl, “Shortlag spatial coherence of backscattered echoes: Imaging characteristics,” IEEE Trans. Ultrason., Ferroelect., Freq. Control, vol. 58, no. 7, pp. 1377–1388, Jul. 2011. [34] W. Qiu et al., “A modulated excitation imaging system for intravascular ultrasound,” IEEE Trans. Biomed. Eng., to be published. [35] L. Wang et al., “A programmable microsystem using system-on-chip for real-time biotelemetry,” IEEE Trans. Biomed. Eng., vol. 52, no. 7, pp. 1251–1560, Jul. 2005. [36] I. Kim et al., “CMOS ultrasound transceiver chip for high-resolution ultrasonic imaging systems,” IEEE Trans. Biomed. Circuits Syst., vol. 3, no. 5, pp. 293–303, Oct. 2009. [37] H. Choi, X. Li, S.-T. Lau, C. Hu, Q. Zhou, and K. K. Shung, “Development of integrated preamplifier for high-frequency ultrasonic transducers and low-power handheld receiver,” IEEE Trans. Ultrason., Ferroelect., Freq. Control, vol. 58, no. 12, pp. 2646–2658, Dec. 2011. [38] C. C. Huang, P.-Y. Lee, P.-Y. Chen, and T.-Y. Liu, “Design and implementation of a smartphone-based portable ultrasound pulsed-wave Doppler device for blood flow measurement,” IEEE Trans. Ultrason., Ferroelect., Freq. Control, vol. 59, no. 1, pp. 182–188, Jan. 2012. [39] G.-Z. Wu, S.-N. Tang, C.-C. Chang, C.-J. Lee, K.-H. Lin, and O. T. C. Chen, “High-frequency and power-efficiency ultrasound beamforming processor for handheld applications,” in Proc. 27th IEEE Int. System-Chip Conf., Sep. 2014, pp. 420–424. [40] J. Worsøe et al., “Gastric transit and small intestinal transit time and motility assessed by a magnet tracking system,” BMC Gastroenterol., vol. 11, no. 1, p. 145, 2011. [41] A. Wang et al., “Wireless capsule endoscopy,” Gastrointestinal Endoscopy, vol. 78, no. 6, pp. 805–815, 2013. [42] A. Koulaouzidis, D. K. Iakovidis, A. Karargyris, and E. Rondonotti, “Wireless endoscopy in 2020: Will it still be a capsule?” World J. Gastroenterol., vol. 21, no. 17, pp. 5119–5130, 2015.
