502 ISSN 1062-8738, Bulletin of the Russian Academy of Sciences: Physics, 2018, Vol. 82, No. 5, pp. 502–506. © Allerton Press, Inc., 2018. Original Russian Text © P.V. Subochev, A.G. Orlova, I.V. Turchin, Yu.S. Petronyuk, E.A. Khramtsova, V.M. Levin, 2018, published in Izvestiya Rossiiskoi Akademii Nauk, Seriya Fizicheskaya, 2018, Vol. 82, No. 5. High-Resolution Ultrasound Technologies for Studying Biological Objects P. V. Subochev a, * , **, A. G. Orlova a , I. V. Turchin a , Yu. S. Petronyuk b, c , E. A. Khramtsova b , and V. M. Levin b a Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, 603950 Russia b Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow, 119334 Russia c Scientific and Technological Center of Unique Instrumentation, Russian Academy of Sciences, Moscow, 117342 Russia *e-mail: pavel.subochev@gmail.com **e-mail: jps7@mail.ru Abstract—Russian experience in the development of high-resolution ultrasound technologies for bioimaging is considered. Two types of ultrasound biomicroscopy (UBM) systems for the in vivo imaging of skin are described: a UBM system based on a resonant transducer with the electrical excitation of probing pulses and a UBM system based on a wideband polyvinylidene difluoride detector (PVDF) with laser thermoelastic excitation of the probing pulses. DOI: 10.3103/S1062873818050271 INTRODUCTION Ultrasonography is a widespread technique for the noninvasive imaging of soft biological tissues that is widely used in routine medical diagnostics [1, 2]. Structural ultrasonography means probing a biologi- cal object with acoustic pulses and then recording the backscattered signals. As a result, ultrasonography allows us to visualize inhomogeneities of acoustic impedance in an investigated biological tissue. The spatial resolution and depth of ultrasonography are determined by the frequency range of the acoustic transducer. Clinical ultrasound tomographs function in the range of frequencies up to 20 MHz and provide submillimeter spatial resolution at a diagnostic depth of one centimeter. Advances in the technology for producing high- frequency acoustic antennas [3] and automated sys- tems for the generation and registration of ultrasound pulses [4] have led to the development of a relatively new line of ultrasound diagnostics, ultrasound biomi- croscopy (UBM) [5]. UBM is based on scanning a biological sample with high-frequency focused pulses (>20 MHz), allowing us to achieve a spatial resolution of tens of microns at a diagnostic depth of several mil- limeters. UBM imaging has been successfully used in the diagnostics of small laboratory animals [6–8] and for imaging human skin [9]. Russian research in high resolution ultrasound technologies for studying biological objects is con- ducted at two centers of the Russian Academy of Sci- ences: the Laboratory of Acoustic Microscopy of the Emanuel Institute of Biochemical Physics and the Department for Radiophysical Methods in Medicine of the Institute of Applied Physics. In this work, we consider Russian devices for UBM imaging and the results from their use on biological objects. Two types of ultrasound biomicroscopes are considered for in vivo imaging: a UBM system based on a resonant transducer in the frequency range of 50–200 MHz with electrical excitation [10–12] and a UBM system based on a nonresonant polyvinylidene difluoride detector (5–40 MHz) with laser thermoelastic exci- tation [13]. EXPERIMENTAL Imaging Principles, UBM Main Modes When a short ultrasound pulse interacts with an object in a scanning ultrasound microscope, the out- put signal of the acoustic system is formed as a series of echo pulses (A-scan), each of which corresponds to the reflections from different structural elements in the volume or caused by the excitation of different acoustic modes. Since short pulses are separated in time, we can obtain acoustic images at different depths of an object’s volume; each image is a combination of signals acquired by the receiving transducer after a focused ultrasound beam is reflected (or transmitted) by different points of the object. Point-to-point varia- tions in the amplitude and in the phase of the signal determine the contrast of the acoustic image. The ori- gin of the acoustic contrast, i.e., the relationship between these variations and the local values of the acoustic parameters of the sample (density, elasticity, viscosity), is the basis of ultrasound microscopy. At