Nominal Center Frequency Research Articles

High-Frequency Ultrasonic Spectroscopy of Structure Gradients in Injection-Molded PEEK Using a Focusing Transducer.

For high-performance thermoplastic materials, material behavior results from the degree of crystallization and the distribution of crystalline phases. Due to the less stiff amorphous and the stiffer and anisotropic crystalline phases, the microstructural properties are inhomogeneous. Thus, imaging of the microstructure is an important tool to characterize the process-induced morphology and the resulting properties. Using focusing ultrasonic transducers with high frequency (25 MHz nominal center frequency) enables the imaging of specimens with high lateral resolution, while wave propagation is related to the elastic modulus, density and damping of the medium. The present work shows experimental results of high-frequency ultrasonic spectroscopy (HF-US) applied to injection-molded polyether-ether-ketone (PEEK) tensile specimens with different process-related morphologies. This work presents different analysis procedures, e.g., backwall echo, time of flight and Fourier-transformed time signals, facilitating the mapping of gradual mechanical properties and assigning them to different crystalline content and morphological zones.

Design and fabrication of a Wilkinson power divider with harmonic suppression for LTE and GSM applications

Conventional Wilkinson power dividers (WPDs) can provide acceptable performance close to the nominal center frequency. However, these WPDs can also exhibit poor out-of-band performance while requiring a large footprint. In order to improve on the current state of the art, a modified microstrip WPD is proposed that exhibits a substantially improved stopband and high isolation. A lowpass filter (LPF) structure is utilized in both branches of the power divider to provide harmonic suppression. According to the obtained results, the input return loss (|S11|), output return loss (|S22|), output insertion loss (|S21|) and isolation (|S32|) are better than 34.2 dB, 26.2 dB, 3.52 dB and 31.2 dB, respectively. The proposed modified WPD has a wide 20 dB stopband (from 2.54 GHz to 13.48 GHz) and filters the second to seventh harmonics with attenuation levels of greater than 20 dB. The proposed WPD has a small size of 33.8 mm × 27 mm (0.42 λg × 0.33 λg), where λg is the guided wavelength at the operating frequency of 1.8 GHz. The WPD has been fabricated and tested and shows good agreement between simulated and measured results and the proposed design has desirable characteristics for LTE and GSM applications.

Evaluation of Air-Cavities behind Concrete Tunnel Linings Using GPR Measurements

The primary objectives of this study are to investigate the interference of ground penetrating radar (GPR) signals with air-cavities behind concrete linings subjected to three experimental parameters (GPR antenna frequency, thickness of concrete lining, and thickness of air-cavities), and their effects on the evaluation of important engineering parameters (thickness of concrete, and length and thickness of air-cavities) for tunnel structure inspection using GPR. For these purposes, first, a concrete model specimen is fabricated in the laboratory, which simulates air-cavity defects with various thicknesses (0 mm, 30 mm, 100 mm, 200 mm, and 300 mm) behind concrete with four different thicknesses (100 mm, 200 mm, 300 mm, and 400 mm) in tunnel structures. Second, a series of GPR survey is performed on the fabricated concrete model specimen using three ground-coupled GPR antennas with nominal center frequencies of 400 MHz, 900 MHz, and 1600 MHz. Third, a practical signal interpretation method is proposed to evaluate air-cavities in concrete tunnel linings subjected to the three experimental parameters. It is demonstrated that the cross-correlation analysis is effective for identifying air-cavities behind concrete, and for characterizing the length of the air-cavities. In addition, the thicknesses of air-cavities are estimated by a new approach in this study, measuring the apparent time delay of partially overlapped electromagnetic wave reflections within air-cavities. The results in this study provide a fundamental basis to improve GPR signal interpretation techniques for the evaluation of air-cavities behind concrete tunnel linings.

Defect Detection in Aluminum Bars Using Impedance and Ultrasonic Attenuation

Aluminum alloys are mainly used to manufacture automated machinery and in aeronautic, automotive, and biomedical structures, as well as tools for functions requiring strength, lightness, and precise movements. Monitoring and characterization of this material is very important to guarantee quality for those structures. This study proposes a new methodology for nondestructive testing and characterization of these materials using attenuation of ultrasonic waves and electrical impedance of piezoelectric ceramic plates attached to aluminum alloy bars. Five solid aluminum bars measuring 250 mm $\times \,\, 50$ mm $\times \,\, 50$ mm were used; in four, three holes of varying diameters and depths were drilled to simulate defects, while one bar was left intact as a reference. Three piezoelectric ceramic plates measuring 12.7 mm $\times \,\,12.7$ mm $\times \,\,0.52$ mm were attached to each bar near the manufactured defects and at the same position in the reference sample. Electrical impedance was assessed, and attenuation of the ultrasonic waves was measured using a function generator to excite the ceramic plates with a single 20 Vpp sine pulse in transmit/receive and pulse-echo modes at 90, 145, 230, and 376 kHz. Broadband attenuation was assessed using two pairs of transducers with nominal center frequency of 500 kHz and 5 MHz. The signals were acquired using a Tektronix TDS2022 digital oscilloscope and then processed in MATLAB. The results showed the viability of this technique for identifying defects in metallic aluminum structures and characterizing these materials using lower frequencies.

Nonlinear frequency modulated excitation signal and modified compressing filter for improved range resolution and side lobe level of ultrasound echoes

PurposeA Compensated Frequency Modulated (CFM) code is proposed as an excitation signal of an ultrasound pulse-echo system. It has a flat envelope and a non-uniform spectral energy density distributed throughout the time span and is tuned to equalize the frequency losses imposed by the system, including the transmitting/receiving electronic instrumentation, the transducer and the propagation medium. The CFM synthesis and the compression filter rely on arbitrary variables, one in determining the CFM spectrum magnitude and the other in determining the spectral magnitude of the compression filter that optimizes the side lobe level and duration (range resolution) of the compressed echo pulse. MethodsThe first step is to determine the system transfer function. It is derived from the Fourier transform of an echo signal from a flat reflector, with the transmit/receiving transducer excited by a linear frequency modulated (LFM) signal swept in a frequency range four times the transducer bandwidth, spread symmetrically about the nominal center frequency of the transducer employed in the present work. Experiments were conducted based on a transducer with a half power frequency bandwidth corresponding to 45% of its central frequency and a sweep signal with a time span of 20µs. Computational simulation was also implemented to determine the effects on the range resolution due to the noise level over the echo signals. ResultsThe most relevant results in this research are the range resolution as low as 0.23mm and the maximum temporal lobes below −36dB. The range resolution obtained with LFM excitation based on the same ultrasonic system setup was on the order of 1.0mm. ConclusionsThe novelty of this approach resides in the pseudo-inversion of the system transfer function magnitude. The combined techniques of CFM pre-filtering and pulse compression mode yielded improved performance in relation to the echo signal duration and temporal side lobes; in addition, a gain of 12 dB over the received echo signal was achieved when using an LFM type excitation signal.

Metrological Validation of a Measurement Procedure for the Characterization of a Biological Ultrasound Tissue-Mimicking Material

The speed of sound and attenuation are important properties for characterizing reference materials such as biological phantoms used in ultrasound applications. There are many publications on the manufacture of ultrasonic phantoms and the characterization of their properties. However, few studies have applied the principles of metrology, such as the expression of the uncertainty of measurement. The objective of this study is to validate a method for characterizing the speed of sound and the attenuation coefficient of tissue-mimicking material (TMM) based on the expression of the measurement of uncertainty. Six 60-mm-diameter TMMs were fabricated, three 10 mm thick and three 20 mm thick. The experimental setup comprised two ultrasonic transducers, acting as transmitter or receiver depending on the stage of the measurement protocol, both with a nominal center frequency of 5 MHz and an element diameter of 12.7 mm. A sine burst of 20 cycles and 20-V peak-to-peak amplitude at 5 MHz excited the transmitter transducer, producing a maximum pressure of 0.06 MPa. The measurement method was based on the through-transmission substitution immersion technique. The speed of sound measurement system was validated using a calibrated stainless-steel cylinder as reference material, and normalized errors were <0.8. The attenuation coefficient measurement method was validated using replicated measurements under repeatability conditions. The normalized error between the two measurement sets was <1. The proposed uncertainty models for the measurements of the speed of sound and the attenuation coefficient can help other laboratories develop their own uncertainty models. These validated measurement methods can be used to certify a TMM as a reference material for biotechnological applications.

Impact of element pitch on synthetic aperture ultrasound imaging.

Synthetic aperture imaging was introduced in medical ultrasound to obtain high-quality images. In synthetic aperture ultrasound imaging, spherical transmit waves illuminate a target region from different positions, resulting in low-resolution images for each transmission. By coherent compounding of the resulting low-resolution images, a high-resolution image is obtained. Multiple steered receiving beams need to be created to obtain each low-resolution image and, thus, grating lobes should influence the image quality. In the present study, an array ultrasonic probe with a small element pitch was introduced to reduce the influences of grating lobes, and the effect of element pitch on image quality was examined in detail. A linear array ultrasonic probe at a nominal center frequency of 7.5MHz with an element pitch of 0.1mm has been introduced. This probe does not produce grating lobes within the imaging region in theory because the element pitch of this probe is half of the ultrasonic wavelength. The contrast of an ultrasonic image was evaluated using a cyst phantom. The contrasts obtained by synthetic aperture imaging with element pitches of 0.1 and 0.2mm were 4.88 and 4.69dB, respectively, which were similar to the 4.67dB obtained by conventional beamforming with focused transmit beams, when the number of transmissions was 121. The contrast obtained with an element pitch of 0.1mm was similar (4.34dB) even when the number of transmissions was decreased to 61. However, the contrast obtained with an element pitch of 0.2mm showed a larger degradation (3.77dB) at 31 transmissions. Even with larger element pitches, good image contrast could be obtained when the number of transmissions was large. This is because echoes from grating lobes are incoherent among transmissions, and they are suppressed by compounding low-resolution images obtained by individual transmissions. On the other hand, an array probe with smaller element pitches achieves good image contrast even with a smaller number of transmissions and, thus, it would be preferable to realize a higher frame rate.

Attenuation Coefficient Estimation of the Healthy Human Thyroid In Vivo

Previous studies have demonstrated that attenuation coefficients can be useful towards characterizing thyroid tissues. In this work, ultrasonic attenuation coefficients were estimated from healthy human thyroids in vivo using a clinical scanner. The selected subjects were five young, healthy volunteers (age: 26 ± 6 years old, gender: three females, two males) with no reported history of thyroid diseases, no palpable thyroid nodules, no smoking habits, and body mass index less than 30kg/m2. Echographic examinations were conducted by a trained sonographer using a SonixTouch system (Ultrasonix Medical Corporation, Richmond, BC) equipped with an L14-5 linear transducer array (nominal center frequency of 10MHz, transducer footprint of 3.8cm). Radiofrequency data corresponding to the collected echographic images in both transverse and longitudinal views were digitized at a sampling rate of 40MHz and processed with Matlab codes (MathWorks, Natick, MA) to estimate attenuation coefficients using the spectral log difference method. The estimation was performed using an analysis bandwidth spanning from 4.0 to 9.0MHz. The average value of the estimated ultrasonic attenuation coefficients was equal to 1.34 ± 0.15dB/(cm.MHz). The standard deviation of the estimated average attenuation coefficient across different volunteers suggests a non-negligible inter-subject variability in the ultrasonic attenuation coefficient of the human thyroid.

Characterizing Channel Center Frequencies in AMSU-A and MSU Microwave Sounding Instruments

Abstract Passive microwave observations from the Microwave Sounding Unit (MSU) and the Advanced Microwave Sounding Unit-A (AMSU-A) have been exploited widely for numerical weather prediction (NWP), atmospheric reanalyses, and climate monitoring studies. The treatment of biases in these observations, with respect to models as well as between satellites, has been the focus of much effort in recent years. This study presents evidence that shifts, drifts, and uncertainties in pass band center frequencies are a significant contribution to these biases. Center frequencies for AMSU-A channels 6–14 and MSU channel 3 have been analyzed using NWP fields and radiative transfer models, for a series of operational satellites covering the period 1979–2012. AMSU-A channels 6 (54.40 GHz), 7 (54.94 GHz), and 8 (55.50 GHz) on several satellites exhibit significant shifts and drifts relative to nominal pass band center frequencies. No significant shifts were found for AMSU-A channels 9–14, most probably as a consequence of the active frequency locking of these channels. For MSU channel 3 (54.96 GHz) most satellites exhibit large shifts, the largest for the earliest satellites. For example, for the first MSU on the Television and Infrared Observation Satellite-N (TIROS-N), the analyzed shift is 68 MHz over the lifetime of the satellite. Taking these shifts into account in the radiative transfer modeling significantly improves the fit between model and observations, eliminates the strong seasonal cycle in the model–observation misfit, and significantly improves the bias between NWP models and observations. The study suggests that, for several channels studied, the dominant component of the model–observation bias results from these spectral errors, rather than radiometric bias due to calibration errors.

Reconfigurable ring filter with controllable frequency response.

Reconfigurable ring filter based on single-side-access ring topology is presented. Using capacitive tuning elements, the electrical length of the ring can be manipulated to shift the nominal center frequency to a desired position. A synthesis is developed to determine the values of the capacitive elements. To show the advantage of the synthesis, it is applied to the reconfigurable filter design using RF lumped capacitors. The concept is further explored by introducing varactor-diodes to continuously tune the center frequency of the ring filter. For demonstration, two prototypes of reconfigurable ring filters are realized using microstrip technology, simulated, and measured to validate the proposed concept. The reconfigured filter using lumped elements is successfully reconfigured from 2 GHz to 984.4 MHz and miniaturized by 71% compared to the filter directly designed at the same reconfigured frequency, while, for the filter using varactor-diodes, the frequency is chosen from 1.10 GHz to 1.38 GHz spreading over 280 MHz frequency range. Both designs are found to be compact with acceptable insertion loss and high selectivity.

Frequency-sum beamforming in an inhomogeneous environment

The arrival directions of ray paths between a sound source and a receiving array can be determined by beamforming the array-recorded signals. And, when the array and the signal are well matched, directional resolution increases with increasing signal frequency. However, when the environment between the source and the receivers is inhomogeneous, the recorded signal may be distorted and beamforming results may be increasingly degraded with increasing signal frequency. However, this sensitivity to inhomogeneities may be altered through use of an unconventional beamforming technique that manufactures higher frequency information by summing frequencies from lower-frequency signal components via a quadratic (or higher) product of complex signal amplitudes. This presentation will describe frequency-sum beamforming, and then illustrate it with simulation results and near-field acoustic experiments made with and without a thin plastic barrier between the source and the receiving array. The experiments were conducted in a 1.0-meter-deep and 1.07-m-diameter cylindrical water tank using a single sound projector, a receiving array of 16 hydrophones, and 100 micro-second signal pulses having nominal center frequencies from 30 to 120 kHz. The results from frequency-sum beamforming will be compared to the output of conventional delay-and-sum beamforming for different center frequencies. [Work sponsored by ONR and NAVSEA.]

Angular measurement of acoustic reflection coefficients by the inversion of V(z, t) data with high frequency time-resolved acoustic microscopy

For inspection of mechanical properties and integrity of critical components such as integrated circuits or composite materials by acoustic methodology, it is imperative to evaluate their acoustic reflection coefficients, which are in close correlation with the elastic properties, thickness, density, and attenuation and interface adhesion of these layered structures. An experimental method based on angular spectrum to evaluate the acoustic coefficient as a function of the incident angle, θ, and frequency, ω, is presented with high frequency time-resolved acoustic microscopy. In order to achieve a high spatial resolution for evaluation of thin plates with thicknesses about one or two wavelengths, a point focusing transducer with a nominal center frequency of 25 MHz is adopted. By measuring the V(z, t) data in pulse mode, the reflection coefficient, R(θ, ω), can be reconstructed from its two-dimensional spectrum. It brings simplicity to experimental setup and measurement procedure since only single translation of the transducer in the vertical direction is competent for incident angle and frequency acquisition. It overcomes the disadvantages of the conventional methods requiring the spectroscopy for frequency scanning and/or ultrasonic goniometer for angular scanning. Two substrates of aluminum and Plexiglas and four stainless plates with various thicknesses of 100 μm, 150 μm, 200 μm, and 250 μm were applied. The acoustic reflection coefficients are consistent with the corresponding theoretical calculations. It opened the way of non-destructive methodology to evaluate the elastic and geometrical properties of very thin multi-layers structures simultaneously.

Estimation of spatial resolution for high-frequency imaging systems using a novel anechoic-sphere phantom.

A new method has been developed to estimate the spatial resolution of high-frequency ultrasound (HFU, &amp;gt;20 MHz) imaging systems in 3-D using a tissue-mimicking phantom (TMP). The TMP is divided into eight adjacent compartments containing anechoic spheres (6 vol %) with diameters increasing from 0.1 to 1.09 mm, suspended in an echogenic background consisting of 3.5-μm-diameter glass beads. The ability of an HFU imaging system to detect these spheres against a speckle background provides a realistic estimation of its minimum 3-D resolution. Here, the TMP was scanned using a 40-MHz single-element transducer and a linear array (VisualSonics™ Vevo 770 and 2100, respectively), and a custom HFU annular-array-based system with a 40-MHz nominal center frequency. Depth-of-field and penetration depth of the custom system were increased using synthetic focusing and chirp-coded excitation. Resulting B-mode images indicated that the custom system could resolve spheres down to 0.2 mm, while the commercial systems resolved spheres down to 0.3 mm. In addition, the annular array provided a larger depth-of-field and higher contrast-to-noise ratios at all depths versus the commercial transducers. [Work supported by NIH Grant EB008606.]

Subharmonic response from single, polymer‐shell contrast agents subjected to high‐frequency excitation.

Three polymer‐shelled agents (nominal mean diameters of 0.56, 1.1, and 3.4 μm) from POINT Biomedical were investigated to determine the optimal parameter space for generating a subharmonic response from single agents when subjected to high‐frequency (above 20 MHz) excitation. A flow phantom was constructed to restrict the flow of a dilute contrast agent solution to a small volume. Two single‐element transducers, with nominal center frequencies of 40 and 20 MHz, were aligned such that they were confocal and orthogonal to each other, and their mutual focus was positioned within the flow phantom. The 40 MHz transducer was used in transmit/receive mode while the 20 MHz transducer was used passively in the receive mode. The radio‐frequency backscatter signals from individual contrast agents were digitized simultaneously from both transducers under a variety of pulse durations (5–20 cycles), acoustic pressure levels (1.5–6.0 MPa), and driving frequencies (35–45 MHz). Echo signals from individual contrast agents were windowed and spectra were calculated. For each contrast agent, the magnitude of the subharmonic (20–MHz) response was normalized with respect to the magnitude of the fundamental (40–MHz) backscatter. Experimental results agreed closely with theoretical calculations. [Work supported by NIH EB006372.]

Design and Fabrication of Two Switch Superconducting Microstrip Hairpin Filters Using Series MEMS Switches

A superconductor circuit based on series Micro- Electro-Mechanical (MEM) switches is utilized to switch between two bandpass hairpin filters with 200 MHz bandwidth and nominal center frequencies of 2.1 GHz and 2.6 GHz. This is accomplished using 4 switches actuated in pairs, one pair at a time. When one pair is actuated the first bandpass filter is coupled to the input and output ports. When the other pair is actuated the second bandpass filter is coupled to the input and output ports, thus corresponding output responses are obtained. The device is made of YBa2Cu3O7 thin film deposited on a 20 mm times 20 mm LaAlO3 substrate by pulsed laser deposition. BaTiO3 deposited by RF magnetron sputtering is utilized as the insulation layer at the switching points of contact. Fabrication details are discussed along with simulation data and test results.

High-Frequency Ultrasonic Imaging of the Anterior Segment Using an Annular Array Transducer

Very high-frequency ultrasound (VHFU; >35 megahertz [MHz]) allows imaging of anterior segment structures of the eye with a resolution of less than 40 microm. The low focal ratio of VHFU transducers, however, results in a depth of field (DOF) of less than 1 mm. The aim was to develop a high-frequency annular array transducer for ocular imaging with improved DOF, sensitivity, and resolution compared with conventional transducers. Experimental study. Cadaver eyes, ex vivo cow eyes, in vivo rabbit eyes. A spherically curved annular array ultrasound transducer was fabricated. The array consisted of 5 concentric rings of equal area, had an overall aperture of 6 mm, and a geometric focus of 12 mm. The nominal center frequency of all array elements was 40 MHz. An experimental system was designed in which a single array element was pulsed and echo data were recorded from all elements. By sequentially pulsing each element, echo data were acquired for all 25 transmit-and-receive annuli combinations. The echo data then were focused synthetically and composite images were produced. Transducer operation was tested by scanning a test object consisting of a series of 25-microm diameter wires spaced at increasing range from the transducer. Imaging capabilities of the annular array were demonstrated in ex vivo bovine, in vivo rabbit, and human cadaver eyes. Depth of field, resolution, and sensitivity. The wire scans verified the operation of the array and demonstrated a 6.0-mm DOF, compared with the 1.0-mm DOF of a conventional single-element transducer of comparable frequency, aperture, and focal length. B-mode images of ex vivo bovine, in vivo rabbit, and cadaver eyes showed that although the single-element transducer had high sensitivity and resolution within 1 to 2 mm of its focus, the array with synthetic focusing maintained this quality over a 6-mm DOF. An annular array for high-resolution ocular imaging has been demonstrated. This technology offers improved DOF, sensitivity, and lateral resolution compared with single-element fixed focus transducers currently used for VHFU imaging of the eye.

Anisotropy of apparent backscatter in the short-axis view of mouse hearts

The goals of this investigation were to measure the anisotropy of backscattered ultrasound observed in the short-axis view of mouse hearts in systole and diastole and to compare these measurements with predictions from a computer simulation. Measurements of midmyocardial apparent backscatter were obtained from analyses of the hearts of seven wild-type mice using a clinical imaging system utilizing a linear array with a nominal center frequency of 13 MHz. A computer model simulating the short-axis view was implemented based on previous measurements of the angle of insonification dependence of myocardial backscatter and attenuation. Results demonstrate that the measured backscatter was largest for those myocardial regions corresponding to approximately perpendicular insonification relative to the myofibers and the smallest for regions of approximately parallel insonification, with the minimum to maximum values of apparent backscatter differing by approximately 10 dB. The measured anisotropy of backscatter was similar for end-systole and end-diastole and was in good agreement with the predicted anisotropy obtained from the computer simulations. (E-mail: mrh@wuphys.wustl.edu)

Ophthalmic imaging with a 40-MHz annular array

High-frequency annular arrays provide a means for improving the depth of field versus single-element transducers. An annular array with five equal-area rings has been designed and an experimental system has been assembled to test it. The transducer is fabricated from a 9-μm polyvinylidene fluoride (PVDF) membrane bonded to a copper-clad polyimide film. The transducer has a total aperture of 6 mm, a geometric focus of 12 mm, and a nominal center frequency of 40 MHz with a 6-dB fractional bandwidth of 33%. The device is pressed into a spherically curved geometry and then backfilled with epoxy. Radio-frequency data were acquired for all 25 transmit/receive ring pairs, and then postprocessed with a synthetic focusing algorithm to improve the image depth of field (DOF). The resulting processed data improved DOF by a factor of 6 compared to a single-element transducer of the same total aperture and geometric focus. To test the system, rf data were acquired from excised bovine eyes, human cadaver eyes, and anesthetized rabbits. The tests revealed enhanced resolution away from the geometric focus and a more uniform image brightness than can be achieved with high-frequency, single-element devices. [This work was supported by NIH Grant EY014371.]

Measurement and Modeling of an Ultra-Wide Bandwidth Indoor Channel

This paper describes the results of frequency-domain channel sounding in residential environments. It consists of detailed characterization of complex frequency responses of ultra-wideband (UWB) signals having a nominal center frequency of 5 GHz. A path loss model as well as a second-order autoregressive model is proposed for frequency response generation of the UWB indoor channel. Probability distributions of the model parameters for different locations are presented. Also, time-domain results such as root mean square delay spread and percent of captured power are presented.

Ultrasonic tissue characterization of the mouse myocardium: Successful in vivo cyclic variation measurements

Background Measurements of the systematic variation of backscattered ultrasonic energy from myocardium during the heart cycle (cyclic variation) have been successfully used to characterize a wide spectrum of cardiac pathologies in large animal models and human subjects. The purpose of this study was to evaluate the feasibility of extending cyclic variation measurements to the study of genetically manipulated mouse models of cardiac diseases as a method for developing further insights into the disease-altered properties of the myocardium and its characterization with ultrasound. Methods Parasternal long-axis images of the heart were obtained in 9 wild-type mice under light anesthesia using a commercial imaging system with a 15-MHz nominal center frequency linear array. Images of a tissue-mimicking phantom and the mouse hearts were obtained for a series of specific receiver gains for each of a series of specific dynamic range settings. Analyses of these data formed the basis for gray-scale image calibration. Cyclic variation measurements were obtained by determining the average gray-scale value for a region of interest placed in the midmyocardium of the posterior wall for each frame acquired during 4 cardiac cycles and converting these mean gray-scale values to backscatter values expressed in decibels using the determined calibration. Results are expressed in terms of the magnitude and time delay of cyclic variation. To evaluate repeatability of these measurements the same group of mice underwent the identical imaging protocol 2 weeks after the first study. Results The mean magnitude of cyclic variation was found to be 4.6 ± 0.2 dB with a corresponding normalized time delay of 1.02 ± 0.03 for data averaged over all dynamic range settings. There was no significant difference among results obtained with each of the dynamic range settings. A comparison of these results with those from data acquired 2 weeks after the initial study showed no significant difference. Conclusion This study represents the first reported measurement of cyclic variation in mice and demonstrates that reliable cyclic variation measurements can be obtained among individual animals and over different time points and, hence, forms the basis for subsequent investigations addressing specific cardiac pathologies and effects arising from myocardial anisotropy.