Julien Rouyer

Conformal ultrasound imaging system for anatomical breast inspection

Ultrasound tomography has considerable potential as a means of breast cancer detection because it reduces the operator-dependency observed in echography. A half-ring transducer array was designed based on breast anatomy, to obtain reflectivity images of the ductolobular structures using tomographic reconstruction procedures. The 3-MHz transducer array comprises 1024 elements set in a 190-degree circular arc with a radius of 100 mm. The front-end electronics incorporate 32 independent parallel transmit/receive channels and a 32-to-1024 multiplexer unit. The transmit and receive circuitries have a variable sampling frequency of up to 80 MHz and 12-bit precision. Arbitrary waveforms are synthesized to improve the signal-to-noise ratio and to increase the spatial resolution when working with low-contrast objects. The setup was calibrated with academic objects and a needle hydrophone to develop the data correction tools and specify the properties of the system. The backscattering field was recorded using a restricted aperture, and tomographic acquisitions were performed with a pair of 0.08-mm-diameter steel wires, a low-contrast 2-D breast phantom, and a breast-shaped phantom containing inclusions. Data were processed with dedicated correction tools and a pulse compression technique. Objects were reconstructed using the elliptical back-projection algorithm.

In Vivo Estimation of Attenuation and Backscatter Coefficients From Human Thyroids

Fine-needle aspiration (FNA) remains the gold standard for the diagnosis of thyroid cancer. However, currently, a large number of FNA biopsies result in negative or undetermined diagnosis, which suggests that better noninvasive tools are needed for the clinical management of thyroid cancer. Spectral-based quantitative ultrasound (QUS) characterizations may offer a better diagnostic management as previously demonstrated in mouse cancer models ex vivo. As a first step toward understanding the potential of QUS markers for thyroid disease management, this paper deals with the spectral-based QUS estimation of healthy human thyroids in vivo. Twenty volunteers were inspected by a trained radiologist using two ultrasonic imaging systems, which allowed them to acquire radio-frequency data spanning the 3-16-MHz frequency range. Estimates of attenuation coefficient slope (ACS) using the spectral logarithmic difference method had an average value of 1.69 dB/(cm·MHz) with a standard deviation of 0.28 dB/cm·MHz. Estimates of backscatter coefficient (BSC) using the reference-phantom method had an average value of 0.18 sr-1 · cm-1 over the useful frequency range. The intersubject variability when estimating BSCs was less than 1.5 dB over the analysis frequency range. Further, the effectiveness of three scattering models (i.e., fluid sphere, Gaussian, and exponential form factors) when fitting the experimentally estimated BSCs was assessed. The exponential form factor was found to provide the best overall goodness of fit (R2 = 0.917), followed by the Gaussian (R2 = 0.807) and the fluid-sphere models (R2 = 0.752). For all scattering models used in this study, average estimates of the effective scatterer diameter were between 44 and 56 μm. Overall, an excellent agreement in the estimated attenuation and BSCs with both scanners was exhibited.

Ultrasound tomography dedicated to ANAtomical breast inspection

The main goal of ultrasound tomography (UT) is to provide both a high contrast imaging and a multi-parametric imaging. Within the frame of soft-tissue imaging, we focus our application to breast inspection for early stage cancer detection. Conforming with breast anatomy, ANAI¨S (ANAtomical Imaging and Interventional System) prototype is designed including a semicircular antenna which enables imaging of ductolobular structures sensitive to cancer initiation. The 200-mm diameter half-ring transducer contains 1024 elements with 3-MHz center frequency and 2.25-MHz (−6 dB) bandwidth. Chirp excitation is used to improve contrast with pulse compression method. Performed with a needle hydrophone, calibration studies yield system characteristics such as field distribution or transducer element localization. Taking advantage of a near field reconstruction algorithm, tomographic images of thin wire and of breast anthropomorphic phantom (CIRS) are presented. The low frequency approach and the high density of the ring antenna provide interesting results that, as we expect, may still be enhanced.

Low-contrast lesion detection enhancement using pulse compression technique

Pulse compression methods greatly improve the quality of medical images. In comparison with standard broadband pulse techniques, these methods enhance the contrast-to-noise ratio and increase the probing depth without any perceptible loss of spatial resolution. The Golay compression technique is analyzed here in the context of ultrasonic computed tomography, first on a one-dimensional target and second, on a very low-contrast phantom probed using a half-ring array tomograph. The imaging performances were assessed based on both the point spread function properties and the image contrast-to-noise ratio. The improvement obtained in the image contrast-to-noise ratio (up to 40%) depends, however, on the number of coherently associated diffraction projections. Beyond a certain number, few advantages were observed. Advances in ultrasound computed tomography suggest that pulse compression methods should provide a useful means of optimizing the trade-off between the image quality and the probing sampling density. ...

Novel Ultrasound Tomograph for Anatomical Inspection

A device for ultrasound computed tomography (UCT) is introduced here. An half-ring transducer array was designed in conformity with the breast anatomy and the cancer growth region to perform an early detection. The array comprises 1,024 elements set in a 190-degree circular arc with a radius of 100 mm. The nominal frequency is 3 MHz with a 79% −6 dB bandwidth. The front-end electronics incorporate 32 independent transmit/receive parallel channels and a 32-to-1,024 multiplexer unit. The acquisition circuitries have a variable sampling frequency of up to 80 MHz and a precision of 12 bits. Arbitrary waveforms are synthesized to improve the signal-to-noise ratio and to increase the in-depth resolution. Tomographic acquisitions were realized in diffraction mode using a restricted aperture. The backscattered field was recorded in the case of a string phantom (0.08-mm diameter steel threads) and a breast-shaped phantom containing inclusions. Data were processed with dedicated correction tools processes such as pulse compression. Objects were reconstructed with the ellipsoidal back-projection method.

A regularization approach for ultrasonic attenuation imaging

The quantitative estimation of the attenuation coefficient slope (ACS) has the potential to differentiate between healthy and pathological tissues. However, attempts to characterize ACS maps using pulse-echo data using methods such as the spectral log difference (SLD) technique have been limited by the large variability of the estimates. In the present work, ACSs were estimated using a regularized SLD technique. The performance of the proposed approach was experimentally evaluated using two physical phantoms: a homogeneous phantom, and a phantom with a cylindrical inclusion. The results obtained with the SLD and regularized SLD techniques were compared to the ACS values obtained with through-transmission techniques. In the homogeneous phantom, the use of regularization allowed reducing the standard deviation by more than 90% while keeping the estimation bias around 2%. For the inhomogenenous phantom, a trade-off between contrast-to-noise ratio (CNR) and estimation bias was observed. However, the use of regularization allowed nearly doubling the CNR from 0.54 to 0.97–1.29 when compared to the standard SLD, while achieving an estimation bias between 10% and 20%. The results suggest that the use of regularization methods can effectively reduce the variability of ACS estimation.

Backscatter coefficient estimation in human thyroid carcinoma In vivo

Spectral-based quantitative ultrasound (QUS) characterizations may provide a potential alternative to invasive gold standard technique—fine-needle aspiration (FNA)—in the diagnostic management of the thyroid cancer. Such potentiality was previously demonstrated in mouse thyroid cancer models ex vivo. Recently, the feasibility of the backscatter coefficient (BSC) estimation of human thyroid in vivo was demonstrated for a controlled group of 20 healthy volunteers (24.4 ± 2.9 year-old). Among the volunteer, the integrated BSC parameter was found equal to 1.41x10-2sr-1.cm-1 in the 3 to 9 MHz range. The current study focuses on the estimation of the BSC in a clinical context. Preliminary results on patients having malignant lesions are proposed. A research ultrasound imaging system (SonixTouch with an L14-5/38 linear array, Ultrasonix Medical Corp.) was employed by the radiologists of an oncological center first to record radio frequency data of the lesion and second to guide the FNA. The reference phantom tec...

Backscatter coefficient estimation from human thyroid in vivo

Currently, fine-needle aspiration (FNA) biopsy is the gold standard for the diagnosis of thyroid cancer. Therefore, there is a need to develop non-invasive tools that aid in the identification of malignant tissues in this gland. Quantitative ultrasound imaging using backscatter coefficients (BSCs) has shown potential to characterize thyroid tissues in rodent models ex vivo. As an initial step towards the goal of thyroid cancer diagnosis on a clinical setting, in this study the feasibility of BSC-based imaging in humans in vivo is evaluated. Radiofrequency data was collected using a scanner equipped with a 9-MHz linear probe from ten patients with no clinical records of thyroid disease and no thyroid nodules visible through ultrasonic examination. Backscatter coefficients were estimated using the reference phantom method and considering analysis regions of 4.5 mm by 4.5 mm. Attenuation compensation was performed considering the presence of sub-cutaneous fat, muscle, and thyroid tissues. Images were constructed by calculating the mean BSC within the analysis bandwidth spanning from 3 to 8 MHz The average value of the backscatter coefficients in normal thyroids was 0.056±0.037 1/(sr.cm) within the analysis bandwidth. The coefficient of variation of the mean BSC values of all the thyroid samples was less than 2dB. These results suggest that consistent imaging of BSC-derived parameters from human thyroids in vivo is possible and may play a role in thyroid tissue characterization.

Tissue characterization using simultaneous estimation of backscatter coefficient and elastic shear modulus

Tissue characterization using quantitative ultrasound (QUS) parameters has received significant attention in recent years due to its potential to improve the detection and diagnosis of diseased states. However, the vast majority of studies in QUS tissue typing have used parameters derived from either longitudinal or shear waves in isolation, thereby discarding potentially useful complementary information these parameters may carry. In this study, the simultaneous estimation of backscatter coefficients (derived from longitudinal waves) and shear modulus (derived from shear waves) was implemented on data from a clinical scanner. Both parameters were estimated from five ex vivo porcine kidney samples and used to calculate the anisotropy ratio in the parameters when analyzing the middle and pole regions of the kidneys. For all samples, the estimated parameters were higher in the pole regions than in the middle region, with anisotropy ratios of 1.42±0.11 and 3.07±0.70 for the shear modulus and the backscatter coefficient, respectively. Therefore, these results demonstrate that QUS parameters derived from both longitudinal and shear waves can be estimated simultaneously and may be used in conjunction to track changes in tissue structure and composition.Tissue characterization using quantitative ultrasound (QUS) parameters has received significant attention in recent years due to its potential to improve the detection and diagnosis of diseased states. However, the vast majority of studies in QUS tissue typing have used parameters derived from either longitudinal or shear waves in isolation, thereby discarding potentially useful complementary information these parameters may carry. In this study, the simultaneous estimation of backscatter coefficients (derived from longitudinal waves) and shear modulus (derived from shear waves) was implemented on data from a clinical scanner. Both parameters were estimated from five ex vivo porcine kidney samples and used to calculate the anisotropy ratio in the parameters when analyzing the middle and pole regions of the kidneys. For all samples, the estimated parameters were higher in the pole regions than in the middle region, with anisotropy ratios of 1.42±0.11 and 3.07±0.70 for the shear modulus and the backscatter coefficient, respectively. Therefore, these results demonstrate that QUS parameters derived from both longitudinal and shear waves can be estimated simultaneously and may be used in conjunction to track changes in tissue structure and composition.

Simultaneous estimation of shear elastic modulus and backscatter coefficient: Phantom and in human liver in vivo study

The use of quantitative ultrasound (QUS) parameters to characterize tissue has shown potential to improve current clinical diagnosis. However, most studies in QUS have used parameters derived from either ultrasonic compressional or low frequency shear wave in isolation, thereby discarding additional information these parameters may carry. In this study, the feasibility of estimating both shear wave speed (SWS) and backscatter coefficient (BSC) when using a unique data set is demonstrated both with physical phantoms and in vivo human liver data. The phantom results showed contrast values of 8.16 and 1.71 for BSC and SWS. The in vivo liver results for BSC and SWS were in good agreement with previously reported values in the literature. Therefore, these results demonstrate that multi-parameter tissue characterization using BSC and SWS have a promising potential to track changes in both microscopic and macroscopic properties of tissue.