Aberration correction by polynomial approximation for synthetic aperture ultrasound imaging

Neill M., Burma J., Miutz L.N., Kennedy C., Penner L., Newel K., Smirl J.

Xing P., Porée J., Rauby B., Malescot A., Martineau E., Perrot V., Rungta R.L., Provost J.

Tian Z., Olmstead M., Jing Y., Han A.

jiang C., Li B., Xie L., Liu C., Xu K., Zhan Y., Ta D.

Compounded plane wave imaging (CPWI) allows high-frame-rate measurement and has been one of the most promising modalities for real-time brain imaging. However, ultrasonic brain imaging using the CPWI modality is usually performed with a worn thin or removal of the skull layer. Otherwise, the skull layer is expected to distort the ultrasonic wavefronts and significantly decrease intracranial imaging quality. The motivation of this study is to investigate a CPWI method for transcranial brain imaging with the skull layer. A coordinate transformation ray-tracing (CTRT) approach was proposed to track the distorted ultrasonic wavefronts and calculate the time delays for the ultrasound plane wave passing through the skull layer. With an accurate correction for the time delays in beamforming, the CTRT-based CPWI could achieve high-quality intracranial images with the presence of skulls. The proposed CTRT-based CPWI method was verified using a simplified three-layer transcranial model. The full-wave simulation demonstrated that CTRT could accurately (i.e., relative percentage error less than0.18%) track the distorted transmitting wavefront through skull. Compared with the CPWI without aberration correction, the CTRT-based CPWI provided high-quality intracranial imaging and could accurately localize intracranial point scatterers; specifically, positioning error decreases from 0.5 mm to 0.1 mm on average in the axial direction and from 0.7 mm to 0.1 mm on average in the lateral direction. As the compounded angles increased in the CTRT-based CPWI, the contrast improved by 16.2 dB on average for the region of interest, and the array performance indicator (representing resolution) decreased by 4.0 on average for the intracranial point scatterers. The CTRT is of low computational cost compared with full wave simulation. This study suggested that the proposed CTRT-based CPWI might have the potential for real-time and non-invasive transcranial aberration-corrected imaging.

Leonov D., Kulberg N., Yakovleva T., Solovyova P., Costa-Júnior J.F., Saikia M.J.

The paper addresses a crucial challenge in medical radiology and introduces a novel general approach, which utilises applied mathematics and information technology techniques, for aberration correction in ultrasound diagnostics. Ultrasound imaging of inhomogeneous media inherently suffers from variations in ultrasonic speed between tissue. The characteristics of aberrations are unique to each patient due to tissue morphology. This study proposes a new phase aberration correction method based on the Fourier transform and leveraging of the synthetic aperture mode. The proposed method enables correction after the emission and reception of ultrasonic wave, allowing for the estimation of aberration profiles for different parts of the sonogram. To demonstrate the method’s performance, this study included the conducting of experiments using a commercially available quality control phantom, an ex-vivo temporal human bone, and specially designed distortion layers. At a frequency of 2 MHz, the experiments demonstrated an increase of two-and-three-quarters in echo signal intensity and a decrease of nearly two-fold in the width of the angular distribution compared to the pre-correction state. However, it is important to note that the implementation of the method has a limitation, as it requires an aperture synthesis mode and access to raw RF data, which restricts use in common scanners. To ensure the reproducibility of the results, this paper provides public access to an in-house C +  + code for aberration correction following the proposed method, as well as the dataset used in this study.

Preston C., Alvarez A.M., Allard M., Barragan A., Witte R.S.

Ali R., Brevett T., Zhuang L., Bendjador H., Podkowa A.S., Hsieh S.S., Simson W., Sanabria S.J., Herickhoff C.D., Dahl J.J.

Medical ultrasound images are reconstructed with simplifying assumptions on wave propagation, with one of the most prominent assumptions being that the imaging medium is composed of a constant sound speed. When the assumption of a constant sound speed are violated, which is true in most in vivo or clinical imaging scenarios, distortion of the transmitted and received ultrasound wavefronts appear and degrade the image quality. This distortion is known as aberration, and the techniques used to correct for the distortion are known as aberration correction techniques. Several models have been proposed to understand and correct for aberration. In this review paper, aberration and aberration correction are explored from the early models and correction techniques, including the near-field phase screen model and its associated correction techniques such as nearest-neighbor cross-correlation, to more recent models and correction techniques that incorporate spatially varying aberration and diffractive effects, such as models and techniques that rely on the estimation of the sound speed distribution in the imaging medium. In addition to historical models, future directions of ultrasound aberration correction are proposed.

Kim H., Song I., Kang J., Yoo Y.

Image guidance of extracorporeal shock wave therapy (ESWT) is important to enhance its efficacy while lowering pain in patients. Real-time ultrasound imaging is an appropriate modality for image guidance, but its image quality substantially reduces due to severe phase aberration from the different speed of sound between soft tissues and a gel pad, which is utilized to control a therapeutic focal point in ESWT. This paper presents a phase aberration correction method for improving image quality in the ultrasound imaging guided ESWT. To correct an error from phase aberration, a time delay based on a two-layer model with different speeds of sound is calculated for dynamic receive beamforming. For the phantom and in vivo studies, a rubber type gel pad (i.e., 1400 m/s) with a specific thickness (3 or 5-cm) was placed on the top of soft tissue and full scanline RF data were acquired. In the phantom study, with phase aberration correction, image quality was highly increased compared to image reconstructions with a fixed speed of sound (i.e., 1540 or 1400 m/s), i.e., 1.1 vs. 2.2 and 1.3 mm in -6dB lateral resolution and 0.64 vs. 0.61 and 0.56 in contrast-to-noise ratio (CNR), respectively. From an in vivo musculoskeletal (MSK) imaging, the phase aberration correction method provided a clearly improved depiction of muscle fibers in a rectus femoris region. These results indicate that the proposed method enables effective imaging guidance of ESWT by improving image quality of ultrasound imaging in real-time.

Tan C., Zhang Z., Liu H., Fu R., Yang G., Dong F.

van Hal V.H., Muller J., van Sambeek M.R., Lopata R.G., Schwab H.

Abdominal ultrasound image quality is hampered by phase aberration, that is mainly caused by the large speed-of-sound (SoS) differences between fat and muscle tissue in the abdominal wall. The mismatch between the assumed and actual SoS distribution introduces general blurring of the ultrasound images, and acoustic refraction can lead to geometric distortion of the imaged features. Large aperture imaging or dual-transducer imaging can improve abdominal imaging at deep locations by providing increased contrast and resolution. However, aberration effects for large aperture imaging can be even more severe, which limits its full potential. In this study, a model-based aberration correction method for arbitrary acquisition schemes is introduced for delay-and-sum (DAS) beamforming and its performance was analyzed for both single- and dual-transducer ultrasound imaging. The method employs aberration corrected wavefront arrival times, using manually assigned local SoS values. Two wavefront models were compared. The first model is based on a straight ray approximation, and the second model on the Eikonal equation, which is solved by a multi-stencils fast marching method. Their accuracy for abdominal imaging was evaluated in acoustic simulations and phantom experiments involving tissue-mimicking and porcine material with large SoS contrast (∼100 m/s). The lateral resolution was improved by up to 90% in simulations and up to 65% in experiments compared to standard DAS, in which the use of Eikonal beamforming generally outperformed straight ray beamforming. Moreover, geometric distortions were mitigated in multi-aperture imaging, leading to a reduction in position error of around 80%. A study on the sensitivity of the aberration correction to shape and SoS of aberrating layers was performed, showing that even with imperfect segmentations or SoS values, aberration correction still outperforms standard DAS.

Chan M.Y., Ling Y.T., Chen X., Chan S., Kwong K.K., Zheng Y.

This study measured the rates of success in applying transcranial Doppler (TCD) scanning at the middle, posterior and anterior temporal windows (MTW, PTW and ATW) in the elderly. A hand-held 1.6-MHz pulsed-wave TCD transducer was used to search for cerebral arteries at MTW, PTW and ATW locations. Physical attributes of the head, including head circumference and the distance between tragi on both sides ("tragus-to-tragus arc length"), were also measured to explore the associations with successful rates. Among 396 healthy elderly participants (aged 62.6 ± 6.0 y, 140 men), 81.1% (n = 321; 127 men) had one or more temporal windows penetrable by TCD ultrasound (n = 286 [72.2%] at MTW, n = 195 [49.2%] at PTW and n = 106 [26.8%] at ATW). Regression analysis revealed that successful scanning increased significantly in male participants at three window locations. Younger age significantly increased successful scanning at the MTW and ATW. Smaller tragus-to-tragus arc length increased successful scanning at the MTW, but unsuccessful scanning at the ATW. Our findings support using MTW as the first location when positioning the TCD transducer for the scanning of cerebral arteries in the elderly population. When performing TCD scanning on two temporal windows, we propose choosing the MTW and PTW.

Allen B.C., Kapoor S., Anzalone A., Mayer K.P., Wolfe S.Q., Duncan P., Asimos A.W., D'Agostino R., Winslow J.T., Sarwal A.

Robin J., Demené C., Heiles B., Blanvillain V., Puke L., Perren F., Tanter M.

Abstract Objective. Imaging the human brain vasculature with high spatial and temporal resolution remains challenging in the clinic today. Transcranial ultrasound is still scarcely used for cerebrovascular imaging, due to low sensitivity and strong phase aberrations induced by the skull bone that only enable the proximal part major brain vessel imaging, even with ultrasound contrast agent injection (microbubbles). Approach. Here, we propose an adaptive aberration correction technique for skull bone aberrations based on the backscattered signals coming from intravenously injected microbubbles. Our aberration correction technique was implemented to image brain vasculature in human adults through temporal and occipital bone windows. For each subject, an effective speed of sound, as well as a phase aberration profile, were determined in several isoplanatic patches spread across the image. This information was then used in the beamforming process. Main results. This aberration correction method reduced the number of artefacts, such as ghost vessels, in the images. It improved image quality both for ultrafast Doppler imaging and ultrasound localization microscopy (ULM), especially in patients with thick bone windows. For ultrafast Doppler images, the contrast was increased by 4 dB on average, and for ULM, the number of detected microbubble tracks was increased by 38%. Significance. This technique is thus promising for better diagnosis and follow-up of brain pathologies such as aneurysms, arterial stenoses, arterial occlusions, microvascular disease and stroke and could make transcranial ultrasound imaging possible even in particularly difficult-to-image human adults.

Leonov D., Kodenko M., Leichenco D., Nasibullina A., Kulberg N.

Commercial medical ultrasound phantoms are highly specific as they simulate particular clinical scenarios. This makes them expensive to use in multi-target research and training. General approaches to human tissue and organ modeling are described in the manufacturing methodology, access to which is restricted by the manufacturer's trade secret. Our aim is to propose a reproducible methodology to design a head phantom for transcranial ultrasound training and research from widely available materials and to validate its applicability. To create an anthropomorphic phantom, we used data from real patients obtained by CT and MRI scans. We combined FDM and LCD 3D printing to achieve the desired acoustic performance and ergonomics of the phantom. We fabricated the phantom using polyvinyl chloride plastisol, photopolymer, and PLA to simulate brain tissue, temporal acoustic windows, and acoustically opaque parts of the skull, respectively. Notably, the phantom fabrication method uses only readily available materials and is easy to reproduce. We developed a basic one and anatomical one versions of the head phantom. The basic version contains a simplified brain: tissue-mimicking material is poured into the skull with needles inserted, which specific pattern is easy to recognize in B-mode images. The anatomical version has an anatomically correct brain dummy extracted from MRI data and contains multiple randomly distributed small metal, plastic, and bony objects ranging in size from 1 to 3 mm each. The proposed methodology allows producing head phantoms for transcranial ultrasound training and research. The anatomical accuracy of the model is proved by ultrasonography and CT studies. Both versions of the phantom comprise the skull and the brain and are intended for ultrasound imaging through the temporal bone acoustic window. Needles and small objects serve as navigation targets during the training procedure. The basic version helps learning basic navigation skills, while the anatomical one provides a realistic setting to perform the diagnostic procedure.

Leonov D.V., Kulberg N.S., Yakovleva T.V., Solovyova P.D.

The presence of cranial bones in the ultrasound propagation path seriously complicates the imaging of tissues and blood vessels of the brain since the bones distort the ultrasound field, introducing phase and amplitude aberrations. Such distortions are not always apparent since complete information about the studied object is fundamentally inaccessible. The article develops a new approach that uses the synthetic aperture method to detect wavefront aberrations. A quantitative parameter is proposed that characterizes the presence of aberrations by measuring the RMS width of the angular intensity distribution. Experimental results were obtained at a frequency of 2 MHz using phantom and in vivo transcranial data. It is shown that in the presence of aberrations, the value of the proposed parameter increases by 22–45% with respect to the theoretical value for the aberrationless case.