A linear-array freehand 3-D endoscopic ultrasound

Freehand 3-D Ultrasound Imaging: A Systematic Review

Two-dimensional ultrasound (US) imaging has been successfully used in clinical applications as a low-cost, portable and non-invasive image modality for more than three decades. Recent advances in computer science and technology illustrate the promise of the 3-D US modality as a medical imaging technique that is comparable to other prevalent modalities and that overcomes certain drawbacks of 2-D US. This systematic review covers freehand 3-D US imaging between 1970 and 2017, highlighting the current trends in research fields, the research methods, the main limitations, the leading researchers, standard assessment criteria and clinical applications. Freehand 3-D US systems are more prevalent in the academic environment, whereas in clinical applications and industrial research, most studies have focused on 3-D US transducers and improvement of hardware performance. This topic is still an interesting active area for researchers, and there remain many unsolved problems to be addressed.

Anorectal ultrasound for neoplastic and inflammatory lesions

Accurate staging of rectal and anal carcinoma is crucial for planning surgery and indicating adjuvant therapy. Although, computed tomography and magnetic resonance imaging are very sensitive in detecting metastatic disease, the local staging of rectal cancer with these techniques has been disappointing. Endorectal ultrasound (ERUS) and anal endosonography (AE) remain the most accurate methods for staging rectal and anal cancer. Anal endosonography is also of value in evaluating perianal sepsis: it can assist the surgeon in planning the surgical strategy by delineating the anatomy of fistula tracts, and can aid in puncturing abscesses in the operating room. Continued research and development has made the instrumentation for ERUS and AE more accurate and user-friendly. New techniques that have contributed significantly to the evolution of ERUS include three-dimensional ERUS, high-frequency miniprobes, transrectal ultrasound-guided biopsy techniques and hydrogen peroxide-enhanced endosonography. Further improvements can be expected from contrast enhancement with microbubbles and colour Doppler imaging. In this new millennium, new developments in ERUS and anal endosonography, such as tri-dimensional ERUS and anal endosonography and radial electronic probing, widen the role of ERUS in the staging of rectal and anal carcinoma, as well as for perianal inflammatory conditions.

Three-dimensional linear endoscopic ultrasound-feasibility of a novel technique applied for the detection of vessel involvement of pancreatic masses

BACKGROUND

Endoscopic ultrasound (EUS) can reliably diagnose and stage pancreatic cancer but is less competent for the differentiation between vascular compression (VC) and invasion (VI).

AIM

Prospective comparison of linear EUS with/without three-dimensional (3D) EUS for vessel involvement in pancreatic cancer to evaluate the feasibility of linear 3D ultrasound.

MATERIAL AND METHODS

Linear echoendoscopy was used to identify the pancreatic tumor, the tumor-vessel relation and for EUS-FNA to obtain tissue diagnosis. Immediately afterwards, 3D image acquisition was performed using a magnetic tracked 3D sensor. The acquisition time was 10-20 s.

RESULTS

EUS results of 22 patients with solid pancreatic lesions were compared to surgical histology. This proved adenocarcinoma in 17 patients and chronic pancreatitis in 5. EUS showed VI in 10 patients, VC in 6, and no vascular involvement (NVI) in 6. Additional 3D evaluation showed VI in 6 patients, VC in 10, and NVI in 6. Surgery proved VI in 7 patients, VC in 9, and NVI in 6. EUS showed VI in 3/5 patients with chronic pancreatitis, 3D showed VC only, while surgery found two patients to have VC and with NVI. In two patients with pancreatic cancer, VI was diagnosed on two dimensional (2D), but VC on 3D evaluation. Surgery showed VC and VI in one each. In the 2D, one patient with NVI had VI on surgery; and on 3D one VC proved to have NVI at surgery. In 1/22 patients the result of 3D was false negative, while 4/22 were false positives and one false negative in conventional EUS.

CONCLUSION

Linear 3D EUS seems feasible for pancreatic evaluation. In addition, linear EUS enhanced the evaluation of vascular involvement of pancreatic lesions, especially in chronic pancreatitis.

The radiated fields of focussing air-coupled ultrasonic phased arrays

This paper presents an investigation into the fields radiated into air by ultrasonic phased arrays under transient excitation. In particular, it includes a theoretical prediction of spatial variations in amplitude throughout the both the near-field and far-field of such arrays. The approach has been used to predict the result of phasing to produce a focus in air, which can be seen to be particularly effective in the near-field of the array. Interesting features are observed, which are then described in terms of the performance of both individual elements and the resulting array. It is shown how some elements of design can be used to improve performance in focussing. The predictions are compared to the results of experiments in air using electrostatic arrays, where good focussing could be achieved provided the appropriate design principles were followed. The approach has been developed specifically for use in air, but the results would also hold for modelling in certain medical arrays where a focussing requirement might be needed close to the array itself.