Technical note: Impact of linear array transducer Doppler aperture location on spectral peak velocity measurements - A phantom study.

OBJECTIVE: Ultrasound beams sometimes need to be steered from the edge of linear array transducers to reach the sample volume with a desired Doppler angle in vascular exams. This phantom study aims to evaluate the impact of apertures located at the array edge on peak velocity (PV) measurements. METHODS: Three ultrasound scanner systems equipped with eight transducers from 3 major ultrasound vendors were tested using a flow phantom with a horizontal tube. Five spectral Doppler measurements with the aperture positioned at one edge of the array and 5 with the aperture at the center of the array were obtained using all available scanner-transducer combinations while maintaining all scan parameters and the sample volume in the same tube location. Differences in PVs between center and edge apertures were compared across 4 constant flow rates. RESULTS: The averaged PVs for all phantom flow rates ranged from 24.4 cm/s to 138.2 cm/s from the array center. The averaged PVs from the center aperture were significantly greater than the corresponding measurements from the edge aperture for each flow rate (all p < 0.001). The relative PV differences ranged from 6.7% to 19.4% across all transducers and flow rates. CONCLUSION: Significantly lower PVs were consistently shown with the Doppler beam aperture at the array edge compared to center among all tested systems. This may be due to a narrower aperture width, shifted central axis, and less intrinsic spectral broadening error at the array edge. Controlling variations in Doppler aperture location is important in clinical applications which depend on consistent velocity measurements.

Systematic optimization of ultrasound grayscale imaging presets and its application in abdominal scanning.

PURPOSE: Ultrasound grayscale imaging preset optimization has often been qualitative and dependent upon vendor application specialists. This study aimed to propose a systematic approach for grayscale imaging preset optimization and apply the approach in a clinical abdominal scan setting. METHODS: A six-step approach was detailed including identification of clinical task, adjustment of basic parameters, fine-tuning of advanced parameters, image performance metrics confirmation, clinical evaluation and data analysis, and implementation of new presets and monitoring of clinical usage. Its application in an abdominal scanning task was described for each step with phantoms, volunteers, and software tools. RESULTS: Clinical image data analytics facilitated the understanding of the imaging task, relevant transducers, and target characteristics, in addition to specific requests from radiologists. Quantitative measurements were made on global image contrast and gray map function. In addition, clinically relevant phantoms and volunteer scans without and with acoustic distortion layers were involved to determine the new presets. Furthermore, phantom signal to noise ratio study and clinical evaluation using volunteers with different body habitus were utilized to confirm the superiority of the new presets. Quantitative clinical usage monitoring demonstrated successful implementation of the new presets. CONCLUSIONS: A systematic approach for grayscale imaging preset optimization has been proposed and successfully applied for a specific clinical task. This approach was designed to be generalizable and relatively flexible, which would facilitate movement away from previous qualitative and subjective approaches.

Ultrasound grayscale image quality comparison between a 2D intracavitary transducer and a 3D intracavitary transducer used in 2D mode: A phantom study.

PURPOSE: It is unclear if a 3D transducer with the special design of mechanical swing or 2D array could provide acceptable 2D grayscale image quality for the general diagnosis purpose. The aim of this study is to compare the 2D image quality of a 3D intracavitary transducer with a conventional 2D intracavitary transducer using clinically relevant phantom experiments. METHODS: All measurements were performed on a GE Logiq E9 scanner with both a 2D (IC5-9-D) and a 3D (RIC5-9-D) transducer used in 2D mode. Selection of phantom targets and acquisition parameters were determined from analysis of 33 clinical pelvic exams. Depth of penetration (DOP), contrast response, contrast of anechoic cylinders (diameter: 6.7 mm) at 1.5 and 4.5 cm depths in transverse planes, and in-plane resolution represented by full-width half-maximum of pin targets at multiple depths were measured with transmit frequencies of 7 and 8 MHz. Spherical signal-noise-ratio (SNR) (diameter: 4 and 2 mm) at multiple depths were measured at 8 MHz. RESULTS: RIC5-9-D demonstrated <8% decrease in DOP for both transmit frequencies (7 MHz: 69.7 ± 8.2 mm; 8 MHz: 64.3 ± 7.8 mm) compared with those from IC5-9-D (7 MHz: 73.9 ± 4.4 mm; 8 MHz: 69.4 ± 7.8 mm). A decreased anechoic contrast was observed with a 4.5 cm depth for RIC5-9-D (7 MHz: 23.2 ± 1.8 dB, P > 0.05; 8 MHz: 17.7 ± 0.9 dB, P < 0.01) compared with IC5-9-D (7 MHz: 25.9 ± 1.2 dB; 8 MHz: 21.5 ± 0.8 dB). The contrast response and spatial resolution performance were comparable between the two transducers. RIC5-9-D showed comparable SNR of anechoic spheres compared to IC5-9-D. CONCLUSIONS: 2D images from a 3D probe exhibited comparable overall image quality for routine clinical pelvic imaging.

Use of Image-Based Analytics for Ultrasound Practice Management and Efficiency Improvement.

Our ultrasound practice is becoming even more focused on managing practice resources and improving our efficiency while maintaining practice quality. We often encounter questions related to issues such as equipment utilization and management, study type statistics, and productivity. We are developing an analytics system to allow more evidence-based management of our ultrasound practice. Our system collects information from tens of thousands of DICOM images produced during exams, including structured reporting, public and private DICOM headers, and text within the images via optical character recognition (OCR). Inventory/location information augments the data aggregation, and statistical analysis and metrics are computed such as median exam length (time from the first image to last), transducer models used in an exam, and exams performed in a particular room, practice location, or by a given sonographer. Additional reports detail the length of a scan room's operational day, the number and type of exams performed, the time between exams, and summary data such as exams per operational hour and time-based room utilization. Our findings have already helped guide practice decisions: two defective probes were not replaced (a savings of over $10,000) when utilization data showed that three or more of the shared probe model were always idle; neck exams are the most time-consuming individually, but abdomen exam volumes cause them to consume the most total scan time, making abdominal exams the better candidates for efficiency optimization efforts. A small subset of sonographers exhibit the greatest scanning and between-scan efficiency, making them good candidates for identifying best practices.

Use of Novel Anthropomorphic Breast Ultrasound Phantoms for Radiology Resident Education.

PURPOSE: This study evaluated the training and assessment role of anthropomorphic breast ultrasound phantoms that simulated both the morphological and sonographic characteristics of breast tissue, including lesions, in a group of radiology residents at a large academic medical center. METHODS: This was a prospective study involving nine residents across second to fourth years of a radiology residency program. Two devices (phantom 1 and phantom 2) were designed and constructed to produce similar realistic sonographic images of breast morphology with a range of embedded pathologies to provide a realistic training experience. Baseline assessments of all residents' ability to detect and characterize lesions in phantom 1 were carried out, followed by a 2-hour teaching session on the same phantom. All residents underwent a posttraining, final assessment on phantom 2 to evaluate changes in their lesion detection rate and ability to correctly characterize the lesions. RESULTS: The results demonstrated there was a significant increase in both the pooled detection and correct characterization score for all residents pre- and posttraining of 26% ± 14% and 17% ± 8%, P < .0003, respectively. Posttraining assessment surveys revealed that residents rated the training experience highly. CONCLUSIONS: This study suggests that there is a benefit in including a simulation training workshop with a novel anthropomorphic breast ultrasound training device to a radiology resident education program. Finally, the phantoms used in this study are useful for training and assessment purposes because they provide a lifelike simulation of breast tissue to practice ultrasound imaging without direct exposure to patients, in an environment with no pressure.

Clinical acceptance testing and scanner comparison of ultrasound shear wave elastography.

Because of the rapidly growing use of ultrasound shear wave elastography (SWE) in clinical practices, there is a significant need for development of clinical physics performance assessment methods for this technology. This study aims to report two clinical medical physicists' tasks: (a) acceptance testing (AT) of SWE function on ten commercial ultrasound systems for clinical liver application and (b) comparison of SWE measurements of targets across vendors for clinical musculoskeletal application. For AT, ten GE LOGIQ E9 XDclear 2.0 scanners with ten C1-6-D and ten 9L-D transducers were studied using two commercial homogenous phantoms. Five measurements were acquired at two depths for each scanner/transducer pair by two operators. Additional tests were performed to access effects of different coupling media, phantom locations and operators. System deviations were less than 5% of group mean or three times standard deviation; therefore, all systems passed AT. A test protocol was provided based on results that no statistically significant difference was observed between using ultrasound gel and salt water for coupling, among different phantom locations, and that interoperator and intraoperator coefficient of variation was less than 3%. For SWE target measurements, two systems were compared - a Supersonic Aixplorer scanner with a SL10-2 and a SL15-4 transducer, and an abovementioned GE scanner with 9L-D transducer. Two stepped cylinders with diameters of 4.05-10.40 mm were measured both longitudinally and transaxially. Target shear wave speed quantification was performed using an in-house MATLAB program. Using the target shear wave speed deduced from phantom specs as a reference, SL15-4 performed the best at the measured depth. However, it was challenging to reliably measure a 4.05 mm target for either system. The reported test methods and results could provide important information when dealing with SWE-related tasks in the clinical environment.

Evaluations of UltraiQ software for objective ultrasound image quality assessment using images from a commercial scanner.

We evaluated a commercially available software package that uses B-mode images to semi-automatically measure quantitative metrics of ultrasound image quality, such as contrast response, depth of penetration (DOP), and spatial resolution (lateral, axial, and elevational). Since measurement of elevational resolution is not a part of the software package, we achieved it by acquiring phantom images with transducers tilted at 45 degrees relative to the phantom. Each measurement was assessed in terms of measurement stability, sensitivity, repeatability, and semi-automated measurement success rate. All assessments were performed on a GE Logiq E9 ultrasound system with linear (9L or 11L), curved (C1-5), and sector (S1-5) transducers, using a CIRS model 040GSE phantom. In stability tests, the measurements of contrast, DOP, and spatial resolution remained within a ±10% variation threshold in 90%, 100%, and 69% of cases, respectively. In sensitivity tests, contrast, DOP, and spatial resolution measurements followed the expected behavior in 100%, 100%, and 72% of cases, respectively. In repeatability testing, intra- and inter-individual coefficients of variations were equal to or less than 3.2%, 1.3%, and 4.4% for contrast, DOP, and spatial resolution (lateral and axial), respectively. The coefficients of variation corresponding to the elevational resolution test were all within 9.5%. Overall, in our assessment, the evaluated package performed well for objective and quantitative assessment of the above-mentioned image qualities under well-controlled acquisition conditions. We are finding it to be useful for various clinical ultrasound applications including performance comparison between scanners from different vendors.

Assessment of three methods for detection of ultrasound artifacts.

PURPOSE: The purpose of this work is to measure the performance (sensitivity and specificity) of three different visually based methods of detecting ultrasound artifacts using dynamic clips obtained with a liquid phantom. It is important to detect the presence of these non uniformities as early as possible, so they can be assessed, tracked, and addressed well before clinical image quality is impacted. METHODS: A total of 28 transducers of varying models containing a single artificial artifact created by stretching thin filaments across the transducer face were prepared. A second set of 28 matching transducers contained no artifacts. A 10 s clip was recorded of a dynamic speckle pattern from a custom liquid phantom ("dynamic clip"). A single-frame image was obtained by computing the median values at each pixel location over all frames of the clip ("median image"). This single-frame median image was then subtracted from a baseline image previously obtained with no induced artifact ("subtracted median"). All images were evaluated by six observers. The mean sensitivity and specificity with 95% exact binomial confidence intervals for the three artifact detection methods were estimated. Evaluation time and observer confidence were recorded. RESULTS: Both single-frame median and subtracted median images had a higher sensitivity than the dynamic clip. Overall the subtracted median images had the highest sensitivity of 97%, while maintaining a high specificity of 92%. Observers identified artifacts in the shortest time and with the highest confidence with this method. The subtracted median method removed the original structural variations and non-uniformities, and reduced the likelihood of false-positives. CONCLUSIONS: From the three methods assessed in this study, subtracted median images allow detection of artifacts with very good sensitivity and specificity, low image evaluation times, and a high degree of observer confidence, making these ideal for routine QC. For acceptance testing, where there are no previous baseline images available for subtraction, the use of median images is useful, although comparison with median images from different transducers of the same model and ∕ or comparison of impressions from multiple observers should be made to decrease the incidence of false-positive findings. If median and subtracted median images are not available, direct inspection of the dynamic B-mode clips is useful for acceptance testing and quality control, but with lower sensitivity and somewhat longer evaluation time.

Four-year experience with a clinical ultrasound quality control program.

Ultrasound (US) quality control (QC) program data over a 4-year period from more than 45 scanners and more than 265 transducers were reviewed to optimize the program in terms of efficiency and effectiveness. Our program included evaluations of mechanical integrity, image uniformity, distance measurement accuracy and maximum depth of penetration (DOP). We computed failure rates and fraction of failures detected by each test. A total of 187 equipment problems were identified. Average annual scanner component and transducer failure rates were 10.5% and 13.9%, respectively. The mechanical integrity and uniformity evaluations detected 25.1% and 66.3% of all failures, respectively. Those evaluations plus defects detected by sonographers accounted for 98.4% of all detected failures. DOP and distance measurement accuracy were not effective at detecting equipment failures. For routine US QC, we recommend quarterly mechanical integrity and uniformity assessments of all transducers. A scanner with five transducers could be tested in an estimated 30 min or less.

Evaluation of a low-cost liquid ultrasound test object for detection of transducer artefacts.

Routine quality control of ultrasound scanners and transducers is important for maintaining image quality. Our experience suggests that artefact and uniformity evaluation is the most effective single phantom test for detecting equipment problems. Current methods for assessing ultrasound images for artefacts have important limitations. To overcome these limitations, we have developed a novel, low-cost, liquid phantom with a flexible surface for assessing artefacts. A range of materials were evaluated and the optimal liquid phantom was found to be a water/cornstarch solution contained within a flexible latex balloon. When compared to a rigid tissue-mimicking phantom no deficiencies in overall image appearance or artefact detection for any transducer model was observed for the liquid phantom. With minimal training, reproducible clips were obtained by clinical sonographers with low inter- and intra-operator dependence, for a range of transducers models. The flexible scanning surface of the liquid phantom allows complete rapid coupling of all transducers. Due to its ease of use and low cost this liquid phantom appears superior to rigid phantoms for assessment of non-uniformity artefacts, and should allow clinical practices to perform routine artefact assessments of all ultrasound scanners and transducers.