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.

MRI-guided focused ultrasound ablation of painful lumbar facet joints: a retrospective assessment of safety and tolerability in human subjects.

OBJECTIVE: To evaluate the safety and tolerability of MRI-guided focused ultrasound (MRgFUS) for the treatment of facet joint-mediated pain in human subjects for whom conventional treatment had failed. Secondarily, to evaluate effectiveness of the procedure. METHODS: Consecutive patients who underwent MRgFUS at our institution were retrospectively identified. Chart review was performed to obtain relevant clinical and technical data. All patients had chronic low back pain and positive comparative medial branch blocks. RESULTS: Twenty-six MRgFUS treatments in 20 patients were included. Mean sonication energy was 1436.6 Joules. The procedure was technically successful in all patients. Of the treated patients, 29.6% experienced short-term worsening of low back pain immediately after the procedure, all by 1-4 points on a 0-10 scale. One patient (3.8%) reported temporary worsening of preexisting radicular symptoms after the procedure. Of 21 treatments with clinical follow-up of at least 3 months available, 12 (57.1%) had >3 months' pain relief, 2 (10%) had <3 months' benefit, 6 (30%) reported no benefit, and 1 (5%) patient was lost to follow-up. In patients who reported at least some benefit with prior conventional radiofrequency ablation, 8/10 (80%) benefited from the MRgFUS procedure. CONCLUSION: The present study demonstrates that MRgFUS ablation of the lumbar facet joints is a safe and tolerable procedure in human subjects and could provide another option for patients for whom radiofrequency ablation had failed. More than half of all patients received significant durable pain relief, which jumped to 80% for patients who had experienced at least some benefit from prior radiofrequency ablations.

Prospective Study Assessing Impact of Ethylene Oxide Sterilization on Endoscopic Ultrasound Image Quality.

BACKGROUND & AIMS: Duodenoscope-associated transmission of infections has raised questions about efficacy of endoscope reprocessing using high-level disinfection (HLD). Although ethylene oxide (ETO) gas sterilization is effective in eradicating microbes, the impact of ETO on endoscopic ultrasound (EUS) imaging equipment remains unknown. In this study, we aimed to compare the changes in EUS image quality associated with HLD vs HLD followed by ETO sterilization. METHODS: Four new EUS instruments were assigned to 2 groups: Group 1 (HLD) and Group 2 (HLD + ETO). The echoendoscopes were assessed at baseline, monthly for 6 months, and once every 3 to 4 months thereafter, for a total of 12 time points. At each time point, review of EUS video and still image quality was performed by an expert panel of reviewers along with phantom-based objective testing. Linear mixed effects models were used to assess whether the modality of reprocessing impacted image and video quality. RESULTS: For clinical testing, mixed linear models showed minimal quantitative differences in linear analog score (P = .04; estimated change, 3.12; scale, 0-100) and overall image quality value (P = .007; estimated change, -0.12; scale, 1-5) favoring ETO but not for rank value (P = .06). On phantom testing, maximum depth of penetration was lower for ETO endoscopes (P < .001; change in depth, 0.49 cm). CONCLUSIONS: In this prospective study, expert review and phantom-based testing demonstrated minimal differences in image quality between echoendoscopes reprocessed using HLD vs ETO + HLD over 2 years of clinical use. Further studies are warranted to assess the long-term clinical impact of these findings. In the interim, these results support use of ETO sterilization of EUS instruments if deemed clinically necessary.

Initial testing of pegfilgrastim (Neulasta Onpro) on-body injector in multiple radiological imaging environments.

PURPOSE: An increasing number of implantable or external devices can impact whether patients can receive radiological imaging examinations. This study examines and tests the Neulasta (pegfilgrastim) Onpro on-body injector in multiple imaging environments. METHODS: The injector was analyzed for four imaging modalities with testing protocols and strategies developed for each modality. In x-ray and computed tomography (CT), scans with much higher exposure than clinical protocols were performed with the device attached to an anthropomorphic phantom. The device was monitored until the completion of drug delivery. For magnetic resonance imaging (MRI), the device was assessed using a hand-held magnet and underwent the magnetically induced displacement testing in a 1.5T clinical MRI scanner room. For ultrasound, magnetic field changes were measured around an ultrasound scanner system with three transducers. RESULTS: For x-ray and CT no sign of device error was identified during or after the high radiation exposure scans. Drug delivery was completed at expected timing with expected volume. For MRI the device showed significant attractive force towards the hand-held magnet and a 50-degree deflection angle at 50 cm from the opening of the scanner bore. No further assessment from the gradient or radiofrequency field was deemed necessary. For ultrasound the maximum magnetic field change from baseline was measured to be +11.7 µT in comparison to +74.2 µT at 4 inches from a working microwave. CONCLUSIONS: No device performance issue was identified under the extreme test conditions in x-ray or CT. The device was found to be MR Unsafe. Magnetic field changes around an ultrasound system met the limitation set by manufacture. Patient ultrasound scanning is considered safe as long as the transducers do not inadvertently loosen the device.

Comparison of Clinical Performance Between Two Generations of Magnetic Resonance-guided Focused Ultrasound Systems in Treatments of Uterine Leiomyomas.

OBJECTIVES: The aim of this study was to evaluate the impact of technology improvements on the outcomes of magnetic resonance-guided focused ultrasound (MRgFUS) treatments of symptomatic uterine leiomyomas (uterine fibroids). The study compared ablation volumes and incidence of adverse events in patient groups treated with two generations of MRgFUS systems from a single vendor. METHODS: The present study describes the results of a retrospective comparative study of two groups of women with symptomatic uterine leiomyomas who were clinically treated with MRgFUS at a single institution. Group 1 (n = 130) was treated using the first-generation system between March 2005 and December 2009. Group 2 (n = 71) was treated using the second-generation between December 2013 and September 2019. RESULTS: The second-generation MRgFUS system resulted in significantly improved nonperfused volume ratios in both dark and bright T2 fibroid categories compared with the first-generation system (dark - 80% versus46 %, p = 0.00002 and bright - 46% versus 32%, p = 0.001). There have been no recorded hospital admissions, no skins burns, and no reported major adverse events since the introduction of this second-generation ExAblate 2100 system with advanced safety and treatment planning features. CONCLUSION: This study has demonstrated that improvements to current MRgFUS technology resulted in significantly increased efficacy and patient safety of clinical treatments of patients with symptomatic uterine leiomyomas.

Magnetic Resonance Imaging-Guided Focused Ultrasound Ablation of Lumbar Facet Joints of a Patient With a Magnetic Resonance Image Non-Conditional Pacemaker at 1.5T.

OBJECTIVE: To provide an initial report that patients with magnetic resonance imaging (MRI) non-conditional cardiac implanted electronic device (CIED) can undergo state-of-the-art magnetic resonance imaging-guided focused (MRgFUS) ablation procedures with careful planning and integration of the procedure into an established CIED MRI practice. PATIENT AND METHODS: We describe an MRgFUS ablation treatment of lumbar facet joints in a patient with an MRI non-conditional CIED (pacemaker), completed in accordance with our institutional CIED/MRI practice guidelines. RESULTS: A risk-benefit analysis by a coordinated multidisciplinary team before this treatment was performed to account for the risks associated with the MRI non-conditional pacemaker in the context of the MRgFUS procedure. CONCLUSION: The patient had no adverse cardiac event during or following this procedure.

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.

Development of a robust MRI fiducial system for automated fusion of MR-US abdominal images.

We present the development of a two-component magnetic resonance (MR) fiducial system, that is, a fiducial marker device combined with an auto-segmentation algorithm, designed to be paired with existing ultrasound probe tracking and image fusion technology to automatically fuse MR and ultrasound (US) images. The fiducial device consisted of four ~6.4 mL cylindrical wells filled with 1 g/L copper sulfate solution. The algorithm was designed to automatically segment the device in clinical abdominal MR images. The algorithm's detection rate and repeatability were investigated through a phantom study and in human volunteers. The detection rate was 100% in all phantom and human images. The center-of-mass of the fiducial device was robustly identified with maximum variations of 2.9 mm in position and 0.9° in angular orientation. In volunteer images, average differences between algorithm-measured inter-marker spacings and actual separation distances were 0.53 ± 0.36 mm. "Proof-of-concept" automatic MR-US fusions were conducted with sets of images from both a phantom and volunteer using a commercial prototype system, which was built based on the above findings. Image fusion accuracy was measured to be within 5 mm for breath-hold scanning. These results demonstrate the capability of this approach to automatically fuse US and MR images acquired across a wide range of clinical abdominal pulse sequences.

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.

Implementation of a channelized Hotelling observer model to assess image quality of x-ray angiography systems.

Evaluation of flat-panel angiography equipment through conventional image quality metrics is limited by the scope of standard spatial-domain image quality metric(s), such as contrast-to-noise ratio and spatial resolution, or by restricted access to appropriate data to calculate Fourier domain measurements, such as modulation transfer function, noise power spectrum, and detective quantum efficiency. Observer models have been shown capable of overcoming these limitations and are able to comprehensively evaluate medical-imaging systems. We present a spatial domain-based channelized Hotelling observer model to calculate the detectability index (DI) of our different sized disks and compare the performance of different imaging conditions and angiography systems. When appropriate, changes in DIs were compared to expectations based on the classical Rose model of signal detection to assess linearity of the model with quantum signal-to-noise ratio (SNR) theory. For these experiments, the estimated uncertainty of the DIs was less than 3%, allowing for precise comparison of imaging systems or conditions. For most experimental variables, DI changes were linear with expectations based on quantum SNR theory. DIs calculated for the smallest objects demonstrated nonlinearity with quantum SNR theory due to system blur. Two angiography systems with different detector element sizes were shown to perform similarly across the majority of the detection tasks.

The effect of magnification on sonographically measured nerve cross-sectional area.

INTRODUCTION: The primary aim of this investigation was to determine whether use of write-zoom magnification affects sonographically determined cross-sectional area (CSA) of peripheral nerves. METHODS: CSAs of the median (MN) and posterior interosseous (PIN) nerves were measured in 22 limbs from 11 asymptomatic volunteers using both standard imaging and write-zoom magnification. CSA measurements were repeated on the same images 1 week later. RESULTS: The average CSA of write-zoomed images for the MN was significantly larger at both measurement sessions (week 1: 11.1 mm(2) write-zoom vs. 10.0 mm(2) standard, P = 0.019; week 2: 11.8 mm(2) vs. 10.4 mm(2), P = 0.023). Similar differences were noted for the PIN (week 1: 2.3 mm(2) vs. 1.9 mm(2), P = 0.002; week 2: 2.5 mm(2) vs. 1.9 mm(2), P = 0.001). CONCLUSIONS: Write-zoom magnification may significantly increase the measured CSA of peripheral nerves. These changes appear to be more substantial when smaller nerves are measured.

Use of a radio frequency shield during 1.5 and 3.0 Tesla magnetic resonance imaging: experimental evaluation.

Radiofrequency (RF) shields have been recently developed for the purpose of shielding portions of the patient's body during magnetic resonance imaging (MRI) examinations. We present an experimental evaluation of a commercially available RF shield in the MRI environment. All tests were performed on 1.5 T and 3.0 T clinical MRI scanners. The tests were repeated with and without the RF shield present in the bore, for comparison. Effects of the shield, placed within the scanner bore, on the RF fields generated by the scanner were measured directly using tuned pick-up coils. Attenuation, by as much as 35 dB, of RF field power was found inside the RF shield. These results were supported by temperature measurements of metallic leads placed inside the shield, in which no measurable RF heating was found. In addition, there was a small, simultaneous detectable increase (∼1 dB) of RF power just outside the edges of the shield. For these particular scanners, the autocalibrated RF power levels were reduced for scan locations prescribed just outside the edges of the shield, which corresponded with estimations based on the pick-up coil measurements. Additionally, no significant heating during MRI scanning was observed on the shield surface. The impact of the RF shield on the RF fields inside the magnet bore is likely to be dependent on the particular model of the RF shield or the MRI scanner. These results suggest that the RF shield could be a valuable tool for clinical MRI practices.

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.