Determining Ultrasound Parameters for Bursting Polymer Microbubbles for Future Use in Spinal Cord Injury.

OBJECTIVE: We believe our poly(lactic acid) (PLA) microbubbles are well suited for therapeutic delivery to spinal cord injury (SCI) using ultrasound-triggered bursting. We investigated the feasibility of clinical ultrasound bursting in situ, the optimal bursting parameters in vitro and the loading and release of a model bio-active DNA. METHODS: Microbubbles were tested using clinical ultrasound in a rat cadaver SCI model. Burst pressure thresholds were determined using the change in enhancement after ultrasound exposure. Resonance frequency, acoustic enhancement, sizing and morphology were evaluated by comparing two microbubble porogens, ammonium carbonate and ammonium carbamate. Oligonucleotides were loaded into the shell and released using the found optimized ultrasound bursting parameters. RESULTS: In situ imaging and bursting were successful. In vitro bursting thresholds using frequencies 1, 2.25 and 5 MHz were identified between peak negative pressures 0.2 and 0.5 MPa, believed to be safe for spinal cord. The pressure threshold decreased with decreasing frequencies. PLA bursting was optimized near the resonance frequency of 2.5 to 3.0 MHz using 2.25 MHz and not at lower frequencies. PLA microbubbles, initially with a mean size of approximately 2 µm, remained in one piece, collapsed to between 0.5 and 1 µm and did not fragment. Significantly more oligonucleotide was released after ultrasound bursting of loaded microbubbles. Microbubble-sized debris was detected when using ammonium carbamate, leading to inaccurate microbubble concentration measurements. CONCLUSION: PLA microbubbles made with ammonium carbonate and burst at appropriate parameters have the potential to safely improve intrathecal therapeutic delivery to SCI using targeted ultrasound.

Microbubble cavitation restores Staphylococcus aureus antibiotic susceptibility in vitro and in a septic arthritis model.

Treatment failure in joint infections is associated with fibrinous, antibiotic-resistant, floating and tissue-associated Staphylococcus aureus aggregates formed in synovial fluid (SynF). We explore whether antibiotic activity could be increased against Staphylococcus aureus aggregates using ultrasound-triggered microbubble destruction (UTMD), in vitro and in a porcine model of septic arthritis. In vitro, when bacterially laden SynF is diluted, akin to the dilution achieved clinically with lavage and local injection of antibiotics, amikacin and ultrasound application result in increased bacterial metabolism, aggregate permeabilization, and a 4-5 log decrease in colony forming units, independent of microbubble destruction. Without SynF dilution, amikacin + UTMD does not increase antibiotic activity. Importantly, in the porcine model of septic arthritis, no bacteria are recovered from the SynF after treatment with amikacin and UTMD-ultrasound without UTMD is insufficient. Our data suggest that UTMD + antibiotics may serve as an important adjunct for the treatment of septic arthritis.

Second-Generation Differential Tissue Harmonic Imaging Improves the Visualization of Renal Lesions.

OBJECTIVES: To compare to three nonlinear imaging techniques to conventional, grayscale ultrasound imaging of renal lesions. METHODS: Twenty adults with a known renal lesion and a body mass index >25 kg/m2 were enrolled in this prospective, institutional review board approved study. Each subject was imaged with an Aplio 500 scanner (Canon Medical Systems, Tokyo, Japan) using grayscale ultrasound, tissue harmonic imaging (THI) and two dual-frequency, differential tissue harmonic imaging modes (DTHI and DTHI-II, respectively). In total 184 images were scored by three independent and blinded observers for detail resolution, image quality, margin delineation, and depth penetration. Quantitative contrast-to-noise ratios (CNRs) were also calculated. RESULTS: Readers and CNR values showed that nonlinear imaging was superior to grayscale ultrasound (P < .0014). DTHI-II outperformed DTHI, THI, and grayscale ultrasound with respect to detail resolution, image quality, and margin delineation (P < .012). The depth penetration of DTHI and DTHI-II was similar (P = .16), but superior to grayscale ultrasound and THI (P < .001). Two observers saw improvements in detail resolution with DTHI-II over DTHI (P < .05), while image quality and margin delineation were considered similar by two readers (P > .07) and improved with DTHI-II by one (P < .017). CONCLUSIONS: DTHI-II improves the imaging of renal lesions compared to DTHI, THI, and grayscale ultrasound, albeit based on a limited sample size.

Ultrasound Pressure Estimation for Diagnosing Portal Hypertension in Patients Undergoing Dialysis for Chronic Kidney Disease.

OBJECTIVES: Hepatic venous pressure gradient (HVPG) is considered the standard in quantifying portal hypertension, but can be unreliable in dialysis patients. A noninvasive ultrasound technique, subharmonic-aided pressure estimation (SHAPE), may be a valuable surrogate of these pressure estimates. This study compared SHAPE and HVPG with pathology findings for fibrosis in dialysis patients. METHODS: This was a subgroup study from an IRB-approved trial that included 20 patients on dialysis undergoing SHAPE examinations of portal and hepatic veins using a modified Logiq 9 scanner (GE, Waukesha, WI), during infusion of Sonazoid (GE Healthcare, Oslo, Norway). SHAPE was compared to HVPG and pathology findings using the Ludwig-Batts scoring system for fibrosis. Logistic regression, ROC analysis, and t-tests were used to compare HVPG and SHAPE with pathological findings of fibrosis. RESULTS: Of 20 cases, 5 had HVPG values corresponding to subclinical and clinical portal hypertension (≥6 and ≥10 mmHg, respectively) while 15 had normal HVPG values (≤5 mmHg). SHAPE and HVPG correlated moderately (r = 0.45; P = .047). SHAPE showed a trend toward correlating with fibrosis (r = 0.42; P = .068), while HVPG did not (r = 0.18; P = .45). SHAPE could differentiate between mild (stage 0-1) and moderate to severe (stage 2-4) fibrosis (-10.4 ± 4.9 dB versus -5.4 ± 3.2 dB; P = .035), HVPG could not (3.0 ± 0.6 mmHg versus 4.8 ± 0.7 mmHg; P = .30). ROC curves showed a diagnostic accuracy for SHAPE of 80%, while HVPG reached 76%. CONCLUSION: Liver fibrosis staging in dialysis patients evaluated for portal hypertension appears to be more accurately predicted by SHAPE than by HVPG; albeit in a small sample size.

3D Harmonic and Subharmonic Imaging for Characterizing Breast Lesions: A Multi-Center Clinical Trial.

OBJECTIVE: Breast cancer is the most frequent type of cancer among women. This multi-center study assessed the ability of 3D contrast-enhanced ultrasound to characterize suspicious breast lesions using clinical assessments and quantitative parameters. METHODS: Women with suspicious breast lesions scheduled for biopsy were enrolled in this prospective, study. Following 2D grayscale ultrasound and power Doppler imaging (PDI), a contrast agent (Definity; Lantheus) was administrated. Contrast-enhanced 3D harmonic imaging (HI; transmitting/receiving at 5.0/10.0 MHz), as well as 3D subharmonic imaging (SHI; transmitting/receiving at 5.8/2.9 MHz), were performed using a modified Logiq 9 scanner (GE Healthcare). Five radiologists independently scored the imaging modes (including standard-of-care imaging) using a 7-point BIRADS scale as well as lesion vascularity and diagnostic confidence. Parametric volumes were constructed from time-intensity curves for vascular heterogeneity, perfusion, and area under the curve. Diagnostic accuracy was determined relative to pathology using receiver operating characteristic (ROC) and reverse, step-wise logistical regression analyses. The κ-statistic was calculated for inter-reader agreement. RESULTS: Data were successfully acquired in 219 cases and biopsies indicated 164 (75%) benign and 55 (25%) malignant lesions. SHI depicted more anastomoses and vascularity than HI (P < .021), but there were no differences by pathology (P > .27). Ultrasound achieved accuracies of 82 to 85%, which was significantly better than standard-of-care imaging (72%; P < .03). SHI increased diagnostic confidence by 3 to 6% (P < .05), but inter-reader agreements were medium to low (κ < 0.52). The best regression model achieved 97% accuracy by combining clinical reads and parametric SHI. CONCLUSIONS: Combining quantitative 3D SHI parameters and clinical assessments improves the characterization of suspicious breast lesions.

Gemcitabine-loaded microbubble system for ultrasound imaging and therapy.

Ultrasound imaging presents many positive attributes, including safety, real-time imaging, universal accessibility, and cost. However, inherent difficulties in discrimination between soft tissues and tumors prompted development of stabilized microbubble contrast agents. This presents the opportunity to develop agents in which drug is entrapped in the microbubble shell. We describe preparation and characterization of theranostic poly(lactide) (PLA) and pegylated PLA (PEG-PLA) shelled microbubbles that entrap gemcitabine, a commonly used drug for pancreatic cancer (PDAC). Entrapping 6 wt% gemcitabine did not significantly affect drug activity, microbubble morphology, or ultrasound contrast activity compared with unmodified microbubbles. In vitro microbubble concentrations yielding ≥ 500nM entrapped gemcitabine were needed for complete cell death in MIA PaCa-2 PDAC drug sensitivity assays, compared with 62.5 nM free gemcitabine. In vivo administration of gemcitabine-loaded microbubbles to xenograft MIA PaCa-2 PDAC tumors in athymic mice was well tolerated and provided substantial tumoral image enhancement before and after destructive ultrasound pulses. However, no significant differences in tumor growth were observed among treatment groups, in keeping with the in vitro observation that much higher doses of gemcitabine are required to mirror free gemcitabine activity. STATEMENT OF SIGNIFICANCE: The preliminary results shown here are encouraging and support further investigation into increased gemcitabine loading. Encapsulation of gemcitabine within polylactic acid (PLA) microbubbles does not damage its activity towards pancreatic cancer (pancreatic ductal adenocarcinoma, PDAC) cells. Excellent imaging and evidence of penetration into the highly desmoplastic PDAC tumors is demonstrated. Microbubble destruction was confirmed in vivo, showing that elevated mechanical index shatters the microbubbles for enhanced delivery. The potential to slow PDAC growth in vivo is shown, but higher gemcitabine concentrations are required. Current efforts are directed at increasing drug loading by inclusion of drug-carrying nanoparticles for effective in vivo treatment.

Contrast-Enhanced Ultrasound of Muscle Perfusion May Indicate Patient Response to Left Ventricular Assist Device Therapy.

PURPOSE: Left ventricular assist device (LVAD) support is associated with peripheral vascular abnormalities beyond those associated with heart failure (HF). These abnormalities are associated with persistent functional impairments that adversely impact quality of life (QoL). Methods for measuring peripheral vascular function in this population are needed. METHODS: This pilot study investigated the use of contrast-enhanced ultrasound (CEUS) using standardized protocols to estimate changes in peripheral (quadriceps) muscle perfusion among patients with HF (INTERMACS profile 3) undergoing LVAD implantation (n = 7). Patients were then stratified by those who did ("responders", n = 4) and did not ("nonresponders", n = 3) report QoL improvement with LVAD support. RESULTS: Serial measurements obtained preoperatively and 3 months following LVAD implantation showed no significant change (P > .23) in muscle perfusion by all CEUS-based measures at rest or with an exercise stimulus for the overall population. Responders exhibited improved muscle perfusion at rest (P = .043) and decreased time to peak contrast enhancement (P = .010) at 3 months compared with baseline, suggesting improved delivery of blood to the extremities post-LVAD. Nonresponders showed unchanged resting muscle perfusion (P > .99), time to peak contrast enhancement (P = .59), and response to exercise stimulus (P > .99) following LVAD therapy. CONCLUSION: Our findings suggest that CEUS evaluation is a promising noninvasive, quantitative modality for real-time assessment of peripheral vasculature and muscle perfusion as an indication of treatment response in LVAD recipients and that this modality may capture perfusion measures important to QoL following LVAD implantation.

Hepatic Vein Contrast-Enhanced Ultrasound Subharmonic Imaging Signal as a Screening Test for Portal Hypertension.

BACKGROUND: Portal hypertension is the underlying cause of most complications associated with cirrhosis, with the hepatic venous pressure gradient (HVPG) used for diagnosis and disease progression. Subharmonic imaging (SHI) is a contrast-specific imaging technique receiving at half the transmit frequency resulting in better tissue suppression. AIMS: To determine whether the presence of optimized SHI signals inside the hepatic vein can be used as a screening test for portal hypertension. METHODS: This prospective trial had 131 patients undergoing SHI examination of portal and hepatic veins using a modified Logiq 9 scanner (GE, Waukesha, WI). Images acquired after infusion of the ultrasound contrast agent Sonazoid (GE Healthcare, Oslo, Norway) were assessed for the presence of optimized SHI signals in the hepatic vein and compared to the HVPG values obtained as standard of care. RESULTS: Of 131 cases, 64 had increased HVPG values corresponding to subclinical (n = 31) and clinical (n = 33) portal hypertension (> 5 and > 10 mmHg, respectively), and 67 had normal HVPG values (< 5 mmHg). Two readers performed independent, binary qualitative assessments of the acquired digital clips. Reader one (experienced radiologist) achieved for the subclinical subgroup sensitivity of 98%, specificity of 88%, and ROC area of 0.93 and for the clinical subgroup sensitivity of 100% and specificity of 61%, with an ROC area of 0.74. Reader two (less experienced radiologist) achieved for the subclinical subgroup sensitivity of 77%, specificity of 76%, and ROC area of 0.76 and for the clinical subgroup sensitivity of 88% and specificity of 63%, with an ROC area of 0.70. Readers agreement was of 83% with kappa value of 0.66. CONCLUSION: The presence of optimized SHI signals inside the hepatic vein can be a qualitative screening test for portal hypertension, which could reduce the need for invasive diagnostic procedures.

Diagnosing Portal Hypertension with Noninvasive Subharmonic Pressure Estimates from a US Contrast Agent.

Background The current standard for assessing the severity of portal hypertension is the invasive acquisition of hepatic venous pressure gradient (HVPG). A noninvasive US-based technique called subharmonic-aided pressure estimation (SHAPE) could reduce risk and enable routine acquisition of these pressure estimates. Purpose To compare quantitative SHAPE to HVPG measurements to diagnose portal hypertension in participants undergoing a transjugular liver biopsy. Materials and Methods This was a prospective cross-sectional trial conducted at two hospitals between April 2015 and March 2019 (ClinicalTrials.gov identifier, NCT02489045). This trial enrolled participants who were scheduled for transjugular liver biopsy. After standard-of-care transjugular liver biopsy and HVPG pressure measurements, participants received an infusion of a US contrast agent and saline. During infusion, SHAPE data were collected from a portal vein and a hepatic vein, and the difference was compared with HVPG measurements. Correlations between data sets were determined by using the Pearson correlation coefficient, and statistical significance between groups was determined by using the Student t test. Receiver operating characteristic analysis was performed to determine the sensitivity and specificity of SHAPE. Results A total of 125 participants (mean age ± standard deviation, 59 years ± 12; 80 men) with complete data were included. Participants at increased risk for variceal hemorrhage (HVPG ≥12 mm Hg) had a higher mean SHAPE gradient compared with participants with lower HVPGs (0.79 dB ± 2.53 vs -4.95 dB ± 3.44; P < .001), which is equivalent to a sensitivity of 90% (13 of 14; 95% CI: 88, 94) and a specificity of 80% (79 of 99; 95% CI: 76, 84). The SHAPE gradient between the portal and hepatic veins was in good overall agreement with the HVPG measurements (r = 0.68). Conclusion Subharmonic-aided pressure estimation is an accurate noninvasive technique for detecting clinically significant portal hypertension. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Kiessling in this issue.

A Noninvasive Ultrasound Based Technique to Identify Treatment Responders in Patients with Portal Hypertension.

RATIONALE AND OBJECTIVE: Subharmonic aided pressure estimation (SHAPE) is based on the inverse relationship between the subharmonic amplitude of ultrasound contrast microbubbles and ambient pressure. The aim of this study was to verify if SHAPE can accurately monitor disease progression in patients identified with portal hypertension. MATERIALS & METHODS: A modified Logiq 9 scanner with a 4C curvi-linear probe (GE, Waukesha, WI) was used to acquire SHAPE data (transmitting and receiving at 2.5 and 1.25 MHz, respectively) using Sonazoid (GE Healthcare, Oslo, Norway; FDA IND 124,465). Twenty-one (median age 59 years; 12 Males) of the 178 patients enrolled in this institutional review board approved study (14F.113) were identified as having clinically significant portal hypertension based on their hepatic venous pressure gradient results ≥ 10 mmHg. Repeat SHAPE examinations were done every 6.2 months. Liver function tests and clinical indicators were used to establish treatment response. RESULTS: Of the 21 portal hypertensive subjects, 11 had successful follow up scans with an average follow up time of 6.2 months. There was a significantly larger SHAPE signal reduction in the group who were classified as treatment responders (n = 10; -4.01±3.61 dB) compared to the single nonresponder (2.33 dB; p < 0.001). Results for responders matched the corresponding clinical outcomes of improved model for end stage liver disease (MELD) scores, improvement in underlying cause of portal hypertension, improved liver function tests and reduced ascites. CONCLUSION: SHAPE can potentially monitor disease progression in portal hypertensive patients and hence, may help clinicians in patient management. A larger study would further validate this claim.

Contrast-enhanced Ultrasound Identifies Patent Feeding Vessels in Transarterial Chemoembolization Patients With Residual Tumor Vascularity.

Transarterial chemoembolization (TACE) of hepatocellular carcinoma (HCC) often requires retreatment and identification of feeding vessels supplying the residual/recurrent tumor is an important step in treatment planning. The objective of this study was to determine if contrast-enhanced ultrasound (CEUS) could correctly identify the vessel supplying the residual tumor. To date, 69 patients have undergone CEUS follow-up of HCC TACE therapy at our institution as part of an ongoing institutional review board approved trial (NCT02764801). The CEUS examinations were performed before HCC TACE as well as 1 to 2 weeks and 1 month after treatment using a Logiq E9 scanner with a C1-6 curved array transducer (GE Healthcare, Waukesha, WI). The CEUS images obtained 2 weeks after initial TACE treatment were reviewed, and any feeding vessels supplying the residual HCC were identified. Digital subtraction angiograms during the retreatment TACE were used as reference standard for feeding vessel identification. Thirteen patients with viable HCC post-TACE were included in this study. In these cases, the sonographer correctly identified 85% (11 of 13) of the feeding vessels later confirmed by angiography. Importantly, one of the false-negative cases involved a segment 8 tumor with parasitic blood supply from the medial left hepatic artery. In this case, CEUS identified a largely treated tumor with some residual internal flow, but was unable to visualize any major hepatic vascularity supplying the tumor. In conclusion, CEUS appears to be a valuable tool for planning retreatment of residual HCC post-TACE.

Characterizing Breast Lesions Using Quantitative Parametric 3D Subharmonic Imaging: A Multicenter Study.

RATIONALE AND OBJECTIVES: Breast cancer is the leading type of cancer among women. Visualization and characterization of breast lesions based on vascularity kinetics was evaluated using three-dimensional (3D) contrast-enhanced ultrasound imaging in a clinical study. MATERIALS AND METHODS: Breast lesions (n = 219) were imaged using power Doppler imaging (PDI), 3D contrast-enhanced harmonic imaging (HI), and 3D contrast-enhanced subharmonic imaging (SHI) with a modified Logiq 9 ultrasound scanner using a 4D10L transducer. Quantitative metrics of vascularity derived from 3D parametric volumes (based on contrast perfusion; PER and area under the curve; AUC) were generated by off-line processing of contrast wash-in and wash-out. Diagnostic accuracy of these quantitative vascular parameters was assessed with biopsy results as the reference standard. RESULTS: Vascularity was observed with PDI in 93 lesions (69 benign and 24 malignant), 3D HI in 8 lesions (5 benign and 3 malignant), and 3D SHI in 83 lesions (58 benign and 25 malignant). Diagnostic accuracy for vascular heterogeneity, PER, and AUC ranged from 0.52 to 0.75, while the best logistical regression model (vascular heterogeneity ratio, central PER, and central AUC) reached 0.90. CONCLUSION: 3D SHI successfully detects contrast agent flow in breast lesions and characterization of these lesions based on quantitative measures of vascular heterogeneity and 3D parametric volumes is promising.

Assessing carotid plaque neovascularity and calcifications in patients prior to endarterectomy.

OBJECTIVE: The objective was to use two ultrasound image and signal processing techniques (MicroPure and superb microvascular imaging [SMI]; Toshiba Medical, Tokyo, Japan) to investigate carotid plaque calcification and intraplaque neovascularity flow as biomarkers for plaque vulnerability in patients before endarterectomy. METHODS: Thirty patients, with preoperative computed tomography angiography and scheduled for carotid endarterectomy, were enrolled in an institutional review board-approved study. Bilateral grayscale, power Doppler, SMI and MicroPure imaging of the carotids were performed using an Aplio 500 Platinum scanner (Toshiba). MicroPure combines nonlinear imaging and speckle suppression to mark calcifications as white spots in a blue overlay, and SMI uses clutter suppression to extract microvascular flow signals. Readers counted calcifications and scored them as present or absent; intraplaque neovascularity was scored on a 4-point scale by ultrasound imaging as well as by pathology (as the reference). MicroPure and SMI assessments were compared with conventional ultrasound examination and computed tomography angiography with pathology as the reference standard. RESULTS: Owing to technical difficulties and cancelled operations, 57 carotids were studied; endarterectomies yielded 28 specimens. Intraplaque neovascularization was detected by SMI in significantly more plagues than by power Doppler (41 vs 22 out 57 examined plaques or 72% vs 39%; P < .0001). There was no statistical difference between either reader compared with pathology (P > .37). Sensitivity specificity and accuracy for detecting intraplaque neovascularity based on color SMI and PDI were 84% (95% confidence interval [CI], 64%-96%), 33% (95% CI, 1%-91%), 79% (95% CI, 59%-92%), and 52% (95% CI, 31%-72%), 100% (95% CI, 23%-100%), and 57% (95% CI, 37%-76%), respectively. MicroPure did not correlate with any measures of intraplaque flow (P > .13). CONCLUSIONS: SMI may have potential for providing evidence of plaque vulnerability. MicroPure appears less useful in carotid applications.

Monitoring Progression of Ductal Carcinoma In Situ Using Photoacoustics and Contrast-Enhanced Ultrasound.

Breast cancer is the leading form of cancer in women, accounting for approximately 41,400 deaths in 2018. While a variety of risk factors have been identified, physical exercise has been linked to reducing both the risk and aggressiveness of breast cancer. Within breast cancer, ductal carcinoma in situ (DCIS) is a common finding. However, less than 25% of DCIS tumors actually progress into invasive breast cancer, resulting in overtreatment. This overtreatment is due to a lack of predictive precursors to assess aggressiveness and development of DCIS. We hypothesize that tissue oxygenation and perfusion measured by photoacoustic and contrast-enhanced ultrasound imaging, respectively, can predict DCIS aggressiveness. To test this, 20 FVB/NJ and 20 SV40Tag mice that genetically develop DCIS-like breast cancers were divided evenly into exercise and control groups and imaged over the course of 6 weeks. Tissue oxygenation was a predictive precursor to invasive breast cancer for FVB/NJ mice (P = 0.015) in the early stages of tumor development. Meanwhile, perfusion results were inconclusive (P > 0.2) as a marker for disease progression. Moreover, voluntary physical exercise resulted in lower weekly tumor growth and significantly improved median survival (P = 0.014).

Influence of Data Parsing on Contrast Enhanced Ultrasound Exams.

RATIONALE AND OBJECTIVES: To explore the influence of data parsing (either selection of frames at set time intervals or by an experienced sonographer) of contrast-enhanced ultrasound (CEUS) exams on physician diagnoses and confidence levels. MATERIALS AND METHODS: Forty consecutive CEUS exams consisting of 10 cases each of indeterminate liver lesions, indeterminate renal lesions, renal cell carcinoma postablation follow-up, and hepatocellular carcinoma postchemoembolization follow-up were selected for analysis. Exams were parsed into sets consisting of five images selected by the performing sonographer and sets containing systematically stored frames every 10, 30, and 60 seconds. Three blinded physicians then reviewed the cine loop and each set of images in randomized order and provided a diagnosis and confidence level. RESULTS: For all clinical applications investigated, no statistically significant differences in diagnostic performance measures or reader confidence were observed between review of the entire cine loop and images selected by the performing sonographer (p > 0.42). Diagnostic performance at 10-second intervals did not show statically significant changes compared to the full cine loop review for all applications (p > 0.18), although reader confidence decreased. At 30-60-second intervals, both diagnostic performance and reader confidence showed statistically significant reduction compared to review of the full cine loop (p < 0.045). CONCLUSIONS: Transfer and review of large cine loops from CEUS exams represent a potential barrier to adoption within the United States workflows. This study demonstrates that images selected by a performing trained sonographer may provide the same value without the review time and data storage costs needed for full cine loop review. Parsing by time points reduced reader confidence and diagnostic performance.

Characterization of Breast Microcalcifications Using a New Ultrasound Image-Processing Technique.

OBJECTIVES: To evaluate a new commercial image-processing technique (MicroPure; Toshiba America Medical Systems, Tustin, CA) for detection and characterization of breast microcalcifications in patients undergoing stereotactic or ultrasound-guided biopsies using mammography as the reference standard. METHODS: One hundred female patients, with a total of 104 lesions, scheduled for an image-guided biopsy of an area with breast microcalcifications (identified on a prior mammogram) underwent MicroPure examinations of the breast using an Aplio XG scanner (Toshiba America Medical Systems) with a broad-bandwidth linear array. MicroPure combines nonlinear imaging and speckle suppression to mark suspected calcifications as white spots in a blue overlay image. Four independent and blinded readers (2 radiologists and 2 physicists) analyzed 208 digital clips consisting of dual grayscale ultrasound and MicroPure imaging, counting the number of microcalcifications seen with MicroPure. The observers also assessed the level of suspicion on a qualitative, visual analog, 6-point scale from 0 (no findings) over 1 (benign) to 5 (malignant). RESULTS: The mean number of microcalcifications ± SD seen was 6.3 ± 3.5, whereas mammography saw 28.9 ± 24.6 (P = .66). When the MicroPure level of suspicion scores were compared with pathologic results using a receiver operating characteristic curve analysis, the areas under the curve ranged from 0.54 to 0.59. Nonetheless, malignant cases were seen to have significantly more microcalcifications than benign cases (mean number of microcalcifications, 6.9 ± 5.1 versus 5.3 ± 3.7; P = .02). CONCLUSIONS: MicroPure can be used to identify areas with breast microcalcifications but cannot effectively characterize such areas. Instead, MicroPure may represent a new imaging method for guiding a biopsy to areas of microcalcifications.

On Factors Affecting Subharmonic-aided Pressure Estimation (SHAPE).

Subharmonic-aided pressure estimation (SHAPE) estimates hydrostatic pressure using the inverse relationship with subharmonic amplitude variations of ultrasound contrast agents (UCAs). We studied the impact of varying incident acoustic outputs (IAO), UCA concentration, and hematocrit on SHAPE. A Logiq 9 scanner with a 4C curvilinear probe (GE, Milwaukee, Wisconsin) was used with Sonazoid (GE Healthcare, Oslo, Norway) transmitting at 2.5 MHz and receiving at 1.25 MHz. An improved IAO selection algorithm provided improved correlations ( r from -0.85 to -0.95 vs. -0.39 to -0.98). There was no significant change in SHAPE gradient as the pressure increased from 10 to 40 mmHg and hematocrit concentration was tripled from 1.8 to 4.5 mL/L (Δ0.00-0.01 dB, p = 0.18), and as UCA concentration was increased from 0.2 to 1.2 mL/L (Δ0.02-0.05 dB, p = 0.75). The results for the correlation between the SHAPE gradient and hematocrit values for patients ( N = 100) in an ongoing clinical trial were also calculated showing a poor correlation value of 0.14. Overall, the SHAPE gradient is independent of hematocrit and UCA concentration. An improved algorithm for IAO selection will make SHAPE more accurate.

Three-Dimensional Subharmonic Aided Pressure Estimation for Assessing Arterial Plaques in a Rabbit Model.

OBJECTIVES: To investigate 3-dimensional subharmonic aided pressure estimation (SHAPE) for measuring intraplaque pressure and the pressure gradient across the plaque cap as novel biomarkers for potentially predicting plaque vulnerability. METHODS: Twenty-seven rabbits received a high-cholesterol diet for 2 weeks before a balloon catheter injury to denude the endothelium of the aorta, followed by 8 to 10 weeks of the high-cholesterol diet to create arteriosclerotic plaques. SHAPE imagings of the resulting plaques were performed 12, 16, and 20 weeks after injury using a LOGIQ 9 scanner with a 4D10L probe (GE Healthcare, Milwaukee, WI) before and during an infusion of Definity (Lantheus Medical Imaging, North Billerica, MA) and Sonazoid (GE Healthcare, Oslo, Norway). The ratios of the maximum subharmonic magnitudes at baseline and during the infusion were correlated with the intraplaque pressure and pressure gradient across the plaque cap obtained from direct measurements. RESULTS: Ten rabbits died prematurely after the balloon injury procedure or due to toxicity from the high-cholesterol diet, whereas 2 rabbits were excluded for other conditions. Five rabbits were scanned in the 12-, 16-, and 20-week groups, respectively. Even after 20 weeks, the plaques that developed were very small (mean ± SD, 0.9 ± 0.4 × 0.14 ± 0.05 cm). Definity performed better than Sonazoid in this application but still only achieved a moderate correlation with pressure across the plaque cap (Definity, r = -0.40; Sonazoid, r = 0.22) and intraplaque pressure (Definity, r = -0.19; Sonazoid, r = -0.11). CONCLUSIONS: Initial findings from plaque pressure estimation using 3-dimensional SHAPE technique showed only moderate correlations with reference standards, but that may be have been due to weaknesses in the animal model studied.

Performance of Molecular Lymphosonography for Detection and Quantification of Metastatic Involvement in Sentinel Lymph Nodes.

OBJECTIVES: To assess the performance of molecular lymphosonography with dual-targeted microbubbles in detecting and quantifying the metastatic involvement in sentinel lymph nodes (SLNs) using a swine melanoma model. METHODS: Targeted microbubbles were labeled with P-selectin and αV ß3 -integrin antibodies. Control microbubbles were labeled with immunoglobulin G antibodies. First lymphosonography with Sonazoid (GE Healthcare, Oslo, Norway) was used to identify SLNs. Then dual-targeted and control microbubbles were injected intravenously to detect and quantify metastatic disease in the SLNs. Distant non-SLNs were imaged as benign controls. All evaluated lymph nodes (LNs) were surgically removed, and metastatic involvement was characterized by a histopathologic analysis. Two radiologists blinded to histopathologic results assessed the baseline B-mode images of LNs, and the results were compared to the histologic reference standard. The mean intensities of targeted and control microbubbles within the examined LNs were measured and compared to the LN histologic results. RESULTS: Thirty-five SLNs and 34 non-SLNs from 13 Sinclair swine were included in this study. Twenty-one SLNs (62%) were malignant, whereas 100% of non-SLNs were benign. The sensitivity of B-mode imaging for metastatic LN diagnosis for both readers was relatively high (90% and 71%), but the specificity was very poor (50% and 58%). The sensitivity and specificity of molecular lymphosonography for metastatic LN detection were 91% and 67%, respectively. The mean intensities from dual-targeted microbubbles correlated well with the degree of metastatic LN involvement (r = 0.6; P < 0.001). CONCLUSIONS: Molecular lymphosonography can increase the specificity of metastatic LN detection and provide a measure to quantify the degree of metastatic involvement.