Mary Scott Soo

Acoustic radiation force impulse imaging: in vivo demonstration of clinical feasibility.

The clinical viability of a method of acoustic remote palpation, capable of imaging local variations in the mechanical properties of soft tissue using acoustic radiation force impulse (ARFI) imaging, is investigated in vivo. In this method, focused ultrasound (US) is used to apply localized radiation force to small volumes of tissue (2 mm(3)) for short durations (less than 1 ms) and the resulting tissue displacements are mapped using ultrasonic correlation-based methods. The tissue displacements are inversely proportional to the stiffness of the tissue and, thus, a stiffer region of tissue exhibits smaller displacements than a more compliant region. Due to the short duration of the force application, this method provides information about the mechanical impulse response of the tissue, which reflects variations in tissue viscoelastic characteristics. In this paper, experimental results are presented demonstrating that displacements on the order of 10 microm can be generated and detected in soft tissues in vivo using a single transducer on a modified diagnostic US scanner. Differences in the magnitude of displacement and the transient response of tissue are correlated with tissue structures in matched B-mode images. The results comprise the first in vivo ARFI images, and support the clinical feasibility of a radiation force-based remote palpation imaging system.

Impact of core-needle breast biopsy on the surgical management of mammographic abnormalities.

ObjectiveTo evaluate the accuracy of percutaneous, image-guided core-needle breast biopsy (CNBx) and to compare the surgical management of patients with breast cancer diagnosed by CNBx with patients diagnosed by surgical needle-localization biopsy (SNLBx). Summary Background DataPercutaneous, image-guided CNBx is a less invasive alternative to SNLBx for the diagnosis of nonpalpable mammographic abnormalities. CNBx potentially spares patients with benign lesions from unnecessary surgery, although false-negative results can occur. For patients with malignant lesions, preoperative diagnosis by CNBx allows definitive treatment decisions to be made before surgery and may affect surgical outcomes. MethodsBetween 1992 and 1999, 939 patients with 1,042 mammographically detected lesions underwent biopsy by stereotactic CNBx or ultrasound-guided CNBx. Results were categorized pathologically as benign or malignant and, further, as invasive or noninvasive malignancies. Only biopsy results confirmed by excision or 1-year-minimum mammographic follow-up were included in the analysis. Patients with breast cancer diagnosed by CNBx were compared with a matched control group of patients with breast cancer diagnosed by SNLBx. ResultsBenign results were obtained in 802 lesions (77%), 520 of which were in patients with adequate follow-up. Ninety-five of the 520 evaluable lesions (18%) were subsequently excised because of atypical hyperplasia, mammographic–histologic discordance, or other clinical indications. There were 17 false-negative CNBx results in this group; 15 of these lesions were correctly diagnosed by excisional biopsy within 4 months of CNBx. In two patients (0.9%), delayed diagnoses of ductal carcinoma in situ were made at 15 and 19 months after CNBx. Malignant results were obtained in 240 lesions (23%), 220 of which were surgically excised from 202 patients at our institution. Two lesions diagnosed as ductal carcinoma in situ were reclassified as atypical ductal hyperplasia and considered false-positive results (0.4%). For malignant lesions, the sensitivity and specificity of CNBx for the detection of invasion were 89% and 96%, respectively. During the first surgical procedure, 115 of 199 patients (58%) diagnosed by CNBx underwent local excision; 194 of 199 patients (97%) evaluated by SNLBx underwent local excision. For patients whose initial surgery was local excision, those diagnosed before surgery by CNBx had larger excision specimens and were more likely to have negative surgical margins than were patients initially evaluated by SNLBx. Overall, patients diagnosed by CNBx required fewer surgical procedures for definitive treatment than did patients diagnosed by SNLBx. ConclusionsDiagnosis by CNBx spares most patients with benign mammographic abnormalities from unnecessary surgery. With the selective use of SNLBx to confirm discordant results, missed diagnoses are rare. When compared with SNLBx, preoperative diagnosis of breast cancer by CNBx facilitates wider initial margins of excision, fewer positive margins, and fewer surgical procedures to accomplish definitive treatment than diagnosis by SNLBx.

Tissue harmonic imaging sonography of breast lesions: improved margin analysis, conspicuity, and image quality compared to conventional ultrasound.

The purpose of this preference study is to determine if tissue harmonic imaging (THI) is preferred over conventional sonography for imaging breast masses. A prospective evaluation of 73 identical image pairs (one obtained with conventional sonography, one with THI sonography) was performed, examining 25 cysts, 36 solid masses, and 12 indeterminate lesions. Each image was evaluated for lesion contrast, margins, and overall image quality using a graduated score. Statistical analysis was performed using a modified t test. For cystic and solid lesions, THI was preferred for lesion conspicuity, margin, and overall quality (P<.001). For indeterminate lesions, THI was significantly preferred for lesion conspicuity and overall quality (P<.05), but the preference for margins was not significant. Overall, THI of breast lesions was significantly preferred for lesion contrast and margin evaluation compared to conventional sonography. This modality deserves further evaluation and may improve detection and evaluation of breast lesions.

The detection of breast microcalcifications with medical ultrasound

Microcalcifications are small crystals of calcium apatites which form in human tissue through a number of mechanisms. The size, morphology, and distribution of microcalcifications are important indicators in the mammographic screening for and diagnosis of various carcinomas in the breast. Although x-ray mammography is currently the only accepted method for detecting microcalcifications, its efficacy in this regard can be reduced in the presence of dense parenchyma. Current ultrasound scanners do not reliably detect microcalcifications in the size range of clinical interest. The results of theoretical, simulation, and experimental studies focused on the improvement of the ultrasonic visualization of microcalcifications are presented. Methods for estimating the changes in microcalcification detection performance which result from changes in aperture geometry or the presence of an aberrator are presented. An analysis of the relative efficacy of spatial compounding and synthetic receive aperture geometries in the detection of microcalcifications is described. The impact of log compression of the detected image on visualization is discussed. Registered high resolution ultrasound and digital spot mammography images of microcalcifications in excised breast carcinoma tissue and results from the imaging of suspected microcalcifications in vivo are presented.

Acoustic radiation force impulse imaging of in vivo breast masses

Acoustic radiation force impulse (ARFI) imaging utilizes brief, high energy, focused acoustic pulses to generate radiation force in tissue, and conventional ultrasonic correlation-based methods to track the resulting tissue displacements in order to image the relative mechanical properties of tissue. In an ongoing clinical study, ARFI datasets from in vivo breast masses are acquired prior to core biopsy. Matched B-mode and ARFI images are generated for each mass. Data sets are divided based upon biopsy results, and images are evaluated for differentiating features. The purpose of this study is to acquire in vivo ARFI datasets in real-time, and to identify differentiable features between benign and malignant breast masses in the ARFI images. A modified Siemens SONOLINE Antares/spl trade/ scanner and a VF10-5 probe were programmed to implement ARFI imaging in a multi-focal zone configuration. Under an IRB approved protocol. patients scheduled for breast core biopsy were recruited for participation. Data was acquired in real-time and processed offline. Matched B-mode and ARFI images were evaluated concurrently. To date, 27 masses have been imaged under this experimental protocol. In addition, single focal zone ARFI data acquired from 52 masses with a Siemens SONOLINE Elegra/spl trade/ scanner and a 75L40 transducer were evaluated for consistency of the differentiating features. Of the 27 masses interrogated via multi-focal-zone ARFI, 9 were malignant, 9 were benign fibroadenomas, 4 were cysts, and the rest were other benign masses (i.e. lymph nodes, fat necrosis, etc.) Structures in matched B-mode images are in good agreement with those in ARFI displacement images, with both modalities demonstrating comparable resolution. In general ARFI displacement images of malignant breast masses exhibit increased contrast and improved margin definition over matched B-mode images. Cancers displace less (i.e. they are stiffer) than the surrounding tissue, and generally appear larger than in matched B-mode images. In addition, some malignant masses exhibit a slower recovery time, which has not been observed with benign masses. The cysts and fibroadenomas, in general, exhibit less contrast in ARFI images than in matched B-mode images. In many cases, fibroadenomas are not clearly distinguished from the surrounding tissues in ARFI displacement images, and can appear either stiffer or softer than the surrounding tissue. Acoustic streaming is observed in cyst fluid in response to ARFI excitation. ARFI displacement images portray different, complementary information than matched B-mode images. Some possible differentiating features between malignant and benign breast masses have been identified by this pilot study. Promising features include: differences in B-mode and ARFI lesion size. displacement magnitude, recovery time, and image contrast. These results encourage further study of breast mass characterization using ARFI imaging.

Abbreviated Screening Protocol for Breast MRI: A Feasibility Study

RATIONALE AND OBJECTIVES To compare the performance of two shortened breast magnetic resonance imaging (MRI) protocols to a standard MRI protocol for breast cancer screening. MATERIALS AND METHODS In this Health Insurance Portability and Accountability Act compliant, institutional review board-approved pilot study, three fellowship-trained breast imagers evaluated 48 breast MRIs (24 normal, 12 benign, and 12 malignant) selected from a high-risk screening population. MRIs were presented in three viewing protocols, and a final Breast Imaging-Reporting and Data System assessment was recorded for each case. The first shortened protocol (abbreviated 1) included only fat-saturated precontrast T2-weighted, precontrast T1-weighted, and first pass T1-weighted postcontrast sequences. The second shortened protocol (abbreviated 2) included the abbreviated 1 protocol plus the second pass T1-weighted postcontrast sequence. The third protocol (full), reviewed after a 1-month waiting period, included a nonfat-saturated T1-weighted sequence, fat-saturated T2-weighted, precontrast T1-weighted, and three or four dynamic postcontrast sequences. Interpretation times were recorded for the abbreviated 1 and full protocols. Sensitivity and specificity were compared via a chi-squared analysis. This pilot study was designed to detect a 10% difference in sensitivity with a power of 0.8. RESULTS There was no significant difference in sensitivity between the abbreviated 1 (86%; P = .22) or abbreviated 2 (89%; P = .38) protocols and the full protocol (95%). There was no significant difference in specificity between the abbreviated 1 (52%; P = 1) or abbreviated 2 (45%; P = .34) protocols and the full protocol (52%). The abbreviated 1 and full protocol interpretation times were similar (2.98 vs. 3.56 minutes). CONCLUSIONS In this pilot study, reader performance comparing two shortened breast MRI protocols to a standard protocol in a screening cohort were similar, suggesting that a shortened breast MRI protocol may be clinically useful, warranting further investigation.

MRI-guided vacuum-assisted breast biopsy with a handheld portable biopsy system.

OBJECTIVE The purpose of this study was to evaluate a compact portable 10-gauge handheld battery-operated vacuum-assisted biopsy system for MRI-guided breast biopsy. CONCLUSION The compact portable battery-operated biopsy system can be used successfully for MRI-guided core breast biopsy and is an alternative to current systems.

Wavefront estimation in the human breast

We acquired conventional and harmonic channel r.f. ultrasound echo data using a 3x80 element, 8.5 MHz multirow array from the breasts of eight volunteers. The data acquisition was interleaved to allow direct comparison normal and harmonic echo wavefronts. Harmonic imaging data was acquired using the pulse inversion technique. Data was acquired form extended regions of interest (25 mm deep, 10 mm wide). Time shift estimates from pairs of elements were combined using a weighted least squares algorithm to obtain a wavefront arrival time error estimate. Low spatial frequencies dominated most of the wavefront estimates, and many had a curvature suggesting a gross sound speed error. Wavefront estimates were often stable over lateral translations of a few millimeters, although they often changed significantly with range, particularly at tissue boundaries observed in the B-mode image. Averaging wavefront estimates over range yielded phase aberration estimates that generally improved image quality. We measured relatively small wavefront arrival errors with both conventional (22.9 +/- 7.6 ns r.m.s.) And harmonic (22.8 +/- 8.8 ns r.m.s.) echoes. For any particular measurement, the difference between conventional and harmonic wavefront estimates was small (0 +/- 4.5 ns r.m.s.). Our measurements suggest relatively mild phase aberrations in the breast, although they may be more significant for higher frequency transducers and deeper imaging depths.

Spatial and temporal aberrator stability for real-time adaptive imaging

Reported real-time adaptive imaging systems use near-field phase correction techniques, which are desired because of their simple implementation and their compatibility with current system architectures. Aberrator stability is important to adaptive imaging because it defines the spatial and temporal limits for which the near-field phase estimates are valid. Spatial aberrator stability determines the required spatial sampling of the aberrator, and temporal aberrator stability determines the length of time for which the aberration profile can be used. In this study, the spatial and temporal stability of clinically measured aberrations is reported for breast, liver, and thyroid tissue. Cross correlations between aberration estimates revealed aberrators to have azimuthal isoplanatic patch sizes of 0.44, 0.28, and 0.20 mm for breast, liver, and thyroid tissue, respectively, at 80% correlation. Axial isoplanatic patch sizes were 1.26, 0.76, and 1.80 mm for the same tissue, respectively, at 80% correlation. Temporal stability at 80% correlation was determined to be greater than 1.5 seconds for breast and thyroid tissue, and 0.65 seconds for the liver. The effects of noise, motion, and target nonuniformity on aberrator stability are characterized by simulations and experiments in tissue mimicking phantoms.

Breast tumour imaging using incomplete circular orbit pinhole SPET: A phantom study

Improvements in 99Tcm-sestamibi breast lesion visualization using single photon emission tomography (SPET) may help define the clinical role of this technique alongside X-ray mammography in the diagnosis and management of breast cancer. Pinhole SPET offers the advantages of high resolution and sensitivity when compared to conventional parallel-beam collimation for sources located near the pinhole aperture. In this work, the potential of incomplete (180 degrees) circular orbit (ICO) SPET with pinhole collimation is investigated as a means to visualize small (6.4 and 9.6 mm diameter) spherical simulated tumours, at clinical count densities and tumour-to-background ratios, in a breast phantom. ICO pinhole SPET is compared to complete circular orbit (CCO) pinhole SPET for reference, and planar breast imaging (scintimammography) using parallel-beam and pinhole collimators. A prototype box-shaped pinhole collimator with a 4 mm diameter circular aperture was used to acquire projections of an 890 ml breast phantom both in isolation and mounted on a cylinder filled with a mixture of 99Tcm-pertechnetate and water. A heart phantom containing 99Tcm activity in the myocardium was placed in the cylinder. Simulated tumours containing 99Tcm were placed in the breast phantom and scanned at clinically relevant count densities and scan times with tumour-to-normal tissue concentration ratios of 5.0:1 (9.6 mm sphere) and 7.7:1 (6.4 mm sphere). Phantom data were reconstructed using pinhole filtered backprojection (FBP) and maximum likelihood-expectation maximization (ML-EM). The tumours were not visualized with scintimammography, in which lesion contrast and signal-to-noise were estimated from region of interest analysis to be < 2% and 0.01, respectively. Average (over lesion size and scan time) contrast and signal-to-noise in the ICO (CCO) SPET images were 33% and 1.72 (34% and 1.3), respectively. These values indicate that ICO pinhole SPET has the potential to improve visualization of small (< 10 mm) breast tumours when compared with scintimammography, which may be beneficial for the early classification of cancers of the breast.