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Jonathan M Rubin

Publications and source records attributed to Jonathan M Rubin.

9 recordsLinked to original sources
PubMed2005

Correspondence of ultrasound elasticity imaging to direct mechanical measurement in aging DVT in rats.

Previous ultrasound elasticity imaging experiments supported a generally accepted concept that the hardness of deep venous thrombi increases with thrombus aging. Results also showed that this noninvasive imaging technique can accurately predict thrombus age through strain estimates, in a well-controlled animal study. In the present study, as an alternative means to characterize elastic properties of thrombi, we used a direct mechanical measurement system to estimate Young's modulus of ex vivo thrombi. Unlike conventional indentation tests, the device uses a specific compression geometry for cylindrical tissue specimens. We also proposed an approximation scheme to retrieve Young's modulus from force-displacement measurements made using the device. Finite element simulations and calibrations on tissue-mimicking phantoms validated the system. Then, using two groups of rats with surgically-induced thrombi, we further investigated the correlation between Young's modulus measured ex vivo and elasticity images reconstructed in vivo. This comparison was accomplished by converting the intrathrombus strains measured in the in vivo studies into Young's modulus estimates using a model-based approach. Good agreement between time-dependent Young's modulus estimates observed in vivo and direct measurements of Young's modulus using the mechanical device helps to confirm the ability of elasticity imaging to age deep venous thrombi for efficient treatment.

Aging↗
PubMed2005

Echocardiography-based selection of quiescent heart phases: implications for cardiac imaging.

OBJECTIVE: We compared the potential effectiveness of echocardiography with electrocardiography (ECG) for the selection of phases within the cardiac cycle during which there is relatively little motion. Determination of such phases may be important for triggering other modalities such as computed tomography and magnetic resonance imaging. METHODS: In a preliminary study in 2 volunteers, simultaneous ECG and cardiac echocardiographic data were obtained and analyzed. Various phases of the echocardiographic data were cross-correlated from beat to beat. Time point pairs from different cardiac cycles with correlation of 0.8 were selected. RESULTS: Beat-to-beat correlation values peaked at around 80% of the R-R' interval near the cardiac apex and around 30% of the R-R' interval near the cardiac base for 1 subject. For the other subject, the correlation values peaked at around 75% of the R-R' interval near the cardiac apex. CONCLUSIONS: The cardiac cycle phase having maximum spatial cross-correlation for the longest period varied from subject to subject and also on the portion of the heart that was being imaged. Echocardiography may be superior to ECG in determining points in the cardiac cycle when the heart is relatively stationary and can potentially provide more optimal triggering information for cardiac computed tomography or magnetic resonance imaging.

Adult↗
PubMed2004

Staging deep venous thrombosis using ultrasound elasticity imaging: animal model.

Deep venous thrombi undergo progressive hardening with age. However, the evolution rate remains poorly characterized by both invasive and noninvasive techniques. In a previous study (Emelianov et al. 2002), we demonstrated the potential of ultrasound elasticity imaging to noninvasively detect and age thrombus using a rat-based model. Knowing that thrombi harden over time is useful, but the value of the technique relies on whether the age of a thrombus can be predicted from strain estimates, and how accurate these predictions are. The objective of the present study is to answer these two questions. In the previous study, thrombus elasticity changes were monitored only on day 3, 6 and 9 after surgically induced formation of thrombosis in rat inferior vena cavas. In this study, ultrasound elasticity imaging was performed on two independent groups of rats (16 in total) starting from day 3 through day 10 with more temporal samples through the thrombus maturation process. For each rat, thrombus hardness was quantified at each scan interval by measures of normalized strains and reconstructed relative Young's moduli. In both groups, strain magnitudes exhibit progressive decrease as clots age. The relationship between the normalized strain and the clot age was developed from the first group and evaluated by the second group. Statistical analysis showed that the age estimation accuracy is within 0.8 day. If further research can successfully transfer the animal clot-hardening model to human patients, we believe that elasticity imaging will become a key component of venous compression ultrasound for effective diagnosis and treatment of deep venous thrombosis.

Animals↗
PubMed2004

Feasibility of applying ultrasound strain imaging to detect renal transplant chronic allograft nephropathy.

Chronic renal transplantation fibrosis, often termed Chronic Allograft Nephropathy, may progress undetected. Since renal fibrosis may be accompanied by a change in measurable elastic tissue properties, ultrasound strain management may be useful in it detection. Ultrasound strain imaging was performed for two subjects with renal transplants; one with normal renal function and one with mild renal insufficiency and biopsy demonstrated fibrosis. Subjects underwent ultrasound examination with application of a controlled deformation using phase-sensitive, two-dimensional speckle tracking to evaluate internal tissue motion to measure tissue displacement and strain. Measurements over multiple beams for an equivalent deformational stress showed there was a threefold difference in renal cortical strain between the two subjects. These data suggest that ultrasound elasticity imaging may prove useful in measuring mechanical changes related to fibrosis with the transplant kidney.

Adult↗
PubMed2004

Characterization of a linear streak artifact with pulse inversion tissue harmonics in musculoskeletal sonography.

OBJECTIVE: To understand a linear artifact that projects deep to reflective structures that move rapidly while using tissue harmonic imaging with pulse inversion (PI) sonography. We hypothesize that this artifact is due to a cancellation error between firings in PI imaging, and it is, therefore, similar in generation to the twinkling artifact in color Doppler sonography. This artifact could be studied with the use of surfaces of different roughness to represent different rates of motion, in which roughness corresponds to spatial fluctuations in surface height. Given very slight variations in beam focusing as occurs with sonographic imaging arrays, these spatial fluctuations translate into temporal fluctuations in the received signal as would occur with tissue motion. METHODS: We scanned 4 different sandpaper grits and a smooth surface through a water path using fundamental and PI mode, 1- and 2-pulse techniques, respectively. The sandpaper and the smooth surface were scanned through a water path at mechanical indices of 0.1 to 0.7. Four independent images were subtracted pairwise to remove nonfluctuating signals. These noise pixels were counted and analyzed. RESULTS: Analysis of variance showed that the noise generated behind the different surfaces was highly significantly different. Two-tailed t tests generally showed significant differences in the quantity of noise between fundamental and harmonic imaging behind the roughest 3 grades of sandpaper. A multiple regression model showed significantly greater slopes for harmonic imaging for all grades of sandpaper and the smooth surface. CONCLUSIONS: The noise and, by extension, the linear streak artifact in musculoskeletal imaging are dependent on the mechanical index and are functions of sandpaper roughness. This would be equivalent to a subtraction error between 2 firings due to soft tissue motion, and the artifact may be a way to identify rapid soft tissue motion in PI images.

Acoustics↗
PubMed2004

Model-based reconstructive elasticity imaging of deep venous thrombosis.

Deep venous thrombosis (DVT) and its sequela, pulmonary embolism, is a significant clinical problem. Once detected, DVT treatment is based on the age of the clot. There are no good noninvasive methods, however, to determine clot age. Previously, we demonstrated that imaging internal mechanical strains can identify and possibly age thrombus in a deep vein. In this study the deformation geometry for DVT elasticity imaging and its effect on Young's modulus estimates is addressed. A model-based reconstruction method is presented to estimate elasticity in which the clot-containing vessel is modeled as a layered cylinder. Compared to an unconstrained approach in reconstructive elasticity imaging, the proposed model-based approach has several advantages: only one component of the strain tensor is used; the minimization procedure is very fast; the method is highly efficient because an analytic solution of the forward elastic problem is used; and the method is not very sensitive to the details of the external load pattern--a characteristic that is important for free-hand, external, surface-applied deformation. The approach was tested theoretically using a numerical model, and experimentally on both tissue-like phantoms and an animal model of DVT. Results suggest that elasticity reconstruction may prove to be a practical adjunct to triplex scanning to detect, diagnose, and stage DVT.

Aging↗
PubMed2003

Twinkling artifact on color Doppler sonography: dependence on machine parameters and underlying cause.

OBJECTIVE: The objective of our study was to evaluate the color Doppler sonographic effect known as twinkling artifact. MATERIALS AND METHODS: Struvite (ammonium magnesium phosphate) stone fragments, wire mesh, and a flat surface were scanned in a water bath with a sonography scanner using a high-frequency linear array probe fixed in a ring clamp. Pulse repetition frequency, color-write priority, gray-scale gain, and spectral Doppler gain were varied. Color and spectral Doppler modes were used. RESULTS: Twinkling artifact and spectral broadening were seen most intensely behind struvite stone fragments, and both were seen more strongly behind wire mesh with greater surface roughness than behind wire mesh with less surface roughness or a flat surface. The appearance of the twinkling artifact is highly dependent on machine settings. System noise measured on a flat surface generates a band-limited Doppler shift on spectral displays with a mean frequency shift of 0 Hz and a mean (+/- SD) absolute fluctuation of 86 +/- 10 Hz over a pulse repetition frequency range of 1250-10,000 Hz. Rough surfaces increase the spectral bandwidth. CONCLUSION: The appearance of the twinkling artifact is highly dependent on machine settings and is likely generated by a narrow-band, intrinsic machine noise called phase (or clock) jitter. Surface roughness secondarily broadens the noise spectrum. With a strongly reflecting, rough surface such as a renal stone, the high amplitude, broadband signal appears as random motion in color Doppler sonography. Understanding of the twinkling artifact may result in better use of its clinical appearance.

Artifacts↗
PubMed2003

Clinical application of sonographic elasticity imaging for aging of deep venous thrombosis: preliminary findings.

OBJECTIVE: Aging of deep venous thrombosis is an important and difficult clinical problem. Because it is known that thrombi harden as they mature, we have preliminarily tested sonographic elasticity imaging, a technique that estimates tissue hardness, to age venous thrombi. METHODS: Two adult patients with lower extremity thrombi were studied. One had a clinically chronic thrombus (at least 3 years old), whereas the other patient's thrombus was clinically subacute (25 days old). We performed freehand compression sonographic scans using a 5-MHz linear array transducer. Phase-sensitive B-scan frames were processed offline by a two-dimensional complex correlation-based adaptive speckle-tracking technique. The distribution of internal strains in the wall of the vein, thrombus, and surrounding tissue was analyzed. Clot hardness was normalized to the venous wall. RESULTS: The chronic clot was homogeneous, and the strain in the chronic clot was at least 10 times smaller than that in the vessel wall. The subacute clot was much more heterogeneous, and, on average, the strain magnitude in the clot was 3 to 4 times greater than that in the vessel wall. CONCLUSIONS: In this preliminary work, the 2 thrombi appeared very different, and these results suggest that elasticity imaging may be able to age deep venous thrombosis.

Adult↗