Imaging tumor angiogenesis in small animals is extremely challenging due to the size of the tumor... more Imaging tumor angiogenesis in small animals is extremely challenging due to the size of the tumor vessels. Consequently, both dedicated small animal imaging systems and specialized intravascular contrast agents are required. The goal of this study was to investigate the use of a liposomal contrast agent for high-resolution micro-CT imaging of breast tumors in small animals. A liposomal blood pool agent encapsulating iodine with a concentration of 65.5 mg/ml was used with a Duke Center for In Vivo Microscopy (CIVM) prototype micro- ...
Objectives: There is evidence that ultrasonic backscatter and attenuation features derived from r... more Objectives: There is evidence that ultrasonic backscatter and attenuation features derived from rf echo signals can aid in differentiating benign from malignant breast masses. Previous reports have shown that an effective scatterer size, the acoustic concentration and the integrated backscatter contribute to these successful findings in animal models while recent experiments have demonstrated interlaboratory repeatability of quantitative ultrasound (QUS) estimations in phantoms and in animal models using a variety of clinical instruments. This ongoing study investigates the degree to which these QUS parameters can aid in classifying human breast tumors. Methods: Radiofrequency echo signals are obtained during prebiopsy scans of subjects with suspicious breast masses under an approved IRB. A Siemens S2000 scanner equipped with the Axius Direct research interface and linear array transducers is employed to obtain data from radial (direction of ducts) and antiradial scanning planes, us...
Ultrasound QC hands‐on workshop sponsor list: Ultrasound imaging systems will be provided by: 1. ... more Ultrasound QC hands‐on workshop sponsor list: Ultrasound imaging systems will be provided by: 1. Ultrasonix Medical Corporation Contact: Kris Dickie, ([email protected]) 2. Best Medical International, Inc Contact: David Strong, ([email protected]) 3. Unisyn Medical Technologies, Inc. Contact: G. Wayne Moore, ([email protected]) Ultrasound QC phantoms will be provided by: 1. CIRS, Inc. Contact: Heather Pierce ([email protected]) 2. Gammex RMI, Inc. Contact: Margaret Lescrenier, ([email protected]) and Robert Steinhauser, ([email protected]) Ultrasound electronic testing devices will be provided by: 1. Unisyn Medical Technologies, Inc. Contact: G. Wayne Moore, ([email protected])
Methods: A 13-bit Barker code (pulse duration (PD) 5 4.36 ms), a short chirp (PD 5 4.49 ms), and ... more Methods: A 13-bit Barker code (pulse duration (PD) 5 4.36 ms), a short chirp (PD 5 4.49 ms), and a long chirp (PD 5 8.98 ms) were programmed on the Vantage system (Verasonics Inc.) and compared with a CSP (PD 5 0.33 ms). The Cram er-Rao lower bound (CRLB) was used to predict the SW SNR at given ultrasound radio frequency (RF) signal SNR. Two phantom experiments (with and without pork belly) were designed to test: 1) the penetration of SW detection; 2) the sensitivity to SW motion by gradually decreasing the SW motion; 3) and the robustness to weak RF signal by gradually decreasing the ultrasound transmit voltage. Then an in vivo liver case study was conducted on a healthy subject (BMI 5 40) to compare the performance of the different pulses. Results: The measured SW SNRs were all in good agreement with the theoretically predicted SNRs by CRLB. The phantom studies showed all CE pulses outperformed the CSP by providing SW signals with substantially higher SNR and a penetration gain of 2, 3, and 4 cm for the Barker code, the short chirp, and the long chirp, respectively. All CE pulses also showed superior sensitivity to small motion and robustness to weak RF signals, with the chirp long pulse providing the best performance. The in vivo liver study showed that all CE pulses could provide higher SNR SW signals from the liver than the CSP. Conclusions: The results indicate that by using CE for SW detection, one can benefit from the ultrafast FR and large FOV provided by PWI while preserving good penetration and SW signal quality, which is essential for obtaining robust shear elasticity measurement of tissue.
To test the performance of transrectal ultrasound (US) scanners in the detection of low-contrast ... more To test the performance of transrectal ultrasound (US) scanners in the detection of low-contrast focal lesions as a function of depth, size, and contrast. US images of two phantoms were analyzed by three observers. One phantom was most suitable for US units allowing scanning in the transverse or longitudinal planes, while the other was suitable for any scanning situation. Both phantoms were made of tissue-mimicking material and had six sections. Five sections contained different sizes of low-contrast simulated lesions, which were of different echogenicities and were randomly distributed to a depth of 8 cm. The sixth section contained only background material and served as a reference. A resolution zone, corresponding to the depth range over which a given type of lesion was detectable, was determined for each of the five lesion-containing sections and a figure of merit equal to a weighted sum of resolution zone lengths computed. Data from 12 different scanner configurations were analyzed; a broad range of figures of merit were found. Agreement was found among the three observers regarding relative performance of the scanner configurations. The phantoms are useful for comparing performances of different transrectal US configurations.
Abstraet-A form of tissue-mimicking material is reported in which oil droplets are dispersed in a... more Abstraet-A form of tissue-mimicking material is reported in which oil droplets are dispersed in a water-based gelatin. Broad ranges of ultrasonic parameters, including speed of sound, attenuation coefficient, density and backscatter level, exist for this material. Very important, the attenuation coefficients are nearly proportional to the frequency as in the case of mammalian tissue and the available attenuation coefficient slopes span the range of mammalian tissues. The available range of slopes is 0.1 dB/cm/MHz through at least 2.0 dB/cm/MHz. The available speeds of sound range from a minimum below that of mammalian fat (-1460 m/s) to a maximum above the accepted average for human tissue (1540 m/s). Densities available range from below that of fat (-0.92 gm/cm 3) through about 1.00gm/cm 3. Backscatter levels are easily made negligible compared to clinical levels and compared to those exhibited in previously reported tissue-mimicking materials in which the suspended particles are solid (Madsen et al., 1978; Burlew et al., 1980). Addition of solid or hollow glass scatterers allows backscatter levels to be made comparable to those clinically observed.
In a previous study, theoretical expressions were derived for the correlation between ultrasonic ... more In a previous study, theoretical expressions were derived for the correlation between ultrasonic scatterer-size estimates and their associated spectral measures when echo data are acquired from the same location but at different angles. The results were verified using simulations. In the present work, we further analyze simulation data for these conditions; in addition, we measure the correlations using a cylindrical tissue-mimicking phantom. Experimental and theoretical results show that the relationship of scatterer-size correlation to insonification angle depends on gate duration, gate type and beam profile. Some discrepancies are noted between experimental results and theoretical predictions, particularly when using smaller gated windows. The sources of the discrepancies are discussed. Experimental results using a 6-MHz linear array suggest that, to save acquisition and processing time while reducing variance, a 2°–3° angular increment step provides efficient angular compounding...
Ultrasonic attenuation may be measured accurately with clinical systems and array transducers by ... more Ultrasonic attenuation may be measured accurately with clinical systems and array transducers by using reference phantom methods (RPM) to account for diffraction and other system dependencies on echo signals. Assumptions with the RPM are that the speeds of sound in the sample ( csam) and in the reference medium ( cref) are the same and that they match the speed assumed in the system beamformer ( cbf). This work assesses the accuracy of attenuation measurements by the RPM when these assumptions are not met. Attenuation was measured for two homogeneous phantoms, one with a speed of sound of 1500 m/s and the other with a sound speed of 1580 m/s. Both have an attenuation coefficient approximately equal to that of the reference, in which the speed of sound is 1540 m/s. Echo signals from the samples and the reference were acquired from a Siemens S2000 scanner with a 9L4 linear array transducer. Separate acquisitions were obtained with cbf at its default value of 1540 m/s and when it was s...
The Journal of the Acoustical Society of America, 2005
Previous reports have shown that the variance in ultrasound attenuation measurements is reduced w... more Previous reports have shown that the variance in ultrasound attenuation measurements is reduced when spatial and frequency compounding were applied in data acquisition and analysis. This paper investigates factors affecting the efficiency of compound attenuation imaging methods. A theoretical expression is derived that predicts the correlation between attenuation versus frequency slope ͑͒ estimates as a function of the increment between measurement frequencies (⌬ f) and the angular separation between beam lines ͑⌬͒. Theoretical results are compared with those from attenuation measurements on tissue-mimicking phantoms and from simulation data. Both predictions and measurement results show that the correlation between  estimates as a function of (⌬ f) is independent of the length of the radio frequency ͑rf͒ data segment over which  is derived. However, it decreases with an increase in the length of the data segment used in power spectra estimates. In contrast, the correlation between  estimates as a function of ⌬ decreases when the rf data segment length is longer or the frequency of the signal is higher.
The accuracy of a method of data reduction for determining acoustic backscatter coefficients was ... more The accuracy of a method of data reduction for determining acoustic backscatter coefficients was tested using focused transducers and narrow-band pulses. Two phantoms with welldefined scattering properties were the bases of the tests, one having low attenuation and one with tissue-mimicking attenuation. The experimentally determined backscatter coefficients were found to be independent of transducer-to-scattering-volume distance and to agree very well with theoretical values, typically within 10%.
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 1999
A frequency domain B-mode imaging model applicable to linear and phased array transducers was dev... more A frequency domain B-mode imaging model applicable to linear and phased array transducers was developed for simulating ultrasound images of random media. Computations are based on an approximation that is less restrictive than the Fresnel approximation. The model is compared with the exact time domain impulse response method, regarded as the "gold standard". In a typical application, errors in simulated rf waveforms are less than 1% regardless of the steering angle for distances greater than 2 cm, yet computation times are on the order of 1 150 of those using the exact method. This model takes into account the effects of frequency-dependent attenuation, backscattering, and dispersion. Modern beam-forming techniques such as apodization, dynamic aperture, elevational focusing, multiple transmit focusing, and dynamic receiving focusing also can be simulated.
Radiofrequency (RF) ablation is an interstitial focal ablative therapy that can be used in a perc... more Radiofrequency (RF) ablation is an interstitial focal ablative therapy that can be used in a percutaneous fashion and permits in situ destruction of hepatic tumors. However, local tumor recurrence rates after RF ablative therapy are as high as 34% to 55%, which may be due in part to the inability to monitor accurately temperature profiles in the tissue being ablated, and to visualize the subsequent zone of necrosis (thermal lesion) formed. The goal of the work described in this paper was to investigate methods for the real-time and in vivo monitoring of the spatial distribution of heating and temperature elevation to achieve better control of the degree of tissue damage during RF ablation therapy. Temperature estimates are obtained using a cross-correlation algorithm applied to RF ultrasound (US) echo signal data acquired at discrete intervals during heating. These temperature maps were used to display the initial temperature rise and to continuously update a thermal map of the treated region. Temperature monitoring is currently performed using thermosensors on the prongs (tines) of the RF ablation probe. However, monitoring the spatial distribution of heating is necessary to control the degree of tissue damage produced.
Medical Imaging 2008: Physics of Medical Imaging, 2008
During the last eight years our group has developed radial acquisitions with angular undersamplin... more During the last eight years our group has developed radial acquisitions with angular undersampling factors of several hundred that accelerate MRI in selected applications. As with all previous acceleration techniques, SNR typically falls as least as fast as the inverse square root of the undersampling factor. This limits the SNR available to support the small voxels that these methods can
The Journal of the Acoustical Society of America, 2014
ABSTRACT Quantitative ultrasound augments conventional ultrasound information by providing parame... more ABSTRACT Quantitative ultrasound augments conventional ultrasound information by providing parameters derived from scattering and attenuation properties of tissue. This presentation describes our work estimating attenuation (ATT) and backscatter coefficients (BSC), and computing effective scatterer sizes (ESD) to differentiate benign from malignant breast masses. Radio-frequency echo data are obtained from patients scheduled for biopsy of suspicious masses following an institutional IRB approved protocol. A Siemens S2000 equipped with a linear array and recently a volume scanner transducer is employed. Echo signal power spectra are computed from the tissue and from the same depth in a reference phantom having accurately measured acoustic properties. Ratios of the tissue-to-reference power spectra enable tissue ATT and BSC’s to be estimated. ESD’s are then computed by fitting BSC vs. frequency results to a size-dependent scattering model. A heterogeneity index HDI expresses variability of the ESD over the tumor area. In preliminary data from 35 patients, a Bayesian classifier incorporating ATT, ESD, and HDI successfully differentiated malignant masses from fibroadenomas. Future work focuses on analysis methods when diffuse scattering and stationary signal conditions, implicitly assumed in the power spectra calculations, are not present. This approach tests for signal coherence and generates new parameters that characterize these scattering conditions.
An anthropomorphic breast phantom, built from materials which mimic tissue parenchymae with respe... more An anthropomorphic breast phantom, built from materials which mimic tissue parenchymae with respect to attenuation coefficients, speeds of sound, densities and backscatter levels, is described in detail. One of the outstanding features of the phantom is that 30% of the volume of the glandular region consists of tissue-mimicking fat, the remainder being tissue-mimicking glandular (non-adipose) tissue. The presence of these tissue-mimicking fat globules should cause ultrasound beam distortions similar to those found in clinical scans of the breasts of younger women. Halliwell (1977) has presented direct evidence for such beam distortions in real breasts. Other tissues simulated in the phantom are: skin, subcutaneous and retromammary fat, Cooper's ligaments, ducts and (abnormal) masses. The potential areas of usefulness of the phantom are: aiding in the development of more effective ultrasound imaging machines, discovering-or verifying the causes of-various artifacts in breast imaging, routine testing of instruments being used clinically for breast imaging, and training of ultrasonographers. Ultrasound images of the phantom, made using three different instruments, are displayed and discussed.
Reported here is a phantom-based comparison of methods for determining the power spectral density... more Reported here is a phantom-based comparison of methods for determining the power spectral density (PSD) of ultrasound backscattered signals. Those power spectral density values are then used to estimate parameters describing α( f), the frequency dependence of the acoustic attenuation coefficient. Phantoms were scanned with a clinical system equipped with a research interface to obtain radiofrequency echo data. Attenuation, modeled as a power law α( f) = α0 fβ, was estimated using a reference phantom method. The power spectral density was estimated using the short-time Fourier transform (STFT), Welch’s periodogram, and Thomson’s multitaper technique, and performance was analyzed when limiting the size of the parameter-estimation region. Errors were quantified by the bias and standard deviation of the α0 and β estimates, and by the overall power-law fit error (FE). For parameter estimation regions larger than ~34 pulse lengths (~1 cm for this experiment), an overall power-law FE of 4%...
The accuracy of the spectral difference method for measuring ultrasonic attenuation has been inve... more The accuracy of the spectral difference method for measuring ultrasonic attenuation has been investigated using tissue-mimicking phantoms. Attenuation coefficients of the phantom materials were measured using a narrow-band substitution technique and compared with the results of the spectral difference method. Agreement within ±10 percent was typical for measurements in homogeneous materials. The best agreement between the spectral difference and substitution techniques was obtained when effects due to transducer beam diffraction were taken into account in the analysis. This was found for two types of homogeneous tissue-mimicking materials, both having speed of sound and attenuation properties similar to human liver but each with different backscatter properties. The effects of inhomogeneous tissues interposed between the transducer and the interrogated volume were also studied by simulating these conditions in phantoms. Experimental techniques which minimize the effects of perturbat...
Imaging tumor angiogenesis in small animals is extremely challenging due to the size of the tumor... more Imaging tumor angiogenesis in small animals is extremely challenging due to the size of the tumor vessels. Consequently, both dedicated small animal imaging systems and specialized intravascular contrast agents are required. The goal of this study was to investigate the use of a liposomal contrast agent for high-resolution micro-CT imaging of breast tumors in small animals. A liposomal blood pool agent encapsulating iodine with a concentration of 65.5 mg/ml was used with a Duke Center for In Vivo Microscopy (CIVM) prototype micro- ...
Objectives: There is evidence that ultrasonic backscatter and attenuation features derived from r... more Objectives: There is evidence that ultrasonic backscatter and attenuation features derived from rf echo signals can aid in differentiating benign from malignant breast masses. Previous reports have shown that an effective scatterer size, the acoustic concentration and the integrated backscatter contribute to these successful findings in animal models while recent experiments have demonstrated interlaboratory repeatability of quantitative ultrasound (QUS) estimations in phantoms and in animal models using a variety of clinical instruments. This ongoing study investigates the degree to which these QUS parameters can aid in classifying human breast tumors. Methods: Radiofrequency echo signals are obtained during prebiopsy scans of subjects with suspicious breast masses under an approved IRB. A Siemens S2000 scanner equipped with the Axius Direct research interface and linear array transducers is employed to obtain data from radial (direction of ducts) and antiradial scanning planes, us...
Ultrasound QC hands‐on workshop sponsor list: Ultrasound imaging systems will be provided by: 1. ... more Ultrasound QC hands‐on workshop sponsor list: Ultrasound imaging systems will be provided by: 1. Ultrasonix Medical Corporation Contact: Kris Dickie, ([email protected]) 2. Best Medical International, Inc Contact: David Strong, ([email protected]) 3. Unisyn Medical Technologies, Inc. Contact: G. Wayne Moore, ([email protected]) Ultrasound QC phantoms will be provided by: 1. CIRS, Inc. Contact: Heather Pierce ([email protected]) 2. Gammex RMI, Inc. Contact: Margaret Lescrenier, ([email protected]) and Robert Steinhauser, ([email protected]) Ultrasound electronic testing devices will be provided by: 1. Unisyn Medical Technologies, Inc. Contact: G. Wayne Moore, ([email protected])
Methods: A 13-bit Barker code (pulse duration (PD) 5 4.36 ms), a short chirp (PD 5 4.49 ms), and ... more Methods: A 13-bit Barker code (pulse duration (PD) 5 4.36 ms), a short chirp (PD 5 4.49 ms), and a long chirp (PD 5 8.98 ms) were programmed on the Vantage system (Verasonics Inc.) and compared with a CSP (PD 5 0.33 ms). The Cram er-Rao lower bound (CRLB) was used to predict the SW SNR at given ultrasound radio frequency (RF) signal SNR. Two phantom experiments (with and without pork belly) were designed to test: 1) the penetration of SW detection; 2) the sensitivity to SW motion by gradually decreasing the SW motion; 3) and the robustness to weak RF signal by gradually decreasing the ultrasound transmit voltage. Then an in vivo liver case study was conducted on a healthy subject (BMI 5 40) to compare the performance of the different pulses. Results: The measured SW SNRs were all in good agreement with the theoretically predicted SNRs by CRLB. The phantom studies showed all CE pulses outperformed the CSP by providing SW signals with substantially higher SNR and a penetration gain of 2, 3, and 4 cm for the Barker code, the short chirp, and the long chirp, respectively. All CE pulses also showed superior sensitivity to small motion and robustness to weak RF signals, with the chirp long pulse providing the best performance. The in vivo liver study showed that all CE pulses could provide higher SNR SW signals from the liver than the CSP. Conclusions: The results indicate that by using CE for SW detection, one can benefit from the ultrafast FR and large FOV provided by PWI while preserving good penetration and SW signal quality, which is essential for obtaining robust shear elasticity measurement of tissue.
To test the performance of transrectal ultrasound (US) scanners in the detection of low-contrast ... more To test the performance of transrectal ultrasound (US) scanners in the detection of low-contrast focal lesions as a function of depth, size, and contrast. US images of two phantoms were analyzed by three observers. One phantom was most suitable for US units allowing scanning in the transverse or longitudinal planes, while the other was suitable for any scanning situation. Both phantoms were made of tissue-mimicking material and had six sections. Five sections contained different sizes of low-contrast simulated lesions, which were of different echogenicities and were randomly distributed to a depth of 8 cm. The sixth section contained only background material and served as a reference. A resolution zone, corresponding to the depth range over which a given type of lesion was detectable, was determined for each of the five lesion-containing sections and a figure of merit equal to a weighted sum of resolution zone lengths computed. Data from 12 different scanner configurations were analyzed; a broad range of figures of merit were found. Agreement was found among the three observers regarding relative performance of the scanner configurations. The phantoms are useful for comparing performances of different transrectal US configurations.
Abstraet-A form of tissue-mimicking material is reported in which oil droplets are dispersed in a... more Abstraet-A form of tissue-mimicking material is reported in which oil droplets are dispersed in a water-based gelatin. Broad ranges of ultrasonic parameters, including speed of sound, attenuation coefficient, density and backscatter level, exist for this material. Very important, the attenuation coefficients are nearly proportional to the frequency as in the case of mammalian tissue and the available attenuation coefficient slopes span the range of mammalian tissues. The available range of slopes is 0.1 dB/cm/MHz through at least 2.0 dB/cm/MHz. The available speeds of sound range from a minimum below that of mammalian fat (-1460 m/s) to a maximum above the accepted average for human tissue (1540 m/s). Densities available range from below that of fat (-0.92 gm/cm 3) through about 1.00gm/cm 3. Backscatter levels are easily made negligible compared to clinical levels and compared to those exhibited in previously reported tissue-mimicking materials in which the suspended particles are solid (Madsen et al., 1978; Burlew et al., 1980). Addition of solid or hollow glass scatterers allows backscatter levels to be made comparable to those clinically observed.
In a previous study, theoretical expressions were derived for the correlation between ultrasonic ... more In a previous study, theoretical expressions were derived for the correlation between ultrasonic scatterer-size estimates and their associated spectral measures when echo data are acquired from the same location but at different angles. The results were verified using simulations. In the present work, we further analyze simulation data for these conditions; in addition, we measure the correlations using a cylindrical tissue-mimicking phantom. Experimental and theoretical results show that the relationship of scatterer-size correlation to insonification angle depends on gate duration, gate type and beam profile. Some discrepancies are noted between experimental results and theoretical predictions, particularly when using smaller gated windows. The sources of the discrepancies are discussed. Experimental results using a 6-MHz linear array suggest that, to save acquisition and processing time while reducing variance, a 2°–3° angular increment step provides efficient angular compounding...
Ultrasonic attenuation may be measured accurately with clinical systems and array transducers by ... more Ultrasonic attenuation may be measured accurately with clinical systems and array transducers by using reference phantom methods (RPM) to account for diffraction and other system dependencies on echo signals. Assumptions with the RPM are that the speeds of sound in the sample ( csam) and in the reference medium ( cref) are the same and that they match the speed assumed in the system beamformer ( cbf). This work assesses the accuracy of attenuation measurements by the RPM when these assumptions are not met. Attenuation was measured for two homogeneous phantoms, one with a speed of sound of 1500 m/s and the other with a sound speed of 1580 m/s. Both have an attenuation coefficient approximately equal to that of the reference, in which the speed of sound is 1540 m/s. Echo signals from the samples and the reference were acquired from a Siemens S2000 scanner with a 9L4 linear array transducer. Separate acquisitions were obtained with cbf at its default value of 1540 m/s and when it was s...
The Journal of the Acoustical Society of America, 2005
Previous reports have shown that the variance in ultrasound attenuation measurements is reduced w... more Previous reports have shown that the variance in ultrasound attenuation measurements is reduced when spatial and frequency compounding were applied in data acquisition and analysis. This paper investigates factors affecting the efficiency of compound attenuation imaging methods. A theoretical expression is derived that predicts the correlation between attenuation versus frequency slope ͑͒ estimates as a function of the increment between measurement frequencies (⌬ f) and the angular separation between beam lines ͑⌬͒. Theoretical results are compared with those from attenuation measurements on tissue-mimicking phantoms and from simulation data. Both predictions and measurement results show that the correlation between  estimates as a function of (⌬ f) is independent of the length of the radio frequency ͑rf͒ data segment over which  is derived. However, it decreases with an increase in the length of the data segment used in power spectra estimates. In contrast, the correlation between  estimates as a function of ⌬ decreases when the rf data segment length is longer or the frequency of the signal is higher.
The accuracy of a method of data reduction for determining acoustic backscatter coefficients was ... more The accuracy of a method of data reduction for determining acoustic backscatter coefficients was tested using focused transducers and narrow-band pulses. Two phantoms with welldefined scattering properties were the bases of the tests, one having low attenuation and one with tissue-mimicking attenuation. The experimentally determined backscatter coefficients were found to be independent of transducer-to-scattering-volume distance and to agree very well with theoretical values, typically within 10%.
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 1999
A frequency domain B-mode imaging model applicable to linear and phased array transducers was dev... more A frequency domain B-mode imaging model applicable to linear and phased array transducers was developed for simulating ultrasound images of random media. Computations are based on an approximation that is less restrictive than the Fresnel approximation. The model is compared with the exact time domain impulse response method, regarded as the "gold standard". In a typical application, errors in simulated rf waveforms are less than 1% regardless of the steering angle for distances greater than 2 cm, yet computation times are on the order of 1 150 of those using the exact method. This model takes into account the effects of frequency-dependent attenuation, backscattering, and dispersion. Modern beam-forming techniques such as apodization, dynamic aperture, elevational focusing, multiple transmit focusing, and dynamic receiving focusing also can be simulated.
Radiofrequency (RF) ablation is an interstitial focal ablative therapy that can be used in a perc... more Radiofrequency (RF) ablation is an interstitial focal ablative therapy that can be used in a percutaneous fashion and permits in situ destruction of hepatic tumors. However, local tumor recurrence rates after RF ablative therapy are as high as 34% to 55%, which may be due in part to the inability to monitor accurately temperature profiles in the tissue being ablated, and to visualize the subsequent zone of necrosis (thermal lesion) formed. The goal of the work described in this paper was to investigate methods for the real-time and in vivo monitoring of the spatial distribution of heating and temperature elevation to achieve better control of the degree of tissue damage during RF ablation therapy. Temperature estimates are obtained using a cross-correlation algorithm applied to RF ultrasound (US) echo signal data acquired at discrete intervals during heating. These temperature maps were used to display the initial temperature rise and to continuously update a thermal map of the treated region. Temperature monitoring is currently performed using thermosensors on the prongs (tines) of the RF ablation probe. However, monitoring the spatial distribution of heating is necessary to control the degree of tissue damage produced.
Medical Imaging 2008: Physics of Medical Imaging, 2008
During the last eight years our group has developed radial acquisitions with angular undersamplin... more During the last eight years our group has developed radial acquisitions with angular undersampling factors of several hundred that accelerate MRI in selected applications. As with all previous acceleration techniques, SNR typically falls as least as fast as the inverse square root of the undersampling factor. This limits the SNR available to support the small voxels that these methods can
The Journal of the Acoustical Society of America, 2014
ABSTRACT Quantitative ultrasound augments conventional ultrasound information by providing parame... more ABSTRACT Quantitative ultrasound augments conventional ultrasound information by providing parameters derived from scattering and attenuation properties of tissue. This presentation describes our work estimating attenuation (ATT) and backscatter coefficients (BSC), and computing effective scatterer sizes (ESD) to differentiate benign from malignant breast masses. Radio-frequency echo data are obtained from patients scheduled for biopsy of suspicious masses following an institutional IRB approved protocol. A Siemens S2000 equipped with a linear array and recently a volume scanner transducer is employed. Echo signal power spectra are computed from the tissue and from the same depth in a reference phantom having accurately measured acoustic properties. Ratios of the tissue-to-reference power spectra enable tissue ATT and BSC’s to be estimated. ESD’s are then computed by fitting BSC vs. frequency results to a size-dependent scattering model. A heterogeneity index HDI expresses variability of the ESD over the tumor area. In preliminary data from 35 patients, a Bayesian classifier incorporating ATT, ESD, and HDI successfully differentiated malignant masses from fibroadenomas. Future work focuses on analysis methods when diffuse scattering and stationary signal conditions, implicitly assumed in the power spectra calculations, are not present. This approach tests for signal coherence and generates new parameters that characterize these scattering conditions.
An anthropomorphic breast phantom, built from materials which mimic tissue parenchymae with respe... more An anthropomorphic breast phantom, built from materials which mimic tissue parenchymae with respect to attenuation coefficients, speeds of sound, densities and backscatter levels, is described in detail. One of the outstanding features of the phantom is that 30% of the volume of the glandular region consists of tissue-mimicking fat, the remainder being tissue-mimicking glandular (non-adipose) tissue. The presence of these tissue-mimicking fat globules should cause ultrasound beam distortions similar to those found in clinical scans of the breasts of younger women. Halliwell (1977) has presented direct evidence for such beam distortions in real breasts. Other tissues simulated in the phantom are: skin, subcutaneous and retromammary fat, Cooper's ligaments, ducts and (abnormal) masses. The potential areas of usefulness of the phantom are: aiding in the development of more effective ultrasound imaging machines, discovering-or verifying the causes of-various artifacts in breast imaging, routine testing of instruments being used clinically for breast imaging, and training of ultrasonographers. Ultrasound images of the phantom, made using three different instruments, are displayed and discussed.
Reported here is a phantom-based comparison of methods for determining the power spectral density... more Reported here is a phantom-based comparison of methods for determining the power spectral density (PSD) of ultrasound backscattered signals. Those power spectral density values are then used to estimate parameters describing α( f), the frequency dependence of the acoustic attenuation coefficient. Phantoms were scanned with a clinical system equipped with a research interface to obtain radiofrequency echo data. Attenuation, modeled as a power law α( f) = α0 fβ, was estimated using a reference phantom method. The power spectral density was estimated using the short-time Fourier transform (STFT), Welch’s periodogram, and Thomson’s multitaper technique, and performance was analyzed when limiting the size of the parameter-estimation region. Errors were quantified by the bias and standard deviation of the α0 and β estimates, and by the overall power-law fit error (FE). For parameter estimation regions larger than ~34 pulse lengths (~1 cm for this experiment), an overall power-law FE of 4%...
The accuracy of the spectral difference method for measuring ultrasonic attenuation has been inve... more The accuracy of the spectral difference method for measuring ultrasonic attenuation has been investigated using tissue-mimicking phantoms. Attenuation coefficients of the phantom materials were measured using a narrow-band substitution technique and compared with the results of the spectral difference method. Agreement within ±10 percent was typical for measurements in homogeneous materials. The best agreement between the spectral difference and substitution techniques was obtained when effects due to transducer beam diffraction were taken into account in the analysis. This was found for two types of homogeneous tissue-mimicking materials, both having speed of sound and attenuation properties similar to human liver but each with different backscatter properties. The effects of inhomogeneous tissues interposed between the transducer and the interrogated volume were also studied by simulating these conditions in phantoms. Experimental techniques which minimize the effects of perturbat...
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Papers by J. Zagzebski