Biomedical subjects

Mostafa Fatemi

Publications and source records attributed to Mostafa Fatemi.

25 records · Page 2Linked to original sources

PubMed2004

Application of vibro-acoustography for detection of calcified arteries in breast tissue.

OBJECTIVE: The relationship between breast arterial calcification and coronary artery calcification and stenosis is currently an area of active research. It has been suggested in the literature that calcified arteries in the breast may be positively correlated with coronary artery disease. The sensitivity of x-ray mammography, the main breast imaging method, is reduced in radiologically dense breasts. In a recent study, we showed that vibro-acoustography, a novel noninvasive imaging technique that is based on the dynamic response of the object to a vibrating force, can detect microcalcifications in the breast regardless of breast density. In this study, we examined the application of vibro-acoustography in detecting calcified arteries in breast tissue. METHODS: Experiments were conducted on 207 postsurgical excised human breast tissue samples. Tissues specimens were imaged with a high-resolution x-ray mammography unit. Each sample with confirmed arterial calcification was then scanned by the vibro-acoustography system, and the resulting image was compared with the corresponding mammogram. We also studied the histologic characteristics of each sample to positively identify the disease and the presence of arterial calcification. RESULTS: Initial mammograms clearly showed 14 calcified arteries. The corresponding vibro-acoustographic images showed all calcified arteries as fragmented linear structures. The vibro-acoustographic appearance of the arteries was highly correlated with their distinctive radiographic appearance, which allowed us to identify all the calcified arteries in the vibro-acoustographic images. CONCLUSIONS: Vibro-acoustography can be used to detect calcified arteries in excised breast tissue. This method may eventually play a role in identifying individuals with an increased risk of coronary artery disease.

Arteries↗

PubMed2004

Comparison of stress field forming methods for vibro-acoustography.

Vibro-acoustography is a method that produces images of the acoustic response of a material to a localized harmonic motion generated by ultrasound radiation force. The low-frequency, oscillatory radiation force (e.g., 10 kHz) is produced by amplitude modulating a single ultrasound beam, or by interfering two beams of slightly different frequencies. Proper beam forming for the stress field of the probing ultrasound is very important because it determines the resolution of the imaging system. Three beam-forming geometries are studied: amplitude modulation, confocal, and x-focal. The amplitude of radiation force on a unit point target is calculated from the ultrasound energy density averaged over a short period of time. The profiles of radiation stress amplitude on the focal plane and on the beam axis are derived. The theory is validated by experiments using a small sphere as a point target. A laser vibrometer is used to measure the velocity of the sphere, which is proportional to the radiation stress exerted on the target as the transducer is scanned over the focal plane or along the beam axis. The measured velocity profiles match the theory. The theory and experimental technique may be useful in future transducer design for vibro-acoustography.

Acoustics↗

PubMed2003

Measurement of the ultrasound backscatter signal from three seed types as a function of incidence angle: application to permanent prostate brachytherapy.

PURPOSE: To measure the relative ultrasound backscatter of different seed types as a function of seed orientation and to evaluate the corresponding images of these seeds. METHODS AND MATERIALS: Three seed types were evaluated: OncoSeed (standard), EchoSeed (corrugated), and RAPID Strand(RS). Ultrasound images for angles of incidence varying from 90 degrees (perpendicular) to 20 degrees at 5MHz and 7.5MHz were produced by raster scanning the seeds in a degassed water bath. Seed images were visually inspected and analyzed using the integrated-optical-density (IOD) method. RESULTS: Corrugated seeds appear as contiguous objects over the range of frequencies and orientations examined, whereas standard seeds appear as contiguous objects from 90 degrees to 80 degrees only. The ranges and means of the backscattered IOD ratio of the seeds from 85 degrees to 20 degrees were: (corrugated vs. standard) 1.48 to 3.72 (2.32 +/- 0.62) for 5 MHz and 1.26 to 3.77 (2.19 +/- 0.84) for 7.5 MHz and (corrugated vs. RS) 1.21 to 9.53 (2.98 +/- 2.48) for 5 MHz and 1.008 to 10.86 (2.79 +/- 3.08) for 7.5 MHz. Backscattered signal increase ranged from 1.66 dB to 20.7 dB for the corrugated seed as compared to the other seeds. CONCLUSIONS: Corrugated seeds produce greater backscatter signal and a more readily identifiable seed image over a large range of seed orientation as compared with standard brachytherapy seeds.

Brachytherapy↗

PubMed2003

Selected methods for imaging elastic properties of biological tissues.

For millennia, physicians have used palpation as a part of the physical examination to detect pathology. The ubiquitous presence of "stiffer" tissue associated with pathology often represents an early warning sign for disease, as in the cases of breast or prostate cancer. Very often tumors are found at surgery that were occult even with modern imaging instruments. This implies that methods for estimating "hardness" of tissues would add a weapon to the medical armamentarium. To this end, this review discusses several methods of estimating tissue hardness using internal or external means of applying stress (force per unit area) and several associated methods of detecting the resulting strain (fractional length change) in an effort to image a tissue mechanical property, such as Young's modulus (ratio of stress to strain). Some investigators have developed methods of estimating stiffness or modulus, but most methods result in qualitative images of stiffness. Nevertheless, such estimates may add a great deal of information not currently available to the current field of medical imaging.

Animals↗

PubMed2002

Detection of calcium deposits on heart valve leaflets by vibro-acoustography: an in vitro study.

The presence of calcium deposits on heart valve leaflets constitutes a clinically significant diagnostic indication. A novel method for imaging and detecting calcium deposits on tissue heart valves is presented. The method, called vibro-acoustography, uses the radiation force of ultrasound to vibrate the tissue at low (kHz) frequency and records the resulting acoustic response to produce images that are related to the hardness of the tissue. The method is tested on excised human heart valve tissues. Resulting images clearly show calcium deposits with high contrast and are in agreement with the corresponding radiographs of the specimens.

Algorithms↗

PubMed2002

Vibro-acoustic tissue mammography.

A novel method for detection and imaging of microcalcifications in breast tissue is presented. The method, called vibro-acoustography, uses the radiation force of ultrasound to vibrate tissue at low (kHz) frequency and utilizes the resulting response to produce images that are related to the hardness of the tissue. The method is tested on human breast tissues. The resulting vibro-acoustographic images are in agreement with corresponding X-ray mammography images of the specimens. The existence of microcalcifications in locations indicated by vibro-acoustography is confirmed by histology. Microcalcifications as small as 110 microm in diameter are detected by this method. Resulting vibro-acoustographic images show microcalcifications with high contrast with respect to the background soft tissue. Structures such as dense sclerotic tissue do not seem to interfere with detection of microcalcifications.

Breast Neoplasms↗

PubMed2002

Remote measurement of material properties from radiation force induced vibration of an embedded sphere.

A quantitative model is presented for a sphere vibrated by two ultrasound beams of frequency omega1 and omega2. Due to the interference of two sound beams, the radiation force has a dynamic component of frequency omega2-omega1. The radiation impedance and mechanical impedance of the sphere are then used to compute the vibration speed of the sphere. Vibration speed versus vibration frequency is measured by laser vibrometer on several spheres, both in water and in gel phantom. These experimental results are used to verify the model. This method can be used to estimate the material properties of the medium (e.g., shear modulus) surrounding the sphere.

Elasticity↗