Faculty Bibliography

A projection-operator technique is applied to a general three-component model for magnetization transfer, extending our previous two-component model [R.S. Adler and H.N. Yeung, J. Magn. Reson. A 104, 321 (1993), and H.N. Yeung, R. S. Adler, and S.D. Swanson, J. Magn. Reson. A 106, 37 (1994)]. The PO technique provides an elegant means of deriving a simple, effective rate equation in which there is natural separation of relaxation and source terms and allows incorporation of Redfield-Provotorov theory without any additional assumptions or restrictive conditions. The PO technique is extended to incorporate more general, multicomponent models. The three-component model is used to fit experimental data from samples of human hyaline cartilage and fibrocartilage. The fits of the three-component model are compared to the fits of the two-component model.

The integrated power Doppler signal arising from blood flow is a random process. In this article, a general approach to model this random process is studied. Both the theoretical and experimental results show that the temporal autocorrelation function of the integrated power Doppler signals is directly related to properties of the insonified medium, such as the scattering strengths and velocities of all moving scatterers, and as well as the properties of the Doppler imaging system, such as the point spread function (psf) of the power Doppler images. Some initial experiments are performed to test the proposed model. Its potential application for flow measurement, such as perfusion evaluation, is also discussed.

The relative success of manual palpation in the detection of breast cancer would suggest that a method for remote palpation resulting in a measurement of tissue elasticity could provide a diagnostic tool for detecting cancerous lesions deeper within the breast. This presumption is based in part on the excellent contrast between neoplastic and normal tissue due to the large (orders of magnitude) relative variation in the shear elastic modulus. By comparison, the bulk deformational modulus maintains the same value to within 20% for most soft tissues. A specific method of magnetic-resonance imaging (MRI) which measures tissue displacements has been used in experiments with a phantom containing regions of increased Young's modulus as a demonstration. The spatial modulation of magnetization technique uses the displacement of a spatial grid pattern caused by spin saturation to track regional motion. Mathematical reconstruction of the distribution of elastic moduli is shown for select examples. Any modality, e.g., MRI, ultrasound, etc., which can detect local tissue motion with sufficient spatial resolution can be used and therefore the results presented here should give an indication of the utility of such motion tracking techniques to future measurement of tissue elasticity.

RATIONALE AND OBJECTIVES: We tested whether testicular torsion could completely damp distal arterial pulsatility, resulting in venous-appearing arterial waveforms. METHODS: Progressively increasing testicular torsion was unilaterally produced in five rats. Doppler waveforms of the testicular artery distal to the torsion were obtained as soon as possible after each level of torsion until a complete absence of pulsatility was noted. RESULTS: One animal was not studied further after the first 180 degrees of torsion occluded flow. In three of the remaining four animals, the testicular artery resistive index (RI) at baseline (0.51, 0.58, 0.64) was within the range of the normal human intratesticular RI and decreased with increasing torsion, culminating in nonpulsatile, venous-appearing waveforms at high degrees of torsion. CONCLUSIONS: Testicular torsion can completely damp arterial pulsatility, resulting in nonpulsatile, venous-appearing arterial Doppler waveforms.

PURPOSE: To estimate the fraction of moving blood in tissue with power Doppler ultrasound (US). MATERIALS AND METHODS: Power Doppler US measurements of moving scatterers in a flow tube were made as a function of successive dilutions of the perfusate. Measurements were normalized relative to the maximum Doppler power in the center of the flow tube at the highest concentration and were used to calculate the fractional dilution of the perfusate for each run with each dilution used to represent increasing amounts of non-moving soft tissue in the sample volume. The technique was also applied to two clinical examples. RESULTS: Successive dilutions of the perfusate in the flow experiment showed a monotonic, linear decrease in the Doppler power as a function of dilution. CONCLUSION: The power Doppler US technique has the potential to more accurately estimate alterations in blood flow and has the advantage of being a continuous parameter that can be depth normalized.

The purpose of this study was to evaluate the character and evolution of bone lesions attributable to amyloid deposition in patients on long-term dialysis. Thirty-five patients who were treated with hemodialysis for 5 to 22 years were studied by a review of medical records and hand radiographs. The frequency, distribution, character, and evolution of skeletal cyst-like lesions believed to be secondary to amyloid deposition were evaluated in relation to dialysis duration. The number and size of these lesions increased with dialysis duration, present in 28% of the patients after 5 through 9 years of hemodialysis and in 91% after 15 through 22 years. In contrast, the changes of hyperparathyroidism decreased. Of patients with skeletal wrist lesions, radiographs of symptomatic large joints were available in 15; five had bone abnormalities. Skeletal amyloid deposition was verified pathologically in nine sites (five patients). It is concluded that skeletal lesions believed to be due to amyloid deposition increase with dialysis duration and most commonly affect the wrists. They have a distinctive character, distribution, and evolution and are often associated with carpal tunnel syndrome.

A method for quantitative imaging of internal tissue motion based on speckle tracking is described. Tissue displacement images from eight patients with sonographically apparent breast masses are used to illustrate the technique. The local displacement response of tissues surrounding malignant and benign breast masses is compared, testing the hypothesis that altered mechanical properties may result in motion signatures for many soft tissue tumors relative to their host tissue. In addition, the potential or anticipated influence of various biological and physical factors on tissue motion response is discussed.

Imaging of blood flow perfusion is an area of significant medical interest. Recently, the advantages of using the total integrated Doppler power spectrum as the parameter that is encoded in color has been shown to result in an approximately threefold increase in flow sensitivity, a relative insensitivity to acquisition angle and lack of aliasing. We have taken this mode a step further and demonstrated the potential for quantifying blood flow using correlation-based algorithms applied to the power signal. We show that phi(tau) = phi(0)e-VT, where phi(tau) is the two-time correlation of the fluctuation in the power signal, and v is the specific flow (reciprocal of mean transit time). Scans of a dog's blood, pumped at a constant rate through gum rubber tubing, were obtained using a Diasonics Spectra 10-MHz linear array transducer at standard range-gated spectral mode (PRF = 1400 Hz, wall filter = 50 Hz, sample gate = 1.5 mm). A fixed Doppler angle of 68 degrees was used. Five different flow rates were tested, and the velocities determined by power decorrelation were compared to the mean velocities calculated from the Doppler shifts by linear regression (R2 = 0.987). We believe the results are very encouraging for using power decorrelation in perfusion evaluation.