Citations

We validate a technique for model-free measurement of shear wave velocity and attenuation. A mechanical shaker was used to excite harmonic plane and cylindrical waves in phantoms and excised tissue. Radiation force was used to excite impulsive cylindrical waves. 2D FFT of the displacement yielded the k-space whose coordinates are frequency and the wave number. The shear wave velocity at each frequency was obtained by finding the maximum at the given frequency in k-space and dividing the frequency coordinate by the wave number coordinate. The attenuation (α) at a given frequency was calculated using α = FWHM × π/√3, where FWHM is the full width at half maximum of the k-space peak along the given frequency. This method was applied to measure shear wave velocity and attenuation of transplanted kidneys and livers, and in the thyroid tumor, and compare it to the healthy tissues. The velocities and attenuations at each frequency for various excitation methods agree within one standard deviation. The k-space estimates of velocity and attenuation agreed with those obtained using the phase gradient (velocity) and amplitude decay (attenuation). The transplanted organs and the thyroid tumor had higher velocity and lower attenuation than healthy tissues.

Measurements of viscoelasticity with shear wave velocity dispersion requires measurements over a large bandwidth. In this study, we explored the parameters that modulate the frequency characteristics of shear waves induced using radiation force push beams. We used a Verasonics ultrasound scanner equipped with a linear array transducer. We performed measurements of shear wave motion induced using both focused and unfocused ultrasound beams. Measurements were made in elastic phantoms with shear moduli of 1, 4, and 16 kPa. The number of elements used for the unfocused beams were varied from 8 to 24, and for the focused beams from 16 to 128. The shear wave motion was tracked using plane wave imaging, and a one-dimensional autocorrelation algorithm applied to the acquired in-phase/quadrature data. At each pixel we calculated the fast Fourier transform of the data and found the center frequency, center-of-gravity, and −3 dB bandwidth. We compared the frequency characteristics from the different push beams. The frequency characteristics were found to be spatially variant and dependent on the number of elements used as well as the shear modulus of the medium. The center frequency, center-of-gravity, and the bandwidth were found to be correlated to one another, and strongly associated with the stiffness of the medium.

Robust shear-wave motion detection is essential for producing reliable shear elasticity measurements for ultrasound shear-wave elastography (SWE). However, because shear-wave motion is extracted from radiofrequency signals which can be heavily contaminated by noise, shear-wave motion detection can be very challenging, especially for in vivo applications. This study investigated the implementation of harmonic imaging (HI) to facilitate more robust shear-wave tracking based on HI’s effectiveness in suppressing imaging noise associated with ultrasound reverberation, phase aberration, and clutter noise. A HI shear-wave tracking sequence was developed combining the pulse-inversion HI method with the plane wave imaging technique to transmit phase-inverted pulses at a high frame rate of several kilohertz. The backscattered ultrasound signals from phase-inverted pulses were added to suppress the fundamental and enhance the second harmonic component, from which the shear-wave motion was extracted. A pork belly phantom experiment showed that HI could significantly improve shear-wave motion detection by producing almost three-fold less underestimation of shear-wave motion and over ten-fold more precision for shear-wave speed measurements than fundamental imaging. An in vivo transthoracic case study of a human heart showed that HI substantially improved the success rate of shear-wave motion detection and could provide consistent estimates of the left ventricle myocardium stiffness.

Introduction: Ultrasound radiation force-based methods can quantitatively evaluate tissue viscoelastic material properties. A limitation of current methods includes neglecting the inherent anisotropy nature of tissue. To explore this phenomenon, we created a phantom incorporating fibrous material that has preferential orientations. Methods: Two phantoms were made in a cube-shaped mold using a fibrous material arranged in multiple layers and embedded in porcine gelatin using two different concentrations of the gelatin (8%, 14%). Shear wave measurements were made in the phantoms at different angles by rotating the phantom, where 0° and 180° were defined along the fibers, and 90° and 270° across the fibers. Measurements were performed using a Verasonics ultrasound system equipped with a linear array transducer. Results/Discussion: The mean shear wave speeds and mean standard deviations for 8% and 14% gelatin along the fibers (0°) were (3.60 ± 0.03 and 4.10 ± 0.11 m/s) and across the fibers (90°) were (3.18 ± 0.12 and 3.90 ± 0.02 m/s), respectively. Conclusion: The fibrous gelatin-based phantoms exhibited anisotropy that could be measured using quantitative shear waves speed measurements. Increasing the gelatin percentage increases the shear wave speed and anisotropic moduli. [This study was supported by NIH grant DK092255.]

Thyroid cancer is the fastest growing age and gender adjusted cancer in 2011 according the American Cancer Society. The majority of the clinically diagnosed thyroid nodules are benign while less than 5% represent intrathyroidal cancers. Currently, the clinical gold-standard procedure for assessing the thyroid nodules is needle biopsy, a procedure that is associated with significant financial burden as well as pain and risk for patients. Therefore, a noninvasive, affordable, and potentially widely available method to differentiate between benign and malignant thyroid nodules can play an important role in reducing the number of unnecessary biopsies. In this study, we investigate the feasibility of two acoustic radiation force elastography techniques, shear wave dispersion ultrasound vibrometry (SDUV) and comb-push ultrasound shear wave elastography (CUSE imaging), in identifying thyroid nodules (imaging) and differentiating between benign and malignant pathologies based on their elasticity and viscosity (SDUV measurements). Our preliminary results show that the measured shear elasticity and shear viscosity parameters depend on tissue type; hence, these measurements may be utilized to differentiate between healthy normal thyroid tissue, benign nodules, and malignant nodules. Further studies on a large population of patients is required to better evaluate the role of the combination of elasticity and viscosity properties of tissue in differentiating various thyroid nodules.

Object Biomechanical studies have shown that anterior cervical fusion construct stiffness and arthrodesis rates vary with different reconstruction techniques; however, the behavior of the adjacent segments in the setting of different procedures is poorly understood. This study was designed to investigate the adjacent-segment biomechanics after 3 different anterior cervical decompression and fusion techniques, including 3-level discectomy and fusion, 2-level corpectomy and fusion, and a corpectomy-discectomy hybrid technique. The authors hypothesized that biomechanical changes at the segments immediately superior and inferior to the multilevel fusion would be inversely proportional to the number of fused bone grafts and that these changes would be related to the type of fusion technique. Methods A previously validated 3D finite element model of an intact C3–T1 segment was used. Three C4–7 fusion models were built from this intact model by varying the number of bone grafts used to span the decompression: a 1-graft model (2-level corpectomy), a 2-graft model (C-5 corpectomy and C6–7 discectomy), and a 3-graft model (3-level discectomy). The corpectomy and discectomy models were also previously validated and compared well with the literature findings. Range of motion, disc stresses, and posterior facet loads at the segments superior (C3–4) and inferior (C7–T1) to the fusion construct were assessed. Results Motion, disc stresses, and posterior facet loads generally increased at both of the adjacent segments in relation to the intact model. Greater biomechanical changes were noted in the superior C3–4 segment than in the inferior C7–T1 segment. Increasing the number of bone grafts from 1 to 2 and from 2 to 3 was associated with a lower magnitude of biomechanical changes at the adjacent segments. Conclusions At segments adjacent to the fusion level, biomechanical changes are not limited solely to the discs, but also propagate to the posterior facets. These changes in discs and posterior facets were found to be lower for discectomy than for corpectomy, thereby supporting the current study hypothesis of inverse relationship between the adjacent-segment variations and the number of fused bone grafts. Such changes may go on to influence the likelihood of adjacent-segment degeneration accordingly. Further studies are warranted to identify the causes and true impact of these observed changes.

Total hip replacement (THR) after acetabular fracture presents unique challenges to the orthopaedic surgeon. The majority of patients can be treated with a standard THR, resulting in a very reasonable outcome. Technical challenges however include infection, residual pelvic deformity, acetabular bone loss with ununited fractures, osteonecrosis of bone fragments, retained metalwork, heterotopic ossification, dealing with the sciatic nerve, and the difficulties of obtaining long-term acetabular component fixation. Indications for an acute THR include young patients with both femoral head and acetabular involvement with severe comminution that cannot be reconstructed, and the elderly, with severe bony comminution. The outcomes of THR for established post-traumatic arthritis include excellent pain relief and functional improvements. The use of modern implants and alternative bearing surfaces should improve outcomes further. Cite this article: Bone Joint J 2013;95-B, Supple A:11–16.

The treatment of hip dysplasia should be customised for patients individually based on radiographic findings, patient age, and the patient’s overall articular cartilage status. In many patients, restoration of hip anatomy as close to normal as possible with a PAO is the treatment of choice. Cite this article: Bone Joint J 2013;95-B, Supple A:21–5.

Kayexalate (sodium polystyrene sulfonate), a cation exchange resin often used to treat hyperkalemia, is known to produce gastrointestinal complications in a minority of patients. These complications range from mild gastrointestinal bleeding to perforation with acute abdomen. The typical histopathologic findings include mucosal ulceration, necrosis, and the presence of polygonal basophilic refractile crystals with a “fish scale” appearance. We present a unique case of Kayexalate crystals embedded in a perihepatic inflammatory pseudotumor, developing adjacent to a colostomy site in a 62-year-old woman following Kayexalate treatment. Microscopically, the lesion demonstrated a myofibroblastic proliferation rich in histiocytes and inflammation (lymphocytes, plasma cells, and eosinophils) as well as the presence of scattered typical Kayexalate crystals. This is the first report of extraintestinal Kayexalate identification in association with an inflammatory pseudotumor.