MRI of the knee: value of short echo time fast spin-echo using high performance gradients versus conventional spin-echo imaging for the detection of meniscal tears.

OBJECTIVE: Fast spin-echo (FSE) sequences reduce imaging time compared with conventional spin-echo (CSE) sequences, but may result in blurring. High-performance gradients permit shorter interecho spacing and use of the second echo as the effective TE (20 ms); both improvements reduce blurring. This randomized observer study compared a short TE, second-echo FSE sequence obtained using high-performance gradients and a CSE sequence with similar TR/TE for the detection of meniscal tears in the knee. DESIGN AND PATIENTS: One hundred consecutive MR examinations of the knee using FSE and CSE sequences at 1.5 T were evaluated. The FSE sequence used an effective TE of 20 ms (centered on the second echo at 2 times minimal interecho spacing) and an echo train length of 4. FSE and CSE parameters were otherwise similar. Four independent, masked readers reviewed randomized sagittal FSE and CSE sequences. RESULTS: Cases were assessed for the presence or absence of meniscal tears and, if present, whether tears were medial or lateral and anterior or posterior. Sequence concordance was 93.5% (1496 of 1600 meniscal segments); the intermethod kappa value was 0.78. Sequence quality was graded from 1 to 5. Average quality of CSE images was slightly but statistically significantly preferred by three of the four readers. CONCLUSION: There was no statistically significant difference between CSE imaging and FSE imaging centered on the second echo (20 ms) using high-performance gradients for the detection of meniscal tears in the knee. There was a small preference for the quality of CSE images.

Efficacy of prone positioning during intravenous urography in patients with hematuria or urothelial tumor but no obstruction.

RATIONALE AND OBJECTIVES: The authors prospectively explored the efficacy of using prone positioning during intravenous urography to improve diagnostic visualization and eliminate the need for retrograde pyeloureterography in patients with no obstruction but with hematuria, history of urothelial tumor, or abnormal results of urine cytology. MATERIALS AND METHODS: Prone radiography was added to the usual intravenous urography protocol in 510 patients (347 men, 163 women) without urinary tract obstruction. Interpretations of intravenous urograms and recommendations for retrograde pyeloureterography were made before and after evaluation of the prone image. RESULTS: Confidence in the urographic interpretation was improved with acquisition of the prone radiograph in 100 of 510 patients (19.6%) (95% confidence interval, 82.1, 118). Retrograde pyeloureterography was obviated in 46 of 510 patients (9.0%) (95% confidence interval, 33.1, 58.9). The prone image was most helpful in evaluating the distal ureters (sacral and pelvic segments). CONCLUSION: Prone patient positioning during intravenous urography is useful when complete visualization of the upper urinary tract is desirable. Obtaining the additional image is cost-effective, even when only a few retrograde pyeloureterography studies are obviated.

Effects of etidronate and oophorectomy on the zeta potential of rat bone.

Recent clinical trials in osteoporotic patients show that cyclical etidronate therapy can increase vertebral bone mass and reduce the incidence of vertebral fractures. Stress generated potentials, which are theorized to participate in a negative feedback arrangement regulating bone and which are electrokinetic in origin, can be characterized in vitro by the zeta potential, a measure of electrical surface charge. Thus, the possible effects of etidronate and oophorectomy on the zeta potential of bone were investigated with respect to bone remodeling, pathophysiology, and osteoporosis. Thirty-two oophorectomized and 48 sham oophorectomized rats received subcutaneous etidronate or saline. The zeta potential magnitude of the control group (sham oophorectomized, vehicle only) increased 23.6% from age 6 to 10 months, a period of bone growth. After 6 weeks of etidronate treatment, which decreased bone turnover, the zeta potential magnitude was decreased 14.9% (0.59 mV) compared with that of controls. Decreased zeta potential magnitudes with etidronate treatment also were observed in sham oophorectomized groups at 16 weeks and in oophorectomized groups at 6 and 16 weeks, but the differences were not statistically significant. A large bolus of etidronate had no effect. The zeta potential of bone is a dynamic quantity that may correlate with bone growth or bone turnover. Whether it exerts a causative effect or is a marker remains unknown.

Zeta potential of bone from particle electrophoresis: solution composition and kinetic effects.

The morphology of bone may be influenced by many factors, including electromechanical ones such as electric potentials, electric fields, or zeta potentials. Stress-generated potential studies in bone and particle electrophoresis studies using calcium-deficient hydroxyapatite have shown that the zeta potential depends on the composition of the steeping fluid and steeping time. To better quantify and understand these in situ potential changes in bovine cortical bone, the effects of alterations in calcium, phosphate, and fluoride concentrations in Neuman's Fluid (NF), which simulates in vivo bone extracellular fluid, were investigated using particle electrophoresis. The zeta potential increased in magnitude with increased calcium concentration in NF in as little as 17 min. Increasing phosphate concentration in NF also increased the zeta potential magnitude. These results provide support for a structural model of the bone matrix surface-bone fluid interface, which incorporates the bone surface proper (composed of collagen, mineral, and boundary regions), stationary layer (in which ions, ionic complexes, and proteins may be adsorbed), and bone extracellular fluid. These results, coupled with those of previous studies, indicate that the protein phase probably has an important role in the determination of the physiologic zeta potential; the role of the mineral phase may also be important.

Stress-generated potentials in bone: effects of bone fluid composition and kinetics.

It is now generally accepted that stress-generated potentials (SGPs) at low frequencies are due to an electrokinetic phenomenon in the small interior surfaces of bone and are directly proportional to the zeta potential, a property of the poorly characterized bone surface-bone fluid interface. We hypothesized that this interface would be labile and might explain the controversy over whether or not the polarity of SGPs can invert under certain conditions. In this paper, the effects of alterations in the steeping fluid on SGPs for 87 samples from 15 animals were examined in four-point bending for steeping times of < or = 65 h. Calcium and fluoride in distilled-deionized water and constant ionic strength solutions produced concentration-dependent inversions in the SGP sign. A new steady state was reached in approximately 18 h. The effects of the fluoride anion (unlike the calcium cation) apparently were reversible. The results strongly suggest that the zeta potential at the labile bone surface-bone fluid interface can undergo dramatic changes, not only in magnitude but also in sign. The results further suggest that the preparation of bone samples is critical to the understanding of this interface in vivo, and they support the hypothesis that SGPs have a role in bone remodeling.

Particle microelectrophoresis of calcium-deficient hydroxyapatite: solution composition and kinetic effects.

Concurrent work demonstrates that the zeta potential of bone is multivalued and systematically alterable by changes in sample preparation, steeping fluid composition, and steeping time. Since bone mineral is a mixture of carbonated calcium-deficient hydroxyapatites, and since the zeta potential of calcium-deficient hydroxyapatite (CDHA) is altered by pH and time in HNO3-KOH solutions, the zeta potential of CDHA in physiologic Neuman's fluid (NF) compared with that seen in bone could reveal important information on the contribution of the mineral phase to the zeta potential of bone. In addition, such information may be valuable in designing and evaluating calcium-phosphate ceramics for increased bone ingrowth. Results demonstrate that the zeta potential of CDHA in NF is negative. With increasing calcium in NF, the zeta potential magnitude of CDHA decreases and inverts to positive values given sufficient calcium concentration and steeping time. This result is opposite to that seen in bone, suggesting that exposed CDHA is not the predominant bone microsurface and implicating a bone surface protein component. With increasing phosphate in NF, the zeta potential magnitude increases to more negative values. While low concentrations of fluoride showed no effect, the possibility of an effect with higher concentrations is still to be determined.