Physician noncompete agreements must be carefully tailored.

When covenants not to compete are used, care must also be taken that they are not viewed as a violation of the Medicare anti-kickback statute, 42 U.S.C. Section 1320a-7b(b). Some government officials have asserted that, when physicians selling their practices continue to be affiliated with the buyers of those practices, payments to physicians for intangibles (including covenants not to compete) could be disguised payments for future referrals. See Dec. 22, 1992 letter from D. McCarty Thornton, General Counsel to the Office of Inspector General, to T. J. Sullivan at the Internal Revenue Service. Although the anti-kickback statute is beyond the scope of this article, it must be considered in this context, and care should be taken in any event to assure that purchase prices for physician practices in no event exceed fair market value.

Breast arterial calcification: association with coronary artery disease. Work in progress.

PURPOSE: To assess the association between mammographically detected breast arterial calcification (BAC) and coronary artery disease (CAD) and diabetes mellitus (DM). MATERIALS AND METHODS: The records of 182 women (aged 39-92 years) who underwent both mammography and coronary arteriography were retrospectively reviewed to determine BAC, CAD, and DM status. RESULTS: For women aged less than 59 years (under-59 group) (n = 54), nearly all women with BAC (n = 8) had CAD (n = 7) and also had DM (n = 6). For this group, the positive predictive value of BAC for CAD was 0.88 and the negative predictive value was 0.65 (chi 2 = 7.7, P < .05). DM was a confounding variable. The positive predictive value of DM for CAD increased from 0.62 when BAC was absent to 1.00 when BAC was present (standard error of difference, .22; P < .10). No significant association between BAC and CAD was found for women aged 59 years and older (n = 128). CONCLUSION: BAC in women aged less than 59 years may indicate an additional risk factor for CAD, particularly in diabetic patients.

P-31 magnetic resonance spectroscopy in polymyositis and dermatomyositis. Altered energy utilization during exercise.

OBJECTIVE: To explore alterations in energy utilization as a potential etiology for weakness in polymyositis and dermatomyositis (PM/DM). METHODS: P-31 magnetic resonance spectroscopy studies were performed in patients with acute and treated PM/DM and in normal controls, at rest and with exercise. RESULTS: Patients with acute and treated PM/DM showed increased ratios of inorganic phosphate to phosphocreatine (PCr) during exercise, with loss of ATP disproportional to loss of PCr. CONCLUSION: This study demonstrates changes in energy utilization in PM/DM, thus supporting the notion of a metabolic etiology for the weakness associated with these diseases.

Characterization of normal brain tissue using seven calculated MRI parameters and a statistical analysis system.

A statistical analysis system for classifying normal brain tissue has been applied to the analysis of MRI scans on 45 volunteers. The Bayes Maximum Likelihood method was used to achieve a discrimination accuracy of 84% for 13 tissue types among three age group sets, with classification accuracies for individual regions ranging from 50 to 100%. In order to attain this level of discrimination a set of seven derived relaxation-type parameters was used to categorize the tissue types. Values for these experimentally estimated parameters were derived from the MRI intensities of eight images in the following pulse sequences: (1) a Carr-Purcell-Meiboom-Gill (CPMG) four-echo train, (2) a single-echo inversion recovery, and (3) three single-echo sequences with varying repetition times, TR, and echo delays, TE. The T2 values derived from ratios of single-echo intensities showed better discrimination power than those from the four-echo CPMG train. The general precision of the seven estimated parameters was excellent, with percentage standard deviations ranging from 4 to 18% for the various regions studied. The tissue discrimination achieved by use of just three relaxation parameters, T1, T2, and proton density, calculated from intensities of images from a four-echo sequence, an inversion recovery sequence, and a short TR single-echo sequence, was not as good, being only 55%.

Effect of induced field inhomogeneity on transverse proton NMR relaxation in tissue water and model systems.

The effect of induced field inhomogeneity (IFI) on transverse NMR relaxation of water protons in tissue has been investigated by examining the field dependence of the effective transverse relaxation rates (1/T2 eff) for in vitro canine brain tissue samples. At fields of 0.47, 2.35, 7.05 T (corresponding to 20, 100, and 300 MHz, respectively) the transverse relaxation rates for both white and gray matter samples follow a field dependence of the form 1/T2 eff = C0 + C1 B0, where B0 is the applied field. The linearly dependent term, C1 B0, which reflects the IFI contribution, does not contribute much (i.e., less than 20%) at fields less than 2.0 T. However, at greater field strengths the contribution is appreciable, e.g., greater than 60% at 7.0 T. Results from model systems of glass beads are also reported to illustrate IFI effects. For both the model systems and canine brain tissue samples, the effects of restricted diffusion are qualitatively evident in Hahn spin-echo experiments.

Strategies and tactics in NMR imaging relaxation time measurements. I. Minimizing relaxation time errors due to image noise--the ideal case.

The effect of NMR image noise on errors in calculated values of relaxation times is quantitatively assessed by use of relaxation time noise figures, which are derived on the basis of statistical principles as functions of pulse delay, repetition, and recovery intervals for several types of pulse sequences. Two strategies for determining relaxation times are considered: two point (ratio of intensities for two experiments) and multipoint (least-squares fit of intensities to pulse-sequence functions for n experiments). For given total measurement times, values of pulse interval times are found which give minimum relaxation time noise figures. A comparison of ratio methods shows that the best is a combination saturation-recovery, inversion-recovery (SR/IR) technique. For short measurement times (less than about 10T1) this optimized SR/IR ratio determination is also superior to the best multipoint method, a series of inversion-recovery experiments with equally incremented inversion-recovery times. An examination of the effect of signal averaging on the relaxation time noise shows that up to a measurement time characteristic of the particular method used (e.g., for times up to about 5T1 for the SR/IR ratio determination, 100T1 for the multipoint inversion-recovery method), increased measurement time is more effectively allotted to longer pulse intervals than to signal averaging. Numerical examples are tabulated which can help one to set optimum values for pulse intervals, given a rough estimate of the relaxation time to be determined.

Magnetic resonance of brain tumors: considerations of imaging contrast on the basis of relaxation measurements.

Proton spin-lattice and spin-spin relaxation times have been measured in surgically-removed normal CNS tissues and a variety of tumors of the brain. All measurements were made at 20 MHz and 37 degrees C. Between grey and white matter from autopsy human or canine specimens significant differences in T1 or T2 were observed, with greater differences seen in T1. Such discrimination was reduced in samples obtained from live brain-tumor patients due to lengthening in T1 and T2 of white matter near tumorous lesions. Edematous white matter showed T1 and T2 values higher than those of autopsy disease-free white matter. Compared to normal CNS tissues, most brain tumors examined in this study demonstrated elevated T1 and T2 values. Exceptions, however, did exist. No definitive correlation was indicated on a T1 or T2 basis which allowed a distinction to be made between benign and malignant states. Furthermore, considerable variation in relaxation times occurred from tumor to tumor of the same type, suggesting that within a tumor type there are important differences in physiology, biology, and/or pathologic state. Such variation caused partial overlap in relaxation times among certain tumor types and hence may limit the capability of magnetic resonance imaging (MR) alone for the diagnosis of specific disease. Nonetheless, this study predicts that on the basis of T1 or T2 differences most brain tumors are readily detectable by MR via saturation recovery or inversion recovery with appropriate selections of pulse-spacing parameters. In general, tumors can be discriminated against white matter better than grey matter and contrast between glioma and grey matter is usually superior to that between meningioma and grey matter. This work did not consider tissue-associated proton density which should be addressed together with T1 and T2 for a complete treatment of MR contrast.

Interactions of La2+ with phosphatidylserine vesicles: binding, phase transition, leakage, 31P-NMR and fusion.

The interaction of La2+ with phosphatidylserine vesicles is studied by differential scanning calorimetry, 140La binding, 31P-NMR chemical shifts and relaxation rates, carboxyfluorescein and [14C]sucrose release, X-ray diffraction and freeze-fracture electron microscopy. In the presence of La3+ concentrations above 1 mM and an incubation temperature of 38 degrees C, i.e., at the phase transition temperature of the complex La/phosphatidylserine, the binding ratio of La/lipid exceeds a 1/3 ratio, reaching saturation at a 1/2 ratio. Analysis, employing a modified Gouy-Chapman equation, indicates a significant increase in the intrinsic binding constant of La/phosphatidylserine when the La3+ concentrations exceeds the threshold concentration for leakage. The analysis illustrates that at the molecular level the binding of La3+ can be comparable to or even weaker than that of Ca2+, but that even when present at smaller concentrations La3+ competes with and partially displaces Ca2+ from membranes or other negatively charged surfaces. The results suggest that the sequence La3+ greater than Ca2+ greater than Mg2+ reflects both the binding strength of these cations to phosphatidylserine as well as their ability to induce leakage, enhancement of 31P spin-lattice relaxation rates, fusion and other structural changes. The leakage, fusion, and other structural changes are more pronounced at the phase transition temperature of the La/lipid complex.

Kinetic and magnetic resonance studies of substrate binding to galactose oxidase copper(II).

Alcohol substrate binding to the copper-containing enzyme galactose oxidase (GOase) has been studied by kinetic competition against cyanide and fluoride, 13C nmr relaxation, and esr competition experiments. The 13C nmr spectra of the substrate beta-O-methyl-D-galactopyranoside (beta-O-me-gal) show no apparent paramagnetic relaxation rate enhancement that could be attributed to innersphere equatorial binding of this molecule at the Cu(II) center. Moreover, the kinetics observed when CN- or F- are used as inhibitors of GOase with beta-O-me-gal as the substrate suggest that these anions act as apparent non-competitive inhibitors; the binding of the substrates beta-O-me-gal and O2 is not hindered per se, but the catalytic activity of the enzyme substrate complex is greatly decreased. The esr competition data also confirm that, in the absence of O2, CN- and beta-O-me-gal do not compete for the same GOase binding site. Previously reported esr and 19F nmr data show that CN- binds to the GOase Cu(II) at an equatorial coordination site, as does the F- detected in esr experiments. Thus, the results from the various competition experiments supports a model in which alcohol substrates bind outersphere to the GOase Cu(II), or, possibly, to an axial site.

Ferrocyanide carbon-13 NMR line broadening as a probe of electron transfer reactions.

The electron transfer reaction between ferrocyanide ion and the blue copper protein, stellacyanin, has been investigated by means of 13C NMR line broadening of the inorganic oxidant. The temperature dependence of the ferrocyanide line broadening gives an activation energy for the electron transfer reaction of 17 +/- 3 kJ. The apparent rate constant decreases with increasing concentration of K4Fe(CN)6, a result which can be explained either by formation of a strong precursor ferrocyanide--stellacyanin [Cu(II)] complex or by increased formation of KFe(CN)3-6 ion pairs. The direct electron transfer between ferrocyanide and ferricyanide has also been studied by 13C NMR line broadening of the former species. The ferricyanide concentration dependence of the exchange line broadening yields a value for the apparent second-order rate constant at 25 degrees C of k = 1.65 . 10(3) M-1 . s-1, in agreement with previously reported values derived from 14N NMR and isotope exchange studies. This rate constant shows a linear dependence on the K+ concentration, independent of ionic strength, a result which confirms the importance of ion pair species such as KFe(CN)3-6 and KFe(CN)2-6 in the direct electron transfer mechanism. The general applications of the method are discussed, including the considerations which suggest that a wide range of electron transfer rates, from about 1 s-1 to 4 . 10(3) s-1, are, in principle, accessible to this technique. The potential utility of ferrocyanide 13C spin--lattice relaxation time measurements is decreasing the lower limit of this range is also discussed.

Fluoride ion as an NMR relaxation probe of galactose oxidase-substrate binding.

From the dependence on substrate concentration of fluoride ion spin-lattice and spin-spin paramagnetic relaxation rate enhancements, a value for the dissociation constant, Kd = 0.059 +/0 0.002 M, for the anaerobic binding of dihydroxyacetone (monomer) to the Cu(II) site of the enzyme galactose oxidase (D-galactose:oxygen 6-oxidoreductase, EC 1.1.3.9) has been obtained. This value for Kd lies between previously reported values for Km derived by use of classical Michaelis-Menten kinetics. An analogous calculation for the anaerobic binding of galactose to the enzyme yields Kd = 0.145 +/- 0.004 M, a value different from several reported Michaelis constants. F- NMR relaxation measurements on air-exposed samples of galactose and the enzyme yield a dissociation constant for the active site-oxidation product (presumed to be galactohexodialdose), Kd = 2.2 +/- 0.2 M, a value at least an order of magnitude larger than the Michaelis or dissociation constants calculated for the binding of galactose to the enzyme active site; no value for this constant had been reported previously. Some implications of the competition results for the type of substrate binding are discussed.

Nuclear magnetic resonance studies in normal and edematous brain tissue.

The nmr relaxation rate results show unequivocally that there are at least two fractions of tissue water in both normal and edematous white matter which do not exchange on an nmr time scale (i.e. at times of the order of milli-seconds to fraction of a second). In conjunction with the electron microscopic determination of the extracellular volumes of normal and edematous white matter, the relaxation results can be interpreted in terms of the following model. The two slowly-exchanging water components giving rise to the non-exponential relaxation correspond to cellular and extracellular water; edema changes the relaxation rate of the extracellular component much more than that of the cellular component (the extracellular component becoming more "liquid-like" in its relaxation). Such behavior is consistent with the properties of the extracellular water being due to rapid exchange between motionally restricted water adsorbed at the surface of myelin sheaths, and relatively unrestricted, bulk water. Edema presumably increases the relative amount of the "bulk" water between the axons.

Proton relaxation rates of water in brain and brain tumors.

The distribution of relaxation rates of water in "normal" (autopsy) samples of canine and human brain shows considerable overlap with that for brain tumor samples. The following ranges of values for the spin-spin relaxation rates were observed: for normal brain gray matter, 8.6 to 11.3 sec(-1) (mean, 9.5 sec(-1)); for normal brain white matter, 13.3 to 15.7 sec(-1) (mean, 15.5 sec(-1)); for six types of malignant tumor, 4.8 to 13.4 sec(-1) (mean, 9.3 sec(-1)); for five types of benign tumor, 7.1 to 16.4 sec(-1) (mean, 11.5 sec(-1)). Spin-lattice relaxation rates showed a similar pattern. At least two nonexchanging water components with different relaxation rates were indicated by the analysis of the spin-spin relaxation measurements for the white matter samples.