The Value of a Chest CT in the Evaluation of a Newly Detected Brain Tumor

OBJECTIVE: To create a care pathway for patients with a newly detected brain tumor, by examining common diagnostic pathways for patients diagnosed with a primary brain tumor or a central nervous system metastasis. MATERIALS AND METHODS: All patients diagnosed atMGH between 1/1/95 and 12/31/97 with a primary brain tumor or a central nervous system metastasis were studied. Only patients who displayed one or two brain lesions and presented to the MGH emergency ward or transferred in from another emergency ward were included in the study. Clinical characteristics, use and results of radiological testing, and final diagnostic procedures were evaluated. RESULTS: Forty-eight patients were selected for the study. The most common ancillary test performed was a chest x-ray; 97.9% of the patients received a chest x-ray, while only 18.8% received a chest CT. None of the chest CT examinations showed a diagnostically significant different from the chest x-ray. Other ancillary scanning was done infrequently. DISCUSSION: A relatively small proportion of patients with a newly detected brain lesion received any type of ancillary testing beyond a chest x-ray. A chest x-ray appeared to change the biopsy site from the brain to another site in about 50% of the cases. Not enough chest CT examinations were done to determine their effectiveness. However, the resuhs seem to indicate that the preliminary diagnosis of the admitting physician is not necessarily based upon the results of a chest x-ray or other ancillary testing

The Extraordinarily Rapid Expansion of the X-ray Remnant of Kepler's Supernova (SN1604)

Four individual high resolution X-ray images from ROSAT and the Einstein Observatory have been used to measure the expansion rate of the remnant of Kepler's supernova (SN 1604). Highly significant measurements of the expansion have been made for time baselines varying from 5.5 yrs to 17.5 yrs. All measurements are consistent with a current expansion rate averaged over the entire remnant of 0.239 (+/-0.015) (+0.017,-0.010) % per yr, which, when combined with the known age of the remnant, determines the expansion parameter m, defined as $R\propto t^m$, to be 0.93 (+/-0.06) (+0.07,-0.04). The error bars on these results include both statistical (first set of errors) and systematic (second set) uncertainty. According to this result the X-ray remnant is expanding at a rate that is remarkably close to free expansion and nearly twice as fast as the mean expansion rate of the radio remnant. The expansion rates as a function of radius and azimuthal angle are also presented based on two ROSAT images that were registered to an accuracy better than 0.5 arcseconds. Significant radial and azimuthal variations that appear to arise from the motion of individual X-ray knots are seen. The high expansion rate of the X-ray remnant appears to be inconsistent with currently accepted dynamical models for the evolution of Kepler's SNR.Comment: 14 pages, including 7 postscript figs, LaTeX, emulateapj. Accepted by Ap

Measuring Molecular, Neutral Atomic, and Warm Ionized Galactic Gas Through X-Ray Absorption

We study the column densities of neutral atomic, molecular, and warm ionized Galactic gas through their continuous absorption of extragalactic X-ray spectra at |b| > 25 degrees. For N(H,21cm) < 5x10^20 cm^-2 there is an extremely tight relationship between N(H,21cm) and the X-ray absorption column, N(xray), with a mean ratio along 26 lines of sight of N(xray)/N(H,21cm) = 0.972 +- 0.022. This is significantly less than the anticpated ratio of 1.23, which would occur if He were half He I and half He II in the warm ionized component. We suggest that the ionized component out of the plane is highly ionized, with He being mainly He II and He III. In the limiting case that H is entirely HI, we place an upper limit on the He abundance in the ISM of He/H <= 0.103. At column densities N(xray) > 5x10^20 cm^-2, which occurs at our lower latitudes, the X-ray absorption column N(xray) is nearly double N(H,21cm). This excess column cannot be due to the warm ionized component, even if He were entirely He I, so it must be due to a molecular component. This result implies that for lines of sight out of the plane with |b| ~ 30 degrees, molecular gas is common and with a column density comprable to N(H,21cm). This work bears upon the far infrared background, since a warm ionized component, anticorrelated with N(H,21cm), might produce such a background. Not only is such an anticorrelation absent, but if the dust is destroyed in the warm ionized gas, the far infrared background may be slightly larger than that deduced by Puget et al. (1996).Comment: 1 AASTeX file, 14 PostScript figure files which are linked within the TeX fil

The General Hull-White Model and Super Calibration

Term structure models are widely used to price interest-rate derivatives such as swaps and bonds with embedded options. This paper describes how a general one-factor model of the short-rate can be implemented as a recombining trinomial tree and calibrated to market prices of actively traded instruments such as caps and swap options. The general model encompasses most popular one-factor Markov models as special cases. The implementation and the calibration procedures are sufficiently general that they can select the functional form of the model that best fits the market prices. This allows the model to fit the prices of in- and out-ofthe- money options when there is a volatility skew. It also allows the model to work well very low interest-rate economies such as Japan where other models often fail