Magnetic resonance imaging of the brainstem: normal structure and basic functional anatomy

Normal structure and basic functional anatomy of the brainstem were studied using anatomic sections obtained with a cryomicrotome whole-organ sectioning technique. Major tracts and nuclei were identified and their function summarized. Magnetic resonance imaging of the brainstem was performed on 10 normal volunteers. By comparing these images with the corresponding anatomic sections, normal structures, including major tracts and nuclei, were identified. Knowledge of location and function of clinically important brainstem nuclei and tracts is necessary for optimal magnetic resonance image interpretation.     

Pulse sequence optimization for MR imaging using a paramagnetic hepatobiliary contrast agent

Paramagnetic agents enhance contrast between tissues in magnetic resonance (MR) imaging by altering tissue relaxation times. The effect of these changes on MR image intensity depends in part on the choice of operator-controlled pulse sequence parameters. With the newly described paramagnetic hepatobiliary contrast agent, iron(III) ethylenebis-(2-hydroxyphenylglycine), Fe(EHPG)-, an in vivo experimental analysis of pulse sequence optimization was performed on the rat. We compared the enhancement of the liver divided by background noise, EL/N, of standard inversion-recovery (IR) and spin-echo (SE) T1-weighted pulse sequences and several pulse sequences theoretically predicted to have improved EL/N. Optimization of the echo time (TE = TEmin) gave a substantial (greater than 60%) increase in EL/N over the standard IR and SE pulse sequences. Images obtained with optimized repetition rate and inversion time gave only a slight additional improvement. Within the uncertainties of our relaxation measurements, the measured changes in EL/N with pulse sequence optimization corresponded well with theoretical predictions. With the experimental and theoretical data, the importance of using a short echo time to obtain maximal T1 contrast in contrast-enhanced MR imaging and the relative merits of optimized SE versus IR pulse sequences for contrast-enhanced MR imaging are discussed.     

Distant heart procurement for transplantation.

Between January 1, 1977, and September 15, 1978, 39 cardiac transplants were performed on 38 patients. Twenty donor hearts were removed at Stanford University Hospital, and 19 donor hearts were removed at distant hospitals. The characteristics of recipients and donors in both groups were similar. The only significant difference between donor hearts was the mean ischemia time (154 +/- 30 minutes in distant hearts and 52 +/- 12 minutes in local hearts, P less than 0.001). As of February 1, 1979, the total mortality rate was 32% for the distant heart donors and 40% for the local heart donors. No difference between the two groups was present in immediate myocardial function, the need for postoperative inotropic support, the mortality rate within the first 90 days after operation, the mean maximum serum enzyme levels, the occurrence of rejection or infection, and the histological appearance of the hearts, both early and late. The results of cardiac transplantation when hearts are removed at distant hospitals are entirely comparable to the results with hearts removed on site with a minimum ishchemic time. Distant heart procurement provides an expanded donor pool for potential cardiac recipients.     

In vitro testing of a novel blood pump designed for temporary extracorporeal support

Extracorporeal blood pumps are used as temporary ventricular assist devices or for extracorporeal membrane oxygenation. The ideal pump would be intrinsically self-regulating, carry no risk of cavitation or excessive inlet suction, be afterload insensitive, and valveless thus reducing thrombogenicity. Currently used technology, including roller, centrifugal, and pneumatic pulsatile pumps, does not meet these requirements. We studied a nonocclusive peristaltic pump (M-Pump) in two mock circulatory loops and compared the performance to a frequently used centrifugal pump and a modified prototype of the M-Pump (the BioVAD). The simple resistance loop consisted of the investigated pump, a fixed height reservoir at 150 mm Hg, and a variable inflow reservoir. The pulsatile circulation used a mock patient simulator with adjustable resistance elements connected to a pneumatic pulsatile pump. The M-Pump intrinsically regulated flow with changing preload, was afterload insensitive, and did not cavitate, unlike the centrifugal pump. The BioVAD also demonstrated these features and could augment output with the use of vacuum assistance. A nonocclusive peristaltic pump may be superior for short-term extracorporeal circulatory assist by mitigating risks of excessive inlet suction, afterload sensitivity, and thrombosis.     

CHANGES IN PULMONARY VASCULATURE IN LUNG DISEASES WHICH LEAD TO PULMONARY HYPERTENSION

The pulmonary vasculature was studied in lung biopsy/autopsy specimens of 20 cases, in conditions likely to lead to pulmonary hypertension. The changes were classified as per Edward and Heath classification and morphometric measurements to gauge medial and intimai hypertrophy were done. Medial hypertrophy was found to be the earliest and commonest change in all cases, irrespective of the pathogenic mechanism of pulmonary hypertension. Variable changes specific to various arteriopathies/vasculopathies were noted.KEYWORDS: Hypertension pulmonary, Pulmonary artery     

The Tritiated Water Skin Barrier Integrity Test: Considerations for Acceptance Criteria with and Without <Superscript>14</Superscript>C-Octanol

Purpose

A study was designed to assess barrier integrity simultaneously using separate compounds (probes) for polar and non-polar pathways through the skin, ³H₂O and ¹⁴C-octanol, respectively; and to determine whether the two probe approach could better define barrier integrity.

Methods

A 5-min dose of water containing ³H₂O and ¹⁴C -octanol was applied to ex vivo human skin mounted in Franz diffusion cells. The receptor solution was sampled at 30 min, analyzed for ³H and ¹⁴C content, and the correlation between water and octanol absorption was determined by statistical tests suitable for non-normally distributed data. This study was conducted on skin from 37 donors with from 3 to 30 replicate skin sections per donor (a total of 426 sections).

Results

The correlation between ³H₂O and ¹⁴C-octanol absorption was low (Pearson correlation coefficient?=?0.3485). The ³H₂O absorption cutoff used in this study to select for a normal skin barrier rejected some sections in which ¹⁴C-octanol absorption was within normal limits and accepted others in which ¹⁴C-octanol absorption was abnormally high. The converse was true for ³H₂O absorption when the ¹⁴C-octanol-based cutoff was used.

Conclusions

The results of the ³H₂O test or of similar tests that primarily assess the permeability of polar pathways through the skin may not necessarily provide information relevant to the absorption of highly lipophilic compounds. Octanol, or another molecule that more closely matches the physicochemical attributes of the test compound, may characterize properties of the skin barrier that are more relevant to compounds of low water solubility.

     

The infinite sites model of genome evolution

We formalize the problem of recovering the evolutionary history of a set of genomes that are related to an unseen common ancestor genome by operations of speciation, deletion, insertion, duplication, and rearrangement of segments of bases. The problem is examined in the limit as the number of bases in each genome goes to infinity. In this limit, the chromosomes are represented by continuous circles or line segments. For such an infinite-sites model, we present a polynomial-time algorithm to find the most parsimonious evolutionary history of any set of related present-day genomes.