Gerald L. Wolf

Assessing burn wound depth using in vitro nuclear magnetic resonance (NMR)

There is no accurate noninvasive method for differentiating between partial-thickness and full-thickness cutaneous burn wounds. Full-thickness burns (FTB) result in slower resorption of wound edema than partial thickness burns (PTB). Since proton NMR parameters, particularly the T1 relaxation time, correlate with tissue water content (TWC), the present study determined whether proton NMR could distinguish PTB from FTB. An area of upper dorsum (approximately 15% BSA) of 35 adult rats was immersed in boiling water for either 3 sec (PTB) or 10 sec (FTB). In 10 control rats, the same area was immersed in room temperature water. Rats were sacrificed at either 3 or 48 hr after burn, and skin samples were analyzed to determine spin-lattice (T1) and spin-spin (T2) relaxation times. TWC was then measured gravimetrically by desiccation. Both T1 and T2 times significantly correlated with TWC (T1: r = 0.74, P less than 0.0001; T2: r = 0.75; P less than 0.0001). Both PTB and FTB resulted in significant elevations of T1, T2, and TWC 3 hr after injury (P less than 0.001). At 48 hr postburn the T1, T2, and TWC of the PTB group had decreased to control values (P less than 0.05), while all FTB parameters remained significantly elevated as compared to both the control and the 48-hr PTB parameters (P less than 0.001). In vitro NMR measurements distinguish PTB from FTB in this rat model within 48 hr. These data provide a basis for investigating in vitro NMR techniques for the noninvasive assessment of burn wound depth.

The oral administration of MnCl2: a potential alternative to IV injection for tissue contrast enhancement in magnetic resonance imaging.

Mn+2 (as MnCl2) was administered to rabbits intravenously and orally (a route of administration which based upon our previous experiments in rats promises to give selective hepatobiliary enhancement with less systemic toxicity). Nuclear magnetic relaxation dispersion or T1 (NMRD) was performed on selected tissues (heart, liver, kidney, serum, and bile) in both animal groups to examine possible qualitative and semiquantitative differences in T1 relaxation at equivalent sacrifice times. One animal was given an oral dose of MnCl2 (620 micromoles/kg) and imaged sequentially (T1 weighted sequence, .12T) for 30 minutes. The NMRD curves for organ tissues show an increase in relaxation efficacy in the 10-20MHz range characteristic of Mn-macromolecular complexes and are similar irrespective of the route of administration. The lack of increased relaxation enhancement for bile in this frequency range reflects cleavage of this complex upon excretion. Decreased overall relaxation in the liver is observed when oral Mn+2 is compared to IV Mn+2 due to the small fraction of administered dose that is absorbed. However, the images document a significant increase in the intensity of liver signal after the oral dose. We suspect this dose may ultimately be adjusted downward to give selective hepatobiliary effects.

The identification of experimentally induced appendicitis using in vitro nuclear magnetic resonance

Appendicitis was induced in six New Zealand white rabbits. The appendices from these animals had significantly higher spin-lattice relaxation times, T1, as determined in vitro by nuclear magnetic resonance (NMR) (10 controls vs 6 experimentals, 413 +/- 23 vs 455 +/- 41, X +/- SD, P less than (0.02). T1 correlated significantly with the water content of the appendiceal tissue (P less than 0.001). These findings suggest that in vivo NMR imaging techniques weighted on T1 might be able to identify human appendicitis noninvasively by detecting localized edema.

Detection of total parenteral nutrition-induced fatty liver infiltration in the rat by in vitro proton nuclear magnetic resonance.

In an effort to determine if NMR techniques might be used to detect TPN-induced hepatic steatosis, the NMR spin-lattice (T1) and spin-spin (T2) relaxation times were measured on liver tissue from rats who received one of five dietary regimens: (1) 100% of nonprotein calories as lipid (Fat); (2) a mixture of 50% lipid and 50% glucose nonprotein calories (50/50); (3) 100% of nonprotein calories as glucose (CHO); (4) intravenous saline and standard laboratory rat chow (Saline); and (5) rat chow alone (Oral). The parenteral diets were isonitrogenous and isocaloric. Serum liver function tests were also measured. Animals in the Fat and 50/50 groups had the greatest amounts of liver fat and significantly longer T1 and T2 times (p less than 0.01) than any other group. Furthermore, the correlation of T2 time with liver fat content (r = 0.82) was far superior (p less than 0.001) to that of serum SGPT (r = 0.48) which was the only liver function test which correlated significantly with liver fat content. In a multiple linear regression analysis, T1 and T2 predicted liver fat content with an r value of 0.84 (p less than 0.001). These data suggest that in vivo NMR imaging techniques might be used to detect TPN-induced fatty infiltration of the liver noninvasively.

In vitro detection of fatty liver infiltration in protein-depleted rats using proton nuclear magnetic resonance

To determine if NMR techniques might be used to detect hepatic steatosis secondary to protein malnutrition, the T1 and T2 relaxation times of liver tissue from rats subjected to long-term protein malnutrition were measured in vitro. The liver tissue from rats fed a protein-deficient rat chow (PD) for 37 days (N = 9) was characterized by increased proportion of fat (P less than 0.001) but decreased water and nitrogen contents (P less than 0.001) relative to controls (N = 9). Mean T1 times were significantly shorter and T2 times significantly longer in liver tissue from protein-depleted animals (P less than 0.001). There was no overlap of T2 times between the protein-depleted and control animals. The consistent changes in T2 that occur with fatty infiltration of the liver should be detectable by current NMR imagers.