A New Approach Using Manganese-Enhanced MRI to Diagnose Acute Mesenteric Ischemia in a Rabbit Model: Initial Experience

Abstract

Purpose: Manganese-enhanced MRI (MEMRI) has been applied to a wide range of biological and disease research. The purpose of the study was to use MEMRI to diagnose the acute mesenteric ischemia (AMI).

Methods: The institutional experimental animal ethics committee approved this study. To optimize the dose of Mn(2+) infusion, a dose-dependent curve was obtained using Mn(2+)-enhanced T 1 map MRI by an intravenous infusion 2.5-20 nmol/g body weight (BW) of 50 nmol/L MnCl2. The eighteen animals were divided into control, sham-operated, and AMI groups. AMI models were performed by ligating the superior mesenteric artery (SMA). T 1 values were measured on T 1 maps in regions of the small intestinal wall and relaxation rate (ΔR 1) was calculated.

Results: A nonlinear relationship between infused MnCl2 solution dose and increase in small intestinal wall ΔR 1 was observed. Control animal exhibited significant Mn(2+) clearance over time at the dose of 15 nmol/g BW. In the AMI model, ΔR 1 values (0.95 ± 0.13) in the small intestinal wall were significantly lower than in control group (2.05 ± 0.19) after Mn(2+) infusion (P < 0.01).

Conclusion: The data suggest that MEMRI shows potential as a diagnostic technique that is directly sensitive to the poor or absent perfusion in AMI.

Figure 1

Example of small intestinal wall images showed the changes of  T ₁ signal in the small intestinal wall for a control rabbit in T ₁-weighted images and T ₁ maps. (a) T ₁-weighted image before Mn²⁺ infusion. (b) T ₁-weighted image after Mn²⁺ infusion. (c) T ₁ map before Mn²⁺ infusion. (d) T ₁ map after Mn²⁺ infusion. The white arrow indicated signal change of the small intestinal wall before and after Mn²⁺ infusion.

Figure 2

Effect of altering the dose of infused Mn²⁺ on small intestinal wall relaxivity. (a) The dose-dependent curve for different dose of MnCl₂ administration. x-axis showed the total dose of infused Mn²⁺ normalized to rabbit BW. y-axis showed the change of relaxation rate, ΔR ₁. As a function of dose, a linear dose-uptake region was noted along with a plateau region above 15 nmol/g BW. The linear fit was shown with total Mn²⁺ infusion dose, X, in nmol/g BW. Data are presented as the mean ± SEM of n = 3. (b) Temporal Mn²⁺ washout curve. x-axis showed the experimental time course after Mn²⁺ infusion. y-axis showed the difference in the change of relaxation rate, ΔR ₁.

Figure 3

Example of post-Mn²⁺ infusion T ₁-weighted image and T ₁ map for a sham-operated rabbit (a and c) and AMI model (b and d). The small intestinal wall of AMI model showed a longer T ₁ relaxation time than that of sham-operated animal. Significant decreasing of T ₁ values can be seen in the small intestinal wall of sham-operated group compared with AMI groups.

Figure 4

Effect of AMI on the uptake of Mn²⁺. Data are presented as the mean ΔR ₁ ± SEM of n = 6. ^∗∗ P < 0.01 versus control group.