MRI‐based large deformation high dimensional mapping of the hippocampus in rats: Development and validation of the technique

Purpose

To report the detection of structural and functional biological changes in living animals using small animal in vivo MRI that complements traditional ex vivo histological techniques. We report the development and validation of the application of large deformation high dimensional mapping (HDM‐LD) segmentation for the hippocampus in the rat.

Materials and Methods

High resolution volumetric T2 weighted MRI images were acquired at 4.7 Tesla from six male in‐breed nonepileptic Wistar rats. Two HDM‐LD segmentations of the hippocampus (automated 1 and automated 2) were compared with the manual segmentations of two investigators who independently segmented the hippocampi (manual 1 and manual 2).

Results

The mean overlap for the hippocampi between automated 1 and automated 2 for the right hippocampi was 94.4% (SD 1.0) and for the left hippocampi was 94.3% (SD 2.5), while the mean overlap between automated 1 and manual 1 for the right hippocampi was 91.4% (SD 1.3) and for the left hippocampi was 91.9% (SD 1.4). Mean values for absolute differences for comparisons of all the segmentations were the following: automated 1 versus automated 2, 3.2% (SD 1.0); manual 1 versus manual 2 6.82% (SD 5.22); automated 1 versus manual 1 13.0% (SD 1.8).

Conclusion

HDM‐LD can be applied to obtain accurate and reproducible three‐dimensional segmentations of the hippocampus from rat MR images. HDM‐LD will be a useful tool for investigations of hippocampal structural changes in vivo in rat models of human disease. J. Magn. Reson. Imaging 2009;29:1027–1034. © 2009 Wiley‐Liss, Inc.     

Quantifying in vivo hemodynamic response to exercise in patients with intermittent claudication and abdominal aortic aneurysms using cine phase‐contrast MRI

Purpose:

To evaluate rest and exercise hemodynamics in patients with abdominal aortic aneurysms (AAA) and peripheral occlusive disease (claudicants) using phase‐contrast MRI.

Materials and Methods:

Blood velocities were acquired by means of cardiac‐gated cine phase‐contrast in a 0.5 Tesla (T) open MRI. Volumetric flow was calculated at the supraceliac (SC), infrarenal (IR), and mid‐aneurysm (MA) levels during rest and upright cycling exercise using an MR‐compatible exercise cycle.

Results:

Mean blood flow increased during exercise (AAA: 130%, Claudicants: 136% of resting heart rate) at the SC and IR levels for AAA participants (2.6 ± 0.6 versus 5.8 ± 1.6 L/min, P < 0.001 and 0.8 ± 0.4 versus 5.1 ± 1.7 L/min, P < 0.001) and claudicants (2.3 ± 0.5 versus 4.5 ± 0.9 L/min, P < 0.005 and 0.8 ± 0.2 versus 3.3 ± 0.9 L/min, P < 0.005). AAA participants had a significant decrease in renal and digestive blood flow from rest to exercise (1.8 ± 0.7 to 0.7 ± 0.6 L/min, P < 0.01). The decrease in renal and digestive blood flow during exercise correlated with daily activity level for claudicants (R = 0.81).

Conclusion:

Abdominal aortic hemodynamic changes due to lower extremity exercise can be quantified in patients with AAA and claudication using PC‐MRI. The redistribution of blood flow during exercise was significant and different between the two disease states. J. Magn. Reson. Imaging 2010; 31: 425–429. © 2010 Wiley‐Liss, Inc.

     

Cross‐validation of magnetic resonance elastography and ultrasound‐based transient elastography: A preliminary phantom study

Purpose:

To cross‐validate two recent noninvasive elastographic techniques, ultrasound‐based transient elastography (UTE) and magnetic resonance elastography (MRE). As potential alternatives to liver biopsy, UTE and MRE are undergoing clinical investigations for liver fibrosis diagnosis and liver disease management around the world. These two techniques use tissue stiffness as a marker for disease state and it is important to do a cross‐validation study of both elastographic techniques to determine the consistency with which the two techniques can measure the mechanical properties of materials.

Materials and Methods:

In this study, 19 well‐characterized phantoms with a range of stiffness values were measured by two clinical devices (a Fibroscan and an MRE system based respectively on the UTE and MRE techniques) successively with the operators double‐blinded.

Results:

Statistical analysis showed that the correlation coefficient was r² = 0.93 between MRE and UTE, and there was no evidence of a systematic difference between them within the range of stiffnesses examined.

Conclusion:

These two noninvasive methods, MRE and UTE, provide clinicians with important new options for improving patient care regarding liver diseases in terms of the diagnosis, prognosis, and monitoring of fibrosis progression, as well for evaluating the efficacy of treatment. J. Magn. Reson. Imaging 2009;30:1145–1150. © 2009 Wiley‐Liss, Inc.