MR neurography: T1 and T2 measurements in acute peripheral nerve traction injury in rabbits

PURPOSE

To prospectively evaluate magnetic resonance (MR) signal abnormalities and the time course of T1 and T2 values in a rabbit model of acute nerve traction injury with histologic and functional recovery correlation.

MATERIALS AND METHODS

All experimental protocols were approved by the institutional animal use and care committee. Acute traction injury was produced in the sciatic nerve of one hind limb in each of 28 rabbits. The contralateral sham-operated nerves served as controls. Sequential MR imaging and T1 and T2 measurements, as well as measurements of functional changes, were obtained over a 70-day follow-up period, with histologic assessments performed at regular intervals. Signal abnormalities and the time course of T1 and T2 values were observed in the proximal, traction, and distal portions of the injured nerves and the sham-operated nerves, and were compared with each other.

RESULTS

Nerves with acute traction injury showed visible hyperintense signals on T2-weighted images and had prolonged T1 and T2 values. Differences of T1 and T2 values were dependent on the sites along the same injured nerve, with the most pronounced and prolonged phase of T1 and T2 increases (peak values of 1333 msec +/- 46 and 79 msec +/- 3.7, respectively) observed in the most severely damaged portion of the injured nerve. T1 and T2 values and functional changes after nerve injury showed a similar time course. A return of T1 and T2 signals to normal values correlated with functional improvement.

CONCLUSION

MR imaging could be used to help predict the degree of nerve damage and monitor the process of nerve recovery in acute peripheral nerve traction injury. (c) RSNA, 2010.

In vivo MR imaging tracking of transplanted mesenchymal stem cells in a rabbit model of acute peripheral nerve traction injury

PURPOSE

To investigate in vivo MRI tracking mesenchymal stem cells (MSCs) in peripheral nerve injures using a clinically available paramagnetic contrast agent (Gd-DTPA) and commercially available rhodamine-incorporated transfection reagents (PEI-FluoR).

MATERIALS AND METHODS

After bone marrow MSCs were labeled with Gd-DTPA and PEI-FluoR complex, the labeling efficacy and longevity of Gd-DTPA maintenance were measured and cell viability, proliferation, and apoptosis were assessed. Thirty-six rabbits with acute sciatic nerve traction injury randomly received 1 × 10(6) labeled (n = 12) or unlabeled MSCs (n = 12) or vehicle alone injection. The distribution and migration of implanted cells was followed by MRI and correlated with histology. The relative signal intensity (RSL) of the grafts was measured.

RESULTS

The labeling efficiency was 76 ± 4.7% and the labeling procedure did not influence cell viability, proliferation, and apoptosis. A persistent higher RSL in grafts was found in the labeled group compared with the unlabeled and vehicle groups until 10 days after transplantation (P < 0.05). The distribution and migration of labeled cells could be tracked by MRI until 10 days after transplantation. Transplanted MSCs were not found to transdifferentiate into Schwann-like cells within 14-day follow-up.

CONCLUSION

Labeling MSCs with the dual agents may enable cellular MRI of the engraftment in the experimental peripheral nerve injury.

Magnetic resonance imaging of mesenchymal stem cells labeled with dual (MR and fluorescence) agents in rat spinal cord injury

RATIONALE AND OBJECTIVES

In vivo tracking cells using gadolinium-based contrast agents have the important advantage of providing a positive contrast on T1-weighted images, which is less likely to be confused with artifacts because of postoperative local signal voids such as metal, hemorrhage, or air. The aim of this study is to paramagnetically and fluorescently label marrow with dual agents (gadolinium-diethylene triamine penta-acetic acid [Gd-DTPA] and PEI-FluoR) and track them after transplantation into spinal cord injury (SCI) with magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Marrow mesenchymal stem cells (MSCs) from Sprague-Dawley rats were incubated with PEI-FluoR (rhodamine-conjugated PEI-FluoR) and Gd-DTPA complex for labeling. After labeling, cellular viability, proliferation, and apoptosis were evaluated. T1 value and longevity of intracellular Gd-DTPA retention were measured on a 1.5 T MRI scanner. Thirty-six SCI rats were implanted with labeled and unlabeled MSCs and phosphate-buffered saline. Then, serial MRI and Basso-Beattie-Bresnehan (BBB) locomotor tests were performed and correlated with fluorescent microscopy. The relative signal intensity (RSL) of the engraftment in relation to normal cord was measured and the linear mixed model followed by post-hoc Bonferroni test was used to identify significant differences in RSL as well as BBB score.

RESULTS

MSCs could be paramagnetically and fluorescently labeled by the dual agents. The labeling did not influence the cellular viability, proliferation, and apoptosis. The longevity of Gd-DTPA retention in labeled MSCs was up to 21 days. The distribution and migration of labeled MSCs in SCI lesions could be tracked until 7 days after implantation on MRI. The relative signal intensities of SCI rats treated with labeled cells at 1 day and 3 days (1.34 +/- 0.02, 1.27 +/- 0.03) were significantly higher than rats treated with unlabeled cells (0.94 +/- 0.01, 0.99 +/- 0.02) and phosphate-buffered saline (0.91 +/- 0.01, 0.95 +/- 0.01) (P < .05). Rats treated with labeled MSCs or unlabeled MSCs achieved significantly higher BBB scores than controls at 14, 21, 28, and 35 days after injury (P < .05).

CONCLUSIONS

Labeling MSCs with the dual agents may enable cellular MRI and tracking in experimental spinal cord injury.

Efficient in vitro labeling rabbit neural stem cell with paramagnetic Gd-DTPA and fluorescent substance

OBJECTIVES

The aim of this study is to label rabbit neural stem cells (NSCs) by using standard contrast agents (Gd-DTPA) in combination with PKH26 and in vitro track them with MR imaging.

MATERIALS AND METHODS

NSCs from prenatal brains of rabbits were cultured and propagated. Intracellular uptake of Gd-DTPA was achieved by using a non-liposomal lipid transfection reagent (Effectene) as the transfection agent. After labeling with Gd-DTPA, cells were incubated with cellular membrane fluorescent dye PKH26. The labeling effectiveness and the longevity of Gd-DTPA maintenance were measured on a 1.5T MR scanner. The influence of labeling on the cellular biological behaviors was assessed by cellular viability, proliferation and differentiation assessment.

RESULTS

The labeling efficiency of Gd-DTPA was up to 90%. The signal intensity on T1-weighted imaging and T1 values of labeled cells were significantly higher than those of unlabeled cells (P<0.05). The minimal number of detectable cells for T1-weighted imaging was 5×10(3). Cellular uptake of Gd-DTPA was maintained until 15 days after initially labeling. There was no significant difference in the cellular viability and proliferation between the labeled and unlabeled NSCs (P>0.05). Normal glial and neuronal differentiation remained in labeled NSCs like unlabeled NSCs.

CONCLUSION

Highly efficient labeling NSCs with Gd-DTPA could be achieved by using Effectene. This method of labeling NSCs allows for tracking cells with MR imaging, and without alterations of cellular biological behaviors.

Magnetic resonance microneurography of rabbit sciatic nerve on a 1.5-T clinical MR system correlated with gross anatomy

This study was performed to investigate the feasibility and accuracy of magnetic resonance (MR) microneurography of the rabbit sciatic nerve on a 1.5-T clinical MR system by correlation with the gross anatomy. The 3D T2-weighted imaging (3D-T2WI), 3D T2-weighted imaging plus spectral presaturation with inversion recovery (SPIR), and T1-weighted imaging (T1WI) of the sciatic nerve in ten rabbits were performed on a 1.5-T MR system. The radiological anatomy of the sciatic nerve was observed and correlated with the gross anatomy. The anterior-posterior diameter of the sciatic nerve trunk was measured on 3D T2WI and on gross anatomy. The T1 and T2 relaxation times were also measured with multiecho spin echo and mixed sequence, respectively. The tibial nerve and peroneal nerve in the sciatic nerve trunk in all ten rabbits could be clearly displayed on T2WI and T2WI. The fine branches of the gastrocnemius nerve, posterior femoral cutaneous nerve, and the posterior gluteal nerve could be clearly depicted on T2WI. The T1 and T2 relaxation times of the sciatic nerves were 915 and 40 ms, respectively. The anterior-posterior diameter of sciatic nerve trunk was measured grossly, and on T2WI was 3.17 +/- 0.21 mm and 3.15 +/- 0.19 mm, respectively. There was no statistically significant difference (t = 0.768, P = 0.462). With the 1.5-T clinical MR system, the microneurography of the sciatic nerve could be revisualized, and the finer structure of the sciatic nerve trunk could be clearly and accurately delineated.

Bone marrow MR imaging as predictors of outcome in hemopoietic stem cell transplantation

The purpose of this study is to investigate the role of femoral marrow MR imaging as predictor of outcome for hemopoietic stem cell transplantation (HSCT) in beta-thalassemia major. MR imaging of the proximal femur, including T1- and T2-weighted spin echo and short-tau inversion recovery and in-phase and out-of-phase fast field echo images, was prospectively performed in 27 thalassemia major patients being prepared for HSCT. The area of red marrow and its percentage of the proximal femur were measured, and the presence of marrow hemosiderosis was assessed. Age-adjusted multivariate logistic regression was used to determine the relationship between red marrow area percentage and marrow hemosiderosis and HSCT outcome. Red area percentage were less in patients with successful (90.25 +/- 4.14%) compared to unsuccessful transplants (94.54% +/- 2.93%; p = 0.01). Red marrow area percentage correlated positively with duration of symptoms(r = 0.428, p = 0.026) and serum ferritin (r = 0.511, p = 0.006). In multivariate-adjusted logistic regression analyses, red marrow area percentage was significantly inversely associated with successful HSCT (OR = 1.383, 95% CI: 1.059-1.805, p = 0.005). Marrow hemosidersosis and duration of sympotms and serum ferritin were not associated with HSCT outcome(p = 0.174, 0.974, 0.762, respectively). Red marrow area percentage of proximal femur on MR imaging is a useful predictor of HSCT outcome.

Morphologic analysis of normal human lumbar dorsal root ganglion by 3D MR imaging

BACKGROUND AND PURPOSE

The dorsal root ganglion (DRG) of the spinal nerve has been considered a key structure in the mechanism of low-back pain and radicular symptoms. The purpose of this study was to clarify the normal morphologic features and variations of the lumbar DRGs in a healthy population by using 3D MR imaging.

METHODS

3D fast-field echo (FFE) with water selective excitation coronal MR images of lumbar spine obtained in 115 healthy volunteers were further reconstructed into a radial stack of 15 coronal images by using maximum intensity projection technique. The DRGs from L1 through L5 were assessed for the location, signal intensity, architecture, and dimensions.

RESULTS

Most DGRs were foraminal in location. Only 5.7% of the L5 DGRs were located intraspinally. The sizes of L1, L2, and L5 DRGs in men were larger than those in women (P < .05). The dimensions of the DRGs gradually increased from L1 to L5 (P < .0001). The biganglia (2 ganglial components) frequently occurred in the L4 and L3 DRGs, whereas the singular ganglion (1 ganglial component), in the L5 and L1 DRGs.

CONCLUSION

The normal anatomy and variants of the lumbar DRG could be better demonstrated by 3D MR imaging with water selective excitation technique. The relatively larger and more proximally located DRGs in the lower lumbar region may be more susceptible to compression. An appreciation of normal anatomy and variants of DRGs radiologically is helpful for the diagnosis and proper treatment for radiculopathy.

[Quantitative magnetic resonance (MR) imaging of bone marrow in leukemia]

BACKGROUND & OBJECTIVE

There were many studies on the relationship between magnetic resonance (MR) imaging of bone marrow and clinical laboratory variables of the patients with leukemia; however, few of them had separated lymphoid leukemia (LL) from myeloid leukemia (ML). The current study was designed to investigate the role of signal intensity ratio (SIR) of MR Imaging in the characteristic diagnosis and tumor burden evaluation in leukemia by separately measurement of spinal marrow SIR in LL and ML.

METHODS

Spinal marrow in 20 LL patients and 10 ML patients in initial consultant were examined with MR imaging. The diagnosis of leukemia in all the patients was proved by iliac marrow cytological examination. MR imaging of spinal marrow was performed with 0.5T super-conducting system. T1-weighted imaging with spin-echotechniques and T2-weighted imaging with turbo spin-echo techniques were performed. The SIR of spinal marrow to spinal cord in leukemia was calculated on midline sagittal T1-weighted imaging. Meanwhile,peripheral blood routine examination and bone marrow cytological examination was performed.

RESULTS

The SIR of spinal marrow in 20 LL patients and 10 ML patients were 0.72+/-0.11 and 0.73+/-0.11, respectively. There was no statistically significant difference between LL and ML(P=0.836). The SIR of spinal marrow in LL negatively correlated with the percentage of blast lymphocyte in marrow(r =-0.836,P= 0.000),while the SIR of spinal marrow in ML negatively correlated with the percentage of blast myelocyte in marrow (r=-0.673,P= 0.033).

CONCLUSION

The SIR of spinal marrow is limited in the characteristic diagnosis of leukemia because of its inability to differential LL from ML. The SIR of spinal marrow can be used to evaluate tumor burden in leukemia.

[Investigation of proximal femoral marrow with magnetic resonance imaging in recovered patients with severe acute respiratory syndrome]

OBJECTIVE

To determine the effect of corticosteroid treatment and severe acute respiratory syndrome (SARS) infection itself on the marrow conversion in the proximal femoral marrow in the recovered patients of health care workers with SARS.

METHODS

The distribution of proximal femoral marrow on MR imaging of 148 health care workers with recovered SARS including 106 cases treated with varied dosage of steroids and 42 cases without steroid, and 97 age and sex matched health adults as controls were observed. The index of marrow conversion (signal intensity of the femoral neck and intertrochanteric area divided by signal intensity of the greater trochanter multiplied by 100%) was quantitatively measured and compared between SARS patients treated with steroid and without steroid and the normal control group.

RESULTS

In 106 cases treated with steroid of the 148 health care workers, femoral head osteonecrosis was found in 4 cases, bilateral femoral marrow edema in 2 cases, femoral marrow infarction in 1 case. The index of marrow conversion in the normal controls, in SARS patients treated without and with steroids was (79.4 +/- 6.8)%, (86.9 +/- 7.4)%, (88.6 +/- 5.9)%, respectively. There was significantly statistical difference between groups (P < 0.05).

CONCLUSION

In addition to fat conversion in the proximal femoral marrow due to steroid treatment, the infection of SARS itself may promote an excessively conversion of the red marrow to yellow marrow of the femoral neck in SARS patients.

[Report on the investigation of lower extremity osteonecrosis with magnetic resonance imaging in recovered severe acute respiratory syndrome in Guangzhou]

OBJECTIVE

To report the occurrence of lower extremity avascular abnormalities in 124 cases of recovered severe acute respiratory syndrome (SARS) health care workers of four hospitals in Guangzhou and preliminary investigate the correlation with the treatment of steroid.

METHODS

124 health care workers with recovered SARS from four hospitals in Guangzhou were examined with MR imaging of the lower extremity including bilateral hips and knees. In 124 health care workers, 38 cases have not treated with steroid, while 86 cases have treated with varied dosage. The imaging protocol was consisted of screening and full examination. Coronal T1-weighted imaging and short tau inversion recovery sequence were defined as the screening examination. The full examination was defined as images from the screening examination plus three additional imaging sequences: transverse and coronal T2-weighted imaging and short tau inversion recovery sequence.

RESULTS

In 86 health care workers, 5 cases were found positive in the lower extremity. Osteonecrosis was found in 3 cases. One was involved in bilateral femoral head, and another was unilateral femoral head, and the remaining one was bilateral femoral heads and unilateral femoral condyle and tibial condyle. Bilateral femoral and tibial marrow edema were found in one case. Femoral infarction with significant calcification occurred in one health care worker. Logistic regression analysis indicated that the presence of avascular abnormalities was related with maximum daily dosage.

CONCLUSION

Osteonecrosis definitely exists in the minority of health care workers with recovered SARS in Guangzhou, who had treated with steroid. The maximum daily dosage of steroid may significantly influence on the occurrence of avascular abnormalities.