manganese enhanced mri: a method to assess
MANGANESE ENHANCED MRI: A METHOD TO ASSESS PUTATIVE PHYSIOLOGICAL MARKERS OF TINNITUS IN RODENTS Amandine Laboulais 1 2, Maïda Cardoso 1, Sergio Gonzalez 2, Gaëlle Naert 2, Yves Cazals 3, Arnaud J. Noreña 3, Sylvie Cosnier-Pucheu 2, Celia Belline 2, Christophe Goze Bac 1
T1-weighted 2D spin echo images were acquired using 9,4T VNMRS horizontal bore scanner. Imaging parameters were, Field of view: 60x30mm, matrix size: 512x256, axial slices: 1mm, slice thickness: no gap, TR=500ms, TE= 12,63ms, averages=8, number of slice=16, scan time=17m45s.
Two analysis methods are used: Signal to Noise Ratio (SNR) and T2-rate cartography.
T2--rate cartography: Using homebuilt program developed under Matlab interface, we determine the relaxation rate of tissues. Applying 1/T2 formula voxel by voxel to obtain RGB cartography. For each tissue, the higher is the ratio between first and second echo is, the faster is the relaxation rate.
The protocol based on MEMRI technique uses an transtympanic manganese injection in rats with the salicylate model of tinnitus induction.
Relaxation rate formula 1 1 𝑒𝑐ℎ𝑜1 = log 𝑇2 𝑇𝐸 𝑒𝑐ℎ𝑜2
Salicylate-induced tinnitus model Acclimatation (5 days)
Day 1
Day 2
Day 3
Day 4
Day 5
5 animals / group
PERITONEAL INJECTIONS Sodium Salicylate IP 350 mg/Kg 9,4T VNMRJ INTRATYMPANIC horizontal bore INJECTION 24h before MRI scanner (Varian MnCl2 TT 0,2 mmol/Kg Inc)
40
46
38
44
36
42
34
38 36 32 30
1/T2 rate cartography (RGB colormap) superimposed over T1-weighted MR image
Signal Noise Ratio (SNR) Comparison of MnCl2 uptake (signal to noise ratio) in the region of interests of the auditory system, 24h after MnCl2 administration via intratympanic injection in salicylate treated group (n=5) and in control group (n=5).
muscle
b
c d
a
T1-weighted MR images of lower to upper level of rat brain stem after transtympanic administration of MnCl2 Normalized SNR in different auditory structures between salicylate treated and control rats
32 30
0.3
Total voxels = 2993
0.3
28 Total voxels = 3969
0.25
0.25 0.2
0.2
0.15
0.15 0.1
0.1
0.05
0.05 0 25 30 35 40 45 50 Relaxation Rate Values
0 25 30 35 40 45 50 Relaxation Rate Values
1/T2 rate cartography results (up) and normalized histograms of cartography 1/T2 repartition Voxels (down) : on the left ( control rat), on the right (salicylate treated rat).
RESULTS
e
ABR Animals with threshold shift strictly above 40dB at 16kHz in one ear are excluded
42
28
muscle
46
48
40
Signal Noise Ratio (SNR):
Mn2+ uptake measure for signal to noise ration SNR in the regions of interest of the auditory system including cochlea (a), cochlear nerve (b), cochlear nucleus (c), superior olivary complex (d) and inferior colliculus (e).
48
44
34
SNR is defined as the mean MRI signal intensity of the ROI divided by the standard deviation of the noise. To correct for possible inhomogeneity between animals, the SNRs were normalized with mean MRI signal intensity of muscle.
50
50
Manganese-Enhanced MR Image analysis
MATERIALS AND METHODS
T2-rate cartography
1/T2 rate (s-1)
The present study was designed to show physiopathological markers of tinnitus in rodents. The Manganese Enhanced MRI or MEMRI technique was used. The use of manganese chloride as an MRI contrast agent enables to follow brain neuronal activity. In fact, paramagnetic manganese ions (Mn2+) enter excitable cells using some of the same transport system as Ca2+ and bind to a number of intracellular sites.
MRI data acquisition
An enhancement of the SNR is observed in the region where Mn2+ is more accumulated, specifically in auditory structures, after salicylate treatment, suggesting putative tinnitus.
Normalized Repartition Voxels
Tinnitus is an auditory phantom sensation (crackling, humming, whistling) experienced in absence of an external stimulus. This common disorder affects 10-15% of the population at one time or another in life. It creates discomfort sometimes associated with pain. The prevalence of tinnitus shows a worrying growth curve. The new lifestyles of developed and emerging countries (exposure to noise, urbanization, …) accelerate this trend and turn it a major public health problem.
T1-weighted MRI images are collected in order to investigate the specific areas activated in presence of tinnitus or not.
Normalized Repartition Voxels
INTRODUCTION
Charles Coulomb Laboratory (L2C-BioNanoNMRI team), UMR 5221 Centre National de la Recherche Scientifique – Université de Montpellier, France 2 CILcare SAS, Advanced solution for drug development in hearing disorder, Montpellier, France 3 Laboratoire de Neurosciences integratives et Adaptives (UMR 7260), Aix-Marseille Université and CNRS, Marseille, France
1/T2 rate (s-1)
1
A higher relaxation rate in auditory structures is observed in salicylate treated rats. The relaxation rate of MnCl2 is higher compared to body tissues. Moreover, histograms confirm higher relaxation rate values and total voxels for treated rats. Thus, in salicylate treated rats, the RGB cartography and histograms bring out MnCl2 concentration, suggesting putative tinnitus.
CONCLUSION SNR and T2 rate cartography results focus on higher MnCl2 concentration in salicylate treated rats. Its usefulness awaits full quantization (T2-rate cartography) and comparison with classical SNR in order to validate its efficacy. Manganese-enhanced MRI seems a suitable tool for evaluating tinnitus presence in rodents.
T1-weighted 2D spin echo images were acquired using 9,4T VNMRS horizontal bore scanner. Imaging parameters were, Field of view: 60x30mm, matrix size: 512x256, axial slices: 1mm, slice thickness: no gap, TR=500ms, TE= 12,63ms, averages=8, number of slice=16, scan time=17m45s.
Two analysis methods are used: Signal to Noise Ratio (SNR) and T2-rate cartography.
T2--rate cartography: Using homebuilt program developed under Matlab interface, we determine the relaxation rate of tissues. Applying 1/T2 formula voxel by voxel to obtain RGB cartography. For each tissue, the higher is the ratio between first and second echo is, the faster is the relaxation rate.
The protocol based on MEMRI technique uses an transtympanic manganese injection in rats with the salicylate model of tinnitus induction.
Relaxation rate formula 1 1 𝑒𝑐ℎ𝑜1 = log 𝑇2 𝑇𝐸 𝑒𝑐ℎ𝑜2
Salicylate-induced tinnitus model Acclimatation (5 days)
Day 1
Day 2
Day 3
Day 4
Day 5
5 animals / group
PERITONEAL INJECTIONS Sodium Salicylate IP 350 mg/Kg 9,4T VNMRJ INTRATYMPANIC horizontal bore INJECTION 24h before MRI scanner (Varian MnCl2 TT 0,2 mmol/Kg Inc)
40
46
38
44
36
42
34
38 36 32 30
1/T2 rate cartography (RGB colormap) superimposed over T1-weighted MR image
Signal Noise Ratio (SNR) Comparison of MnCl2 uptake (signal to noise ratio) in the region of interests of the auditory system, 24h after MnCl2 administration via intratympanic injection in salicylate treated group (n=5) and in control group (n=5).
muscle
b
c d
a
T1-weighted MR images of lower to upper level of rat brain stem after transtympanic administration of MnCl2 Normalized SNR in different auditory structures between salicylate treated and control rats
32 30
0.3
Total voxels = 2993
0.3
28 Total voxels = 3969
0.25
0.25 0.2
0.2
0.15
0.15 0.1
0.1
0.05
0.05 0 25 30 35 40 45 50 Relaxation Rate Values
0 25 30 35 40 45 50 Relaxation Rate Values
1/T2 rate cartography results (up) and normalized histograms of cartography 1/T2 repartition Voxels (down) : on the left ( control rat), on the right (salicylate treated rat).
RESULTS
e
ABR Animals with threshold shift strictly above 40dB at 16kHz in one ear are excluded
42
28
muscle
46
48
40
Signal Noise Ratio (SNR):
Mn2+ uptake measure for signal to noise ration SNR in the regions of interest of the auditory system including cochlea (a), cochlear nerve (b), cochlear nucleus (c), superior olivary complex (d) and inferior colliculus (e).
48
44
34
SNR is defined as the mean MRI signal intensity of the ROI divided by the standard deviation of the noise. To correct for possible inhomogeneity between animals, the SNRs were normalized with mean MRI signal intensity of muscle.
50
50
Manganese-Enhanced MR Image analysis
MATERIALS AND METHODS
T2-rate cartography
1/T2 rate (s-1)
The present study was designed to show physiopathological markers of tinnitus in rodents. The Manganese Enhanced MRI or MEMRI technique was used. The use of manganese chloride as an MRI contrast agent enables to follow brain neuronal activity. In fact, paramagnetic manganese ions (Mn2+) enter excitable cells using some of the same transport system as Ca2+ and bind to a number of intracellular sites.
MRI data acquisition
An enhancement of the SNR is observed in the region where Mn2+ is more accumulated, specifically in auditory structures, after salicylate treatment, suggesting putative tinnitus.
Normalized Repartition Voxels
Tinnitus is an auditory phantom sensation (crackling, humming, whistling) experienced in absence of an external stimulus. This common disorder affects 10-15% of the population at one time or another in life. It creates discomfort sometimes associated with pain. The prevalence of tinnitus shows a worrying growth curve. The new lifestyles of developed and emerging countries (exposure to noise, urbanization, …) accelerate this trend and turn it a major public health problem.
T1-weighted MRI images are collected in order to investigate the specific areas activated in presence of tinnitus or not.
Normalized Repartition Voxels
INTRODUCTION
Charles Coulomb Laboratory (L2C-BioNanoNMRI team), UMR 5221 Centre National de la Recherche Scientifique – Université de Montpellier, France 2 CILcare SAS, Advanced solution for drug development in hearing disorder, Montpellier, France 3 Laboratoire de Neurosciences integratives et Adaptives (UMR 7260), Aix-Marseille Université and CNRS, Marseille, France
1/T2 rate (s-1)
1
A higher relaxation rate in auditory structures is observed in salicylate treated rats. The relaxation rate of MnCl2 is higher compared to body tissues. Moreover, histograms confirm higher relaxation rate values and total voxels for treated rats. Thus, in salicylate treated rats, the RGB cartography and histograms bring out MnCl2 concentration, suggesting putative tinnitus.
CONCLUSION SNR and T2 rate cartography results focus on higher MnCl2 concentration in salicylate treated rats. Its usefulness awaits full quantization (T2-rate cartography) and comparison with classical SNR in order to validate its efficacy. Manganese-enhanced MRI seems a suitable tool for evaluating tinnitus presence in rodents.
