in this study , 20 healthy volunteers with no history of seizures , significant head trauma or other neurologic abnormalities , formed the normal control group .
fifteen were male and five were female , and their ages ranged from 24 to 38 ( mean , 29 ) years .
twenty - five patients with intractable temporal lobe epilepsy , whose mr imaging diagnosis was unilateral hippocampal sclerosis , comprised the patient group .
thirteen were male and 12 were female , and they were aged between 19 and 55 ( mean , 30 ) years .
an mr imaging diagnosis of hippocampal sclerosis was based on the presence of either unilateral atrophy or high t2 signal intensity of the hippocampus , or both , by visual assessment .
patients with bilateral hippocampal abnormalities or any other abnormalities in addition to hippocampal lesion were excluded .
for all mr imaging procedures , a clinical 1.5-t system ( signa advantage ; general electric medical systems , milwaukee , wi ) was used . for control subjects ,
the procedure involved conventional spin - echo t1-weighted sagittal and fast spin - echo t2-weighted axial and oblique coronal sequences . for patients , a t2-weighted fast spin - echo sequence with 3-mm - thick sections , and a t1-weighted 3-d spoiled gradient - echo ( spgr ) sequence with 1.5-mm - thick sections
the angle of oblique coronal imaging was perpendicular to the long axis of the hippocampus .
in - plane spatial resolution was approximately 1.01.0 mm ( matrix , 256256 ; fov , 25 cm ) .
single - voxel h-1 mrs was carried out immediately after acquisition of routine mr imaging , using the same 1.5-t unit . in each control
subject , four spectra were obtained from two different sizes of the volume of interest ( voi ) ( 6.0 cm = 2.02.01.5 cm , and 2.25 cm = 1.51.51.0 cm ) .
the voi included most of the hippocampal head and parts of its body , the amygdala , the parahippocampal gyrus and csf in the temporal horn .
in addition , spectra with voi of 1.0 cm ( 1.01.01.0 cm ) mostly confined to the hippocampal head were obtained in five of the 20 control subjects . in 25 patients ,
spectra were obtained with a voi of either 6.0 cm ( n = 14 ) or 2.25 cm ( n = 11 ) from the same area as that of control subjects . because the signal - to - noise ratio was low , spectra with a voi of 1.0 cm were not obtained in the patient group . to avoid potential magnetic susceptibility artifacts from the skull base and sphenoid sinus , and contamination by fat in the skull base ,
spectra were obtained using a point - resolved spin - echo spectroscopy ( press ) sequence with an echo time of 136 msec , repetition time of 1500 msec , and 128 scans . before spectroscopic measurements ,
field homogeneity was optimized over the selected voi by observing the h-1 mr signal of tissue water with a spatially selective press sequence . in most examinations ,
typical full widths at half maximum ( fwhm ) of 4 - 8hz were achieved .
the water signal was suppressed by a frequency - selective saturation pulse at the water resonance .
a sweep width of 1000 hz was used with data size of 1024 points , and only the second half of the echo was acquired .
following the zero - filling of 4096 points in all free induction decay ( fid ) data , exponential line broadening ( center : 0 msec , half time : 150 msec ) was performed before fourier transformation .
the metabolite peaks seen on mrs were assigned for n - acetyl aspartate ( naa ) at 2.0 ppm , for the creatine complex ( cr ) at 3.0 ppm , and for choline compound ( cho ) at 3.2 ppm . the metabolite ratios of naa / cho and naa / cr were calculated from the relative peak height measurements obtained on the workstation , and in both control subjects and patients , mean and standard deviation ( sd ) were calculated for those ratios . in control subjects ,
mean naa / cho and naa / cr ratios were compared between two different sizes of voi , and between the right and left sides .
ninety - five percent confidence levels ( 2 sds ) of naa / cho and naa / cr ratios in control subjects were used as threshold ( cut - off ) values to determine abnormal naa / cho and naa / cr ratios in patients ; either an naa / cho or naa / cr ratio below the threshold values was interpreted as abnormal . the ability of mrs to lateralize an epileptogenic lesion and to detect bilateral abnormalities was assessed using the visual mr imaging diagnosis as a standard of reference . when the abnormal side seen on mrs was concordant with that seen on mr imaging , lateralization was considered correct .
when mrs showed bilateral abnormalities , this was also considered indicative of correct lateralization , regardless of which side was shown by mrs to be more affected .
in this study , 20 healthy volunteers with no history of seizures , significant head trauma or other neurologic abnormalities , formed the normal control group .
fifteen were male and five were female , and their ages ranged from 24 to 38 ( mean , 29 ) years .
twenty - five patients with intractable temporal lobe epilepsy , whose mr imaging diagnosis was unilateral hippocampal sclerosis , comprised the patient group .
thirteen were male and 12 were female , and they were aged between 19 and 55 ( mean , 30 ) years .
an mr imaging diagnosis of hippocampal sclerosis was based on the presence of either unilateral atrophy or high t2 signal intensity of the hippocampus , or both , by visual assessment .
patients with bilateral hippocampal abnormalities or any other abnormalities in addition to hippocampal lesion were excluded .
for all mr imaging procedures , a clinical 1.5-t system ( signa advantage ; general electric medical systems , milwaukee , wi ) was used . for control subjects ,
the procedure involved conventional spin - echo t1-weighted sagittal and fast spin - echo t2-weighted axial and oblique coronal sequences . for patients , a t2-weighted fast spin - echo sequence with 3-mm - thick sections , and a t1-weighted 3-d spoiled gradient - echo ( spgr ) sequence with 1.5-mm - thick sections
the angle of oblique coronal imaging was perpendicular to the long axis of the hippocampus .
in - plane spatial resolution was approximately 1.01.0 mm ( matrix , 256256 ; fov , 25 cm ) .
single - voxel h-1 mrs was carried out immediately after acquisition of routine mr imaging , using the same 1.5-t unit . in each control
subject , four spectra were obtained from two different sizes of the volume of interest ( voi ) ( 6.0 cm = 2.02.01.5 cm , and 2.25 cm = 1.51.51.0 cm ) .
the voi included most of the hippocampal head and parts of its body , the amygdala , the parahippocampal gyrus and csf in the temporal horn .
in addition , spectra with voi of 1.0 cm ( 1.01.01.0 cm ) mostly confined to the hippocampal head were obtained in five of the 20 control subjects . in 25 patients
, spectra were obtained with a voi of either 6.0 cm ( n = 14 ) or 2.25 cm ( n = 11 ) from the same area as that of control subjects . because the signal - to - noise ratio was low , spectra with a voi of 1.0 cm were not obtained in the patient group . to avoid potential magnetic susceptibility artifacts from the skull base and sphenoid sinus , and contamination by fat in the skull base ,
spectra were obtained using a point - resolved spin - echo spectroscopy ( press ) sequence with an echo time of 136 msec , repetition time of 1500 msec , and 128 scans . before spectroscopic measurements ,
field homogeneity was optimized over the selected voi by observing the h-1 mr signal of tissue water with a spatially selective press sequence . in most examinations ,
typical full widths at half maximum ( fwhm ) of 4 - 8hz were achieved .
the water signal was suppressed by a frequency - selective saturation pulse at the water resonance .
a sweep width of 1000 hz was used with data size of 1024 points , and only the second half of the echo was acquired .
following the zero - filling of 4096 points in all free induction decay ( fid ) data , exponential line broadening ( center : 0 msec , half time : 150 msec ) was performed before fourier transformation .
the metabolite peaks seen on mrs were assigned for n - acetyl aspartate ( naa ) at 2.0 ppm , for the creatine complex ( cr ) at 3.0 ppm , and for choline compound ( cho ) at 3.2 ppm .
the metabolite ratios of naa / cho and naa / cr were calculated from the relative peak height measurements obtained on the workstation , and in both control subjects and patients , mean and standard deviation ( sd ) were calculated for those ratios . in control subjects ,
mean naa / cho and naa / cr ratios were compared between two different sizes of voi , and between the right and left sides .
ninety - five percent confidence levels ( 2 sds ) of naa / cho and naa / cr ratios in control subjects were used as threshold ( cut - off ) values to determine abnormal naa / cho and naa / cr ratios in patients ; either an naa / cho or naa / cr ratio below the threshold values was interpreted as abnormal .
the ability of mrs to lateralize an epileptogenic lesion and to detect bilateral abnormalities was assessed using the visual mr imaging diagnosis as a standard of reference . when the abnormal side seen on mrs was concordant with that seen on mr imaging , lateralization was considered correct .
when mrs showed bilateral abnormalities , this was also considered indicative of correct lateralization , regardless of which side was shown by mrs to be more affected .
in 20 control subjects , mr imaging revealed symmetry in the size and signal intensity of both hippocampi .
representative spectra with three different sizes of voi from the hippocampus of control subjects are shown in fig .
, signal - to - noise ratios of metabolites decreased as the voi was reduced . in control subjects , the naa peak was usually slightly higher than the cho and cr peaks . with a voi of 6.0 cm ,
the naa / cho ratio was 1.100.27 ( meansd ) and 1.100.18 on the right and left sides , respectively , whereas with a voi of 2.25 cm , this ratio was 1.200.42 and 1.100.29 , respectively ( table 1 ) . with a voi of 6.0 cm , the naa / cr ratio was 1.300.28 and 1.300.22 on the right and left sides , respectively , whereas with a voi of 2.25 cm , the ratio was 1.400.52 and 1.400.77 , respectively ( table 2 ) .
there were no statistically significant differences in either naa / cho or naa / cr ratios between sides , and between different sizes of voi . in five control subjects who underwent mrs with a voi of 1.0 cm , signal - to - noise ratios of the metabolites were lower than those of the larger voi , making it difficult to calculate the metabolite ratios .
regardless of voi size ( i.e. , 6.0 cm or 2.25 cm ) , the naa / cho ratio in control subjects was greater than 0.8 and the naa / cr ratio was greater than 1.0 , with a 95% confidence level .
representative spectra from the affected hippocamus and contralateral normal - appearing hippocampus are illustrated in fig .
the naa / cho ratio was 0.810.13 ( meansd ) on the affected side and 0.900.19 ( meansd ) on the contralateral side . with a voi of 2.25 cm , this ratio was 0.780.22 ( meansd ) on the affected side and 0.800.15 ( meansd ) on the contralateral side . with a voi of 6.0 cm , the naa / cr ratio was 0.990.14 ( meansd ) on the affected side and
1.200.27 ( meansd ) on the contralateral side and with a voi of 2.25 cm , the ratio was 0.930.15 ( meansd ) on the affected side and 1.100.25 ( meansd ) on the contralateral side .
naa / cho and naa / cr ratios on the affected side were significantly lower than those on the contralateral side in patients , and than those of control subjects ( p < .05 ) ( tables 3 , 4 ) . on the contralateral side , these ratios were lower in patients than in control subjects , but the differences were not statistically significant .
the distributions of naa / cho and naa / cr ratios on the affected and contralateral sides in both patients and control subjects are shown in figs . 3 and 4 .
. the correct lateralization rate of mrs was significantly higher when the naa / cho ratio was used as a cut - off value than when the naa / cr ratio was used ( 64% versus 48% , p < .05 ) .
the correct lateralization rate of mrs was lower with a voi of 6.0 cm than with one of 2.25 cm ( 64% versus 82% , p < .05 ) .
mrs was interpreted as bilaterally normal ( i.e. , false negative ) in 28% of cases ( 7/25 ) ( fig .
6 ) ; 24% ( 6/25 ) on the basis of an abnormal naa / cho ratio , and 20% ( 5/25 ) on the basis of an abnormal naa / cr ratio .
in 20 control subjects , mr imaging revealed symmetry in the size and signal intensity of both hippocampi .
representative spectra with three different sizes of voi from the hippocampus of control subjects are shown in fig .
, signal - to - noise ratios of metabolites decreased as the voi was reduced . in control subjects , the naa peak was usually slightly higher than the cho and cr peaks . with a voi of 6.0 cm ,
the naa / cho ratio was 1.100.27 ( meansd ) and 1.100.18 on the right and left sides , respectively , whereas with a voi of 2.25 cm , this ratio was 1.200.42 and 1.100.29 , respectively ( table 1 ) . with a voi of 6.0 cm , the naa / cr ratio was 1.300.28 and 1.300.22 on the right and left sides , respectively , whereas with a voi of 2.25 cm , the ratio was 1.400.52 and 1.400.77 , respectively ( table 2 ) .
there were no statistically significant differences in either naa / cho or naa / cr ratios between sides , and between different sizes of voi . in five control subjects who underwent mrs with a voi of 1.0 cm , signal - to - noise ratios of the metabolites were lower than those of the larger voi , making it difficult to calculate the metabolite ratios .
regardless of voi size ( i.e. , 6.0 cm or 2.25 cm ) , the naa / cho ratio in control subjects was greater than 0.8 and the naa / cr ratio was greater than 1.0 , with a 95% confidence level .
representative spectra from the affected hippocamus and contralateral normal - appearing hippocampus are illustrated in fig .
the naa / cho ratio was 0.810.13 ( meansd ) on the affected side and 0.900.19 ( meansd ) on the contralateral side . with a voi of 2.25 cm , this ratio was 0.780.22 ( meansd ) on the affected side and 0.800.15 ( meansd ) on the contralateral side . with a voi of 6.0 cm , the naa / cr ratio was 0.990.14 ( meansd ) on the affected side and 1.200.27 ( meansd ) on the contralateral side and with a voi of 2.25 cm , the ratio was 0.930.15 ( meansd ) on the affected side and 1.100.25 ( meansd ) on the contralateral side .
naa / cho and naa / cr ratios on the affected side were significantly lower than those on the contralateral side in patients , and than those of control subjects ( p < .05 ) ( tables 3 , 4 ) . on the contralateral side , these ratios were lower in patients than in control subjects , but the differences were not statistically significant .
the distributions of naa / cho and naa / cr ratios on the affected and contralateral sides in both patients and control subjects are shown in figs . 3 and 4 .
. the correct lateralization rate of mrs was significantly higher when the naa / cho ratio was used as a cut - off value than when the naa / cr ratio was used ( 64% versus 48% , p < .05 ) . the correct lateralization rate of mrs was lower with a voi of 6.0 cm than with one of 2.25 cm ( 64% versus 82% , p < .05 ) .
mrs was interpreted as bilaterally normal ( i.e. , false negative ) in 28% of cases ( 7/25 ) ( fig .
6 ) ; 24% ( 6/25 ) on the basis of an abnormal naa / cho ratio , and 20% ( 5/25 ) on the basis of an abnormal naa / cr ratio .
in control subjects , naa concentration and naa / cho and naa / cr ratios in the temporal lobe were significantly lower than in other regions of the brain such as the frontal lobe , parietal lobe or thalamus ( 10 , 11 ) . because of this regional variation in metabolite concentrations in normal brain ,
it is important for lateralization of the epileptogenic foci , that mrs findings should be compared between anatomically similar regions .
compared with other regions of the brain , water line width of the temporal lobe was occasionally greater , a fact presumably attributable to the magnetic susceptibility effect arising from the air - tissue interface of the petrous air cells .
this increased line width may give rise to significantly poor resolution , insufficient water suppression and low signal - to - noise ratios , and may be one of the factors which limits the applicability of h-1 mrs to temporal lobe epilepsy .
signal - to - noise ratios can be improved by use of the press sequence , which is more sensitive than steam ( 12 ) , and this is the reason why we used this sequence rather than steam . in our study , mean naa / cho and naa / cr ratios of control subjects were 1.10 - 1.20 and 1.30 - 1.40 , respectively with no difference between sides .
there were no significant differences in either naa / cho or naa / cr ratios between voi sizes of 2.25 cm and 6.0 cm , and on the basis of our results , we used an naa / cho ratio lower than 0.8 , and naa / cr lower than 1.0 , as cut - off values .
recent preliminary reports of single - voxel mrs have described promising but variable results in the evaluation of mesial temporal lobe epilepsy .
most mrs studies in patients with this condition have shown a decreased in naa , naa / cr , and/or naa / cho+cr values ( 13 - 16 ) .
some studies showed decreased naa only , without changes in cr or cho ( 17 , 18 ) , whereas others reported increase in both cr and cho ( 7 , 13 ) .
common to all studies is lower naa values found in affected temporal lobes of patients than in control subjects . in that naa / cho or naa / cr ratios were lower in the affected hippocampus of patients with hippocampal sclerosis than in normal control subjects , the results of our study are consistent with those of others ( 13 - 16 ) . a reduction in naa / cho or naa / cr can be interpreted as either decreased naa , reflecting neuronal loss , or increased cho or cr , presumably reflecting gliosis ( 7 , 19 ) , or both . in our study ,
mean naa / cho and naa / cr ratios in affected hippocampus were significantly lower than those in control subjects , and on the contralateral side , mrs correctly lateralized the lesion in only 72% of cases ( 18/25 ) . in 28% ( 7/25 ) , mrs appeared normal ( i.e. , false positive ) .
this low concordance rate of 72% between mri and mrs might be mainly due to the partial volume averaging effect resulting from the fact that a relatively large voi contained a small part of the atrophied hippocampus and a large portion of adjacent tissue .
the correct lateralization rate was lower with a voi of 6.0 cm than with one of 2.25 cm ( 64% versus 82% ) , a finding which appears to support the explanation provided by the partial volume averaging effect .
this effect may be reduced by using two - dimensional chemical shift imaging , which allows sampling of a smaller voi . in our study , the signal - to - noise ratio of mr spectra obtained with a voi of 1 cm in five volunteers was too low to be analyzed , showing that two - dimensional chemical shift imaging was necessary .
in some patients with hippocampal sclerosis in whom a voi of either 6.0 cm or 2.25 cm encompassed not only the hippocampus but also adjacent temporal lobe structures , mrs demonstrated markedly decreased naa / cho or naa / cr ratios , or both .
this can hardly be explained by loss or damage of hippocampal neurons only , and likely reflects the widespread damage found in the temporal lobe of these patients .
this finding is supported by pathologic studies which showed that neuronal loss and reactive gliosis often extended beyond the hippocampus ( 1 ) . in our study ,
findings relating to the contralateral hippocampus in patients with hippocampal sclerosis differ from those described in other reports ( 7 , 20 ) .
a previous study stated that the contralateral hippocampus of patients with temporal lobe epilepsy showed mrs features similar to those in control subjects ( 20 ) .
( 7 ) , however , reported that naa and cho levels , and naa / cho+cr ratios were significantly lower in the contralateral hippocampus of patients with temporal lobe epilepsy than in control subjects .
they also found bilateral abnormalities in 40% of cases ( 10/25 ) , as seen on mrs .
this finding is consistent with the result of a previous study in which bilateral pathology was present in up to 50% of patients with temporal lobe epilepsy ( 21 ) . even though the significance of bilateral abnormalities is not fully understood , the demonstration of their existence is important if the neurobiology and pathology of epilepsy are to be understood and the patients clinically evaluated .
it is not clear how the presence of contralateral abnormalities may affect the outcome of temporal lobe surgery . in our study ,
bilateral abnormalities were seen on mrs in 24% of cases ( 6/25 ) , and although the differences were not statistically significant , mean naa / cho and naa / cr ratios of the contralateral hippocampus in the patients with hippocampal sclerosis were lower than those of control subjects
. these varied results might be due to selection bias and the small sample sizes of the studies .
we think that a limitation of our study is the matter of patient selection ; in only nine was hippocampal sclerosis pathologically proven , and the mri diagnosis of unilateral hippocampal sclerosis was based on visual evaluation only .
most previous in vivo mrs studies reported the ratios of metabolite intensities , often using the cr value as an internal reference . in our control
subject data , however , cr and cho intensities varied , the former showing great variation .
furthermore , the correct lateralization rate of hippocampal sclerosis , and the detection rate of bilateral abnormalities were higher when based on naa / cho ratio than on the naa / cr ratio ( 64% versus 48% ) . this might be because cho was higher than cr , secondary to gliosis , although the exact cause is not certain . in conclusion ,
single - voxel h-1 mrs is an useful and promising diagnostic tool in the evaluation of temporal lobe epilepsy , particularly for the detection of bilateral abnormalities .
however , current mrs with semiquantitation using metabolite ratios is of limited value for accurate lateralization of the epileptogenic focus in hippocampal sclerosis . to improve the diagnostic accuracy of h-1 mrs , data acquisition with smaller voxel size but with a higher signal - to - noise ratio , and measurement of the absolute amount of metabolites ,
 objectivethe purpose of our study was to determine the ability of h-1 mr spectroscopy ( mrs ) to lateralize the lesion in patients with hippocampal sclerosis.materials and methodstwenty healthy volunteers and 25 patients with intractable temporal lobe epilepsy whose mr imaging diagnosis was unilateral hippocampal sclerosis were included . 
 this diagnosis was based on the presence of unilateral atrophy and/or high t2 signal intensity of the hippocampus . 
 single - voxel h-1 mrs was carried out on a 1.5-t unit using press sequence ( te , 136 msec ) . 
 spectra were obtained from hippocampal areas bilaterally with volumes of interest ( vois ) of 6.0 cm3 and 2.25 cm3 in healthy volunteers , and of either 6.0 cm3 ( n = 14 ) or 2.25 cm3 ( n = 11 ) in patients . 
 metabolite ratios of naa / cho and naa / cr were calculated from relative peak height measurements . 
 the capability of mrs to lateralize the lesion and to detect bilateral abnormalities was compared with mr imaging diagnosis as a standard of reference.resultsin healthy volunteers , naa / cho and naa / cr ratios were greater than 0.8 and 1.0 , respectively . in patients , 
 the mean values of these ratios were significantly lower on the lesion side than on the contralateral side , and lower than those of healthy volunteers ( p < .05 ) . 
 the overall correct lateralization rate of mrs was 72% ( 18/25 ) ; this rate was lower with a voi of 6.0 cm3 than of 2.25 cm3 ( 64% versus 82% , p < .05 ) . 
 bilateral abnormalities on mrs were found in 24% ( 6/25 ) of cases.conclusionalthough its rate of correct lateralization is low , single - voxel h-1 mrs is a useful and promising diagnostic tool in the evaluation of hippocampal sclerosis , particularly for the detection of bilateral abnormalities . to improve the diagnostic accuracy of h-1 mrs , further investigation , including the use of a smaller voi and measurement of the absolute amount of metabolites , are needed . 
MATERIALS AND METHODS
Subjects
MRI and MRS techniques
Data evaluation
RESULTS
Control subjects
Epilepsy patients
DISCUSSION