for many years , nuclear imaging techniques have been used to visualize disease - related changes in brain perfusion and glucose metabolism in neurodegenerative brain diseases .
were the first to report that under physiological steady state conditions , cerebral blood flow ( cbf ) is coupled to the level of cerebral oxygen ( cmro2 ) and glucose consumption ( sokoloff , 1977 ) .
leenders et al . measured rcbf and rcmro2 in patients with parkinson 's disease ( pd ) .
they showed an increase of regional blood flow and oxygen metabolism in the basal ganglia of the affected hemisphere in pd patients with predominantly unilateral disease ( leenders , and wolfson , 1984 ) . in the 1980s ,
a spect tracer , tcm - hexamethylpropyleneamine oxime ( tcm - hm - pao ) , was developed to detect cerebral blood flow with spect - imaging .
the pet tracer [ f]-fluorodeoxyglucose ( fdg ) allows the measurement of cerebral metabolic rate of glucose ( cmrglc ) .
regional differences in cerebral glucose metabolism have been reported in parkinsonian syndromes using univariate methods ( teune et al . , 2010 ) .
data - driven multivariate methods are increasingly used to examine disease - specific metabolic covariance patterns in parkinsonian syndromes ( ma et al .
this has improved our understanding of the pathophysiology of these diseases as well as our ability to diagnose patients at an earlier disease stage ( tang et al . , 2010a ) .
ma et al . reproduced this pd - related metabolic covariance pattern , using h2o pet scanning , indeed suggesting that cerebral blood flow and glucose metabolism are tightly coupled in pd patients ( ma et al . , 2007 ) .
however , in clinical practice , blood flow measurements with pet are not widely used because it is a demanding and time - consuming procedure , while spatial resolution of spect is less optimal .
recently , it has become possible to measure brain perfusion with a relatively new mr technique , pseudo - continuous arterial spin labeling ( pcasl ) .
it permits the noninvasive measurement of perfusion with mri by using a train of radio frequency ( rf ) pulses and magnetic field gradient pulses to achieve labeling of spins in flowing blood ( dai et al . , 2008 ; van osch et al . , 2009
ma et al . analyzed the expression of the existing pd - related metabolic covariance pattern in a small number of parkinsonian patients using perfusion mri ( continuous arterial spin labeling ) and concluded that perfusion mri can be used for accurate quantification of disease - related covariance patterns ( ma et al . , 2010 ) .
were the first to identify a pd - related perfusion covariance pattern ( melzer et al . , 2011 ) .
in this study we identified a pd - related perfusion and metabolic covariance pattern in the same patients using pcasl and fdg - pet imaging and assessed ( dis)similarities in the disease - related pattern between perfusion and metabolism in pd patients .
the study was approved by the medical ethics committee of the university medical center groningen .
voluntary written informed consent was obtained from each subject after verbal and written explanation of the study , in accordance with the declaration of helsinki .
this study aimed to include 17 healthy controls and 20 pd patients in which fdg - pet and different mr image modalities were to be recorded .
three pd patients appeared not to be mri proof ( due to dental implants , large artifacts on functional mri ) and in 2 pd patients pcasl was not correctly recorded due to technical issues . in the current analysis
we have 17 gender and age - matched healthy controls ( hc ) ( 5 females , 12 males ; mean age 61.5  years ) and 19 pd patients ( 6 females , 13 males ; mean age 63.9  years ) but only 14 pd patients ( 4 females , 10 males ; mean age 63.8  years ) who underwent both fdg - pet and pcasl .
pd patients had to fulfill the uk brain bank criteria for pd ( litvan et al . , 2003 ) .
healthy controls were not allowed to have first - degree family members with parkinsonism or dementia .
all subjects underwent mri and within 8  weeks an fdg - pet scan and two neuropsychological tests ( mini mental state examination ( mmse ) and frontal assessment battery ( fab ) ) and pd patients underwent examination using the unified parkinson s disease rating scale ( updrs ) part 3 : motor symptoms .
neuropsychological scores did not differ significantly between groups ( mean hc : mmse 29 , fab 17 ; mean pd ( 19 ) : mmse 29 , fab 16 , mean pd ( 14 ) : mmse 28 , fab 16 ) indicating that pd patients were non - demented .
pd patients had mild to moderate motor symptoms with hoehn & yahr stage : mean ( in both 19 and 14 groups ) 1 and standard deviation ( sd ) 1 vs 0.5 and a updrs part 3 : in both 19 and 14 groups mean 18 ; sd 7 .
antiparkinsonian medication was withheld for at least 12  hours and benzodiazepines were withheld 24  hours before mri and fdg - pet scanning .
mr imaging was performed on a 3  t mri scanner ( achieva 3 tesla , philips healthcare , best , the netherlands ) using a standard 8-channel sense head coil .
subjects were wearing ear protection and instructed to lie still with their eyes closed , and to avoid falling asleep .
pseudo - continuous labeling was performed by employing a train of hanning - shaped rf pulses ( tip angle 18 , duration 0.5  ms ) with an interpulse pause of 0.5  ms in combination with a balanced gradient scheme .
pcasl images were obtained in a dynamic mode of 2    30 volumes ( labeled and control ) with an echo time of 14  ms , repetition time ( tr ) of 4200  ms , 23 axial slices , field of view ( fov ) of 240  mm with an 80    80 matrix and an isotropic voxel size of 3    3    6  mm .
all 30 labeled and control volumes were first motion - corrected in spm8 ( functional imaging laboratory , running in matlab 7.10.0 ( r2010a , mathworks ) ) .
volumes were smoothed with an 8  mm full - width - at - half - maximum isotropic gaussian kernel ( fwhm ) .
( 2010 ) labeled and control images were filtered against a time - course extracted from a roi in white matter and cerebrospinal fluid ( csf ) drawn on a t1 image .
removal of signal from csf and white matter is motivated by the fact that these regions contain a relatively high proportion of physiological noise ( e.g. cardiac and respiratory cycles ) .
thereafter , labeled perfusion - weighted images were subtracted from control images , creating one mean pcasl image per subject .
fdg - pet imaging was performed in a 3d mode using a siemens biograph mct-64 pet scanner .
image acquisition was performed in a resting state with the subject 's eyes closed in a dimly lighted room with minimal auditory stimulation .
a 6-minute static frame was acquired starting 30  min after the injection of 200  mbq fdg in 4  ml saline .
the fdg - pet images were iteratively reconstructed using the osem algorithm with 3 iterations and 24 subsets on a matrix of 400    400 and smoothed with 5  mm fwhm .
no zoom was applied , resulting in images with an isotropic voxel - size of 2  mm with a specified resolution of 5  mm in the center of the field of view . scatter and attenuation corrections
a study - specific template of all mean pcasl images was spatially normalized to a standard brain pet template ( montreal neurological institute ; mni , supplied in spm8 ) and then used to spatially normalize the individual mean pcasl images .
an example of the mean pcasl images of seventeen healthy controls is shown in fig . 
fdg - pet images were directly spatially normalized to a pet template and then both were smoothed with 10  mm fwhm .
ssm / pca was applied using software written in - house , based on the methods of spetsieris and eidelberg ( 2011 ) .
the correctness of the in - house written script was verified in an earlier validation study of the already identified pd , msa and psp metabolic brain patterns ( teune et al . , 2010 ; spetsieris and eidelberg 2011 ) .
we performed both the analysis with the eidelberg software and our own software , which provided identical results .
a 35% threshold of the whole - brain intensity maximum was applied to remove out - of - brain voxels which results in a mask of mainly gray matter , followed by a log transformation ( spetsieris and eidelberg 2011 ) .
this gray matter mask was applied to the pcasl images without subsequent log transformation . after removing between - subject and between
a disease - related metabolic covariance pattern was determined by a linear combination of the selected principal components with the lowest aic ( akaike information criterion ) value in a stepwise regression procedure .
thereafter , a leave - one - out cross validation procedure was performed , providing an average estimate of the disease - related metabolic brain patterns and the error of this average per voxel . by dividing the average estimate by its standard error of the mean
the metabolic pd - related pattern ( pdrp - mct17hc19pd ) was thresholded at t  =  3.7 ( corresponding to p  =  0.001 ) assuming normality of data .
the perfusion brain pattern ( pdrp - pcasl17hc14pd ) was thresholded at t  =  2.5 ( corresponding to p  =  0.02 ) and overlaid onto a t1 mr template using mricron . for comparison purposes using the same hc and pd subjects , a second metabolic brain pattern ( pdrp - mct17hc14pd )
furthermore , for pdrp - mct17hc19pd , a leave - one - out cross validation was performed . for each subject left out , its subject score was calculated using the pattern obtained from the remaining subjects .
these subject scores were transformed into z - scores with respect to the healthy control population ( z - score with a mean of zero and a standard deviation of one ) and displayed in a scatter plot .
receiver - operating - characteristic ( roc ) curves were determined for the probability values of pd .
optimum cut - off probability values for classifying individual patients were calculated by identifying an inflection point on the roc curve that corresponded to the best combination of sensitivity and specificity .
patients were classified as correctly diagnosed if their probability value was higher than the cut - off value .
thereafter , we calculated sensitivity , specificity , and positive and negative predictive values ( ppv and npv respectively ) . to compare the present pdrp - mct17hc19pd using a high resolution mct camera with our previously published pd - related metabolic brain pattern using an hr+ camera ( pdrp - hr18hc20pd ) ( teune et al . , 2010 )
z - scores were calculated for the hc and pd subjects scanned on the mct camera by using the pdrp - hr18hc20pd as a reference and vice versa . moreover ,
subject scores of the pcasl images were calculated and transformed into z - scores with respect to the pcasl healthy control population using the pdrp - mct17hc19pd as a reference .
the study was approved by the medical ethics committee of the university medical center groningen .
voluntary written informed consent was obtained from each subject after verbal and written explanation of the study , in accordance with the declaration of helsinki .
this study aimed to include 17 healthy controls and 20 pd patients in which fdg - pet and different mr image modalities were to be recorded .
three pd patients appeared not to be mri proof ( due to dental implants , large artifacts on functional mri ) and in 2 pd patients pcasl was not correctly recorded due to technical issues . in the current analysis
we have 17 gender and age - matched healthy controls ( hc ) ( 5 females , 12 males ; mean age 61.5  years ) and 19 pd patients ( 6 females , 13 males ; mean age 63.9  years ) but only 14 pd patients ( 4 females , 10 males ; mean age 63.8  years ) who underwent both fdg - pet and pcasl .
pd patients had to fulfill the uk brain bank criteria for pd ( litvan et al . , 2003 ) .
healthy controls were not allowed to have first - degree family members with parkinsonism or dementia .
all subjects underwent mri and within 8  weeks an fdg - pet scan and two neuropsychological tests ( mini mental state examination ( mmse ) and frontal assessment battery ( fab ) ) and pd patients underwent examination using the unified parkinson s disease rating scale ( updrs ) part 3 : motor symptoms .
neuropsychological scores did not differ significantly between groups ( mean hc : mmse 29 , fab 17 ; mean pd ( 19 ) : mmse 29 , fab 16 , mean pd ( 14 ) : mmse 28 , fab 16 ) indicating that pd patients were non - demented .
pd patients had mild to moderate motor symptoms with hoehn & yahr stage : mean ( in both 19 and 14 groups ) 1 and standard deviation ( sd ) 1 vs 0.5 and a updrs part 3 : in both 19 and 14 groups mean 18 ; sd 7 .
antiparkinsonian medication was withheld for at least 12  hours and benzodiazepines were withheld 24  hours before mri and fdg - pet scanning .
mr imaging was performed on a 3  t mri scanner ( achieva 3 tesla , philips healthcare , best , the netherlands ) using a standard 8-channel sense head coil .
subjects were wearing ear protection and instructed to lie still with their eyes closed , and to avoid falling asleep .
pseudo - continuous labeling was performed by employing a train of hanning - shaped rf pulses ( tip angle 18 , duration 0.5  ms ) with an interpulse pause of 0.5  ms in combination with a balanced gradient scheme .
pcasl images were obtained in a dynamic mode of 2    30 volumes ( labeled and control ) with an echo time of 14  ms , repetition time ( tr ) of 4200  ms , 23 axial slices , field of view ( fov ) of 240  mm with an 80    80 matrix and an isotropic voxel size of 3    3    6  mm .
all 30 labeled and control volumes were first motion - corrected in spm8 ( functional imaging laboratory , running in matlab 7.10.0 ( r2010a , mathworks ) ) .
volumes were smoothed with an 8  mm full - width - at - half - maximum isotropic gaussian kernel ( fwhm ) .
( 2010 ) labeled and control images were filtered against a time - course extracted from a roi in white matter and cerebrospinal fluid ( csf ) drawn on a t1 image .
removal of signal from csf and white matter is motivated by the fact that these regions contain a relatively high proportion of physiological noise ( e.g. cardiac and respiratory cycles ) .
thereafter , labeled perfusion - weighted images were subtracted from control images , creating one mean pcasl image per subject .
fdg - pet imaging was performed in a 3d mode using a siemens biograph mct-64 pet scanner .
image acquisition was performed in a resting state with the subject 's eyes closed in a dimly lighted room with minimal auditory stimulation .
a 6-minute static frame was acquired starting 30  min after the injection of 200  mbq fdg in 4  ml saline .
the fdg - pet images were iteratively reconstructed using the osem algorithm with 3 iterations and 24 subsets on a matrix of 400    400 and smoothed with 5  mm fwhm .
no zoom was applied , resulting in images with an isotropic voxel - size of 2  mm with a specified resolution of 5  mm in the center of the field of view .
a study - specific template of all mean pcasl images was spatially normalized to a standard brain pet template ( montreal neurological institute ; mni , supplied in spm8 ) and then used to spatially normalize the individual mean pcasl images .
an example of the mean pcasl images of seventeen healthy controls is shown in fig . 
fdg - pet images were directly spatially normalized to a pet template and then both were smoothed with 10  mm fwhm .
ssm / pca was applied using software written in - house , based on the methods of spetsieris and eidelberg ( 2011 ) .
the correctness of the in - house written script was verified in an earlier validation study of the already identified pd , msa and psp metabolic brain patterns ( teune et al . , 2010 ; spetsieris and eidelberg 2011 ) .
we performed both the analysis with the eidelberg software and our own software , which provided identical results .
a 35% threshold of the whole - brain intensity maximum was applied to remove out - of - brain voxels which results in a mask of mainly gray matter , followed by a log transformation ( spetsieris and eidelberg 2011 ) .
this gray matter mask was applied to the pcasl images without subsequent log transformation . after removing between - subject and between
a disease - related metabolic covariance pattern was determined by a linear combination of the selected principal components with the lowest aic ( akaike information criterion ) value in a stepwise regression procedure .
thereafter , a leave - one - out cross validation procedure was performed , providing an average estimate of the disease - related metabolic brain patterns and the error of this average per voxel . by dividing the average estimate by its standard error of the mean
, a t - score was obtained . the metabolic pd - related pattern ( pdrp - mct17hc19pd )
was thresholded at t  =  3.7 ( corresponding to p  =  0.001 ) assuming normality of data .
the perfusion brain pattern ( pdrp - pcasl17hc14pd ) was thresholded at t  =  2.5 ( corresponding to p  =  0.02 ) and overlaid onto a t1 mr template using mricron . for comparison purposes using the same hc and pd subjects , a second metabolic brain pattern ( pdrp - mct17hc14pd )
furthermore , for pdrp - mct17hc19pd , a leave - one - out cross validation was performed . for each subject left out , its subject score was calculated using the pattern obtained from the remaining subjects .
these subject scores were transformed into z - scores with respect to the healthy control population ( z - score with a mean of zero and a standard deviation of one ) and displayed in a scatter plot .
receiver - operating - characteristic ( roc ) curves were determined for the probability values of pd .
optimum cut - off probability values for classifying individual patients were calculated by identifying an inflection point on the roc curve that corresponded to the best combination of sensitivity and specificity .
patients were classified as correctly diagnosed if their probability value was higher than the cut - off value .
thereafter , we calculated sensitivity , specificity , and positive and negative predictive values ( ppv and npv respectively ) . to compare the present pdrp - mct17hc19pd using a high resolution mct camera with our previously published pd - related metabolic brain pattern using an hr+ camera ( pdrp - hr18hc20pd ) ( teune et al
. , 2010 ) z - scores were calculated for the hc and pd subjects scanned on the mct camera by using the pdrp - hr18hc20pd as a reference and vice versa . moreover ,
subject scores of the pcasl images were calculated and transformed into z - scores with respect to the pcasl healthy control population using the pdrp - mct17hc19pd as a reference .
spatial covariance analysis was performed on fdg - pet scans and pcasl scans from pd patients .
the model with the lowest aic value and hereafter considered as disease - related was determined by a linear combination of principal components ( pcs ) 1 , and 2 with variance accounted for ( vaf ) of 27.1% ( 16.7 and 10.4% respectively ) for pdrp - mct17hc19pd ; pcs 1 , 2 , 4 , and 5 ( 37.7% vaf ( 18.4 , 8.9 , 5.6 and 4.8% respectively ) ) for pdrp - mct17hc14pd and pcs 3 and 5 ( 16.1% vaf ( 9.9 and 6.1% respectively ) ) for pdrp - pcasl17hc14pd .
a leave - one - out cross validation was subsequently performed resulting in disease - related patterns ( fig . 
the pd - related metabolic covariance pattern ( pdrp - mct17hc19pd ) was characterized by relatively decreased cortical metabolic activity in the temporal , posterior parietal , inferior parietal , lateral occipital , and prefrontal association cortices and sma .
relative increases were seen in the cerebellum and pons , thalamus and pallidum , sensorimotor cortex , limbic association cortex , paracentral lobule and left sma ( fig . 
the pd - related perfusion covariance pattern ( pdrp - pcasl17hc14pd ) was characterized by relatively decreased cortical perfusion activity bilaterally in the temporal , insular , posterior parietal , inferior parietal , lateral occipital and prefrontal association cortices .
relative increases were seen in the cerebellum and pons , right thalamus and pallidum , sensorimotor cortex , paracentral lobule and supplementary motor area ( sma ) ( fig . 
the pd - related metabolic brain pattern was shown using the same group as was used to determine the perfusion related pattern ( pdrp - mct17hc14pd ) .
the same regions were visible as in the pdrppdrp - mct17hc19pd , although at a lower statistical threshold .
the corresponding z - scores showed an overlap between the patients and healthy controls using pdrp - mct17hc19pd .
a cut - off value of z  =  0.31 resulted in a sensitivity of 94.7% , positive predictive value of 75% , specificity of 64.7% and negative predictive value of 91.7% for correct pd classification of an individual patient ( fig . 
the pdrp - mct17hc19pd 
 z - scores did not correlate with the updrs motor scores of pd patients ( spearman 's rho  =  0.294 and p  =  0.222 ) . the present pd - related metabolic brain pattern using a high - resolution mct ( pdrp - mct17hc19pd ) showed high reproducibility with our previously published pd - related metabolic brain pattern using an hr+ camera ( pdrp - hr18hc20pd ) ( fig . 
we computed the z - scores of the fdg and pcasl images of 17 healthy controls and 14 pd patients on the pdrp - mct17hc19pd ( fig .  2c ) and performed a correlation analysis .
in this study we identified pd - related perfusion and glucose metabolic brain patterns measured in the same patients .
the pd - related metabolic covariance brain pattern is in high accordance with previously described disease - related metabolic brain patterns in different cohorts in pd patients using standard clinical fdg - pet imaging ( ma et al .
this is probably related to the relatively short disease duration of the pd patients in comparison with previous reports with more advanced stage pd patients ( ma et al . , 2010 ; tang et al . , 2010b ) .
our disease - related pattern is comparable to the pd - related perfusion brain pattern described by melzer et al .
characterized by decreased perfusion in the posterior parieto - occipital cortex , and middle frontal gyri and preserved perfusion in the globus pallidus , putamen , anterior cingulate and post / precentral gyri ( melzer et al . , 2011 ) .
the most characteristic difference between our perfusion brain pattern and previous reports is the decrease of cerebral perfusion in the insular cortex on both sides in our data .
however , helmich et al . have shown that pd patients had decreased connectivity between the posterior putamen and various cortical regions contributing to the corticostriatal loop , including the insula using resting - state functional mri data ( helmich et al . ,
performing pcasl and fdg - pet imaging in the same patients enabled a comparison between both patterns .
z - scores of pcasl datasets onto the metabolic pattern correlated positively ( 0.5 ) with the z - scores of fdg datasets onto the metabolic pattern .
this value indicates that there is an overlap , however , not complete . as discussed above
, there was a larger perfusion decrease in the pd - related pattern in cortical regions including the insula than in the metabolic brain pattern .
another difference is the less pronounced increased perfusion in the basal ganglia in the perfusion - related pattern compared to the metabolic brain pattern .
it is known that mri head coils with multiple receive channels result in better signal to noise ratio in the cortex than in deeper brain structures .
our data shows that pcasl is a promising technique , which could be developed further as an additional measurement to improve image - based diagnosis of parkinsonian syndromes .
our results need to be replicated in larger samples , particularly in prospective validation samples and especially in pcasl data .
we identified pd - related perfusion and metabolic brain patterns using pcasl and fdg - pet in the same patients which were comparable with results of existing research . in this respect
, pcasl appears to be a promising addition in the early diagnosis of individual parkinsonian patients .
 introductionunder normal conditions , the spatial distribution of resting cerebral blood flow and cerebral metabolic rate of glucose are closely related . 
 a relatively new magnetic resonance ( mr ) technique , pseudo - continuous arterial spin labeling ( pcasl ) , can be used to measure regional brain perfusion . 
 we identified a parkinson 's disease ( pd)-related perfusion and metabolic covariance pattern in the same patients using pcasl and fdg - pet imaging and assessed ( dis)similarities in the disease - related pattern between perfusion and metabolism in pd patients.methodsnineteen pd patients and seventeen healthy controls underwent [ 18f]-fluorodeoxyglucose positron emission tomography ( fdg - pet ) imaging . 
 of 14 pd patients and all healthy controls pcasl - mri could be obtained . 
 data were analyzed using scaled subprofile model / principal component analysis ( ssm / pca).resultsunique parkinson 's disease - related perfusion and metabolic covariance patterns were identified using pcasl and fdg - pet in the same patients . 
 the pd - related metabolic covariance brain pattern is in high accordance with previously reports . 
 also our disease - related perfusion pattern is comparable to the earlier described perfusion pattern . 
 the most marked difference between our perfusion and metabolic patterns is the larger perfusion decrease in cortical regions including the insula.conclusionwe identified pd - related perfusion and metabolic brain patterns using pcasl and fdg - pet in the same patients which were comparable with results of existing research . in this respect 
 , pcasl appears to be a promising addition in the early diagnosis of individual parkinsonian patients . 
Introduction
Patients & methods
Subjects
Image acquisition and preprocessing
Statistical analysis
Results
Discussion
Conclusion
Disclosure