University of Western Ontario, London, Ontario, Canada
Roberts Research Institute, London, Ontario, Canada
University of Western Ontario, London, Ontario, Canada
St Joseph's Health Centre, London, Ontario, Canada
Correspondence: Professor P.C.Williamson, Department of Psychiatry, London Health Science Centre, University Campus, Rm IONI5, London, Ontario, Canada N6A 5A5
Declaration of interest This work was funded by the Canadian Institute of Health Research Grant MT-1078.
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aims In this 4.0 Tesla 31P-MRS study of people with schizophrenia, membrane phospholipid metabolism was examined in brain regions previously inaccessible due to their small volumes.
Method Three-dimensional chemical-shift imaging (3DCSI) examined 15 cc volumes in 12 brain regions in 11 people with chronic schizophrenia and 11 healthy control volunteers.
Results Glycerophosphoethanolamine was decreased in the anterior cingulate, right prefrontal cortex and left thalamus, but increased in the left hippocampus and cerebellum in those with schizophrenia. Phosphoethanolamine and glycerophosphocholine were decreased in the right prefrontal region and phosphocholine was decreased in the anterior cingulate. No significant difference in membrane phospholipid levels existed between groups in the parieto-occipital and posterior cingulate regions.
Conclusions Altered membrane phospholipid metabolism was demonstrated in all regions implicated in schizophrenia.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
METHOD |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
The healthy volunteers were recruited from the community by advertisement and were assessed by a psychiatrist (P.C.W., Y.S.) with the SCID. Controls were of comparable age, gender, handedness and parental education levels. No patients or controls had a history of head injury, drug or alcohol misuse or serious medical illnesses.
1H-MRI
All experiments were performed on a 4.0 Tesla (Varian/Siemens/Unity-INOVA)
whole-body magnetic resonance scanner operating at 170.3 MHz. A single-tuned,
1H quadrature hybrid-birdcage volume headcoil was used for shimming
and imaging. Subjects were positioned supine with their heads secured in a
plexiglas cradle and a 10 x 10 x 6 cm (6 cm superior-inferior)
volume positioned mid-sagittally was shimmed with an automated shim protocol
(Gruetter, 1993). A 2D-FLASH
imaging sequence acquired anatomical sagittal and coronal images of the brain
for 31P voxel positioning (TR=11 ms, TE=6 ms, 256 phase-encodes,
0.93 x 0.93 mm pixels). Thirty-two T1-weighted transverse
images were acquired on the brain using a magnetisation-prepared (adiabatic
inversion pulse 0.5 secs prior to data collection) 3D-FLASH imaging sequence
(TR=11 ms, TE=6.2 ms, total acquisition time <3 minutes) with a nominal
slice thickness of 4.375 mm and 1.09 x 1.09 mm in-plane resolution.
These images were used to calculate grey matter, white matter and
cerebrospinal fluid (CSF) ratios in the 31P-CSI volumes.
Image segmentation/partial-volume estimation
The transverse image data set for each subject was first separated into
three distinct binary tissue maps: grey matter, white matter and CSF/air/bone
by thresholding the original high-contrast image set, which best displayed the
ventricles, corpus callosum and grey matter of the anterior cingulate. The
thresholding co-efficients were then varied until each segmented image type
matched the corresponding anatomy in the original reference image. The
thresholding values differed between subjects since image signal intensity
depended on receiver gain and coil loading. To obtain the tissue ratio
contribution for each 31P region of interest (ROI), the three
segmented image data sets were convolved with the calculated 3D-PSF of the
31P-CSI acquisition (Jensen et al, 2001). The partial
volume contribution for each tissue type was then expressed as a percentage of
total tissue contribution for each ROI.
In vivo 31P-MRS
Once the 1H-shimming and imaging were completed, the
1H-head coil was manually replaced with a single-tuned,
31P quadrature, 14 cm long birdcage head-coil with the subject
still in place in the plexiglas cradle inside the magnet. Previous phantom
experiments verified that manual coil replacement did not affect the shim. A
31P external reference standard (methylene diphosphonic acid (MDP),
270 mM, T1@ 4.0T6 secs) was fastened to the plexiglas head cradle just
left of the patient's head The 1.5 cm diameter reference tube was positioned
so its length ran axially, spanning the sensitive region of the
31P-RF coil. Transmit/receive frequency was centred on PCr, as
measured with a global free induction decay (FID). Tip angle, optimised for
the PME/PDE resonance at a 500 ms TR, was 32 degrees. In vivo
31P-MRS utilised an optimised 3D-CSI sequence: TR=500 ms; Rx
bandwidth=±2 kHz; complex-points=1600; readout duration=400 ms;
pre-pulses=20; Rx gain=94 dB; pre-acquisition delay=1.905 ms; field of view
(FOV) (x,y,z)=280 mm; nominal volume=5.4 cc; maximum phase-encode
matrix dimension (x,y,z) 14 x 14 x 14 (zero-filled out to
16 x 16 x 16 prior to reconstruction). The 3D-CSI sequence used a
reduced phase-encoding scheme based on prior work
(Ponder et al, 1994). This scheme allows for the inclusion of spherically bound, reduced-point,
weighted k-space acquisition, providing approximately 40% more
signal-to-noise for a given scan time and effective voxel volume over
conventional methods.
In vivo post-processing and spectral analysis
All in vivo CSI/image data were processed and viewed using Varian
Nuclear Magnetic Resonance (VNMR) software, Version 6.1b and software designed
and written on site. Prior to Fast Fourier Transform (FFT) reconstruction to
spatially resolve the CSI spectra, the collected k-space data was
centred in a 16 x 16 x 16 cubic matrix. Each time-domain FID was
then zero-filled out to 2048 complex points and left-shifted five points to
remove residual bone/rigid membrane signal.
Using the 1H images, the 3D-CSI data grid was shifted in the x, y and z dimensions in order to position each voxel in the appropriate 31P ROI. For all subjects, the Brodmann area and Talairach coordinates for voxel centres (x,y,z) in the brain were evaluated for every 31P ROI using SPM99b-Statistical Parametric Mapping (Ashburner et al, 2000) and are listed in Table 2. Partial overlap with adjacent structures was unavoidable in many of the regions due to voxel volume and shape (Fig. 1).
|
|
All in vivo spectra were fit in the time-domain using a non-linear, iterative fitting program developed on site. The fitting routine is based on the MarquardtLevenberg algorithm, utilising prior spectral knowledge for the relative amplitudes, linewidths, lineshapes, peak positions and J-coupling constants to model the in vivo 31P brain spectrum (Potwarka et al, 1999b). Since it was positioned along the inner face of the coil, the reference standard was subject to different RF power than the subject and was volume-bound by the x and y tube dimension (1.5 cm diameter), both requiring correction. Therefore, the MDP reference area, fitted with a single Gaussian peak, was corrected for T1-saturation, RF coil sensitivity and volume. Each 31P metabolite area was also T1-corrected, then normalised to the MDP signal and finally corrected by the brain water fraction of 75% to obtain absolute millimolar values per unit brain water (mM/L H2O) for each 31P metabolite. Human in vivo 31P metabolite T1-values at 4.1T for Pi, PCr and ATP of 1.59 secs, 2.39 secs and 0.79 secs were used for the T1-correction (Heatherington et al, 2001). T1-values averaged from the literature at 1.9-2.0T of 2.35 secs and 2.14 secs for the PME and PDE metabolites, respectively, were also used (Boska et al, 1990; Bottomley et al, 1994; Oberhaensli et al, 1987). These values agreed closely with our own in vivo T1-values at 4.0 Tesla obtained from a global FID with a 90 degree pulse and TR values ranging from 0.5 to 20 secs. The fitted metabolite amplitudes are not T2-weighted since the fitting algorithm back-extrapolates to time zero. No partial volume corrections were made to any of the derived 31P metabolite concentrations.
Statistics
All statistical calculations used SPSS version 10.0 for Windows. A
two-tailed t-test was used to test for significant differences in
age, parental education, grey matter, white matter and CSF partial volumes
between groups (P <0.05). Statistical treatment of all 10
31P metabolite ratios for each region first involved a one-factor
MANCOVA including the covariate of age with a between-subjects factor of
group. ANCOVA was used to detect what individual metabolites differed
significantly (P<0.05) between groups. In each region where
significant group differences in 31P were found, Pearson
correlations were computed, within the patient group, between 31P
metabolite levels and each of the following variables: SANS and SAPS scores,
age, parental education, duration of illness and 31P metabolite
levels in all regions where significant group differences in 31P
metabolites were found. Significance for the Pearson correlate was set to
P<0.01.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
![]() |
IMPLICATIONS OF ALTERED PHOSPHODIESTER LEVELS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
OTHER METABOLITES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Effects of medication
Patients were chronic and on neuroleptic medication. However, two recent
31PMRS studies demonstrated that neuroleptic medications decreased
PDE levels in the temporal lobe (Fukuzako
et al, 1999) and increased PDE levels in the frontal
lobes (Volz et al,
1999). As our findings went in the opposite direction in these
locations, it is difficult to attribute differences to neuroleptics.
Spectroscopy limitations
Due to the short repetition-time (500 ms) in our acquisition, the resulting
31P spectra are T1-weighted. The observed changes in
metabolite levels in schizophrenia may therefore partially result from
differing T1-values in the affected regions, and may not be purely
due to concentration differences. However, based on literature T1
values, T1 values in people with schizophrenia would have to change
considerably, up to 400%, in order to equalise the metabolite ratios between
groups. This is unlikely and there is no evidence to date suggesting that
brain phosphorus metabolite T1 values are altered in schizophrenia.
Our 15 cc voxels are the smallest used in a schizophrenia 31P-MRS
study to date, but this volume is still large resulting in considerable
contribution from adjacent tissue in the hippocampus, the anterior cingulate
and the thalamus. The fall off in the 31P RF coil
B1-sensitivity prevented ideal positioning of a 15 cc volume in the
cerebellum, resulting in partial contribution of the spectra from the
occipital lobes (see Fig. 1).
However, the nearby voxels entirely within the parieto-occipital region showed
no phospholipid changes, rendering it unlikely that our reported change in
GPEth in the left cerebellum is from the occipital region.
Partial-volume limitations
People with schizophrenia have been shown to possess less cortical grey
matter and more CSF than controls
(Zipursky et al,
1992). A partial-volume correction was therefore applied to all
brain regions showing significant changes in 31P metabolites, using
literature estimates for 31P metabolite concentration differences
between tissue-type (Buchli et al,
1994; Hetherington et
al, 2001).
Partial volumes of grey matter, white matter and CSF in the anterior cingulate, left thalamus, right parieto-occipital cortex and right prefrontal cortex differed by only 2-5% between the groups, which was not significant. The effect of these small volume differences on the 31P metabolite concentrations is very slight and does not explain the observed group differences in the 31P metabolites in any of these regions. The 15% reduction in grey matter in the left hippocampus of the schizophrenia group, as well as 13% more white matter in this region, explain only about 4% of the observed 64% increase in GPEth in this group, based on 40% greater PDE levels in white matter (Buchli et al, 1994). Although not found to be significant, the 15% increase in grey matter partial volume, as well as the 7% reduction in white matter and 8% reduction in CSF partial volumes, in the left cerebellum in schizophrenia patients cannot account for the observed 60% increase in GPEth in this region.
![]() |
Clinical Implications and Limitations |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
LIMITATIONS
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Andreasen, (1984b) Scale for the Assessment of Positive Symptoms. Iowa City, IA: University of Iowa.
Andreasen, (1999) A unitary model of
schizophrenia. Archives of General Psychiatry,
56,
781-793.
Ashburner, J., Fristor, K., Holmes, A., et al (2000) Statistical Parametric Mapping (SPM99b). Website: http://www.fil.ion.ucl.ac.uk/spm
Benes, M. F. (1998) Model generation and testing to probe neural circuitry in the cingulate cortex of postmortem schizophrenic brain. Schizophrenia Bulletin, 24, 219-230.[Medline]
Borka, M. D., Hubesch, D. J., Meyerhoff, D. B., et al (1990) Comparison of 31P-MRS and 1H-MRI and 1.5 and 2.0T. Magnetic Resonance in Medicine, 13, 228-238.[Medline]
Bottomley, P. A. & Ouwerkerk, R. (1994) Optimum flip angles for exciting NMR with uncertain T1 values. Magnetic Resonance in Medicine, 32, 137-141.[Medline]
Bryden, P. (1977) Measuring handedness with questionnaires. Neuropsychologia, 15, 617-624.[Medline]
Buchli, R., Duc, C. O., Martin, E., et al (1994) Assessment of absolute metabolite concentrations in human tissue by 31P-MRS in vivo. Part 1: Cerebrum, cerebellum, cerebral gray and white matter. Magnetic Resonance in Medicine, 33, 447-452.
Carlsson, M. & Carlsson, A. (1990) Schizophrenia: a subcortical neurotransmitter imbalance syndrome? Schizophrenia Bulletin, 16, 425-432.[Medline]
Feinberg, I. & Guazzelli, M. (1999) Schizophrenia a disorder of the corollary discharge systems that integrate the motor systems of thought with the sensory systems of consciousness. British Journal of Psychiatry, 174, 169-204.
First, M. B., Spitzer, R. L., Gibbon, M., et al (1997) Structured Clinical Interview (SCID) for DSM-IV Axis I Disorders. Washington, DC: American Psychiatric Press.
Friston, K. J. (1998) The disconnection hypothesis. Schizophrenia Research, 30, 115-125.[CrossRef][Medline]
Fukuzako, H., Fukuzako, T., Kodama, S., et al (1999) Haloperidol improves membrane phospholipid abnormalities in temporal lobes of schizophrenic patients. Neuropsychopharmacology, 21, 542-549.[CrossRef][Medline]
Grace, A. A., Moore, H. & O'Donnell, P. (1998) The modulation of corticoaccumbens transmission by limbic afferents and dopamine: a model for the pathophysiology of schizophrenia. Advances in Pharmacology, 42, 721-724.[Medline]
Gruetter, R. (1993) Automatic, localized in vivo adjustment of all first and second-order shim coils. Magnetic Resonance in Medicine, 29, 804-811.[Medline]
Hetherington, H. P., Spencer, D. D., Vaughan, J. T., et al (2001) Quantitative 31P spectroscopic imaging of human brain at 4 Tesla: Assessment of gray and white matter differences of phosphocreatine and ATP. Magnetic Resonance in Medicine, 45, 46-52.[CrossRef][Medline]
Horrobin, D. D., Glen, A. I. M. & Vaddadi, K. (1994) The membrane hypothesis of schizophrenia. Schizophrenia Research, 13, 195-207.[CrossRef][Medline]
Jones, E. G. (1997) Cortical development and thalamic pathology in schizophrenia. Schizophrenia Bulletin, 23, 483-501.[Medline]
Kilby, P. M., Bolas, N. M. & Radda, G. K. (1991) 31P-NMR Study of brain phospholipid structures in vivo. Biochimica et Biophysica Acta, 1085, 257-264.[Medline]
Lipska, B. K. & Weinberger, D. R. (1993) Delayed effects of neonatal hippocampal damage on haloperidol-induced catalepsy and apomorphine-induced sterotypic behaviors in the rat. Developmental Brain Research, 75, 213-222.[Medline]
Oberhaensli, R. D., Galloway, G. J., Hilton-Jones, D., et al (1987) The study of human organs by phosphorus-31 topical magnetic resonance spectroscopy. British Journal of Radiology, 60 367-373.[Abstract]
Ponder, S. L. & Twieg, D. B. (1994) A novel sampling method for 31P spectroscopic imaging with improved sensitivity, resolution and sidelobe suppression. Journal of Magnetic Resonance (Series B), 104, 85-88.[Medline]
Potwarka, J., Drost, D. J., Williamson, P. C., et al (1999a) A 1H decoupled 31P chemical shift imaging study of medicated schizophrenic patients and healthy controls. Biological Psychiatry, 45, 687-693.[CrossRef][Medline]
Potwarka, J., Drost, D. J., & Williamson, P. C., et al (1999b) Quantifying 1H decoupled in vivo 31P brain spectra. NMR in Biomedicine, 12, 8-14.[CrossRef][Medline]
Selemon, J. D. & Goldman-Rakic, P. S. (1999) The reduced neuropil hypothesis: a circuit based model of schizophrenia. Biological Psychiatry, 45, 17-25.[CrossRef][Medline]
Stanley, J. A., Williamson, P. C., Drost, D. J., et al (1995) An in vivo study of the prefrontal cortex of schizophrenic patients at different stages of illness via phosphorus magnetic resonance spectroscopy. Archives of General Psychiatry, 52, 399-406.[Abstract]
Volz, H.-P., Rössger, G., Riehemann, S., et al (1999) Increase of phosphodiesters during neuroleptic treatment of schizophrenics: a longitudinal 31P-magnetic resonance spectroscopic study. Biological Psychiatry, 45, 1221-1225.[CrossRef][Medline]
Williamson, P. C. & Drost, D. J. (1999) 31P magnetic resonance spectroscopy in the assessment of brain phospholipid metabolism in schizophrenia. In Phospholipid Spectrum Disorder in Psychiatry (eds A. I. M. Glen & D. F. Horrobin), pp. 45-55. Carnforth: Marius Press.
Zipursky, R. B., Lim, K. O., Sullivan E. V., et al (1992) Widespread cerebral grey matter volume deficits in schizophrenia. Archives of General Psychiatry, 49, 195-205.[Abstract]
Received for publication March 28, 2001. Revision received June 14, 2001. Accepted for publication June 14, 2001.