Poster Abstracts Tuesday, November 8, 2005 $261

oxy- and deoxy-hemoglobin, this complementary approach allows to analyse neurovascular coupling non-invasively in the human brain. We recorded DC-MEG and trNIRS simultaneously over the left primary motor cortex hand area in healthy subjects during finger movements of the right hand. DC-fields and trNIRS parameters followed closely tile motor task cycles revealing statistically significant differences between periods of finger movements and rest. In subjects with suffident signal-to-noise ratio the analysis of variance of photon time of flight for a 2-layer model demonstrates task-related changes originating from tile deeper layer, i.e., tile cortex. Notably, while onset and relaxation started sinmltaneously trNIRS signals reached 50% of the mmximum level 1-4 sec later than MEG-signals. This approach provides an opportunity to analyse the "hemodynamJc inverse problem" which refers to the challenge of making valid and predse estimates of underlying cortical neuronal activity from measured hemo- dynamic resposes, e.g., in tMRL In addition, tile feasibility to non-invasively monitor cortical low amplitude DC-fields, deoxy- and oxy-Hb simultaneously in humans will allow to scrutinise pathophy- siological stroke concepts, e.g. anoxic depolarisation, periinfarct- depolarisation and spreading depression. Notably fields of even higher magtfftude (up to 2pT) than resolved in this MEG-study have been shown in animal studies.

0636 Quantitation of Regional Brain Iron Content with Magnetic Resonance Imaging

Martin, W 1, Wieler, M a, Gee, M 1. 1University of Alberta, Edmonton, Canada

Background: The distribution of iron in the human brain is hetero- geneous with lffgh concentrations observed primarily in basal ganglia structures. Neurodegenerative disorders such as Parkinson's disease (PD) have been reported to be associated with changes in regional brain iron content, based on direct tissue measurements. The possibility of a non-invasive, semi-quantitative measurement of brain iron with magnetic resonance imaging (MR[) is suggested by the knoval effect of iron on transverse relaxation rates, although trans- verse relaxation is also affected by other sources of magnetic field inhomogeneity, such as that evident at the air-tissue interface in sinuses. Method: We have previously reported a method for measuring brain iron with MRI that mitigates other contributions to changes in transverse relaxation, making the technique most sensitive to iron content, particularly at high field strengths ([Wild et al., Magn Reson Meal 2002; 48:867-876). Tiffs technique was applied on a 3.0 T imaging system in a series of untreated patients with early PD and in age- matched controls. Results: A very close relationship was found between measurements of transverse relaxation rate and literature values for regional brain iron content in basal ganglia structures. The only significant difference between PD patients and controls was in the medial substantia uigra compacta, consistent with increased iron in tiffs structure in early PD. Conclusion: These results support the use of this MRI method at high field strengths for performing in vivo measurements of regional brain iron content, and suggest that nigral iron content may be abnormal in early PD.

0637 Semi-quantitative assess~nent of brain protein synthesis using L-[l-11C]-leucine PET

Muzik, O 1"2, Sundaram, S 1"3, Mu, F 2, Mangner, T 2, Chugani, D 1"2, Chugani, H 12'3. 1Carman and Ann Adams Dept of Pediatrics, Children's Hospital of Ivlichigan PET Center, Wayne State University, Detroit, United States; 2Department of Radiology, Children's Hospital of Michigan, IVayne State University, Detroit, United States; SDepartment of Neurology, Children's Hospital of Michigan, IVayne State University, Detroit, United States

Background: The objective of this study was to derive a stable index of brain protein synthesis based on the unidirectional uptake rate constant (Kcplx) of L-J1-11C]-leucine (LEU) in brain. Method: Fourteen healthy volunteers (6 males, 20-45 years) underwent dyaanffc LEU PET imaging. The tracer LEU (0.35 mCi/kg) was adnffnistered and arterial blood samples were drawll and analyzed for metabolites. The fraction of unmetabolized LEU in plasma was fitted with a sigmoidal function. Time activity curves were fitted with a two- tissue compartmental model consisting of an unidirectional protein pool and a combined pool representing both free and metabolized leucine in cytoplasnc The fraction of leucine originating from exogenous sources was estimated as k2/(k2+k3). Furthermore, the Patlak plot was used to determine the unidirectional uptake rate constant (Kcplx -- (Klk3/(k2 + k3)). Results: Identifiability of individual parameters was excellent (COV < 20%). The fraction of leucine incorporated into protein originating from exogenous amino acids was 0.65 + 0.02 and did not differ between males and females. In contrast, regional Kcplx values in males were in general 30% lower than those in females but following the same rank order ([visual cortex > cerebellum > brainstem > thalamus > frontal cortex > wlffte matter). Kcplx values derived from a Patlak

plot using data between 30 and 60 man pi. were within 10% of these values. Lastly, application of a population-derived blood metabolite correction had only a manor effect on the Kcplx (< 10'%). Conclusion: We conclude that the Kcplx is a stable index of brain protein synthesis rate well-suited for routine application.

0638 In-vivo magnetic lield correlation hnaging of bmnan brain at 3 tesla

Ramani, A 1, Jensen, JH 1 , Kacynski, KR 3, Helpern, JA 1,2,4. 1Department of Radiology, New York University School of Medicine, New York, NY; 2Departments of Psychiatry and Physiology & Neuroscience, New York University School of Medicine; 3Siemens Medical Systems, USA; 4Center for Advanced Brain Imaging; 4The Nathan S. Kline Institute, Orangeburg, New York

Introduction: As water molecules diffuse through a tissue under the influence of a strong uniform applied magnetic field, typically encountered in a MRI scanner, they sample a complex landscape of field inhomogeneities generated by variations in magnetic suscept- ibility. These susceptibility variations arise not only from macroscopic structures, such as air cavities and large veins, but also from micro- scopic structures, such as capillaries and iron-rich cells. The field inhomogeneities experienced by water molecules can be quantified by their magnetic field correlation (MFC). Tiffs is formally defined by Eqn.

K(t2 h) - (B(t2)B(h)} [11

where B(t} is the field shift, relative to the uniform background field, for a particular water molecule at a time t and with the angle brackets indicating an averaging over all the molecules within a given region of interest (1). The MFC can be calculated using an asynmietric spin echo (ASE) sequence (1). In this abstract, we have demonstrated tile feasibility of M F C imaging at 3 Tesla by showing in-vivo MFC images of the human brain and have also correlated M F C values with putative iron concentrations in spedfic brain regions. This technique may provide important information in the assessment of neurological disorders with associated iron abnomlalities, such as Parkinson's disease, Alzheimer's disease, Hallervorden-Spatz syndrome etc. THEORY: Consider an asymmetric SE sequence in wlffch tile 180 ° refocusing pulse is shifted by a time t+ from its standard position (i.e. t,. - 0 corresponds to a conventional SE sequence). If the field inhomogeneities are not too large, then we can write:

, , T E S(t0 S0exp[ 2t~'f K ( . T ) ] [2]

$262 Tuesday, November 8, 2005 Poster Abstracts

where S is the signal intensity, TE is the echo time, and 5" is the proton gyromagnetic ratio (1, 2). M F C maps are generated by fitting the signal intensities as a function of the pulse shifts on a pixel- by-pixel basis, to Eqn. [2]. The validity of tiffs equation for biological tissues has been confirmed both with Monte Carlo simulations (1) and suspensions of yeast cells containing a paramagnetic contrast agent (12). Methods: ASE images were acquired using a se~nented EPI sequence from six normal volunteers on a Siemens Allegro 3 Tesla scanner. Four echo times were used (TE -- 26,32,50,69 ms) with five refocusing pulse shifts (0.0, 3.0, 6.0, 9.0, and 12.0 ms) for each TE. Using a repetition time of 2000 ms, FOV of 230 mm, 10 averages and a matrix size of 128 x128, M F C data was acquired from 20 slices (1.8 m_m thick). Signal intensities were measured from brain regions including putamen (PUT), globus pallidus (GP), substantia uiagra (SN), thalanms (THL), caudate head (CHD), frontal white matter (FWM) and cortical gray matter (CGM). MFC maps were extracted as explained above. The transverse relaxation rate R.2 was calculated by fitting the signal intensifies (corresponding to the four TEs) as a function of TE. Single-shot diffusion-weighted EPI was also performed using the following parameters: TR 2000 ms, TE 88 ms, slice thickness 1.2 mm with 10 averages. SE images were obtained using three b values (300, 600 and 900 seconds/mm2), comprised of 128×96 pixels and covered an FOV of 230 nmt from which ADC maps were extracted. Results: A strong correlation (r - 0.975) was observed between MFC and established age-related iron concentrations (13), suggesting that MFC imaging is sensitive to iron-induced differences in brain-tissue susceptibility. It was observed that the regional variation in MFC values is higher than both A D C and T2 values. A typical MFC map acquired at an echo time of 50 ms showed that the most interesting structures are near the center of the image, associated with the globus pallidus, a region knovat for its high iron content. The MFC was found to decrease with increasing TE, reflecting the diffusion of water molecules through microscopic gradients.

0639 Brain MRI in elderly population - retrospective study

Semnic, R ~, Semnic, M ~, Kozic, D 1 , Ostojic, J 1, Ocic, G ~, Djilas Ivanovic, D 1, Popovic, S 1, Bogdanovic, D 1, Miucin Vukadinovic, I ~, Prvulovic, N ~. ~Institute Of Oncology; 2Institute of Neurology, Novi Sa& 3Institute of Neurology, Belgrade

Purpose: To evaluate brain pathology in elderly patients using Magnetic Resonance Imaging/MR angiography and to compare findings in two age groups: group A (range, 65-74 years) and group B (aged 75 and more). Methods: Retrospective study of 1805 brain MRI in period 1994-2002 was done. Routine M R I / M R A brain protocol was performed on 1.5 Tesla imager. Results: Group A in our study represents 0.08% (11602 patients) of all M R neurocases (118000 patients) and group B 0.01% only (1202 patients). After age of 72, number of examined patients was siguificantly lower. Pathological changes in brain parenchyma were revealed in 80"/o of cases. Ischemic changes dominated (48.5%) followed by vascular degenerative changes (18.5%) and intracranial hemorrhage (ICH) - 4.7%. Brain metastases and glial brain tumors were equally distributed (13.9"/o and 3.6%). Pathoguomonic diseases for eldery population as cortical dementias, diffuse brain atrophy, Parkinson disease and normotensive hydrocephalus were presented rarely (18 cases, 6%, 1% and 1% respectively). Comparison between two observed groups showed cummulation trend for ischemic encephalopathy (4% of all patients for group A and 8% for group B), common ischemic lesions (42%:50%), brain atrophy (5.6%:7%) and ICH (4.6%:6%). Number of cases with normal brain MRI was consecutively lower in group B.

Conclusion: Number of elderly patients who underwent MRI in period 1994-2002 is low which may reflects level of living standard in our country. IschemJc changes (including ICH) are dominant pathology in our population and brain atrophy is second most frequent. Pts with brain diseases typical for aging are uncommlon M R finding. Expectance of new cases with ischemJc changes is significantly high after the age of 75 and equally represented for newcomming patients with brain atrophy and ICH.

0640 Clinicoradiological correlation and response to treahnent in Acute Transeverse Myelitis

Sharma, CM l, Sharma, AK 1, Singh, R ~, Kankane, AK 1, Kumawat, BL 1. 1Department of neurology, SMS Medical College, Jaipur, India

Aim: Tiffs study was carried out to lffghlight dinico-radiological correlation in transverse myelitis and response to treatment. Material and Methods: Twenty five patients were diagnosed as transverse myelitis on the basis of criteria by Jeffery et al. Detailed neurological examination was carried out and all patients were subjected to 1.5 Tesla superconducting magnetic resonance imaging. Other relevant investigations were done to rule out other causes of non compressive myelopathy.Twenty patients were treated with intravenous methylpreduisolone at a dose of lgm/day and followed for one year. Results: The study included 15 females and 10 males (F:M::I.5:I). Mean age of onset was 40 (range 15-50). The presenting features were quadriparesis in 15 patients (60%), Paraparesis in 10 (40%). Bladder and bowel involvement was seen in 22 patients (88"/o) and definite sensory level in 18(72%).A11 the patients had acute onset of symptoms which peaked in 6.5(range 1-15) days.Cerebrospinal fluid was normal in all patients. High signal intensity on T2 weighted magnetic resonance imaging was seen in 23 (180"/o), 2 patients showed only cord expansion. Three patients showed hypointensity on T1. The lesion extended for a mean of 6 spinal segments (range 4-12 segments).The high signal intensity on mxial T2 weighted images was centrally located in all patients and occupied more than 2/3 "a of the cross sectional area of the cord in 21 (1847,'8) patients. 20 patients showed central dot sign. Conclusion: Prognosis is poor in the patients having long hyperintense signals and necrosis and there is a beneficial effect of methylpredni- solone.

0641 Brain responses to Hypoxia in the intrauterine growth restricted piglet uleasuxed by magnetic resonance spectroscopy and diflilsion weighted hnaging

Sinclair, K 1, Rose, S 3, Cowin, G 3, Burke, C 2, Colditz, p2. ~Brain Research Institute, Melbourne, Australia; 2Perinatal Research Centre; 3Centre for Magnetic Resonance, University of Queensland, Australia

Background: Intrauterine growth restriction (IUGR) is associated with chronic fetal hypoxia and an increased incidence of neurodevelop- mental disability. The pathophysiology linking IUGR and brain injury is not well understood. Hypothesis: Newborn I U G R piglets, compared to appropriately grown (AGA) littermates, have a different acute cellular and metabolic response to hypoxia. Methods: Eight pairs o f piglet littermates < 24 h age were selected by weight, ( IUGR < 5th percentile, AGA > 25th percentile). Piglets were anaesthetised, ventilated, physiological parameters monitored and normothermia maintained. Proton magnetic resonance spectroscopy (~H-MRS) was performed in a aT magnet to measure brain lactate, and diffusion weighted imaging (DWI) performed to calculate the apparent diffusion coefficient (ADC), wlffch reflects cellular edema associated with hypoxic primary energy failure. Measurements were