Published online before print March 27, 2003, 10.1148/radiol.2272020311
(Radiology 2003;227:538-541.)
© RSNA, 2003
Perirolandic Cortex of the Normal Brain: Low Signal Intensity on Turbo FLAIR MR Images1
Ercan Karaarslan, MD and
Arzu Arslan, MD
1 From the Department of Radiology, Intermed Medical Center, Istanbul, Turkey (E.K.); and Department of Radiology, Kocaeli University Medical School, Turkey (A.A.). Received March 31, 2002; revision requested June 11; final revision received September 15; accepted September 30. Address correspondence to E.K., Department of Radiology, American Hospital, Guzelbahce sok 20, 80200 Nisantasi, Istanbul, Turkey (e-mail: e_karaarslan@hotmail.com).
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ABSTRACT
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PURPOSE: To evaluate the signal intensity (SI) characteristics of the perirolandic cortex (PRC) in the neurologically normal population on turbo fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) images.
MATERIALS AND METHODS: Turbo FLAIR MR images of 112 neurologically normal patients were evaluated retrospectively. SI of the PRC was graded by consensus of both authors as isointense (grade 0), mildly hypointense (grade 1), or definitely hypointense (grade 2) when compared to the SI of the superior frontal cortex. Kolmogorov-Smirnov and Kruskal-Wallis one-way analysis of variance tests were used for the statistical analysis of the differences in grades between the two sexes and between the age groups, respectively.
RESULTS: PRC was isointense (grade 0) in six (5%) and hypointense (grade 1 or 2) in 106 (95%) of 112 patients. The difference in grades was statistically significant between age groups (P < .001). Grade 0 was encountered most often in older patients and grade 2 in younger patients. There was no significant difference in grades between age-matched groups of male and female patients (P = .66).
CONCLUSION: On turbo FLAIR images the PRC generally has a low SI in the neurologically normal brain, and this helps as an additional landmark in identifying the sensorimotor cortex.
© RSNA, 2003
Index terms: Brain, anatomy, 13.92 • Brain, cortex, 13.92 • Brain, MR, 13.121411, 13.121413
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INTRODUCTION
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Identification of the precentral and postcentral gyri at computed tomography and magnetic resonance (MR) imaging is important in order to evaluate the location of various pathologic conditions in the brain, especially in surgical candidates, since the primary motor area occupies the precentral gyrus and the primary somesthetic area occupies the postcentral gyrus (1). Different methods of identifying the central sulcus have been defined, such as by observing the surface arrangement of the sulci (2) and the medullary pattern of the cerebral white matter (3) and by using advanced functional MR techniques. We hypothesized that the signal intensity (SI) of the perirolandic cortex (PRC) in comparison to the SI of the superior frontal cortex (SFC) might help in identifying the central sulcus. Decreased SI of the motor cortex has been defined in certain diseases such as amyotrophic lateral sclerosis (4–6), Alzheimer disease (6), bulbospinal muscular atrophy, leukoencephalopathy, Binswanger disease (4), and multiple sclerosis (7), and it has also been defined as a natural component of the normal aging process as a result of iron deposition (4,8). The purpose of our study was to evaluate the SI characteristics of the PRC in the neurologically normal population on turbo fluid-attenuated inversion-recovery (FLAIR) MR images.
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MATERIALS AND METHODS
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The eligible population for the study included 112 patients—40 male patients (age range, 7–79 years; mean age, 42.5 years) and 72 female patients (age range, 9–74 years; mean age, 37.4 years)— selected from a consecutive group of patients who had been referred from theneurology departments of various hospitals and clinics for routine brain MR imaging. The criteria for study selection were normal findings at neurologic examination, no history of neurologic disease, and normal results of brain MR imaging. Indications for MR imaging included headache (n = 65), dizziness (n = 21), paresthesia (n = 8), suspected seizure disorder (n = 6), psychiatric symptoms (n = 4), senility (n = 2), peripheral facial palsy (n = 2), trauma (n = 2), double vision (n = 1), and tremor (n = 1). The study was approved by our institutional review board and protocol review committee. Informed consent was not required by the institutional review board, but we had obtained blanket consent from all patients for use of their findings for research and education with patient privacy being maintained.
MR Imaging
MR examinations were performed with a 1.5-T imager (Magnetom Vision; Siemens, Erlangen, Germany). In all patients, transverse T1-weighted spin-echo (repetition time msec/echo time msec, 550/12), transverse T2-weighted fast spin-echo (repetition time msec/echo time [effective] msec, 3,986/99; echo train length of 11), and transverse turbo FLAIR, sagittal T1-weighted spin-echo (450/15) and coronal turbo FLAIR (repetition time msec/echo time msec/inversion time msec, 8,000/110/2,500) images were obtained. MR imaging was completed in about 20 minutes on average.
Transverse turbo FLAIR images (8,000/110/2,500, echo train length of 11) were obtained with 5-mm section thickness, 2-mm intersection gap, and one signal acquisition. The image matrix was 176 x 256, with a field of view of 210 x 230 mm. The images were angled parallel to the bicommissural line (the line passing by the superior border of the anterior commissure and the inferior border of the posterior commissure), depicting the entire brain from the foramen magnum to the vertex.
Hard copies of transverse turbo FLAIR MR images were obtained with regular clinical window width (400 ± 100) and level (300 ± 50) settings. The evaluation process was carried on by consensus of both authors. The central sulcus at the level of the centrum semiovale was identified on the basis of the previously defined methods (2,3). SI of the PRC was compared with that of the SFC and graded with a three-point scoring system: SI of the PRC was graded as isointense (grade 0), mildly hypointense (grade 1), or definitely hypointense (grade 2) compared with the SI of the SFC (Fig 1). We used the transverse image at the level of the centrum semiovale because (a) the superior frontal gyrus and the PRC were best appreciated on the same section at the level of centrum semiovale in the transverse image and (b) the low SI of the PRC was more noticeable in the upper levels of the brain.
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Figure 1a. Transverse turbo FLAIR MR images (8,000/110/2,500, echo train length of 11) show SI grades of PRC. (a) Grade 0 SI of the PRC in a 71-year-old man. The PRC (black arrows) is isointense with the SFC (white arrow). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (b) Grade 1 SI of the PRC in a 62-year-old woman. The PRC (black arrows) is mildly hypointense compared with the SFC (white arrow). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (c) Grade 2 SI of the PRC in a 33-year-old woman. The PRC (black arrows) shows definite hypointensity compared with the SFC (white arrow) (window width: 304, level: 347). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (d) Same section as c. On this image with a narrow window (width: 62, level: 347), the lower SI of the PRC (thin arrows) in comparison with that of the SFC (thick arrow) is more prominent.
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Figure 1b. Transverse turbo FLAIR MR images (8,000/110/2,500, echo train length of 11) show SI grades of PRC. (a) Grade 0 SI of the PRC in a 71-year-old man. The PRC (black arrows) is isointense with the SFC (white arrow). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (b) Grade 1 SI of the PRC in a 62-year-old woman. The PRC (black arrows) is mildly hypointense compared with the SFC (white arrow). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (c) Grade 2 SI of the PRC in a 33-year-old woman. The PRC (black arrows) shows definite hypointensity compared with the SFC (white arrow) (window width: 304, level: 347). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (d) Same section as c. On this image with a narrow window (width: 62, level: 347), the lower SI of the PRC (thin arrows) in comparison with that of the SFC (thick arrow) is more prominent.
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Figure 1c. Transverse turbo FLAIR MR images (8,000/110/2,500, echo train length of 11) show SI grades of PRC. (a) Grade 0 SI of the PRC in a 71-year-old man. The PRC (black arrows) is isointense with the SFC (white arrow). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (b) Grade 1 SI of the PRC in a 62-year-old woman. The PRC (black arrows) is mildly hypointense compared with the SFC (white arrow). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (c) Grade 2 SI of the PRC in a 33-year-old woman. The PRC (black arrows) shows definite hypointensity compared with the SFC (white arrow) (window width: 304, level: 347). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (d) Same section as c. On this image with a narrow window (width: 62, level: 347), the lower SI of the PRC (thin arrows) in comparison with that of the SFC (thick arrow) is more prominent.
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Figure 1d. Transverse turbo FLAIR MR images (8,000/110/2,500, echo train length of 11) show SI grades of PRC. (a) Grade 0 SI of the PRC in a 71-year-old man. The PRC (black arrows) is isointense with the SFC (white arrow). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (b) Grade 1 SI of the PRC in a 62-year-old woman. The PRC (black arrows) is mildly hypointense compared with the SFC (white arrow). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (c) Grade 2 SI of the PRC in a 33-year-old woman. The PRC (black arrows) shows definite hypointensity compared with the SFC (white arrow) (window width: 304, level: 347). Thick black arrow = precentral motor cortex, thin black arrow = postcentral somatosensory cortex. (d) Same section as c. On this image with a narrow window (width: 62, level: 347), the lower SI of the PRC (thin arrows) in comparison with that of the SFC (thick arrow) is more prominent.
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Statistical Analysis
Statistical analysis was carried out by using the Kolmogorov-Smirnov test to look for significant differences in grades between male and female patients. Kruskal-Wallis one-way analysis of variance test was used for the statistical analysis of the differences in grades between age groups. Each age group represented 1 decade. The study group included very few patients younger than 20 or older than 60 years old; therefore, the first (children and adolescents) and last groups each represented 2 decades. A P value of less than .001 was considered as demonstrating statistical significance.
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RESULTS
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There was no difference in visual grading between the right and left hemispheres.
In all patients, the PRC was lined by a very thin rim (ie, the most superficial part of the PRC), which was isointense to the SFC adjacent to the central sulcus (Fig 2). In all patients, the deeper part of the PRC was either isointense (six patients, 5%) or hypointense (106 patients, 95%) to the SFC. Grades of SI of this deeper part of the PRC with respect to age groups are shown in the Table; the thin rim of superficial PRC that was isointense to the SFC was excluded. Grade 0 was typically encountered in older (mean age, 69 years) and grade 2 in younger (mean age, 33 years) patients (ie, hypointensity of the PRC is more conspicuous in younger patients), and with increasing age SI of the PRC becomes more similar to that of the SFC. The difference in grades was statistically significant between age groups (P < .001).
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Figure 2. Transverse turbo FLAIR MR image obtained in a 33-year-old woman. There is a very thin ribbon surrounding the central sulcus (superficial part of the PRC) (short arrows). The deeper part of the PRC (arrowhead) is definitely hypointense (grade 2) compared with the SFC (long arrow) and cannot be differentiated from the adjacent subcortical white matter.
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Of 40 male patients, three (8%) had grade 0 SI, 10 (25%) had grade 1 SI, and 27 (68%) had grade 2 SI. Of the 72 female patients, three (4%) were grade 0, 10 (14%) were grade 1, and 59 (82%) were grade 2. There was no significant difference in grades between age-matched groups of male and female patients (P = .66).
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DISCUSSION
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SI of the motor cortex was previously studied in patients with degenerative neuron diseases (4–6). Only limited information about the SI of the motor cortex in the neurologically normal population is available from the control groups of these studies. To our knowledge, no previous large studies examined the SI of the PRC in the neurologically normal population with respect to age and sex.
Previous studies of patients with amyotrophic lateral sclerosis, which demonstrated low SI in the motor cortex of the patients, disclosed similar low SI in T2-weighted spin-echo and FLAIR images of the control groups with prevalences ranging from 2% to 38% (4–6). In our study with the turbo FLAIR sequence, the PRC was hypointense in 106 of 112 (95%) patients. These different results may be due to different age characteristics of the observed populations and different MR units and imaging parameters that might affect SI of the cerebral cortex (9).
Cellular composition of cortices might account for the different SI on FLAIR images (10). However, the precentral cortex and SFC have the similar agranular type of neocortical organization (1) yet different SI, whereas the postcentral cortex has the granular type of cortex (1) but still shows a low SI similar to that of the precentral cortex.
Another explanation for the decreased SI on T2-weighted images could be the magnetic susceptibility effect (11). T2 shortening because of the heterogeneity of the magnetic field could be due to iron deposition, oxygen free radicals (5,6,12), and increased lipofuscin granules in the motor neurons (12) in certain areas of the brain in normal (as a result of the aging process) and in abnormal conditions (5,7,8,11,13). Iron and paramagnetic species with local susceptibility effects are best seen on T2-weighted and gradient-echo images (6). FLAIR sequences have a limited ability to depict the effects of paramagnetic susceptibility because of the use of fast spin-echo techniques (10,14). We still observed low SI with the turbo FLAIR sequence, and it was observed more prominently in younger patients. These findings suggested that iron deposition was not the only factor causing the low SI.
Barkovich et al (15) reported low SI in the pre- and postcentral gyri on T2-weighted MR images of neonates, the histologic background of which had later been speculated to be because of the more advanced development of the neurons, density of synapses, and formation of dendrites, which might cause decreased interstitial water and increased lipid content of the membranes in the cortex (16,17).
Changes in T2 relaxation of brain tissue in different locations has been attributed to various factors such as water diffusion and composition of cytoplasmic and extracellular spaces (10,18). Previous studies showed that T2 relaxation times were significantly higher in the insular cortex and cingulate gyrus (18) and significantly lower in the primary auditory and visual cortices (19). Although to our knowledge the PRC was not the subject of the previous studies, one possible explanation of the lower SI in the PRC might be lower water content of the extracellular space. The extracellular matrix of the brain is not homogeneously organized throughout the neural tissue. Certain neuron populations are ensheathed by perineuronal nets, which consist of chondroitin sulfate proteoglycans, complexed with hyaluronan and colocalized with tenascins (20–22). The perineuronal nets develop postnatally and contribute to cell migration, neurite outgrowth, synaptogenesis, and maintenance of synaptic structure and function in the developing and adult brain (21,23).
Previous studies have shown that neurons with perineuronal nets were most numerous in the primary motor, somatosensory, primary auditory, and visual cortices (20,22,24). Their number was significantly lower in prefrontal areas, and cingulate and entorhinal cortices (22). Thus, in our study the lower SI of the PRC corresponds to the regions that are rich in perineuronal nets and the higher SI of the SFC corresponds to the prefrontal area, which is poor in perineuronal nets. Lower SI on T2-weighted images has also been reported in sensory (11), visual (22), and auditory (25) cortices on the basis of findings at visual inspection. Considering the results of the above mentioned neurochemical studies (20–22,24), we believe that the distribution of perineuronal nets is one of the reasons for the lower SI in the sensorimotor cortex, as well as in the auditory and visual cortices.
Cortical layers in neocortical organization are not uniform. In the precentral motor cortex, layers II and IV are very poorly developed, but pyramidal cells in layers III and V are very well developed (1). Considerable numbers of net-associated pyramidal cells populate predominantly layers III and V in both the precentral motor and the postcentral somatosensory areas (24). The thin ribbon of relatively higher SI (isointense to the SFC) lining the superficial part of the PRC might represent layer I, which is poor in perineuronal nets. The deeper part of the PRC, which was hypointense to the SFC in 106 of 112 (95%) of our patients, might represent layers III and V (Fig 2). There are not enough data to determine whether the concentration of perineuronal nets decreases in the elderly brain. We suspect it could be the reason why low SI of the PRC is more prominent in younger patients. All these comments on this subject remain speculative and deserve further histologic study with MR correlation.
To conclude, SI of the PRC is generally lower compared with the SI of the SFC on turbo FLAIR MR images of the neurologically normal brain. The PRC can be readily identified on MR images because of its conspicuous low SI, which can be used as an additional landmark for identification of the sensorimotor cortex.
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ACKNOWLEDGMENTS
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We thank Omer Uysal, PhD, for the statistical analysis of the study.
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FOOTNOTES
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Abbreviations: FLAIR = fluid-attenuated inversion recovery,
PRC = perirolandic cortex,
SFC = superior frontal cortex,
SI = signal intensity
Author contributions: Guarantor of integrity of entire study, E.K.; study concepts and design, E.K., A.A.; literature research, A.A., E.K.; clinical studies, E.K.; data acquisition and analysis/interpretation, E.K., A.A.; manuscript preparation, A.A.; manuscript definition of intellectual content, editing, revision/review, and final version approval, A.A., E.K.
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REFERENCES
|
|---|
- Snell RS. The structure and functional localization of the cerebral cortex In: Clinical neuroanatomy for medical students. 4th ed. Philadelphia, Pa: Lippincott-Raven, 1997; 275-294.
- Gado M, Hanaway J, Frank R. Functional anatomy of the cerebral cortex by computed tomography. J Comput Assist Tomogr 1979; 3:1-19.[Medline]
- Iwasaki S, Nakagawa H, Fukusumi A, et al. Identification of pre- and postcentral gyri on CT and MR images on the basis of the medullary pattern of cerebral white matter. Radiology 1991; 179:207-213.[Abstract/Free Full Text]
- Waragai M. MRI and clinical features in amyotrophic lateral sclerosis. Neuroradiology 1997; 39:847-851.[CrossRef][Medline]
- Oba H, Araki T, Ohtomo K, et al. Amyotrophic lateral sclerosis: T2 shortening in motor cortex at MR imaging. Radiology 1993; 189:843-846.[Abstract/Free Full Text]
- Bowen BC, Pattany PM, Bradley WG, et al. MR imaging and localized proton spectroscopy of the precentral gyrus in amyotrophic lateral sclerosis. AJNR Am J Neuroradiol 2000; 21:647-658.[Abstract/Free Full Text]
- Russo C, Smoker WRK, Kubal W. Cortical and subcortical T2 shortening in multiple sclerosis. AJNR Am J Neuroradiol 1997; 18:124-126.[Abstract]
- Drayer BP. Imaging of the aging brain. I. Normal findings. Radiology 1988; 166:785-796.[Abstract/Free Full Text]
- Korogi Y, Hirai T, Komohara Y, et al. T2 shortening in the visual cortex: effect of aging and cerebrovascular disease. AJNR Am J Neuroradiol 1997; 18:711-714.[Abstract]
- Hirai T, Korogi Y, Yoshizumi K, Shigematsu Y, Sugahara T, Takahashi M. Limbic lobe of the human brain: evaluation with turbo fluid-attenuated inversion-recovery MR imaging. Radiology 2000; 215:470-475.[Abstract/Free Full Text]
- Hirai T, Korogi Y, Sakamoto Y, Hamatake S, Ikushima I, Takahashi M. T2 shortening in the motor cortex: effect of aging and cerebrovascular disease. Radiology 1996; 199:799-803.[Abstract/Free Full Text]
- Cheung G, Gawal MJ, Cooper PW, Farb RI, Ang LC. Amyotrophic lateral sclerosis: correlation of clinical and MR imaging findings. Radiology 1995; 194:263-270.[Abstract/Free Full Text]
- Drayer B, Burger P, Hurwitz B, Dawson D, Cain J. Reduced signal intensity on MR images of thalamus and putamen in multiple sclerosis: increased iron content? AJNR Am J Neuroradiol 1987; 149:357-363.
- Alexander JA, Sheppard S, Davis PC, Salverda P. Adult cerebrovascular disease: role of modified rapid fluid-attenuated inversion-recovery sequences. AJNR Am J Neuroradiol 1996; 17:1507-1513.[Abstract]
- Barkovich AJ, Kjos BO, Jackson DE, Norman D. Normal maturation of the neonatal and infant brain: MR imaging at 1.5 T. Radiology 1988; 166:173-180.[Abstract/Free Full Text]
- Korogi Y, Takahashi M, Sumi M, et al. MR signal intensity of the perirolandic cortex in the neonate and infant. Neuroradiology 1996; 38:578-584.[Medline]
- Yoshiura T, Iwanaga S, Yamada K, et al. Perirolandic cortex in infants: signal intensity on MR images as a landmark of the sensorimotor cortex. Radiology 1998; 207:385-388.[Abstract/Free Full Text]
- Whittal KP, Mackay AL, Graeb DA, Nugent RA, Li DKB, Paty DW. In vivo measurement of T2 distributions and water contents in normal human brain. Magn Reson Med 1997; 37:34-43.[Medline]
- Georgiades CS, Itoh R, Golay X, van Zijl PCM, Melhem ER. MR imaging of the brain at 1.5 T: regional variations in transverse relaxation rates in the cerebral cortex. AJNR Am J Neuroradiol 2001; 22:1732-1737.[Abstract/Free Full Text]
- Bruckner G, Seeger G, Brauer K, Hartig W, Kacza J, Bigl V. Cortical areas are revealed by distribution patterns of proteoglycan components and parvalbumin in the Mongolian gerbil and rat. Brain Res 1994; 658:67-86.[Medline]
- Bruckner G, Grosche J. Perineuronal nets show intrinsic patterns of extracellular matrix differentiation in organotypic slice cultures. Exp Brain Res 2001; 137:83-93.[CrossRef][Medline]
- Bruckner G, Hausen D, Hartig W, Drlicek M, Arendt T, Brauer K. Cortical areas abundant in extracellular matrix chondroitin sulphate proteoglycans are less affected by cytoskeletal changes in Alzheimer’s disease. Neuroscience 1999; 92:791-805.[CrossRef][Medline]
- Kurazono S, Okamoto M, Sakiyama J, et al. Expression of brain specific chondroitin sulfate proteoglycans, neurocan and phosphacan, in the developing and adult hippocampus of Ihara’s epileptic rats. Brain Res 2001; 898:36-48.[CrossRef][Medline]
- Hausen D, Bruckner G, Drlicek M, Hartig W, Brauer K, Bigl V. Pyramidal cells ensheathed by perineuronal nets in human motor and somatosensory cortex. Neuroreport 1996; 7:1725-1729.[Medline]
- Yoshiura T, Higano S, Rubio A, et al. Heschl and superior temporal gyri: low signal intensity of the cortex on T2-weighted MR images of the normal brain. Radiology 2000; 214:217-221.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
