Current practice of emergency radiology in Turkey and future expectations: a survey study

PURPOSE: The development of emergency radiology (ER) in Turkey has accelerated with the increase in the number of patients admitted to emergency departments. We aimed to present and discuss the responses to a survey distributed to radiologists in Turkey, which included questions about the current practice of ER and future expectations. METHODS: A survey with 29 questions enquiring about the infrastructure of respondents' hospitals and radiology units, information about emergency services and ER (including patient volume), the number of staff and equipment, the ER working plan and reporting method, and training in the field of ER were distributed to members of the Turkish Radiological Society by email. RESULTS: The response rate was 21.97% (328/1.493). The presence of distinct ER units in radiology departments was confirmed by 40.55% of respondents, while for 34.25%, ER was located inside the emergency room. Of the respondents, 26.96% stated they believed that emergency cases should be reported by emergency radiologists, and the necessity for an ER subunit in the emergency room was agreed upon by 58.64% of contributors. The majority of respondents (69.54%) agreed with the opinion that residents should receive their ER training in an ER unit. CONCLUSION: Keeping abreast of current ER practices and radiologists' expectations may be helpful for improving national ER practices and academic studies.

Emergency Radiology: Evolution, Current Status, and Future Directions.

Emergency Radiology is a clinical practice and an academic discipline that has rapidly gained increasing global recognition among radiology and emergency/critical care departments and trauma services around the world. As with other subspecialties, Emergency Radiology practice has a unique scope and purpose and presents with its own unique challenges. There are several advantages of having a dedicated Emergency Radiology section, perhaps most important of which is the broad clinical skillset that Emergency Radiologists are known for. This multi-society paper, representing the views of Emergency Radiology societies in Canada and Europe, outlines several value-oriented contributions of Emergency Radiologists and briefly discusses the current state of Emergency Radiology as a subspecialty.

Diffusion tensor imaging in anorectal malformations: a pilot study for the evaluation of lumbosacral plexus.

INTRODUCTION: Neurogenic bladder with anorectal malformations (ARM) is a well-known yet understudied topic. Diffusion tensor imaging (DTI) is a special usage of MRI that can evaluate peripheric nerves. The aim of this study is to evaluate the lumbosacral plexuses of patients with ARM using DTI. PATIENTS AND METHODS: Patients with ARM willing to participate were included. Patient files were reviewed, a questionnaire was made, and DTI was performed. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were computed for the right and left lumbosacral plexuses. RESULTS: There were 18 patients and 12 controls. Groups were similar in terms of sex (p = 0.232) and age (p = 0.853). There was a significant difference only for ADC of the left plexus. There was visible asymmetry in tractographies and DTI parameters of two patients with severely deformed pelvises (image 1) but also in another patient with a normal sacrum. In addition, despite asymmetry, FA and ADC were similar to controls also in these patients. CONCLUSION: This is the first study presenting quantitative data about the lumbosacral plexus in ARM. We think the most interesting finding of this study was observing the normal values even in the patients with severely malformed sacrum which is yet to be validated with further studies.

Effects of the dopamine transporter gene on neuroimaging findings in different attention deficit hyperactivity disorder presentations.

Attention-Deficit/Hyperactivity Disorder (ADHD) is a phenotipically and neurobiologically heterogeneous disorder. Deficiencies at different levels in response inhibition, differences in dopamine transporter genotype (DAT1) and various symptomatic presentations contribute to ADHD heterogeneity. Integrating these three aspects into a functional neuroimaging research could help unreval specific neurobiological components of more phenotipically homogeneous groups of patients with ADHD. During the Go-NoGo trial, we investigated the effect of the DAT1 gene using 3 T MRI in 72 ADHD cases and 24 (TD) controls that typically developed between the ages 8 and 15 years. In the total ADHD group, DAT1 predicted homozygosity for the 10R allele and hypoactivation in the anterior cingulate cortex and paracingulate cortex. There were no significant activation differences between DAT1 10R/10R homozygotes and 9R carriers in TD controls. Subjects with predominantly inattentive ADHD (ADHD-I) presentation with DAT1 10R/10R homozygous reduced neuronal activation during Go trial particularly in the frontal regions and insular cortex, and in the parietal regions during NoGo trial (brain regions reported as part of Default Mode Network- DMN). Additionally, DAT1 10R/10R homozygousness was associated with increased occipital zone activation during only the Go trial in the ADHD combined presentation (ADHD-C) group. Our results point the three main findings: 1) The DAT1 gene is 10R homozygous for differentiated brain activation in ADHD cases but not in the TD controls, supporting the DAT1 gene as a potential marker for ADHD, 2) The relationship between the DAT1 gene and the occipital regions in ADHD-C group which may reflect compensatory mechanisms, 3) The relationship between DAT1 gene and the reduced DMN suppression for 9R carriers probabaly stems from the ADHD-I group.

Increased cerebral blood flow in the right anterior cingulate cortex and fronto-orbital cortex during go/no-go task in children with ADHD.

OBJECTIVE: Arterial spin labeling (ASL) is a relatively new imaging modality in the field of the cognitive neuroscience. In the present study, we aimed to compare the dynamic regional cerebral blood flow alterations of children with ADHD and healthy controls during a neurocognitive task by using event-related ASL scanning. METHODS: The study comprised of 17 healthy controls and 20 children with ADHD. The study subjects were scanned on 3 Tesla MRI scanner to obtain ASL imaging data. Subjects performed go/no-go task during the ASL image acquisition. The image analyses were performed by FEAT (fMRI Expert Analysis Tool) Version 6. RESULTS: The mean age was 10.88 ± 1.45 and 11 ± 1.91 for the control and ADHD group, respectively (p = .112). The go/no-go task was utilized during the ASL scanning. The right anterior cingulate cortex (BA32) extending into the frontopolar and orbitofrontal cortices (BA10 and 11) displayed greater activation in ADHD children relative to the control counterparts (p < .001). With a lenient significance threshold, greater activation was revealed in the right-sided frontoparietal regions during the go session, and in the left precuneus during the no-go session. CONCLUSION: These results indicate that children with ADHD needed to over-activate frontopolar cortex, anterior cingulate as well as the dorsal and ventral attention networks to compensate for the attention demanded in a given cognitive task.

The practice of emergency radiology throughout Europe: a survey from the European Society of Emergency Radiology on volume, staffing, equipment, and scheduling.

OBJECTIVES: To obtain information from radiology departments throughout Europe regarding the practice of emergency radiology METHODS: A survey which comprised of 24 questions was developed and made available online. The questionnaire was sent to 1097 chairs of radiology departments throughout Europe using the ESR database. All data were collected and analyzed using IBM SPSS Statistics software, version 20 (IBM). RESULTS: A total of 1097 radiologists were asked to participate, 109 responded to our survey. The response rate was 10%. From our survey, 71.6% of the hospitals had more than 500 beds. Ninety-eight percent of hospitals have an active teaching affiliation. In large trauma centers, emergency radiology was considered a dedicated section. Fifty-three percent of institutions have dedicated emergency radiology sections. Less than 30% had all imaging modalities available. Seventy-nine percent of institutions have 24/7 coverage by staff radiologists. Emergency radiologists interpret cross-sectional body imaging, US scans, and basic CT/MRI neuroimaging in more than 50% of responding institutions. Cardiac imaging examinations/procedures are usually performed by cardiologist in 53% of institutions, while non-cardiac vascular procedures are largely performed and interpreted by interventional radiologists. Most people consider the European Diploma in Emergency Radiology an essential tool to advance the education and the dissemination of information within the specialty of emergency radiology. CONCLUSION: Emergency radiologists have an active role in the emergency medical team. Indeed, based upon our survey, they have to interact with emergency physicians and surgeons in the management of critically ill patients. A broad skillset from ultrasonography and basic neuroimaging is required. KEY POINTS: • At most major trauma centers in Europe, emergency imaging is currently performed by all radiologists in specific units who are designated in the emergency department. • Radiologists in the emergency section at present have a broad skillset, which includes cross-sectional body imaging, ultrasonography, and basic neuroimaging of the brain and spine. • A dedicated curriculum that certifies a subspecialty in emergency radiology with a diploma offered by the European Society of Emergency Radiology demonstrates a great interest by the vast majority of the respondents.

European Society of Emergency Radiology: guideline on radiological polytrauma imaging and service (short version).

BACKGROUND: Although some national recommendations for the role of radiology in a polytrauma service exist, there are no European guidelines to date. Additionally, for many interdisciplinary guidelines, radiology tends to be under-represented. These factors motivated the European Society of Emergency Radiology (ESER) to develop radiologically-centred polytrauma guidelines. RESULTS: Evidence-based decisions were made on 68 individual aspects of polytrauma imaging at two ESER consensus conferences. For severely injured patients, whole-body CT (WBCT) has been shown to significantly reduce mortality when compared to targeted, selective CT. However, this advantage must be balanced against the radiation risk of performing more WBCTs, especially in less severely injured patients. For this reason, we recommend a second lower dose WBCT protocol as an alternative in certain clinical scenarios. The ESER Guideline on Radiological Polytrauma Imaging and Service is published in two versions: a full version (download from the ESER homepage, https://www.eser-society.org ) and a short version also covering all recommendations (this article). CONCLUSIONS: Once a patient has been accurately classified as polytrauma, each institution should be able to choose from at least two WBCT protocols. One protocol should be optimised regarding time and precision, and is already used by most institutions (variant A). The second protocol should be dose reduced and used for clinically stable and oriented patients who nonetheless require a CT because the history suggests possible serious injury (variant B). Reading, interpretation and communication of the report should be structured clinically following the ABCDE format, i.e. diagnose first what kills first.

What is the role of diffusion tensor imaging (DTI) in detecting subclinical pyramidal tract dysfunction in Behçet's and neuro-Behçet's cases?

The aim of this study is to investigate the pyramidal tract integrity with DTI in Behçet's and neuro-Behçet's cases. We performed this technique in two subgroups of neuro-Behçet's patients (parenchymal and vascular), and Behçet's cases without neurological involvement and control group. Totally, 28 patients were investigated. The control group was composed of 14 healthy people. Cranial MR and DTI were performed in three patient groups and the control group. At DTI, circular regions of interest (ROI) were symmetrically drawn on axial slices on the left and right sides along the pyramidal tract pathway at two levels: middle one third of the cerebral peduncle and posterior limb of the internal capsule. Fractional anisotropy (FA) values for each ROI were obtained by averaging all voxels within the ROI. Calculated FA values on both sides (left and right) of the posterior limb of the internal capsule and cerebral peduncle are significantly lower in all three patient groups when compared to the control group. But there is no any difference of FA values in the selected brain regions of three patient groups. FA values on the posterior limb of the internal capsule and cerebral peduncle do not show a statistically significant difference in parenchymal neuro-Behçet's cases. Our study demonstrates that DTI can detect subclinical pyramidal tract dysfunction in neuro-Behçet's and Behçet's patients. Detection of subclinical nervous system involvement is crucial for morbidity in Behçet's disease. For this reason, studies based on DTI, which include a large number of patients and explore different brain regions, are needed to guide clinicians.

Nonneuropathic Neuropathic Bladder-Is it Really Nonneuropathic?

PURPOSE: Hinman syndrome is a rare disease with urodynamic findings and a clinical course resembling neuropathic bladder, without a neuropathic etiology. Diffusion tensor imaging is a special technique of magnetic resonance imaging that has recently been used to evaluate the peripheral nerves but has been demonstrated to be applicable for evaluation of the lumbosacral plexus. We examined the lumbosacral plexus using diffusion tensor imaging, which has not previously been reported in patients with Hinman syndrome. MATERIALS AND METHODS: The study included 12 patients who fulfilled criteria for Hinman syndrome, with severe bladder dysfunction on urodynamics, renal scarring on scintigraphy and no pathological findings on magnetic resonance imaging. The 12 subjects serving as controls required pelvic or spinal magnetic resonance imaging for reasons other than spinal abnormalities. Evaluation was performed with a 3.0 Tesla magnetic resonance imaging system and 16-channel body coil. Tractography was done to examine the lumbosacral plexus. Fractional anisotropy and mean diffusivity were computed and compared between groups for the right and left plexuses. RESULTS: Mean fractional anisotropy was 0.24 and 0.35 for the right plexus in patients and controls, respectively, and 0.24 and 0.36 for the left plexus. Mean diffusivity was 1.39 for the right and left plexuses in patients, and 1.28 for the right and left plexuses in controls (p <0.001 for all). CONCLUSIONS: Our study focusing on the lumbosacral plexus as a possible origin of neuropathy revealed abnormal findings in patients with Hinman syndrome resembling nerve injury series. This is the first known study to provide data showing that Hinman syndrome may have a neuropathic etiology.

Relationship of stylohyoid chain and cervical internal carotid artery detected by 3D angiography.

OBJECTIVE: The calcification of the stylohyoid chain (SHC), elongated styloid process (SP), larger SP' angle and its shortened distance of cervical internal carotid artery (CICA) are risk factors for bony compression and the stylocarotid syndrome. METHODS: 3D-CTAs of 125 patients were analyzed in terms of the SP length, its angulations, type of the SHC and relationships of its proximity to the CICA. RESULTS: Elongated SP was observed frequently both in females (47%) and males (55%). The mean distance of the CICA to the SP was calculated as 8.2 ± 3.3 mm. This short distance between the CICA and the SP was observed more frequently in males (28.1%) and females (10.7%). The anterior and medial angulations of the SP were calculated as 71.2 ± 4.3°, and 57.3 ± 9.3°, respectively. In the present study, the SHC was determined as normal SP (54.2%), absence of the SP (1%), duplication of the SP (1%), elongated SP (26%), complete ossification of the SHC (1%), segmentation of the SHC (9%), fracture of ossification of the SHC (1.6%) and pseudo articulations of the SHC (5.6%). CONCLUSION: 3D-CTA was the most appropriate radiological investigation analyzing and measuring SHC (elongated, larger angle, shorter distances with CICA) and identifying types (duplicated, segmented, complete and fractured) resulting from pressures on the CICA. Our study also revealed the pressure on the artery not only arose from the tip of the SP but could also result from types stretching over the artery wall. In those specimens, there is a higher probability of formation of the stylocarotid syndrome due to the long-term pressure on the sympathetic chain around the CICA.

Altered structural connectivity is related to attention deficit/hyperactivity subtypes: A DTI study.

This study aimed to provide novel insights into the white matter (WM) microstructural properties of Attention Deficit/Hyperactivity Disorder (ADHD) subtypes by recruiting a relatively large sample of stimulant-naïve children and adolescents who had no comorbidity other than Oppositional Defiant Disorder and were homogenous according to the DAT1 gene polymorphism. A sample of 72 ADHD subjects and 24 controls aged 8-15 years were enrolled in the study. We applied tract-based spatial statistics to the DTI measures for obtaining fractional anisotropy (FA) and axial, radial diffusivity (AD, RD) measures to explore ADHD type-related differences in WM for the whole brain. Comparing ADHD-Combined group (ADHD-C) with the ADHD predominantly inattentive group (ADHD-I) we detected increased RD in several bilateral brain area and increased AD mostly in left side of the brain, including the body and splenium of the corpus callosum; the anterior and posteriors limbs of the internal capsule; the superior, anterior and posterior corona radiata; the posterior thalamic radiation; and the superior longitudinal fasciculus. Likewise, mostly in the overlapping brain areas, the ADHD-C group presented increased AD values than ADHD-RI. Significant differences among ADHD types could be a preliminary evidence that they have distinct microstructural properties. There were no significant differences in diffusivity between controls and both the ADHD group as whole or any ADHD subgroups.

Decreasing ADHD phenotypic heterogeneity: searching for neurobiological underpinnings of the restrictive inattentive phenotype.

During the process of developing the DSM-5, a new phenotype of ADHD was proposed-the ADHD restrictive inattentive presentation (ADHD-RI), describing subjects with high endorsement of inattentive symptoms and a low level of hyperactivity. However, this phenotype was not included in the DSM-5 because of the lack of robust neurobiological data. We aimed to assess the specific neurobiological underpinnings of individuals presenting ADHD-RI. We compared a sample of 301 subjects (101 ADHD-Combined; 50 ADHD-RI; 50 ADHD predominantly inattentive type and 100 typically developing subjects) aged 8-15 years, using a complete neuropsychological battery, molecular genetic data (DRD4 and DAT1 most studied polymorphisms) and functional MRI during a Go-No/Go task. Subjects with ADHD-RI had a significantly different neuropsychological profile compared with the other groups, including lower psychomotor speeds, longer reaction times and the worst overall performance in the global neurocognitive index. The proportion of subjects with the presence of DRD4-7 repeat allele was significantly higher in ADHD-RI. The fMRI data suggested that more attention-related posterior brain regions (especially temporo-occipital areas) are activated in ADHD-RI during both Go and No-Go cues compared to TD controls and ADHD predominantly inattentive type. ADHD-RI may represent a different phenotype than other types of ADHD. In addition, our results suggest that reducing the phenotypic heterogeneity may aid in the search for the neurobiological underpinnings of ADHD.

A non-alcoholic Wernicke's encephalopathy case with atypical MRI findings: Clinic versus radiology.

Wernicke's Encephalopathy is an acute neuropsychiatric syndrome that can be seen in both alcohol abusers and non-alcoholic population as a result of thiamine deficiency. We herein report a non-alcoholic patient with typical clinical presentations but atypical MRI findings. Early clinical suspicion of WE is especially important in non-alcoholic patients with atypical MRI findings. The diagnosis of this group is more difficult to make and the prognosis of the syndrome mostly depends on early initiation of thiamine supplementation.

Symptomatic Spinal Migration of Subarachnoid Hemorrhage due to Ruptured Intradural Vertebral Artery Aneurysm.

A 55-year-old patient was admitted to the hospital with severe acute back pain. Thoracolumbar magnetic resonance (MR) imaging showed hemorrhage in subarachnoidal-subdural space. On cranial MR imaging and MR angiography, an aneurysm was suspected in the V4 segment of the right vertebral artery. Angiography showed a fusiform dissecting aneurysm in the V4 segment of right vertebral artery. The final diagnosis was ruptured V4 segment aneurysm with subsequent symptomatic migration of hemorrhage into the spinal subarachnoidal-subdural space. The patient was treated endovascularly by coil occlusion of both the aneurysm and vertebral artery. This rare cause and possible mechanisms for spinal migration of intracranial hemorrhage after aneurysmal rupture is discussed.

Manganese-enhanced MRI to evaluate neurodegenerative changes in a rat model of kainic acid-induced excitotoxicity.

PURPOSE: Manganese-enhanced magnetic resonance imaging (MEMRI) has been used to detect brain activity based on the ability of active neurons to take up manganese ions through calcium channels. Kainic acid (KA), an analog of excitotoxic glutamate, can elicit selective neuronal death in the brains of rodents, of which the pathological changes partially mimic neurodegeneration in the central nervous system. We used in vivo MEMRI to evaluate neurodegenerative changes in an excitotoxicity model induced by KA in rats. MATERIALS AND METHODS: Adult Sprague-Dawley rats (220-250 g) were injected with either KA or saline into the right lateral ventricle. Precontrast and postcontrast MEMRI sessions were obtained. Region of interest (ROI) analyses were performed on both injected (saline and KA) and contralateral (normal) sites in the hippocampal area. All brains were evaluated histologically following MEMRI. RESULTS: Analysis of percentage change in ROI intensities of T1-weighted fluid-attenuated inversion-recovery MR images in the hippocampal area revealed a significant difference between the KA-injected (ipsilateral) and contralateral sites (P = 0.008), whereas no significant difference was observed between the saline-injected and contralateral sites. Furthermore, there was a significant difference between ipsilateral sites of the saline-treated and KA-treated groups (P = 0.026). The histological results supported these findings. CONCLUSION: MEMRI is a simple and useful in vivo method for detecting neurodegenerative changes due to excitotoxicity in the rat brain. The development of a manganese-based contrast agent that can be safely used in humans is warranted to investigate neurological disorders.

Diagnostic tools of early brain disturbances in an asymptomatic neonate with maple syrup urine disease.

Maple syrup urine disease (MSUD) is a rare inherited metabolic disorder resulting from the defective activity of branched-chain 2-ketoacid dehydrogenase complex. Routine screening of newborn with tandem mass spectroscopy on the third day of life may detect elevated branched-chain amino acids in blood before the appearance of encephalopathic symptoms in MSUD cases. If undiagnosed by such a routine screening test, patients often present with encephalopathy and seizures. Clinical neurologic examination is supplemented by electroencephalography and imaging. Here, we report abnormal amplitude-integrated electroencephalography, electroencephalography, magnetic resonance imaging, and magnetic resonance imaging spectroscopy findings in a neurologically asymptomatic male newborn who was diagnosed with MSUD at the third week of life. These neurologic disturbances disappeared at the fourth month of life with appropriate special diet. Therefore, even in already asymptomatic cases, early neurologic deterioration of brain metabolism and structure can be detected with these early laboratory findings, indicating the importance of early diagnosis and management. Patients may also benefit from these investigations during the follow-up period.

Impact of poststroke seizures on neurological deficits: magnetic resonance diffusion-weighted imaging study.

BACKGROUND: The impact of poststroke seizures on the neurological deficits related to ischemic stroke is not well known. It has been reported that following poststroke epilepsy, transient or long-lasting worsening of the poststroke sequelae may develop, but the underlying mechanism of deficit worsening has not been systematically studied by magnetic resonance diffusion-weighted imaging (MRI-DWI). METHODS: From 2008 to 2009, 1,010 ischemic stroke patients were admitted to our stroke unit at the Ege University Hospital with first-time strokes. Of these, 76 (7.5%) patients developed delayed seizures in a follow-up period of 18 months. We extracted the clinical and imaging data of the patients from our Stroke Registry databases and other medical records, and evaluated brain MRI, including spin-echo DWI with apparent diffusion coefficient (ADC) maps, FLAIR and T2-weighted images. RESULTS: There were 15 (20%) patients who had long-lasting worsening of the previous neurological sequelae, which we called long-lasting neurological worsening (LLW); 38 (50%) had transient neurological worsening (TNW) and 23 (30%) were without neurological worsening (WNW) after poststroke seizures. DWI findings were present in 3/23 (13%) patients with simple partial-type seizure, in 4/17 (29%) patients with complex partial-type seizure, and in 7/13 (54%) patients with generalized toni-clonic type seizure (p = 0.002). Patients with LLW showed more frequent changes on DWI than those with TNW (53 vs. 16%; p = 0.009). Forty percent of patients with LLW and 5% of those with TNW had ADC decrease (p = 0.004). Patients with LLW had DWI changes in the occipital region more frequently than those with TNW (57 vs. 18%; p = 0.05). Correlation analysis found a significant association between LLW and DWI changes, multiple DWI lesions, ADC decrease, and recurrent seizures. In the control MRI-DWI 1 month after the poststroke seizure, no signal abnormalities were detected in neuroimaging studies of all patients. Despite no functional outcome differences between the groups before the seizure, the functional scales 1 week after the seizure (National Institutes of Health Stroke Scale, Modified Rankin Scale and Barthel Index) showed significantly worse neurological functional statements in the patients with LLW than those with TNW and WNW (p = 0.001). CONCLUSIONS: Poststroke seizures may affect poststroke sequelae transiently, which we see more often, but some seizure types may prolong the duration of deficits. Multiple DWI changes and LLW following recurrent and longer poststroke seizures were strongly associated, and this may be due to the effect of seizures causing additional metabolical changes.

The relationship between the anterior corpus callosum size and prefrontal cortex volume in drug-free depressed patients.

INTRODUCTION: An evolving literature suggests a volume reduction and a loss of functional integrity of prefrontal cortex in depressed patients. Interhemispheric prefrontal functional integrity is mediated via the anterior portion of the corpus callosum. Until recently interhemispheric fibers connecting prefrontal cortex have not been well defined. In this study, we compared the corpus callosum area of depressed patients with controls using a novel schema proposed by Hofer and Frahm (2006) which defined a specific anterior callosal area for prefrontal interhemispheric fibers. We further investigated the correlation between callosal area and prefrontal cortical volume. METHODS: Thirty-six patients with major depressive disorder and thirty-three healthy controls were recruited. All subjects were psychotropic medication-free and right-handed. The imaging was performed on a 1.5T MR unit (Magnetom Vision Siemens). The images obtained from 3D MP-RAGE sequence were used for analyses. Medical Image Processing, Analyzing and Visualization (MIPAV) software was used for callosal and prefrontal measurements. RESULTS: Depressed patients had reduced prefrontal cortical volume and a loss of the normal callosal/gray matter correlation, but normal white matter volume and normal callosal areas. LIMITATIONS: It is not known if the observed changes were preexisting or acquired. CONCLUSION: Our results indicate that the normal structural relationship between anterior callosal area and prefrontal cortical volume is disrupted in major depressive disorder and that the disruption is due to reduced cortical volume rather than to changes in interhemispheric connections.