Normal Swallowing and Functional Magnetic Resonance Imaging: A Systematic Review

Unknowns about the neurophysiology of normal and disordered swallowing have stimulated exciting and important research questions. Previously, these questions were answered using clinical and animal studies. However, recent technologic advances have moved brain-imaging techniques such as functional magnetic resonance imaging (fMRI) to the forefront of swallowing neurophysiology research. This systematic review has summarized the methods and results of studies of swallowing neurophysiology of healthy adults using fMRI. A comprehensive electronic and hand search for original research was conducted, including few search limitations to yield the maximum possible number of relevant studies. The participants, study design, tasks, and brain image acquisition were reviewed and the results indicate that the primary motor and sensory areas were most consistently active in the healthy adult participants across the relevant studies. Other prevalent areas of activation included the anterior cingulate cortex and insular cortex. Review limitations and suggested future directions are also discussed. This research was supported by the National Institutes of Health (NIH), NCRR K12 Roadmap, Training and Education to Advance Multidisciplinary-Clinical-Research (TEAM) Program. Project number 8K12RR023268-02.     

Magnetic Resonance Imaging of the Rectum During Distension

PURPOSE A knowledge of the relationships between the rectum and its surrounding structures during distention may improve our understanding of the results of studies assessing rectal sensory-motor responses to distention. This magnetic resonance imaging study was designed to assess the shape of the rectum and the degree of distention at which the surrounding structures are compressed.METHODS Nine healthy patients underwent magnetic resonance imaging of the rectum under resting conditions and after the inflation of a plastic bag to volumes of 50, 100, 150, 200, and 250 ml. The thickness of the rectovesical space was assessed as a measure of the compression of the perirectal structures, and the perception of sensations were recorded.RESULTS The shape of the rectum changed from being quasicylindrical at distention volumes of <100 ml to bean-shaped at larger volumes. The thickness of the rectovesical space at a distention volume of 50 ml was the same as when the bag was not inflated, but it progressively decreased until the difference became statistically significant at distention volumes of ≥200 ml, corresponding to a mean ± standard deviation rectal radius of 2.66 ± 0.37 cm. Statistically significant compression of the rectovesical space was recorded when the sensations of gas, desire to defecate, and urgency were perceived. CONCLUSIONS The shape of the rectum changes during distention; it significantly compresses the extrarectal structures in the tested range of distention that induces nonpainful sensations. Magnetic resonance imaging is a useful means of assessing the morphologic changes in the rectum during distention.Presented at the Digestive Disease Week, New Orleans, Louisiana, May 15 to 20, 2004.Supported by the Associazione Amici della Gastroenterologia del Padiglione Granelli, Milano, Italy.     

Activation of Cerebellum and Basal Ganglia on Volitional Swallowing Detected by Functional Magnetic Resonance Imaging

Although regions of the sensorimotor cortex, insula, and anterior cingulate gyrus are reported to be activated during swallowing, findings concerning contributions of the cerebellum and basal ganglia have been contradictory. We investigated cerebellar and basal ganglionic activation using functional magnetic resonance imaging (fMRI). In 11 subjects, single-shot gradient-echo echoplanar image volumes sensitive to BOLD contrast were acquired in block design fashion using an oblique orientation covering both cerebrum and cerebellum. Using statistical parametric mapping, regional activation upon swallowing was observed in the sensorimotor cortex, insula, cerebellum, putamen, globus pallidus, thalamus, anterior cingulate gyrus, supplementary motor area, superior temporal gyrus, and substancia nigra. The cerebellum was activated bilaterally, especially on the left; activation of the putamen and globus pallidus was also found bilaterally. Thus, volitional swallowing involves the cerebellum and basal ganglia as well as cortical structures. The method used was well tolerated by normal subjects and should also be applicable to patients with dysphagia. This work was supported by a grant-in-aid for exploratory research (13877281) awarded to M. Suzuki.     

Ultrasound Imaging of Infant Swallowing During Breast-Feeding

Coordination of infants’ suck-swallow-breathing patterns is integral to safe and efficient feeding. However, assessment of these patterns is difficult and often invasive, particularly in breast-fed infants less than 4 months of age. The aims of this study were to develop an ultrasound approach to visualize swallowing in term breast-feeding infants and to determine the accuracy of ultrasound imaging of swallowing compared to respiratory inductive plethysmography (RIP). On ultrasound, the breast milk bolus was observed as a predominantly echogenic area moving inferiorly. Of the 388 swallows detected with ultrasound, 379 correlated with the swallow apneas detected by RIP (R ² = 0.98). The mean duration of the swallow was 0.63 ± 0.06 s. Ultrasound imaging is a noninvasive accurate method for detection of swallowing by visualization of movement of the milk bolus through the pharyngeal area of a breast-feeding infant. These techniques may potentially provide useful information for infants experiencing breast-feeding difficulties.     

The Effect of the Cervical Orthosis on Swallowing Physiology and Cervical Spine Motion During Swallowing

Cervical orthosis is used to immobilize the neck in various disorders such as trauma and post-operation. However, it is still uncertain how cervical orthosis restricts the degree of movement of the cervical spine during swallowing and how they affect swallowing physiology. The purpose of this study was to evaluate these issues using the Philadelphia^® Collar. We conducted videofluorography of swallowing in 39 healthy subjects (23 men, 16 women; mean age of 34.3 years) with and without cervical orthosis. To compare the two conditions regarding the cervical spine motion, we determined the angular and positional changes of the occipital bone (C0) and each cervical vertebra (C1–C7) from the oral phase to the pharyngeal phase. Similarly, to compare swallowing physiology, we assessed the start and end times and the durations of soft palate elevation, rapid hyoid anterosuperior movement, epiglottis inversion, closure of the laryngeal vestibule, and pharyngoesophageal segment (PES) opening. Finally, we compared the transit times of contrast agent in the two conditions. The respective extensions of C1, C2, and C3 were 0.31°, 0.07°, and 0.05° (mean) with cervical orthosis, and the respective flexions of C1, C2, and C3 were 0.98°, 1.42°, and 0.85° (mean) without. These results suggested that cervical orthosis restricted the flexion of C1–C3. Analysis of swallowing physiology revealed that the average durations of hyoid anterosuperior elevation, epiglottic inversion, and PES opening were prolonged by 0.09, 0.19, and 0.05 s, respectively. In conclusion, the cervical orthosis restricted the movement of the cervical spine during swallowing and changed swallowing physiology.     

Modulation of Activity in Swallowing Motor Cortex Following Esophageal Acidification: A Functional Magnetic Resonance Imaging Study

Esophageal acid exposure induces sensory and motility changes in the upper gastrointestinal tract; however, the mechanisms involved and the effects on activity in the brain regions that control swallowing are unknown. The aim of this study was to examine functional changes in the cortical swallowing network as a result of esophageal acidification using functional magnetic resonance imaging (fMRI). Seven healthy volunteers (3 female, age range=20-30 years) were randomized to receive either a 0.1 M hydrochloric acid or (control) saline infusion for 30 min into the distal esophagus. Postinfusion, subjects underwent four 8 min blocks of fMRI over 1 h. These alternated between 1 min swallowing water boluses and 1 min rest. Three-dimensional cluster analysis for group brain activation during swallowing was performed together with repeated-measures ANOVA for differences between acid and saline. After acid infusion, swallowing-induced activation was seen predominantly in postcentral gyrus (p<0.004). ANOVA comparison of acid with saline showed a significant relative reduction in activation during swallowing of the precentral gyrus (M1) BA 4 (p<0.008) in response to acid infusion. No areas of increased cortical activation were identified with acid vs. saline during swallowing. Esophageal acidification inhibits motor and association cortical areas during a swallowing task, probably via changes in vagal afferent or nociceptive input from the esophagus. This mechanism may play a protective role, facilitating acid clearance by reduced descending central motor inhibition of enteric/spinal reflexes, or by preventing further ingestion of injurious agents.     

Assessment of Ischemic Heart Disease Using Magnetic Resonance First-Pass Perfusion Imaging

METHODS: Cardiovascular magnetic resonance (MR) perfusion imaging has matured to a point where it can be routinely applied to assess patients with coronary artery disease and ischemic cardiomyopathy. The method has been compared to invasive, catheter-based as well as other noninvasive imaging modalities (echocardiography, single-photon emission computed tomography [SPECT], and positron emission tomography [PET]) for the evaluation of patients with coronary artery disease. Besides qualitative evaluation of MR perfusion images, an absolute quantification of global, regional and transmural myocardial perfusion is possible. A relative or absolute myocardial perfusion reserve has been determined noninvasively with MR perfusion imaging, and can provide good agreement with the invasive assessment. Based on the perfusion reserve, the severity of an epicardial coronary stenosis can be evaluated in patients with known or suspected coronary artery disease. Besides the absence of radiation exposure, MR perfusion imaging offers good temporal and excellent spatial resolution. In particular, the spatial resolution increases the sensitivity and specificity for the detection of coronary artery disease. New parameters such as the "endo-/epimyocardial resting perfusion ratio", may under some circumstances sufficiently enhance the sensitivity for detecting an abnormal perfusion, and thus avoid potentially harmful and expensive stress testing in patients with suspected ischemic heart disease. New revascularization modalities such as therapeutic angiogenesis need to be matched by sensitive imaging tools to prove their benefits. Thus, the optimization of therapeutic angiogenesis may profit from the diagnostic advantages provided by MR perfusion imaging. Furthermore, MR might yield new insights into the pathophysiology of cardiac diseases such as "syndrome X", or might help in the repetitive assessment of heart transplant recipients, possibly obviating the need for further invasive testing. CONCLUSION: The breadth of cardiac MRI allows the combined noninvasive assessment of myocardial perfusion, function, as well as myocardial viability. The combination gives MRI a unique and strong position in the field of noninvasive diagnostic cardiology.     

Magnetic Resonance Imaging and radiofrequency ablations

Cardiac MRI has evolved one of the major imaging technologies in cardiology. Increasingly MRI has also been used for electrophysiological applications. Anatomically based procedures such as the circumferential pulmonary vein ablation emphasized the importance of including the individual's cardiac anatomy in a tailored ablation approach. Today, many centers routinely perform pre-ablation imaging to identify left atrial anatomy. Three-dimensional reconstructions based on MRI are frequently integrated in clinical mapping systems to provide cardiac anatomy during the ablation procedure. Similarly, MRI is a clinically very valuable tool in assessing potential ablation complications such as pulmonary vein stenosis. New innovative use of MRI is likely to occur in three areas over the next several years. During ventricular tachycardia ablations volume rendering/fusion imaging will enable a detailed three-dimensional substrate evaluation and provide supplementary scar characterization using a combination of different imaging approaches. With the ongoing technical improvements real-time MRI will likely emerge as a stand-alone clinical modality to directly guide catheter ablation procedures. The advent of stronger field strength MRI, faster imaging protocols, and improved gating techniques will allow accurate peri- and post-procedural visualization of ablation lesions. These developments should result in shorter procedure times and decreased complications rates. Ultimately, they will enable the development of novel ablation strategies and expand the current indications for electrophysiological ablations.     

Reduced Cerebral Grey Matter Observed in Alcoholics Using Magnetic Resonance Imaging

Twenty-eight chronic alcoholics and 36 age- and sex-matched non-alcoholic controls were examined with magnetic resonance imaging and brain morphometric analyses. Results confirmed large increases in subarachnoid cerebrospinal fluid (CSF) volume and mild ventricular enlargement in the alcoholics and revealed associated volume reductions of localized cortical and subcortical cerebral structures. Volume losses in the diencephalon, the caudate nucleus, dorsolateral frontal and parietal cortex, and mesial temporal lobe structures were the most prominent. Significant correlations between increments in cortical and ventricular CSF and decrements in the volume of cortical and subcortical grey matter were noted. Although there was little evidence for relationships between performance on neuropsychological tests and volume of grey matter structures, significant correlations between some cognitive measures and subcortical and cortical fluid volumes were found. The parallels between this pattern of affected structures and recent neuropathological findings are discussed.     

颅内出血的磁共振成像

MRI的常规序列T1加权成像、T2加权成像和液体衰减反转恢复(FLAIR)序列均可敏感地检出亚急性期和慢性期颅内出血;梯度回波成像可检出各期颅内出血,但血肿信号强度与血肿存在的时间无相关性。弥散加权成像和表观弥散系数能提供更多有关血肿中心区、周围区和梗死后出血的信息。