Real-Time Magnetic Resonance Imaging

Real‐time magnetic resonance imaging (RT‐MRI) allows for imaging dynamic processes as they occur, without relying on any repetition or synchronization. This is made possible by modern MRI technology such as fast‐switching gradients and parallel imaging. It is compatible with many (but not all) MRI sequences, including spoiled gradient echo, balanced steady‐state free precession, and single‐shot rapid acquisition with relaxation enhancement. RT‐MRI has earned an important role in both diagnostic imaging and image guidance of invasive procedures. Its unique diagnostic value is prominent in areas of the body that undergo substantial and often irregular motion, such as the heart, gastrointestinal system, upper airway vocal tract, and joints. Its value in interventional procedure guidance is prominent for procedures that require multiple forms of soft‐tissue contrast, as well as flow information. In this review, we discuss the history of RT‐MRI, fundamental tradeoffs, enabling technology, established applications, and current trends

Cardiac magnetic resonance assessment of central and peripheral vascular function in patients undergoing renal sympathetic denervation as predictor for blood pressure response

Background: Most trials regarding catheter-based renal sympathetic denervation (RDN) describe a proportion of patients without blood pressure response. Recently, we were able to show arterial stiffness, measured by invasive pulse wave velocity (IPWV), seems to be an excellent predictor for blood pressure response. However, given the invasiveness, IPWV is less suitable as a selection criterion for patients undergoing RDN. Consequently, we aimed to investigate the value of cardiac magnetic resonance (CMR) based measures of arterial stiffness in predicting the outcome of RDN compared to IPWV as reference. Methods: Patients underwent CMR prior to RDN to assess ascending aortic distensibility (AAD), total arterial compliance (TAC), and systemic vascular resistance (SVR). In a second step, central aortic blood pressure was estimated from ascending aortic area change and flow sequences and used to re-calculate total arterial compliance (cTAC). Additionally, IPWV was acquired. Results: Thirty-two patients (24 responders and 8 non-responders) were available for analysis. AAD, TAC and cTAC were higher in responders, IPWV was higher in non-responders. SVR was not different between the groups. Patients with AAD, cTAC or TAC above median and IPWV below median had significantly better BP response. Receiver operating characteristic (ROC) curves predicting blood pressure response for IPWV, AAD, cTAC and TAC revealed areas under the curve of 0.849, 0.828, 0.776 and 0.753 (p = 0.004, 0.006, 0.021 and 0.035). Conclusions: Beyond IPWV, AAD, cTAC and TAC appear as useful outcome predictors for RDN in patients with hypertension. CMR-derived markers of arterial stiffness might serve as non-invasive selection criteria for RDN

Sensitivity and specificity of BERAphone® as a screening tool for neonatal hearing loss in a tertiary care hospital in India

Hearing loss is a silent crippling sensory disorder of childhood. If left undiagnosed it can result in speech, hearing and communication problems. Early detection through screening as recommended in the universal screening protocol is mandatory. The present study was done to evaluate the effectiveness of the screening tool BERAphone when it is used to screen high volumes of babies in the natural ward setting with background noise. Our study had used the updated version of the MB 11 device which is known to increase the amplitude of the ABR response using a chirp stimulus. These studies were carried out on healthy newborns who did not present with any particular audiologic risk factors within the first days of life. The present report shows the data analysis from 37 newborns screened using the MB11 BERAphone® as a screening tool. The first stage of the two staged hearing screening was performed in the postnatal ward and the second stage in the audiology lab. After the two stage screening the pass rate was 41.9% and the referral rate was 58.1%. The screening tool BERAphone showed a sensitivity of 92.86%, a specificity of 50%, positive predictive value of 30.23 % and negative predictive value 96.77% for the diagnosis of hearing loss. The results that were obtained show that MB11 is a good screening tool among infants and can be used as a first level diagnostic tool for suspected hearing loss but must be verified with Auditory Brainstem Response (ABR) which is the “gold standard” test essential to a correct neonatal screening programme. CONCLUSION: From our experience, the MB11 BERAphone® is a reliable device for use in a two stage newborn hearing screening based on auditory brainstem response. It gives good results within a very short time with minimal cost of materials since no disposables are necessary to be used compared to other ABR screening devices. Due to the implemented automated detection algorithm for ABR, the device is suitable for use by trained technicians in a post natal environment. The machine shows good specificity as predicted where it is able to identify those who do not have the disease but it has a low sensitivity than expected when used in the ward setting with surrounding high ambient noise. Thus it must be used along with a confirmatory test like ABR to establish hearing loss

Dynamic 3-D visualization of vocal tract shaping during speech

Noninvasive imaging is widely used in speech research as a means to investigate the shaping and dynamics of the vocal tract during speech production. 3-D dynamic MRI would be a major advance, as it would provide 3-D dynamic visualization of the entire vocal tract. We present a novel method for the creation of 3-D dynamic movies of vocal tract shaping based on the acquisition of 2-D dynamic data from parallel slices and temporal alignment of the image sequences using audio information. Multiple sagittal 2-D real-time movies with synchronized audio recordings are acquired for English vowel-consonant-vowel stimuli /ala/, /ara/, /asa/, and /a∫a/. Audio data are aligned using mel-frequency cepstral coefficients (MFCC) extracted from windowed intervals of the speech signal. Sagittal image sequences acquired from all slices are then aligned using dynamic time warping (DTW). The aligned image sequences enable dynamic 3-D visualization by creating synthesized movies of the moving airway in the coronal planes, visualizing desired tissue surfaces and tube-shaped vocal tract airway after manual segmentation of targeted articulators and smoothing. The resulting volumes allow for dynamic 3-D visualization of salient aspects of lingual articulation, including the formation of tongue grooves and sublingual cavities, with a temporal resolution of 78 ms.11 page(s