Static Magnetic Resonance Imaging Research Articles

The use of ultrasound in the assessment of the glenoid labrum of the glenohumeral joint. Part I: Ultrasound anatomy and examination technique and W. Krzyżanowski, M. Tarczyńska The use of ultrasound in the assessment of the glenoid labrum of the glenohumeral joint. Part II: Examples of labral pathologies.

I was very pleased when I received the invitation of the Editors of the “Journal of Ultrasonography” to comment on the articles of Dr Wojciech Krzyzanowski and Dr Marta Tarczynska(1, 2). For the first time, I became familiar with Dr Krzyzanowski's study on the ultrasound imaging of the glenoid labrum of the glenohumeral joint during the clinical and radiological symposium on shoulder diagnostics organized in September 2012 by my medical center in Katowice. The convincing dynamic images of the labrum that I saw during his presentations persuaded me to look through the literature on ultrasound (US) examinations of the labrum with regard to their usefulness in clinical practice. The extraordinary progress of US shoulder diagnostics has made it equally reliable in the recognition of rotator tendon injuries with the magnetic resonance imaging (MRI) which is expensive, time-consuming and uncomfortable for patients. In calcareous degeneration of the tendons the sensitivity and specificity of this imaging method is even superior to MRI. So far, the visualization of the glenoid labrum, whose pathologies constitute the cause of shoulder dysfunctions in a significant number of patients, has not been possible by means of the ultrasound. The first studies on using ultrasonography in the labrum diagnostics were conducted at the end of the 1980s and the latest research was performed at the beginning of the 21st century(3–5). In the subsequent years, this subject was not discussed. Dr Krzyzanowski and Dr Tarczynska decided to verify this avoided issue – is it possible to effectively use ultrasound in the diagnosis of the glenoid labrum injuries of the glenohumeral joint? As a practitioner of shoulder surgery, I am interested not only in the aspect of visualizing the labrum in the ultrasound examination, but above all, in the practical aspect, i.e. the cases in which the labrum US would have a crucial influence on therapeutic decisions. The visualization of the labrum in the case of documented instability in the form of repeated dislocations is of little importance with regard to the diagnosis and therapeutic decision-making. However, when such information has not been obtained during the interview or in the case of other disease entities caused by labrum injuries, a reliable imaging is of great significance. The examples constitute recurrent instability in the form of subluxations, whose direction cannot be determined on the basis of clinical and X-ray examinations, as well as so-called unstable painful shoulder – an entity described by Boileau et al.(6), the authors of internal glenoid impingement syndrome which leads to the damage of posterosuperior labrum in the peel back mechanism. Another example is a specific damage of the posteroinferior labrum which was described by Kim et al.(7) and whose diagnosis may pose difficulties even during arthroscopy due to undamaged superficial and articular part of the labrum. Ultrasound imaging might prove useful in the aforementioned instances as it allows for the visualization of deep layers of the labrum and performance of dynamic examination. Apart from this, it is only an imaging exam which may facilitate the recognition of paralabral cysts and determination of their localizations. Another problematic clinical and diagnostic issue in MR imaging is the injuries of the superior labrum of SLAP type (superior labrum anterior-posterior). In the case of this damage, the outcomes of clinical examination and MRI are similar and equally unsatisfactory. Contrast-enhanced MRI improves the specificity of the diagnostics of superior labrum injuries. One of the factors causing difficulties in imaging diagnostics of pathologies in this part of the labrum is surely a considerable variability of its anatomy. Even during arthroscopy, after filling the glenohumeral joint with fluid, the operator is not able to differentiate between type II SLAP injury and normal meniscoid variant without joint mobilization with the use of a hook probe. The possibility of dynamic US imaging gives a chance to improve the diagnostics in comparison with static US or MRI, even after administration of a contrast medium. In their study, the authors prove that a large part of the labrum and its pathologies may be visualized on ultrasound when proper technique is used. This is not a popular view since currently MRI and MRA are used as routine imaging methods of labrum pathologies. No reliable research results have been published concerning the value and repeatability of the US diagnosis of labrum injuries. Determining the sensitivity and specificity of ultrasound for both particular parts of the labrum and different types of labral injuries, thus determining its clinical usefulness, by means of prospective research associated with arthroscopic verification would certainly be an essential and logical continuation of these quite interesting articles.

Diffusion tensor imaging and fiber tractography for the visualization of the female pelvic floor

In the past decade, the evaluation of the pelvic support for understanding pelvic floor dysfunction by means of magnetic resonance imaging (MRI) has been an emerging area of research. Both static and dynamic MRI techniques have been effectively applied as a diagnostic resource to reveal abnormalities to the muscular pelvic support, but fail to unravel the precise pathophysiology of this complex disorder. Diffusion tensor imaging (DTI) and tractography comprise enhanced MRI techniques that enable the three-dimensional visualization of anisotropic tissue, such as muscle fibers, and provide a quantitative description of tissue organization and integrity. Quantifying DTI and fiber tractography might be able to reveal microstructural abnormalities in the pelvic support that are not noticeable using conventional MRI techniques. In this article, we discuss relevant anatomy, the current state of DTI and tractography in the evaluation of the female pelvic floor, and their potential future clinical applications.

Predicting three‐dimensional patellofemoral kinematics from static imaging‐based alignment measures

Patellofemoral pain syndrome causes significant discomfort and disability among much of the general population. Despite recent breakthroughs in dynamic three-dimensional imaging technologies to assess pathological patellofemoral motion, such tools remain costly for clinical diagnostics applications. Thus, this study investigated whether three-dimensional patellofemoral kinematics could be predicted from routine two-dimensional static measures of patellofemoral joint alignment quantified from magnetic resonance imaging (MRI) data acquired in full knee extension. Twenty-six volunteers clinically diagnosed with patellofemoral pain (19 F/7 M, 25.9 ± 11.1 years) and 26 control subjects (19 F/7 M, 25.3 ± 7.7 years) were included in this IRB-approved study. Static three-dimensional sagittal T1-weighted gradient recall echo and dynamic MRI scans were acquired. For the dynamic image acquisition, subjects cyclically flexed and extended their knee (at 30 cycles/min) while a full cine-phase contrast MRI set (24 time frames of anatomic images and x-, y-, and z-velocity images) was acquired. From these data, static measures of patellofemoral alignment and three-dimensional patellofemoral kinematics were derived. Single and multiple regressions between static and kinematic variables were evaluated. Although shown reliable, the static MRI measures could only partially predict patellofemoral kinematics, with r(2) -values ranging from 16% to 77%. This makes it imperitave that the current precise, accurate, 3D, dynamic imaging techniques be translated into clinical tools.

Medical and Surgical Management of Pelvic Floor Disorders Affecting Defecation

Pelvic floor disorders that affect stool evacuation include structural (for example, rectocele) and functional disorders (for example, dyssynergic defecation (DD)). Meticulous history, digital rectal examination (DRE), and physiological tests such as anorectal manometry, colonic transit study, balloon expulsion, and imaging studies such as anal ultrasound, defecography, and static and dynamic magnetic resonance imaging (MRI) can facilitate an objective diagnosis and optimal treatment. Management consists of education and counseling regarding bowel function, diet, laxatives, most importantly behavioral and biofeedback therapies, and finally surgery. Randomized clinical trials have established that biofeedback therapy is effective in treating DD. Because DD may coexist with conditions such as solitary rectal ulcer syndrome (SRUS) and rectocele, before considering surgery, biofeedback therapy should be tried and an accurate assessment of the entire pelvis and its function should be performed. Several surgical approaches have been advocated for the treatment of pelvic floor disorders including open, laparoscopic, and transabdominal approach, stapled transanal rectal resection, and robotic colon and rectal resections. However, there is lack of well-controlled randomized studies and the efficacy of these surgical procedures remains to be established.

Poster - Thur Eve - 16: Four-dimensional x-ray computed tomography and hyperpolarized 3 He magnetic resonance imaging of gas distribution in lung cancer.

Dynamic imaging methods such as four-dimensional computed tomography (4DCT) and static imaging methods such as noble gas magnetic resonance imaging (MRI) deliver direct and regional measurements of lung function even in lung cancer patients in whom global lung function measurements are dominated by tumour burden. The purpose of this study was to directly compare quantitative measurements of gas distribution from static hyperpolarized 3 He MRI and dynamic 4DCT in a small group of lung cancer patients. MRI and 4DCT were performed in 11 subjects prior to radiation therapy. MRI was performed at 3.0T in breath-hold after inhalation 1L of hyperpolarized 3 He gas. Gas distribution in 3 He MRI was quantified using a semi-automated segmentation algorithm to generate percent-ventilated volume (PVV), reflecting the volume of gas in the lung normalized to the thoracic cavity volume. 4DCT pulmonary function maps were generated using deformable image registration of six expiratory phase images. The correspondence between identical tissue elements at inspiratory and expiratory phases was used to estimate regional gas distribution and PVV was quantified from these images. After accounting for differences in lung volumes between 3 He MRI (1.9±0.5L ipsilateral, 2.3±0.7 contralateral) and 4DCT (1.2±0.3L ipsilateral, 1.3±0.4L contralateral) during image acquisition, there was no statistically significant difference in PVV between 3 He MRI (72±11% ipsilateral, 79±12% contralateral) and 4DCT (74±3% ipsilateral, 75±4% contralateral). Our results indicate quantitative agreement in the regional distribution of inhaled gas in both static and dynamic imaging methods. PVV may be considered as a regional surrogate measurement of lung function or ventilation.

Morphology and dynamics of the male pelvic floor before and after retrourethral transobturator sling placement: first insight using MRI

We prospectively evaluated changes in morphology and dynamics of the male pelvic floor on magnetic resonance imaging (MRI) associated with retrourethral transobturator sling (RTS) placement. Twenty-six men with post-prostatectomy incontinence consecutively underwent functional cine-MRI before and 12 months after RTS. The membranous urethra length (MUL) and severity of periurethral/urethral fibrosis were assessed on static MRI. A lowering of the posterior bladder wall (BPW), the bladder neck (BN), the external urinary sphincter (EUS) and symphysial rotation of these structures were analysed on dynamic MR images. The success rate was defined as cure (0-1 dry 'security' pad) or improvement (pad reduction ≥ 50 %). The success rate was 77 % (20/26 patients). The mean follow-up was 20.4 months. The MUL significantly increased post-operatively (p < 0.001). There were no significant pre- and post-operative differences in severity of periurethral/urethral fibrosis. Significant elevation of the BPW (p < 0.021), BN and EUS (p < 0.002) was observed post-operatively. The RTS failure was significantly associated with the severity of periurethral fibrosis pre- (p < 0.032) and post-operatively (p < 0.003). RTS placement is associated with MUL increase, elevation of the BN, BPW and EUS. De novo development of periurethral or urethral fibrosis seems not to be confirmed. The RTS failure was related to the severity of pre- and post-operative periurethral fibrosis. The impact of MRI on pre-operative diagnostics of RTS failure needs further evaluation.

Dynamic pelvic floor imaging: MRI techniques and imaging parameters

Magnetic resonance imaging (MRI) is an excellent tool to understand the complex anatomy of the pelvic floor and to assess pelvic floor disorders. MRI enables static and dynamic imaging of the pelvic floor. Using static T2-weighted sequences the morphology of the pelvic floor can be visualized in great detail. A rapid half-Fourier T2-weighted, balanced steady state free precession, or gradient-recalled echo sequence are used to obtain sagittal images while the patient is at rest, during pelvic squeeze, during pelvic strain and to document the evacuation process. On these images the radiologist identifies the pubococcygeal line (PCL) (which represents the level of the pelvic floor). In normal findings, the base of the anterior and the middle compartment are above the PCL at rest, and the pelvic floor elevates during contraction. During straining the pelvic floor muscles should relax and the pelvic floor descends normally less than 3 cm below the PCL. Pelvic floor MRI based on the static and dynamic MRI sequences allows for the detection and characterization of a vast array of morphologic and functional pelvic floor disorders. In this review, we focus on technical aspects of static and dynamic pelvic floor MRI.

고자장 MRI에서의 영상 영역에 대한 B1+균질성

In high static field magnetic resonance imaging(MRI) systems, fields of 7 T and 9.4 T, the impressed RF field shows larger inhomogeneity than in clinical MRI systems with B0 fields of 1.5 T and 3.0 T. In multi-channel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the non-uniformity of the impressed RF field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected ROI(Region of Interest). To demonstrate the technique, the multichannel transmission line coil was modeled together with a human head phantom at 400 MHz for the 9.4 T MRI system and fields are obtained. In this paper, all the optimized in each isolated ROIs are combined to achieve significantly improved homogeneity over the entire field of view. The simulation results for 9.4 T MRI systems are discussed in detail.

Transcranial static magnetic field stimulation in man: making things as simple as possible?

Transcranial static magnetic field stimulation in man: making things as simple as possible?

Transcranial static magnetic field stimulation in man: Making things as simple as possible?

Transcranial static magnetic field stimulation in man: Making things as simple as possible?

Prenatal Magnetic Resonance Imaging (MRI) Findings of a Foregut Duplication Cyst of the Tongue

Foregut duplication cysts of the oral cavity or lingual choristomas have a potential risk of airway obstruction. Two cases are reported that were initially detected by screening sonography. Further imaging with both static and real-time cine magnetic resonance imaging confirmed the lingual origin, relationship of the mass to fluid-filled spaces within the oral cavity, motion of the mass with the tongue during fetal swallowing, and airway patency. The additional information provided by magnetic resonance imaging aided in planning delivery and obviated the need for an ex utero intrapartum treatment procedure because airway patency was confirmed in both cases.

The relationship between infratentorial lesions, balance deficit and accidental falls in multiple sclerosis

Objective The role of static posturography and magnetic resonance imaging (MRI) in identifying patients at high risk of falls was investigated. Relationships between static posturography measures and MRI metrics were also investigated. Methods A total of 31 ambulatory MS patients (EDSS ranging from 2.0 to 5.0) with a predominant balance disorder were recruited. Each patient underwent a static posturography with a monoaxial platform and a conventional 1.5 T brain MRI scan. Measurements of T1-hypointense and T2-hyperintense lesion volumes (LVs), focusing on lesions selectively located at infratentorial levels, were performed by two operators unaware of clinical data. The self-reported number of falls in the previous 6 months was considered as the main outcome measure. Results Fourteen (45%) patients reported 1 or more falls over the past 6 months. When compared to non-faller patients, they had a higher EDSS score, poorer static standing balance, and greater brainstem and middle cerebellar peduncle (MCP) T2-LVs. A strength correlation between brainstem T2-LV and impaired static standing balance in an open eye condition was also found. In the multivariate analysis, the variables more strictly associated with recurrent falls were greater T2-LV at the MCP (beta: 6.2; p = 0.01) and brainstem (beta: 5.8; p = 0.001) levels, and a wider displacement of the body center of pressure in the closed eye condition (beta: 0.02; p = 0.03). Conclusion Our data suggests that the damage of specific infratentorial areas negatively affect the static standing balance and may predispose MS patients to accidental falls. These findings might contribute in selecting patients requiring a proper rehabilitation intervention program.

Clinical and Radiographic Characteristics of Upper Lumbar Disc Herniation: Ten-Year Microsurgical Experience

Upper and lower lumbar disc herniation apparently have different background, symptoms, and operative results. This retrospective study reviewed the clinical records of 403 patients (409 discs) who underwent lumbar microdiscectomy performed by different surgeons at our institute between 1999 and 2009. The 290 male (72.0%) and 113 female (28.0%) patients were aged from 19 to 77 years (mean 44 years). Demographics, symptoms, and static and dynamic radiographic and magnetic resonance images obtained at the L1-2, L2-3, L3-4, L4-5, and L5-S1 intervertebral levels were analyzed. Of the 409 herniations, 3 were at L1-2, 9 at L2-3, 21 at L3-4, 166 at L4-5, and 210 at L5-S1. The mean age at herniation at L1-2 and L2-3 levels was 55.7 years. Patients with herniation of discs at L3-4 or above were significantly older than patients who suffered herniation at L4-5 or below (p < 0.0001), and the incidence of urinary disturbance was significantly higher in patients with herniation at L1-2 and L2-3 levels (p = 0.0013). The incidence of degenerative scoliosis was significantly higher in patients with herniation at L1-2 and L2-3 than in those with herniated discs at L3-4 or below (p < 0.0001). Patients with upper lumbar disc herniation were older and manifested a higher incidence of urinary disturbance. A high incidence of degenerative scoliosis was noted in the course of prolonged degenerative processes.

Comparison of static and dynamic knee kinematics during squatting

Background There long has been debate whether static knee kinematics measured using magnetic resonance imaging are the same as knee kinematics in dynamic weight-bearing motion. Magnetic resonance imaging provides excellent volumetric detail but is static. Fluoroscopic imaging provides for dynamic observation of knee kinematics but provides no direct observation of the soft-tissue structures. We attempted to answer the question ‘Are knee kinematics the same during static and dynamic squatting?’ Methods Knee kinematics data from two previously reported studies of healthy knee kinematics during squatting from 0° to 120° were obtained. The results of the dynamic fluoroscopic study were reformatted to perform a direct comparison of femoral anteroposterior translation and internal–external rotation with the static magnetic resonance imaging study. Findings Comparison of internal–external rotations and lateral femoral condyle anteroposterior translations did not reveal significant differences between static and dynamic data. The medial femoral condyle demonstrated 0 (SD = 3) mm posterior translation during dynamic squatting from 0° to 120° flexion compared to 5 (SD = 3) mm posterior translation during static squatting ( P = 0.01, Cohen's d = 1.7). Interpretation For squatting types of motions, static and dynamic study protocols appear to produce equivalent knee kinematics with no functionally important differences. Differences in medial condyle translations can be attributed to differences in foot position during the study. Investigators can choose the modality that best fits their goals and resources with the knowledge that the results for squatting activities are comparable.

Effect of increasing depth of dexmedetomidine anesthesia on upper airway morphology in children

This prospective study examines the dose-response effects of dexmedetomidine on upper airway morphology in children with no obstructive sleep apnea (OSA). To determine the effect of increasing doses of dexmedetomidine on static and dynamic magnetic resonance (MR) images of the upper airway in spontaneously breathing children with no OSA. General anesthetics and sedatives attenuate upper airway muscle activity, rendering the airway vulnerable to obstruction. Dose-response effects of dexmedetomidine on upper airway of children are not known. We prospectively examined the dose-response effects of dexmedetomidine on upper airway morphology in children. Increasing doses of dexmedetomidine was administered to 23 children scheduled for MR imaging of the brain while breathing spontaneously via the native airway. Static axial and dynamic sagittal midline MR ciné images of the upper airway were obtained during low (1 mcg.kg(-1).h(-1)) and high (3 mcg.kg(-1).h(-1)) doses of dexmedetomidine. The airway anteroposterior diameter, transverse diameter, and cross-sectional areas were measured manually by two independent observers. Static airway measurements were taken at the level of the nasopharyngeal airway (sagittal images) and retroglossal airway (RGA) (sagittal and axial images). Dynamic change in cross-sectional area of airway between inspiration and expiration was considered a measure of airway collapsibility. Static axial measurements of RGA did not change with increasing dose of dexmedetomidine. Most sagittal airway dimensions demonstrated clinically modest, although statistically significant, reductions with high dose compared to low dose dexmedetomidine. Although, the dynamic changes in nasopharyngeal and retroglossal area with respiration were marginally greater for high dose than for low dose dexmedetomidine, no subject exhibited any clinical evidence of airway obstruction. Upper airway changes associated with increasing doses of dexmedetomidine in children with no OSA are small in magnitude and do not appear to be associated with clinical signs of airway obstruction. Even though these changes are small, all precautions to manage airway obstruction should be taken when dexmedetomidine is used for sedation.

Value of MR imaging in the differentiation of benign and malignant orbital tumors in adults

PurposeTo prospectively evaluate magnetic resonance (MR) imaging including dynamic contrast-enhanced MR imaging in the differentiation of benign from malignant orbital masses and to evaluate which MR imaging features are most predictive of malignant tumors.Materials and methodsThe study was approved by the institutional review board and signed informed consent was obtained. Nonenhanced, static, and dynamic contrast-enhanced MR imaging was performed in 102 adult patients with an orbital mass. Diagnosis was based on histologic findings. MR imaging features of benign and malignant orbital lesions were evaluated correlated with histological findings. Multivariate logistic regression analysis was employed to identify the best combination of MR imaging features that might be predictive of malignancy.ResultsNonenhanced, static, and dynamic enhancement MR imaging was significantly superior to two other models in prediction of malignancy (p < 0.05). Multivariate logistic regression analysis identified that the most discriminating MR imaging features were isointense mass on T2-weighted imaging and a washout-type time–intensity curve for both observers.ConclusionNonenhanced, static, and dynamic enhancement MR imaging improved differentiation between benign and malignant orbital masses in adult patients.

From MRI to anatomical simulation of the hip joint

AbstractThis paper describes a methodology for the simulation of musculoskeletal disorders. Our clinical study is related to osteoarthritis (OA) of the hip, a pathogenesis possibly due to impingements. These bone collisions lead to abnormal joint mechanics which is characterized by contact pressure and stress distribution upon the joint cartilages. The proposed methodology combines different approaches from modeling to simulation. The simulation is based on patient‐specific anatomical models, where acquisition modalities are noninvasive and flexible. Based on static magnetic resonance imaging (MRI) data, a discrete deformable models method is used for modeling the organs of the musculoskeletal system. Femoroacetabular movements are estimated using an optical motion capture system and are validated by a dynamic MRI analysis. To achieve accurate deformations, techniques to generate volumetric meshes are developed based on the medial axis (MA) information. Finally, a computationally efficient fast functional joint model is used to simulate the mechanical behavior of the soft tissues. The goal of such a simulation is to allow the investigation of the relevant contact and cartilages deformation under movement, which can be useful for diagnosis, pre‐ or post‐operative planning and training. This will benefit further developments in surgical techniques and minimally invasive procedures. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Effect of cervical dynamics on adjacent segment degeneration after anterior cervical fusion with cages

The objective of this study is to evaluate the effect of anterior cervical discectomy and fusion (ACDF) on the motion of the cervical spine and dynamic stress (tendency to kyphosis) on adjacent segments and on the overall spinal alignment which may predispose to symptomatic disc diseases at other levels. Twenty consecutive patients underwent ACDF with a mean follow-up of 28 months (range 13-38). Preoperative and postoperative clinical assessments were done by using the neck disability index (NDI) and the Japanese Orthopedic Association (JOA) score. In all cases, at the last follow-up control, a neuro-radiographic assessment [cervical spine static and dynamic X-ray and magnetic resonance imaging (MRI)] was done. The angle of the operated disc space, the disc space angle of contiguous segments, and their range of motion (ROM) and the kyphotic Cobb angle (C2-7) were measured by computer software. The study was done at Sant'Andrea Hospital, Rome, Italy in the period from November 2003 to November 2005. We observed that: the mean Cobb angle improved significantly (p < 0.001) from 3.4 degrees (kyphosis) to postoperative 14.5 degrees. This normalization of angle showed a direct effect on improvement of myelopathic patients, but it had a statistically nonsignificant effect on adjacent segments degeneration (ASD). The mean segmental ROM of adjacent segments did not show significant instability. The mean was 11.1 degrees at upper and 10.2 degrees at lower levels (close to normal). In six cases, the ROM was higher than normal: five of these patients demonstrated symptomatic adjacent segment pathology. Postoperative improvement of mean JOA and NDI scores was statistically significant (p < 0.001). Anyway, symptomatic ASD was observed in five patients (20%): in four of them, the higher disc spaces and in one, the lower disc spaces were involved. In four cases, the preoperative MRI showed slight and asymptomatic disc degeneration at the same levels involved subsequently. This ASD was significantly related to the increased ROM at the segments involved. Follow-up X-rays showed solid fusion with absence of movement in all but one case (at 13-month follow-up), who showed slight movement in the operated level in spite of clinical improvement. The follow-up MRI showed, in all cases, good decompression in the treated levels. Compensatory increase in ROM of the contiguous motion segments in patients subjected to ACDF may lead to ASD especially in those cases with asymptomatic adjacent subclinical degenerative disease. If these preliminary results will be confirmed by larger series, it could be reasonable in young selected patients with soft disc herniation to adopt total disc arthroplasty instead of fusion after cervical micro-discectomy.

All-in-one magnetic resonance arthrography of the shoulder in a vertically open magnetic resonance unit

Magnetic resonance (MR) arthrography frequently involves joint injection under imaging guidance followed by MR imaging in static positions. To evaluate if MR arthrography of the shoulder joint can be performed in a comprehensive fashion combining the MR-guided injection procedure, static MR imaging, and dynamic motion MR imaging in a single test. Twenty-three shoulder joints were injected with Gd-DTPA2- under MR guidance. Static MR imaging was performed and included a three-point Dixon method to achieve water-selective images. Dynamic motion MR imaging with and without applying pressure to the upper arm was used to evaluate glenohumeral joint instability. In 10 cases, surgical correlation was available. The all-in-one MR arthrography technique was successful in all patients, and took an average time of 65 min. All but one glenohumeral injection procedure were performed with a single needle pass, and no complications were observed. Out of eight labrum tears seen with static MR imaging, seven were confirmed at surgery. In 10 cases, dynamic motion MR imaging correlated well with the surgeon's intraoperative evaluation for presence and direction of instability. MR arthrography of the shoulder joint using a vertically open magnet can be performed as a single comprehensive test, including the injection and the static and dynamic motion MR imaging. Good diagnostic accuracy for intraarticular lesions and glenohumeral instability was found in a small sample.

Small vocal-tract cavities revealed by magnetic resonance imaging and their acoustic influences.

In natural speaking conditions, the vocal tract exhibits small cavities in the hypopharyx and oral cavity, while their acoustic effects have not been fully recognized. Acoustic studies based on static and dynamic magnetic resonance imaging of the vocal tract in three dimensional have shown that these cavities cause regional resonance and antiresonance in the vocal tract. The hypopharyngeal cavities, including the supraglottal laryngeal cavity and bilateral cavities of the piriform fossa, characterize vowel spectra in the higher frequencies and contribute to determining voice quality and speaker characteristics. The laryngeal cavity functions as a Helmholtz resonator to generate an extra formant in the vicinity of 3 kHz, and the piriform fossa forms a pair of side-branches of the vocal tract to cause spectral zeros in the vicinity of 4–5 kHz. The bilateral interdental spaces form a pair of side-branches in the oral cavity in nonlow vowels, and their geometry varies with articulation. Their antiresonance frequency is below 2 kHz in /i/, while it rises toward /a/ crossing the second formant in transition, and thus causing a small discontinuity of that formant between the two vowels.