Uncertainty in Reverberation-Chamber Antenna-Efficiency Measurements in the Presence of a Phantom.

The effect of a user's proximity on wireless device performance is critical to test the device under realistic conditions. In this work, we propose and demonstrate an improved uncertainty estimation method for antenna efficiency measurements in a reverberation chamber. The improved method separately computes uncertainties due to the effects of chamber loading by a phantom and the effects of antenna mismatch introduced by this phantom, illustrating the sensitivity of uncertainty to close-proximity user effects. We demonstrate that, while the impact of the phantom may be significant on antenna efficiency, and, it has some influence on the uncertainty in the measurement, its impact on overall uncertainty may be insignificant. This is demonstrated using the two-antenna method in the presence of a phantom close to the antenna under test. We illustrate the method by summarizing the antenna efficiencies with their uncertainties and the impact of the phantom for important communication bands. Due to the large effect of the user on antenna performance, this type of measurement and its uncertainty evaluation is a valuable way to characterize antenna efficiency including user effects.

Perfusion MR neuroimaging in patients undergoing balloon test occlusion of the internal carotid artery.

BACKGROUND AND PURPOSE: We sought to investigate whether the combination of conventional, diffusion-weighted, and perfusion-weighted MR imaging increases the diagnostic accuracy of balloon test occlusion of the internal carotid artery. We describe perfusion anomalies and patterns of enhancement seen in areas of altered brain perfusion during MR-monitored temporary balloon occlusion of the internal carotid artery. METHODS: Nine patients underwent balloon occlusion testing under standard angiographic conditions with continuous clinical and EEG monitoring. One patient who failed the test by clinical criteria underwent an external carotid to internal carotid bypass operation, followed by a repeat balloon test occlusion, thereby bringing the total number of procedures to 10. Patients were further imaged at 1.5 T with perfusion- and diffusion-weighted imaging as well as with conventional noncontrast and contrast-enhanced turbo fluid-attenuated inversion recovery (FLAIR) and T1-weighted sequences. RESULTS: Seven of 10 patients who tolerated unilateral carotid test occlusion without adverse clinical neurologic or EEG changes exhibited delayed first-pass transit of contrast material through the affected cerebral hemisphere, indicative of altered perfusion without significant concurrent cerebral blood flow or blood volume changes. Four of these patients and both symptomatic patients showed pial or subarachnoid contrast staining in areas of altered perfusion without abnormalities on diffusion-weighted images. CONCLUSION: Our findings indicate that MR perfusion-weighted imaging is safe and easily accomplished in a high-field-strength magnet and that contrast-enhanced turboFLAIR imaging may provide clinically useful MR imaging evidence of abnormal cerebral blood flow and subclinical ischemia.

Real-time, cine magnetic resonance imaging for evaluation of the pediatric airway.

BACKGROUND: Standard magnetic resonance imaging (MRI) and computed tomographic (CT) modalities are limited in their ability to image dynamic organs. New real-time, dynamic, cine magnetic resonance imaging (CMRI) techniques have the potential to image moving structures. OBJECTIVE: We therefore investigated the feasibility of using CMRI techniques to dynamically image the human airway, to assess laryngeal and tracheal patency and function. METHODS: A cohort of 10 pediatric patients, 10 adult patients, and 10 normal volunteers underwent routine static MRI, as well as CMRI using a Siemens 1.5 T Vision system (Siemens, Erlangen, Germany). Patients also underwent endoscopic evaluation. Cine axial, coronal, and sagittal sequences of the larynx and trachea were obtained during quiet respiration, as well as during a variety of provocative maneuvers. RESULTS: CMRI readily demonstrated normal vocal cord mobility and tracheal stability in normal volunteers. Abnormal vocal mobility was easily appreciated using the CMRI imaging system. Similarly, dynamic effects of tracheomalacia were clearly demonstrated using CMRI. Dynamic extrinsic tracheal compression resulting from mass lesions or anomalous vasculature was also visualized using CMRI. CONCLUSIONS: Cine MRI of the airway has the potential to provide novel data regarding laryngeal and tracheal patency and function. This evolving modality may serve as a valuable adjunct to static MR and CT imaging, as well as endoscopy, in the assessment of the airway.

Handheld metal detector localization of ingested metallic foreign bodies: accurate in any hands?

OBJECTIVE: To demonstrate the accuracy of handheld metal detectors (HHMDs) for identification and localization of ingested metallic foreign bodies when used by experienced and inexperienced investigators. DESIGN: Prospective study comparing HHMD scanning with radiography. SETTING AND PATIENTS: A consecutive sample of all eligible patients (N = 176) presenting to the emergency departments of Children's Medical Center of Dallas, Dallas, Tex, and Children's Hospital of the King's Daughters, Norfolk, Va, who were known or suspected to have ingested a metallic foreign body. INTERVENTION: Each patient underwent HHMD scanning and radiographic evaluation. MAIN OUTCOME MEASURES: Statistical evaluation compared HHMD scanning with radiography and experienced vs inexperienced investigator HHMD scanning to determine the accuracy of the screening tool and investigators. RESULTS: Experienced investigators performed HHMD scans on 140 subjects; inexperienced investigators scanned all subjects. Disease was defined as a foreign body in the esophagus on radiograph. The 3 experienced investigators demonstrated sensitivity of 100% (95% confidence interval [CI], 94%-100%), specificity of 92.4% (95% CI, 84.2%-97.2%), positive predictive value (PPV) of 90.9% (95% CI, 81.3%-96.6%), and negative predictive value (NPV) of 100% (95% CI, 95.1%-100%); the proportion correct was 95.7% (95% CI, 90.8%-98.4%). The inexperienced investigators demonstrated sensitivity of 95.7% (95% CI, 88.0%-99.1%), specificity of 81.0% (95% CI, 72.1%-88.0%), PPV of 77.0% (95% CI, 66.8%-85.4%), and NPV of 96.6% (95% CI, 90.4%-99.3%); the proportion correct was 86.9% (95% CI, 80.9%-91.5%). The McNemar test demonstrated no statistically significant difference between HHMD scanning by experienced vs inexperienced investigators. CONCLUSIONS: Handheld metal detector scanning is an accurate, inexpensive, radiation-free screening tool and should be used for evaluation of patients suspected of ingesting coins and coinlike foreign bodies.

A new role for magnetic resonance imaging in the diagnosis of laryngeal relapsing polychondritis.

BACKGROUND: Relapsing polychondritis involving the upper airway is a rare cause of airflow obstruction and hoarseness. The diagnosis of relapsing polychondritis depends on clinical signs, characteristic findings on cartilage biopsy, and response to treatment. Delays in diagnosis and treatment can increase the morbidity and mortality of the disease. METHODS: We present a case report of primary laryngeal relapsing polychondritis. RESULTS: Serologic testing, direct laryngoscopy, and endoscopic biopsy could not establish the diagnosis of relapsing polychondritis. Magnetic resonance imaging (MRI) examination demonstrated findings consistent with the histopathological diagnosis obtained on open biopsy. Follow-up MRI after treatment showed resolution of the initial findings. CONCLUSION: This case demonstrates the usefulness of MRI in the diagnosis and management of relapsing polychondritis involving the upper airway.

Preoperative permanent balloon occlusion of internal carotid artery in patients with advanced head and neck squamous cell carcinoma.

OBJECTIVE/HYPOTHESIS: To determine the value of preoperative balloon occlusion in predicting the safety of carotid artery resection in advanced recurrent head and neck squamous cell carcinoma. STUDY DESIGN: Retrospective chart review of all cases undergoing planned carotid artery resection for recurrent disease at a major university hospital. METHODS: If the carotid artery was encased, a nonemergent carotid artery balloon test occlusion was performed for 30 minutes. If the patient tolerated this, he or she underwent permanent carotid artery occlusion. RESULTS: Twenty-three patients were prospectively evaluated for resection. Three underwent emergent carotid artery ligation. Twenty others underwent nonemergent carotid artery test occlusion. Of these, 5 patients failed preoperative carotid artery balloon occlusion and 15 patients successfully underwent permanent carotid balloon occlusion. Although eight of these patients died of recurrent disease in less than 1 year, seven patients survived more than 1 year with two patients surviving more than 2 years. CONCLUSIONS: Preoperative carotid balloon occlusion predicted patients who could tolerate permanent occlusion. All patients eventually developed recurrent disease, but in 14 of the 15 patients, no hemorrhages occurred.

Intrathecal granuloma complicating chronic spinal infusion of morphine. Report of three cases.

Intrathecal morphine delivered by implanted pumps has been used in the treatment of pain caused by terminal cancer. Some authors supports its use in benign pain as well. The authors present three cases in which chronic infiltration of intraspinal narcotic medication was complicated by the formation of a granulomatous mass that became large enough to exert mass effect and induce neurological dysfunction.

Design and analysis of a silicon-based antiresonant reflecting optical waveguide chemical sensor.

The design of a silicon-based antiresonant reflecting optical waveguide (ARROW) chemical sensor is presented, and its theoretical performance is compared with that of a conventional structure. The use of an ARROW structure permits incorporation of a thick guiding region for efficient coupling to a single-mode fiber. A high-index overlay is added to fine tune the sensitivity of the ARROW chemical sensor. The sensitivity of the sensor is presented, and design trade-offs are discussed.

Middle cerebral artery dissection: a clinicopathologic study.

We present a case report of a 17-year-old young man who developed fatal dissection of the middle cerebral artery after what appeared to be trivial trauma. The dissection was not evident on cerebral arteriogram but was identified at autopsy. Arterial dissection should be considered in the differential diagnosis of supraclinoid occlusion of the internal carotid artery seen by cerebral angiography.

Steady-state free precession imaging of the inner ear.

The authors describe a steady-state free precession technique for imaging the inner ear. Although the signal-to-noise ratio is not as great as with other three-dimensional MR techniques, the inherent high contrast of inner ear structures makes this a valuable technique for patients with sensorineural hearing loss and for those who refuse paramagnetic contrast material.

Radiologic diagnosis and staging of head and neck squamous cell carcinoma.

The predominant extracranial head and neck cancer in adults is squamous cell carcinoma. The purpose of this article is to discuss the radiographic evaluation of these patients with computed tomography (CT) or magnetic resonance (MR) imaging prior to therapeutic intervention. Specific focus is given to the efficacy of CT and MR imaging, as an adjunct to clinical staging, for evaluation of the primary tumor, and metastatic adenopathy. MR imaging, because of its improved soft tissue contrast and multiplanar capability, is probably superior to CT for evaluation of the primary tumor in patients with squamous cell carcinoma. CT, however, remains the gold standard for identifying metastatic adenopathy and in most institutions remains the study of choice for evaluating this patient population.

Diagnostic imaging of the brain stem.

The small size of the brain stem, its location between the petrous pyramids, and the density of neuroanatomic structures in its substance make imaging of the brain stem one of the most challenging aspects of diagnostic neuroradiology. The relative value of CT, MRI, and angiography in the diagnosis of various brain stem lesions is reviewed. The contributions that can be made by more advanced diagnostic and functional imaging techniques are presented.

Magnetic resonance imaging of brain herniation into the middle ear.

Four patients with cholesteatoma were shown to have a large area of eroded tegmen tympani on computed tomography (CT). Magnetic resonance imaging (MRI) in the coronal and sagittal plane showed temporal lobe herniation in three cases and cholesteatoma with abscess elevating the dura in one case. In the patient with a cholesteatoma and an eroded tegmen tympani on CT, MRI is indicated to rule out brain herniation into the middle ear.

Effects of magnetic susceptibility artifacts and motion in evaluating the cervical neural foramina on 3DFT gradient-echo MR imaging.

The purpose of this study was to evaluate in vitro the effects of magnetic susceptibility and motion on the estimation of neural foraminal diameter with three-dimensional Fourier transformation (3DFT) gradient-recalled MR imaging as compared with CT. A cervical spine phantom was constructed from desiccated human cervical vertebral bodies embedded in a water-based proteinaceous gel. The phantom was imaged with thin-section 1.5-mm axial CT and 1.5-mm axial 3DFT gradient-recalled MR using a constant TR (35 msec) and flip angle (5 degrees), while the TE was varied from 11 to 22 msec. During imaging, the phantom either was kept stationary or underwent subtle, intermittent motion. Compared with CT, MR consistently underestimated the diameters of the neural foramina, leading to overestimation of neural foraminal stenosis. The degree of over-estimation varied directly with increasing TE values, from 8% (TE = 11 msec) to 27% (TE = 22 msec). Motion artifacts also increased foraminal overestimation and mimicked osseous hypertrophy. The effect of image degradation due to motion was noted to increase with longer TE values. Image degradation caused by magnetic susceptibility and motion artifacts can be minimized by using the shortest TE possible. We do not recommend the use of 3DFT gradient-recalled MR imaging for the evaluation of cervical radiculopathy if patient motion is anticipated.

Pulsatile tinnitus and the vascular tympanic membrane: CT, MR, and angiographic findings.

The radiologic studies of 107 patients with pulsatile tinnitus or a vascular retrotympanic mass were retrospectively reviewed. Of the 100 patients with pulsatile tinnitus, 25 had objective tinnitus. A vascular tympanic membrane was present in 37 cases (35%). Normal vascular variants were present in 23 patients (21%). Twenty-seven patients (25%) had acquired vascular lesions. Temporal bone tumors were found in 33 patients (31%). No abnormality was identified in 21 cases (20%). To ensure optimal radiologic examination, it is imperative to know the nature of the tinnitus (objective vs subjective) and the appearance of the tympanic membrane. All patients with subjective pulsatile tinnitus or a vascular retrotympanic mass should undergo high-resolution computed tomography of the temporal bone as the initial imaging study. Angiography is recommended for patients with objective tinnitus and a normal tympanic membrane. The role of MR imaging, even with the addition of gradient-echo techniques, remains limited and secondary.

The radiologic evaluation of pulsatile tinnitus and the vascular tympanic membrane.

PT may be the only symptom signalling a need for imaging the temporal bone region. Since a wide variety of processes may be responsible for this symptom, the goal of the radiologist should be to ensure a complete, cost-effective work-up. This evaluation is best directed by the type of tinnitus, objective v subjective, and the presence or absence of a vascular retrotympanic mass. HRCT is the initial examination of choice in the majority of instances. Normal vascular variants can be confidently differentiated from paragangliomas with this study. While angiography continues to play an important role in the initial evaluation of a select group of these patients, the role of MR should be adjunctive.

Knee ligament reconstruction: plain film analysis.

New concepts in knee ligament reconstruction have recently emerged, significantly improving the success of surgical reconstruction of anterior and posterior cruciate ligaments, using high-strength bone-patellar tendon-bone grafts, as well as medial and lateral collateral soft-tissue ligament reconstructions. We reviewed plain radiographs of 50 patients with a total of 72 ligament reconstructions to determine radiographic signs of complications. A major early complication relates to reconstructed ligament positioning. Isometric positioning of the reconstruction is important for all ligaments, but it is most crucial for the femoral portion of the anterior cruciate ligament. Three cases of nonisometric ligament positioning were identified, two anterior cruciate ligaments and one medial collateral ligament. Another early complication is graft fracture, identified in two cases of anterior cruciate ligament reconstruction. Hardware failure did not occur in this series. Late complications include motion of the graft (none in this series) and patellar fracture (one case in this series). Effusions resolved by 4 weeks in 92% of the cases. However, prolonged effusions are usually sterile and should not be mistakenly diagnosed as representing a septic joint if they are an isolated finding. Nonunion of the graft within its osseous tunnel is unusual. Union occurred in 79% of cases by 6 weeks and in 95% of cases by 5 months. Osseous tunnel sclerosis alone is not considered a complication. We conclude that postoperative plain film radiography is important for assessment of graft and hardware position as well as for the detection of early and late surgical complications.

Bleeding rates necessary for detecting acute gastrointestinal bleeding with technetium-99m-labeled red blood cells in an experimental model.

Proponents of [99mTc]sulfur colloid for GI bleeding studies argue that, although labeled red blood cells are useful for intermittent bleeding, they are not capable of detecting low bleeding rates. Studies of dogs with experimental GI bleeding have indicated bleeding rates of 0.05 ml/min can be detected with [99mTc]sulfur colloid. Since similar data in the dog model were unavailable for 99mTc-labeled red blood cells, we undertook this study. To simulate lower GI bleeding, catheters were inserted into the bowel lumen. Each dog's blood was labeled with 99mTc using an in vitro technique. Venous blood was then withdrawn and re-infused into the lumen of the bowel using a Harvard pump. Fourteen dogs were studied, ten receiving a bleeding rate from 4.6-0.02 ml/min in the descending colon and four with proximal jejunal bleeds of 0.20-0.02 ml/min. Bleeding rates of 4.6-0.2 ml/min were detected within 10 min in the colon and bleeding rates as low as 0.04 ml/min were seen by 55 min. Slower bleeding rates were not detected. Similar findings were noted for proximal jejunal bleeds. Based on the time of appearance, a minimum volume of approximately 2-3 ml labeled blood was necessary to detect bleeding. We conclude that 99mTc-labeled RBCs are sensitive for low bleeding rates in the dog model. The rates are comparable to those described for [99mTc]sulfur colloid in this experimental setting. The time of appearance of activity is related to the bleeding rate.

Systemic absorption of gallbladder sclerosing agents in the rabbit. A preliminary study.

The absorbed levels of ethanol or tetracycline, used as gallbladder sclerosing agents, were measured in the systemic blood circulation of 16 rabbits. The maximal systemic level of ethanol was 46 mg/dl and of tetracycline was 4.6 micrograms/ml after 30 minutes of gallbladder exposure. Comparable serum levels would be considered nontoxic in humans. As a gallbladder sclerosing agent, tetracycline (50 mg/cc) was slightly more effective than 95% ethanol exposed for either 15 or 30 minutes.