Background The countercurrent arrangement of capillary blood flow in the medulla of mammalian kidneys generates a gradient of oxygen tension between the renal cortex and the papillary tip that results in a state of relative hypoxia within the renal medulla. Exploration of the pathophysiological implications of medullary hypoxia has been hampered by the absence of a noninvasive technique to estimate intrarenal oxygenation in different zones of the kidney. In the present study, we demonstrate the feasibility of such a method on the basis of blood oxygenation level–dependent (BOLD) MRI, which allows sequential measurements in humans in response to a variety of physiological/pharmacological stimuli in health and disease. Methods and Results BOLD MRI measurements were obtained in healthy young human subjects (n=7), and the effects of three different pharmacological/physiological maneuvers that induce diuresis were studied. Spin-spin relaxation rate, R2*, was measured, which is directly related to the amount of...

Noninvasive Evaluation of Intrarenal Oxygenation With BOLD MRI

The algorithm for imaging the salivary glands depends on the clinical scenario with which the patient presents to the clinician. Because of the importance of identifying small calculi in the gland or salivary duct as the cause of the symptom complex, nonenhanced computed tomography is often the best initial study for the evaluation of the painful gland. If an infiltrative neoplasm is highly suspected, nonenhanced and enhanced magnetic resonance (MR) imaging may be superior in demonstrating perineural, meningeal, and skull base invasion. Sialography is reserved for the evaluation of chronic sialadenitides unrelated to sialolithiasis. Thin-section MR techniques for MR sialography may soon replace conventional sialography.

Major salivary gland imaging.

Technical advances in T2-weighted cardiovascular MR (CMR) imaging allow for accurate identification and quantification of tissue injuries that alter myocardial T2 relaxation. Of these, myocardial edema is of special relevance. Increased myocardial water content is an important feature of ischemic as well as nonischemic cardiomyopathies, which are often associated with acute myocardial inflammation. In this article, we review technical considerations and discuss clinical indications of myocardial T2-weighted imaging. J. Magn. Reson. Imaging 2007;26:452–459. © 2007 Wiley-Liss, Inc.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jmri.21028

T2-weighted cardiovascular magnetic resonance imaging.

Additive manufacturing or 3D printing is becoming an alternative to subtractive manufacturing or milling in the area of computer-aided manufacturing. Research on material for use in additive manufacturing is ongoing, and a wide variety of materials are being used or developed for use in dentistry. Some materials, however, such as cobalt chromium, still lack sufficient research to allow definite conclusions about the suitability of their use in clinical dental practice. Despite this, due to the wide variety of machines that use additive manufacturing, there is much more flexibility in the build material and geometry when building structures compared with subtractive manufacturing. Overall additive manufacturing produces little material waste and is energy efficient when compared to subtractive manufacturing, due to passivity and the additive layering nature of the build process. Such features make the technique suitable to be used with fabricating structures out of hard to handle materials such as cobalt chromium. The main limitations of this technology include the appearance of steps due to layering of material and difficulty in fabricating certain material generally used in dentistry for use in 3D printing such as ceramics. The current pace of technological development, however, promises exciting possibilities.

Additive Technology: Update on Current Materials and Applications in Dentistry

BACKGROUND AND PURPOSE: The surgical approach to parotid tumors is different for benign and malignant neoplasms, but the clinical symptoms do not correlate well with histology. Difficulties in tumor classification also arise in imaging modalities, in which sonography has the lowest and MR imaging, the highest accuracy. The purpose of this study was to review our experience using conventional MR imaging of the neck in the evaluation of parotid tumors and to evaluate which MR imaging findings are best able to predict malignant histology. MATERIALS AND METHODS: Eighty-four consecutive patients (43 males, 41 females; median age, 56 years; range, 9–85 years) with parotid gland tumors who underwent MR imaging before surgery were prospectively included in the present study and retrospectively analyzed. Histology was available for all tumors. We analyzed the following MR imaging parameters: signal intensity, contrast enhancement, lesion margins (well-defined versus ill-defined), lesion location (deep/superficial lobe), growth pattern (focal, multifocal, or diffuse), and extension into neighboring structures, perineural spread, and lymphadenopathy. RESULTS: The 57 (68%) benign and 27 (32%) malignant tumors consisted of 29 pleomorphic adenomas, 17 Warthin tumors, 11 various benign tumors, 5 mucoepidermoid carcinomas, 3 adenoid cystic carcinomas, 1 acinic cell carcinoma, 1 carcinoma ex pleomorphic adenoma, 9 metastases, and 8 various malignant neoplasms. Specific signs predictive of malignancy were the following: T2 hypointensity of the parotid tumor ( P = .048), ill-defined margins ( P = .001), diffuse growth ( P = .012), infiltration of subcutaneous tissue ( P = .0034), and lymphadenopathy ( P = .012). CONCLUSIONS: Low signal intensity on T2-weighted images and postcontrast ill-defined margins of a parotid tumor are highly suggestive of malignancy.

http://www.ajnr.org/content/ajnr/32/7/1202.full.pdf

MR imaging of parotid tumors: typical lesion characteristics in MR imaging improve discrimination between benign and malignant disease

PURPOSE To investigate whether MR imaging is an accurate means of assessing mandibular invasion in patients with carcinoma. METHODS We retrospectively studied the MR scans of 22 patients with pathologic or surgical confirmation of mandibular invasion from oral and oropharyngeal cancers. The MR images were blindly analyzed using primary criteria of: (a) cortical breakdown, (b) replacement of bone marrow fat, or (c) gadopentetate dimeglumine enhancement of a mass at the bone marrow defect. Secondary criteria of: (a) contiguous soft-tissue mass, and (b) mass on both sides of the mandibular cortex were also examined. Mandibular invasion was graded as periosteal/cortical, medullary, or no invasion. RESULTS Primary positive findings of cortical breakdown and abnormal bone marrow signal were highly sensitive (100%) for periosteal/cortical invasion and medullary involvement, respectively. However, a high rate of false-positive studies hampered the MR accuracy, which fell into the 73% to 77% range. A negative MR study was highly predictive, but a positive study was less valuable. Gadolinium enhancement added little to the MR study9s accuracy. False-positive studies mainly occurred in the setting of prior irradiation, osteoradionecrosis, and odontogenic infections. CONCLUSIONS MR imaging is a sensitive method for detecting mandibular invasion but has a low positive predictive value. A negative study virtually excludes cortical/periosteal or bone marrow invasion.

http://www.ajnr.org/content/ajnr/15/10/1949.full.pdf

MR of mandibular invasion in patients with oral and oropharyngeal malignant neoplasms

Magnetic resonance images were made of rabbits at 1.4 tesla for the purpose of measuring the T1 relaxation times of the kidney in vivo with the animal in different states of hydration. In the normally hydrated animal, the outer cortex has a T1 of about 600 msec and there was a steep T1 gradient with an increase to about 1200 msec at the tip of the inner medulla. The relaxation time gradient was not affected by overhydration with intravenous fluid, but dehydration by withholding water for 24 hours decreased the values in the inner medulla. The T1 and T2 relaxation times and total water content were measured in vitro on tissue samples. The values for both T1 and T2 correlated with the regional renal water content.

Water content and NMR relaxation time gradients in the rabbit kidney.

PURPOSE To determine which MR techniques are best for identifying intraparotid masses and to assess the utility of MR for predicting specific diagnosis. METHODS A retrospective review of 31 intraparotid masses was performed. Lesion conspicuity and signal intensity characteristics were evaluated by objectively measured regions of interest and by subjective visual review. RESULTS The T1-weighted images produced the highest lesion conspicuity in 25 of 31 masses. All the masses were easily detected as hypointense lesions on the T1-weighted scans with good or excellent conspicuity; on the T2-weighted images nine lesions appeared isointense to the normal parotid tissue, including six malignancies. Gadolinium-enhanced images were not helpful for identifying the intraparotid masses. Warthin tumors and malignancies tended to be hypointense or low in conspicuity on T2-weighted images. CONCLUSIONS The T1-weighted images were best for detecting parotid masses. The T2-weighted images may help in limiting a differential diagnosis, but a specific diagnosis cannot be made without biopsy.

http://www.ajnr.org/content/ajnr/14/5/1173.full.pdf

MR of intraparotid masses.

In order to examine the accuracy of magnetic resonance imaging (MRI)-based diagnosis of neuromyelitis optica (NMO) versus multiple sclerosis (MS), we performed a retrospective, rater-blinded review of 29 cases of NMO and 30 cases of MS using the criteria of long (more than three vertebral levels), continuous lesions with a central cord location for NMO and more peripheral and patchy lesions for MS. Using these criteria, two raters were able to distinguish the two conditions with a good degree of confidence, particularly when the imaging was performed at the time of an acute cord attack. The sensitivity and specificity for diagnosis of NMO were 86.2% and 93.3%, respectively, for Rater A and 96.4% and 78.6%, respectively, for Rater B, with a kappa value of 0.72. Thus there are significant differences in lesion characteristics that allow the distinction on spinal cord imaging between MS and NMO with a moderately high degree of confidence. The location of the lesion as evident on MRI of the spine can be regarded as a distinguishing diagnostic feature between MS and NMO.

/pdf/differentiation-of-neuromyelitis-optica-from-multiple-3pt5j10sxi.pdf

Differentiation of Neuromyelitis Optica from Multiple Sclerosis on Spinal Magnetic Resonance Imaging

We report the case of a 35 year old African American female who developed hypertrophic olivary degeneration secondary to resection of a pontine cavernous malformation. The patient initially complained of headaches and diplopia. Unenhanced computed tomography (CT) and magnetic resonance images (MRI) of the brain revealed a left pontine cavernous malformation with scattered foci of recent and remote hemorrhage. The patient subsequently underwent surgical resection of the lesion. Follow up MRI 7 months post surgery demonstrated hypertrophy and T2 signal hyperintensity in the ipsilateral inferior olivary nucleus secondary to hypertrophic olivary degeneration. Familiarity with this diagnosis and its imaging characteristics is required of the radiologist to prevent erroneous diagnoses of other pathology.

http://www.radiologycases.com/index.php/radiologycases/article/viewFile/603/pdf

Bruce Schlakman

Papers

MR of mandibular invasion in patients with oral and oropharyngeal malignant neoplasms

Water content and NMR relaxation time gradients in the rabbit kidney.

MR of intraparotid masses.

Differentiation of Neuromyelitis Optica from Multiple Sclerosis on Spinal Magnetic Resonance Imaging

Hypertrophic Olivary Degeneration After Resection of a Pontine Cavernous Malformation: A Case Report