Interpretation of magnetic resonance images making use of in vitro examinations of spinal tissue

T1 and T2 relaxation times were determined in vitro at 21 MHz (0.5 T) for a variety of spinal and paraspinal tissues. Intensity formulas for spin echo and inversion recovery sequences were derived and used to calculate the intensities of these tissues as they would appear in magnetic resonance images. The intensity was calculated as a function of various repetition, echo, and inversion times. It is shown that the combination of acquiring in vitro relaxation time values and calculating intensity as a function of pulse timings is useful to predict the parameter setting for optimal contrast between certain tissues without applying series of magnetic resonance images.     

Magnetic resonance imaging of the triangular fibrocartilage complex

Magnetic resonance imaging of seven fresh human cadaveric specimens was used to evaluate the integrity of the triangular fibrocartilage complex of the wrist. A variety of imaging parameters were systematically investigated, including T1-weighted images with and without contrast, long repetition times, short echo time images, and T2-weighted sequences. A variety of imaging planes were also evaluated. Wrist arthrography, dissection, and frozen coronal sections were done to substantiate our interpretations of the magnetic resonance images. T2-weighted images in the coronal plane proved to be of the greatest diagnostic value because the synovial fluid of the joint spaces serves as an excellent endogenous contrast agent. Long repetition time, short echo time sequences could be simultaneously obtained with T2-weighted sequences with the use of a multi-echo pulse sequence to provide an excellent diagnostic package in the future. On the basis of our investigation, the triangular fibrocartilage complex can be consistently and accurately evaluated with magnetic resonance imaging. As magnetic resonance imaging technology improves, wrist probes and suitable magnets should become available that will make the evaluation of triangular fibrocartilage complex abnormalities with magnetic resonance imaging clinically useful.     

High-resolution/high-contrast MRI of human articular cartilage lesions

Background Magnetic resonance microscopy (MRM) is an important experimental tool in the identification of early cartilage lesions.

Methods Normal and degenerated cartilage samples were imaged at 11.74 T using a standard spin echo sequence. Quantitative MR measurements for T₁, T₂, and ADC were obtained and mapping for T₂ and ADC was performed. The bi-exponential model for T₂ relaxation was also explored. Histology was carried out for comparison with MR images.

Results MR images of cartilage samples displaying early stages of degeneration were positively correlated to their histological appearance in 23-μm high-resolu-tion images and also with much shorter imaging times at 47-μm resolution. T₂ maps enable delineation of the actual cartilage zones, distinguishing the super?cial zone in particular. The bi-exponential model can reflect cartilage components at different stages of degeneration.

Interpretation At 11.74 T, with 23-μm resolution or with 47-μm resolution and shorter imaging times, MRM provides images that allow visualization of early stages of cartilage degeneration, including super?cial ?brillation. This has not been shown previously. The images also allow quantitative measurements (T₁, T₂, and ADC) in each cartilage region, which can be indicative of different stages of cartilage degeneration.     

Magnetic resonance imaging of the genitourinary tract

MRI is in its infancy as a clinical imaging tool. It is undergoing intensive investigation in various areas of the body. Evaluation of the brain and spine is superb, and in some areas of the brain, like the posterior fossa, it is thought to be superior to CT. Evolving indications for body scanning include staging of pelvic malignancies, evaluation of liver malignancy, evaluation and staging of musculoskeletal problems, and, to a lesser degree, staging of renal malignancies and evaluation of vascular disease. The main problem in body imaging stems from image degradation because of respiratory motion that is transmitted to upper abdominal organs. Respiratory gating of image acquisition or utilization of short heavily T1-weighted pulse sequences will likely overcome this problem in due time. Minimizing motion artifact will make MR images comparable to, if not better than, CT images with regard to transverse anatomic display, and MR images have the added advantage of multiplanar scanning, which can be done directly, without need of additional computer reconstruction time and without having to move the patient. The second major problem in MRI is the lack of understanding of equipment potential. Unlike conventional radiography and CT, in which the behavior of the X-ray beam is understood with regard to image formation, in MRI new parameters are used to generate images. As stated earlier, MR signal intensity is due to hydrogen concentration, T1 and T2 relaxation times of the tissue, and flow of protons through the imaged volume. How these factors are weighted depends on pulse sequence selection, and thus image contrast and information content of the scans change. On the surface, these images display anatomic information as do other imaging modalities, but manipulation of pulse sequences may ultimately lead to the ability to demonstrate physiologic and chemical parameters previously unavailable in imaging. Current research is geared to help extract this data by testing new pulse sequences, using different types of receiver RF coils, and using MR-specific contrast materials. Minor MRI problems such as long scan times are being dealt with to decrease time to an acceptable length. The nonvisualization of soft tissue calcifications will probably remain a problem that may have to be weighed against other known advantages. At this time further research and clinical experience are the key to what is needed in MRI, to gain further knowledge with regard to imaging physiologic phenomena, such as flow and spectroscopy, and possibly to monitor the chemical basis of disease.(ABSTRACT TRUNCATED AT 400 WORDS)     

Evaluation of changes in brain tissues surrounding cerebral arteriovenous malformations using NMR-CT

Patients with cerebral arteriovenous malformation (AVM) show various clinical symptoms, but they can be divided into two groups; one resulting from rupture of AVM and another derived from chronic ischemia in surrounding tissues of AVM. Intracerebral or subarachnoid hemorrhages due to rupture of AVM can be detected by X-ray CT scan, however, it is difficult to obtain three dimensional image of changes in the surrounding area of AVM that has never experienced hemorrhagic attacks. We are using 0.15 Tesla NMR-CT (resistive type) produced by Bruker Company in West Germany and its pulse sequence is Carr-Purcell-Meiboom-Gill (CPMG) method which is best reformed type of spin echo. With this machine, we observed images of AVM and its surrounding tissue, made calculated images of T1 and T2 relaxation time and measured T1 and T2 values of ROI. On images of NMR, nidus and many dilated vessels were distinctly revealed as low or no signal intensity area in all cases without contrast media. And it is noteworthy that surrounding areas of AVM on calculated T1 and T2 images were observed as tissues showing elongated relaxation time in all cases. These tendencies were confirmed by measurement of T1 and T2 in ROI compared with contralateral side. We think elongations of T1 and T2 in surrounding tissues mean ischemic or necrotic changes in these areas induced by steal phenomena due to arteriovenous shunting.     

High-resolution/high-contrast MRI of human articular cartilage lesions

Background?Magnetic resonance microscopy (MRM) is an important experimental tool in the identification of early cartilage lesions.

Methods?Normal and degenerated cartilage samples were imaged at 11.74 T using a standard spin echo sequence. Quantitative MR measurements for T₁, T₂, and ADC were obtained and mapping for T₂ and ADC was performed. The bi-exponential model for T₂ relaxation was also explored. Histology was carried out for comparison with MR images.

Results?MR images of cartilage samples displaying early stages of degeneration were positively correlated to their histological appearance in 23-μm high-resolu-tion images and also with much shorter imaging times at 47-μm resolution. T₂ maps enable delineation of the actual cartilage zones, distinguishing the super?cial zone in particular. The bi-exponential model can reflect cartilage components at different stages of degeneration.

Interpretation?At 11.74 T, with 23-μm resolution or with 47-μm resolution and shorter imaging times, MRM provides images that allow visualization of early stages of cartilage degeneration, including super?cial ?brillation. This has not been shown previously. The images also allow quantitative measurements (T₁, T₂, and ADC) in each cartilage region, which can be indicative of different stages of cartilage degeneration.     

Olfactory neuroblastoma with intracranial extension. Report of two cases

Two cases of olfactory neuroblastoma with intracranial extension are described. The radiological features, including those of magnetic resonance (MR) imaging, are emphasized. On plain X-rays, the nasal cavity, ethmoid, sphenoid, and/or frontal sinuses were opacified. Erosion of the bony confines of the sinuses and orbit was seen in Case 1, but no bony destruction was observed in Case 2 despite intracranial tumor invasion via the seemingly intact cribriform plate. Angiography showed tumor staining in the ethmoid sinus, and in Case 1 tumor vessels were also found in the base of the frontal lobe. Computed tomography (CT) disclosed a large, soft, enhanced tissue mass occupying the nasal cavity and paranasal sinuses and extending into the anterior cranial fossa. In Case 1, MR images (0.5 Tesla) with a short spin echo sequence (repetition time [TR], 600 msec; echo time [TE], 26 msec) and a long spin echo sequence (TR, 2100; TE, 30, 60, 90) were obtained. T1-weighted images delineated the tumor accurately in relation to the normal architecture. T2-weighted images revealed widespread brain edema, with the tumor recognizable as a mass of low signal intensity within the high-intensity region of brain edema. The CT and MR imaging findings are by no means specific to olfactory neuroblastoma. However, both modalities, particularly MR imaging, are of special value in demonstrating the precise extent of the tumor in three dimensions.     

Evaluation of intraaxial enhancing brain tumors on magnetic resonance imaging: intraindividual crossover comparison of gadobenate dimeglumine and gadopentetate dimeglumine for visualization and assessment, and implications for surgical intervention

OBJECT: The goal in this article was to compare 0.1 mmol/kg doses of gadobenate dimeglumine (Gd-BOPTA) and gadopentetate dimeglumine, also known as gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA), for enhanced magnetic resonance (MR) imaging of intraaxial brain tumors. METHODS: Eighty-four patients with either intraaxial glioma (47 patients) or metastasis (37 patients) underwent two MR imaging examinations at 1.5 tesla, one with Gd-BOPTA as the contrast agent and the other with Gd-DTPA. The interval between fully randomized contrast medium administrations was 2 to 7 days. The T1-weighted spin echo and T2-weighted fast spin echo images were acquired before administration of contrast agents and T1-weighted spin echo images were obtained after the agents were administered. Acquisition parameters and postinjection acquisition times were identical for the two examinations in each patient. Three experienced readers working in a fully blinded fashion independently evaluated all images for degree and quality of available information (lesion contrast enhancement, lesion border delineation, definition of disease extent, visualization of the lesion's internal structures, global diagnostic preference) and quantitative enhancement (that is, the extent of lesion enhancement after contrast agent administration compared with that seen before its administration [hereafter referred to as percent enhancement], lesion/brain ratio, and contrast/noise ratio). Differences were tested with the Wilcoxon signed-rank test. Reader agreement was assessed using kappa statistics. Significantly better diagnostic information/imaging performance (p < 0.0001, all readers) was obtained with Gd-BOPTA for all visualization end points. Global preference for images obtained with Gd-BOPTA was expressed for 42 (50%), 52 (61.9%), and 56 (66.7%) of 84 patients (readers 1, 2, and 3, respectively) compared with images obtained with Gd-DTPA contrast in four (4.8%), six (7.1%), and three (3.6%) of 84 patients. Similar differences were noted for all other visualization end points. Significantly greater quantitative contrast enhancement (p < 0.04) was noted after administration of Gd-BOPTA. Reader agreement was good (kappa > 0.4). CONCLUSIONS: Lesion visualization, delineation, definition, and contrast enhancement are significantly better after administration of 0.1 mmol/kg Gd-BOPTA, potentially allowing better surgical planning and follow up and improved disease management.     

New diagnostic imaging for navigation surgery

Progress in diagnostic computed tomography (CT) and magnetic resonance (MR) imaging has been remarkable. Multidetector-row CT provides thin-slice images through the upper abdomen, multiphase abdominal imaging, and 3D images of high quality including CT angiography and multiplanar reformation. The development of MR units provides diffusion-weighted images for detecting abdominal tumors, and the steady-state coherent echo method can be used for imaging of vessels without using contrast media. The 3D images provided in CT and MR imaging facilitate anatomic understanding of tumors and vessels and are useful for preoperative navigation. However, we must be careful when using 3D images for diagnosis, because the subjectivity of the 3D image creator may affect the results. Therefore the original axial images should also be referred to.     

Magnetic resonance imaging of experimental brain edema in cats

The authors observed the natural course of experimental brain edema in vivo using magnetic resonance (MR) imaging. To detect and qualify the edematous lesion, they obtained images by the spin echo technique (repetition time, 2100 ms; echo time, 80 ms). These showed the maximal brain edema on the 1st to 3rd days after the operation, as evidenced by a pixel density study and a finding of mass effect. On MR images enhanced with manganese, the inversion recovery technique (repetition time, 2100 ms; inversion time, 500 ms) demonstrated the edematous lesion as a high signal intensity area with good spatial resolution. Moreover, the follow-up inversion recovery images with manganese suggested that there was a system for absorption of edema fluid between blood vessels and the edematous lesion. The authors think that MR imaging is an important technique for observation of the dynamics of experimental brain edema.     

Magnetic resonance imaging assessed cortical porosity is highly correlated with μCT porosity

Cortical bone is typically regarded as “MR invisible” with conventional clinical magnetic resonance imaging (MRI) pulse sequences. However, recent studies have demonstrated that free water in the microscopic pores of cortical bone has a short T2* but a relatively long T2, and may be detectable with conventional clinical spin echo (SE) or fast spin echo (FSE) sequences. In this study we describe the use of a conventional two-dimensional (2D) FSE sequence to assess cortical bone microstructure and measure cortical porosity using a clinical 3 T scanner. Twelve cadaveric human cortical bone samples were studied with MRI and microcomputed tomography (μCT) (downsampled to the same spatial resolution). Preliminary results show that FSE-determined porosity is highly correlated (R² = 0.83; P < 0.0001) with μCT porosity. Bland–Altman analysis suggested a good agreement between FSE and μCT with tight limit of agreement at around 3%. There is also a small bias of − 2% for the FSE data, which suggested that the FSE approach slightly underestimated μCT porosity. The results demonstrate that cortical porosity can be directly assessed using conventional clinical FSE sequences. The clinical feasibility of this approach was also demonstrated on six healthy volunteers using 2D FSE sequences as well as 2D ultrashort echo time (UTE) sequences with a minimal echo time (TE) of 8 μs, which provide high contrast imaging of cortical bone in vivo.     

Magnetic resonance imaging of soft tissue masses

Twenty-nine soft tissue masses were studied with magnetic resonance imaging (MRI) which proved to be useful in the preoperative evaluation of these lesions. Other imaging modalities employed had significant limitations. Plain films were of little value because of the intrinsically low contrast of soft tissues. Angiography was not necessary unless MRI suggested a vascular lesion or proximity to major blood vessels. Computed tomography (CT) and MRI both readily identified fatty lesions and their relationship to adjacent structures. Some soft tissue tumors could not be delineated from normal muscle with CT, but were easily seen with MRI. MRI is ideally suited for the study of suspected soft tissue tumors because of its excellent soft tissue contrast and its ability to image directly in any plane. Optimum evaluation required imaging in at least two planes with spin echo sequences chosen to bring out both T1 and T2 features.     

Prospective comparison of radionuclide, computed tomographic, sonographic, and magnetic resonance localization of parathyroid tumors

The appropriate choice of imaging techniques to localize parathyroid tumors preoperatively remains controversial. We report the first prospective, blinded study to compare the efficacy of four imaging modalities in 100 patients with primary hyperparathyroidism (pHPT). Patients were examined by computer-assisted thallium 201/technetium 99m subtraction scintigraphy (TTS), computed tomography (CT), ultrasonography (US), and magnetic resonance (MR). Each study was performed and interpreted independently. Subsequent neck exploration and "curative" parathyroidectomy allowed correlation of surgical findings with imaging reports to score their accuracy. Overall sensitivities of the four imaging modalities were TTS, 73%, CT, 68%, US, 55%; and MR, 57%; with respective specificities of 94%, 92%, 95%, and 87%. Sensitivities for lesions located below the thyroid gland (thymic tongue and mediastinum) were TTS, 90%; CT, 46%; US, 44%; and MR, 50%; with respective specificities of 100%, 99%, 100%, and 94%. There was a significant increase in overall sensitivity when TTS and CT (90%, p less than 0.01) or TTS and US (85%, p less than 0.05) were used together; however, the combination of any three or even four imaging modalities did not increase sensitivity further. For small parathyroid tumors (less than or equal to 250 mg), no imaging technique had a sensitivity of more than 50%. None of the imaging studies accurately localized small hyperplastic parathyroid glands found in patients with multiple gland disease. Preoperative parathyroid imaging may not be indicated in pHPT patients undergoing first-time neck exploration because surgeons experienced in parathyroid surgery have a 93% to 96% cure rate.     

A review of applications of MRI in soft tissue and bone tumors

Due to excellent soft tissue contrast and multiplanar imaging capability, MRI is assuming a major role in recognition, staging, and treatment planning of soft tissue and bone tumors. Direct sagittal, coronal, and axial images permit assessment of intraosseous and extraosseous extension of tumors and their relationship to the joints and neurovascular structures, and detection of "skip" lesions. MRI allows improved detection of recurrent tumors in the presence of non-ferromagnetic metallic implants as compared to CT. In the evaluation of soft tissue tumors, MRI is more sensitive than CT and allows differentiation among fat, muscle, tendon, bone, and vascular structures based on signal characteristics. Over a period of 18 months, 100 soft tissue masses and bone tumors were evaluated using MRI. Spin echo sequences with T1 and T2 weighted images were most valuable in differentiating normal and abnormal tissues. Calculated comparative measurements of relaxation times showed no reliable difference between benign and malignant tumors.     

Application of MR spectroscopy to the study of tumor biology

Though MR spectroscopy has long been used to analyze the structure of organic compounds in solution, interest in applying it to the study of biologic systems has been slow in evolving because of past problems with spectral resolution in solids and gels. Renewed interest in this area has been stimulated both by the rapid growth of MR imaging as a clinical tool as well as by improvements in MR spectrometer design and use of sophisticated pulse sequences which have greatly improved the analysis of molecular composition. This review specifically focuses on the application of MR spectroscopy to studying the biology of malignant cells. The bulk of MR studies in this area to date have involved either 1H or 31P spectroscopy. Several investigators have now demonstrated that 1H spectra can be used to distinguish both animal and human tumors of differing metastatic properties. Preliminary data suggest that these spectral differences result in part from differences in cell surface glycoproteins and/or glycolipids between cells of low and high metastatic potential. Many of these molecules can absorb cell water potentially affecting T1 of cell water by their relative concentrations. Prolonged T2 relaxation times have been associated with some spectral peaks which distinguish cells of differing metastatic potential. The findings may partly explain why tumors have the prolonged T1 and T2 relaxation times seen in proton MR imaging. Other 1H MR spectroscopic studies suggest that there are detectable differences in plasma lipids in patients with a variety of malignancies compared to normal controls, suggesting possible utility as a screening test.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative evaluation of intracranial epidermoid tumors with computed tomography and magnetic resonance imaging

The diagnosis of intracranial epidermoid tumors with computed tomography (CT) is often difficult because of indistinct margins, close proximity to the skull base, and a density similar to that of cerebrospinal fluid (CSF). Recent experience with six histologically confirmed epidermoid tumors served to emphasize the value of magnetic resonance (MR) imaging in studying these lesions. MR images were obtained using varying spin echo and inversion recovery techniques with a 0.5-tesla superconducting magnet. CT with and without enhancement had been performed in each case. In Case 1, CT showed an ill-defined left cerebellopontine angle hypodensity. MR imaging clearly showed the presence of abnormal tissue at that location. Case 2 showed a CSF density mass in the right upper posterior fossa. MR imaging of that area showed a variegated signal of a mass extending supratentorially. CT of Case 3 showed a left medial middle fossa hypodensity with an enhancing rim. MR imaging showed a clearly extraaxial mass in that location. In Case 4, a diffuse cerebellar hemispheric hypodensity was observed on CT and was clearly demarcated by MR studies. A huge lesion, thought initially to be an arachnoid cyst on CT of Case 5, was seen on MR imaging to be a large, extraventricular mass displacing the temporal lobe. Finally, CT in Case 6 was suggestive of a poorly demarcated right cerebellopontine angle lesion, which was seen on MR images to be extraaxial, displacing the brain stem. Various MR images more clearly demonstrate the extent of abnormal tissue than CT of epidermoid tumors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlation of clinical, surgical, pathologic, and MR fat suppression results for head and neck cancer.

Magnetic resonance (MR) imaging provides superior soft tissue delineation of head and neck tumors compared to previous radiologic studies. Further refinements using fat suppression and gadolinium (Gd-DTPA) enhancement have added to these improved images. We performed MR studies of 16 patients with head and neck tumors with detailed clinical, surgical, and pathologic information. MR studies included standard spin-echo T1-weighted images (T1WI) with and without fat suppression and T2-weighted images (T2WI) with fat suppression. Gadolinium was also administered with fat suppression. Conventional and paired fat suppression MR images were compared by a grading system. Post-Gd-DTPA fat suppression T1WI, and T2WI with fat suppression, showed superior sensitivity for tumor delineation when compared to conventional T1WI. Fat suppression T2WI was the best technique to delineate squamous cell carcinoma both in the primary site and regional lymph nodes. Clinical, surgical, and pathologic results correlated perfectly with imaging findings. These refinements in MR imaging represent a significant advance in the radiologic evaluation of head and neck tumors.     

Dynamic Volume Assessment of Hepatocellular Carcinoma in Rat Livers Using a Clinical 3T MRI and Novel Segmentation

Purpose: In vivo liver cancer research commonly uses rodent models. One of the limitations of such models is the lack of accurate and reproducible endpoints for a dynamic assessment of growing tumor nodules. The aim of this study was to validate a noninvasive, true volume segmentation method using two rat hepatocellular carcinoma (HCC) models, correlating magnetic resonance imaging (MRI) with histological volume measurement, and with blood levels of α-fetoprotein. Materials and methods: We used 3T clinical MRI to quantify tumor volume with follow-up over time. Using two distinct rat HCC models, calculated MRI tumor volumes were correlated with volumes from histological sections, or with blood levels of α-fetoprotein. Eleven rats, comprising six Buffalo rats (n = 9 scans) and five Fischer rats (n = 14 tumors), were injected in the portal vein with 2.5 × 10⁵ and 2.0 × 10⁶ syngeneic HCC cells, respectively. Longitudinal (T1) relaxation time- and transverse (T2) relaxation time-weighted MR images were acquired. Results: The three-dimensional (3D) T1-weighted gradient echo had 0.35-mm isotropic resolution allowing accurate semi-automatic volume segmentation. 2D T2-weighted imaging provided high tumor contrast. Segmentation of combined 3D gradient echo T1-weighted images and 2D turbo spin echo T2-weighted images provided excellent correlation with histology (y = 0.866x + 0.034, R² = 0.997 p < .0001) and with α-fetoprotein (y = 0.736x + 1.077, R² = 0.976, p < .0001). There was robust inter- and intra-observer reproducibility (intra-class correlation coefficient > 0.998, p < .0001). Conclusions: We have developed a novel, noninvasive contrast imaging protocol which enables semi-automatic 3D volume quantification to analyze nonspherical tumor nodules and to follow up the growth of tumor nodules over time.     

Part 1: dual-tuned proton/sodium magnetic resonance imaging of the lumbar spine in a rabbit model

STUDY DESIGN.: Development of a dual-tuned proton/sodium radiofrequency (RF) coil for magnetic resonance imaging (MRI) of the rabbit spine and quantification of sodium concentration in intervertebral discs. OBJECTIVE.: To develop the dual-tuned proton/sodium MRI of rabbit lumbar spine to investigate proteoglycan matrix content and intervertebral disc degeneration (IDD). SUMMARY OF BACKGROUND DATA.: IDD is a common chronic condition that may lead to back pain, limited activity, and disability. Early-stage IDD involves the loss of proteoglycan matrix and water content in the disc. Sodium MRI is a promising noninvasive technique for quantitative measurement of proteoglycan changes associated with IDD. The combined structural (proton) and biochemical (sodium) MRI facilitates the investigation of morphological and molecular changes associated with degeneration of discs. METHODS.: Multichannel dual-tuned proton/sodium transceiver RF coil of the rabbit spine was developed and optimized at 3T human scanner-8 channels allocated for the sodium coil and 4 channels for the proton coil. High-resolution anatomy proton images of the discs were acquired using turbo spin echo and dual echo steady state sequence. Sodium concentration of the discs was quantified from sodium magnetic resonance (MR) images that were calibrated for signal attenuation because of RF field inhomogeneity, sodium MR relaxation times, and disc thickness. Twelve rabbits (～1-yr old, female, 5.2 ± 0.4 kg) were used for measuring disc sodium concentration. RESULTS.: High-resolution in vivo proton and sodium MR images of rabbit discs (≤2-mm thickness) were successfully obtained using an in-house dual-tuned proton/sodium RF coil at 3T. The total acquisition time for each set of images was approximately 40 minutes. Sodium concentration of normal rabbit lumbar discs was measured at 269.7 ± 6.3 mM, and this measurement was highly reproducible, with 5.3% of coefficient of variation. CONCLUSION.: Sodium concentrations of rabbit lumbar discs were reliably measured using our newly developed dual-tuned multichannel proton/sodium RF coil at 3T.