An in vivo magnetic resonance imaging study of changes in the volume (and fluid content) of the lumbar intervertebral discs during a simulated diurnal load cycle.

STUDY DESIGN: Magnetic resonance imaging was used to measure the changes in volume of the lumbar intervertebral disc in vivo during a load cycle. OBJECTIVES: To measure changes in volume of the lumbar intervertebral disc during a load cycle and relate these changes to changes in fluid content. SUMMARY OF BACKGROUND DATA: There have been very few experiments conducted to measure the volume and fluid changes in intervertebral discs in vivo. METHODS: Five healthy subjects were recruited (aged 27, 29, 31, 34, and 52 years) in a study using magnetic resonance imaging to measure the changes in volume of the lumbar intervertebral disc in vivo, during a load cycle. The experiment was designed to simulate a diurnal load cycle, but over less time. The load cycle consisted of bed rest, followed by walking with a 20-kg backpack for 3 hours, followed by bed rest for 3 hours. Magnetic resonance imaging scans of the lumbar spine were obtained 10 times during this load cycle. The disc volume was calculated by summing the disc area contained in each slice of the scan. The changes in volume of the discs (L2-L3, L3-L4, and L4-L5) recorded at the 10 times were then related to the fluid changes. RESULTS: Load-induced changes in disc volume can be detected and measured using MR imaging. The average volume increase 3 hours after removing a highly compressive load was 5.4%. The water content of the nucleus and anulus in the disc of the young human is said to be approximately 80% and 70%, respectively. If the disc gained 5.4% of its initial total volume, and assuming that the initial fluid content was approximately 75%, then it gained approximately 7% (i.e., 5.4%/75% x 100% approximately 7%) of its fluid. CONCLUSIONS: Load-induced changes in disc volume can be detected and measured using magnetic resonance imaging.

Do diurnal changes in loading affect the interpretation of MRI scans of the lumbar spine?

We tested the hypothesis that the visual interpretation of magnetic resonance imaging (MRI) scans of the asymptomatic lumbar spine are affected by diurnal changes in fluid exchange in the intervertebral discs. Ten male subjects carried a 20-kg backpack in the intervening 3-h period between two MRI scans of the lumbar spine. After the subjects arrived at the MRI center (within 45 min of awakening), they lay on a bed for 45 min. The first set of MRI scans were obtained. Each subject was then fitted with a 20-kg backpack. After they walked for 3 h, the pack was removed, and a second set of MRI scans were obtained immediately. The sets of MRI scans were reviewed by three radiologists: none of the three radiologists found differences in the interpretation of the MRI scans. On the basis of these results, diurnal changes in fluid exchange in the asymptomatic intervertebral disc (exaggerated in our case by the backpack) are undetectable by visual reading of MRI scans.

Evaluation of 1H magnetic resonance spectroscopic imaging as a diagnostic tool for the lateralization of epileptogenic seizure foci.

The purpose of this study was to assess whether a visual examination of 1H spectroscopic images could correctly lateralize patients with intractable temporal lobe epilepsy. 20 patients with intractable temporal lobe epilepsy and 10 volunteers were included in this study. Spectroscopic images were analysed using a protocol based on visual inspection. Images of the metabolites N-acetyl aspartate (NAA), choline (Cho), creatine (Cr) and lactate were obtained from a transverse plane oriented along the sylvian fissure. Images from each individual were evaluated independently by six reviewers. Results of the lateralization procedure obtained from the visual examinations were compared with those obtained from quantitative analysis of the spectra and with those obtained by magnetic resonance imaging (MRI), positron emission tomography (PET), neuropsychological examinations, and electroencephalographic (EEG) recordings. NAA images were found to be the most effective, amongst metabolite images, in lateralizing the epileptogenic lobe. Using the site selected for resection as the definition of the correct lateralization, 70% of the patients who underwent temporal lobectomy were correctly lateralized by the majority of the examiners using the visual inspection protocol. Based on the results of this study it is concluded that visual examination of 1H spectroscopic images is potentially valid in lateralizing patients with intractable temporal lobe seizures. Confidence in the visual interpretation increased as the difference in NAA signal intensity between the temporal lobes increased. The threshold above which the majority of the examiners correctly lateralized the patients was approximately 15% in NAA signal loss in the ipsilateral lobe.

Anatomic and physiologic imaging of Alzheimer's disease.

At present, no imaging modality is considered the standard diagnostic test for AD. On anatomic studies, severity of temporal lobe and hippocampal atrophy are the most reliable findings in AD, although overlap of these findings among AD, aging, and other dementias mitigate the value of these measures for application to the individual case. Although somewhat cumbersome for routine use, quantitative MR measurements offer more precise comparison of degrees of atrophy. Functional imaging may demonstrate abnormalities of perfusion or metabolism that precede anatomic changes (PET, SPECT, or MRS), yet these techniques generally require additional anatomic information from MR for interpretation. Newer investigational MR techniques such as MRS and functional MR in combination with conventional MR imaging have the potential to combine metabolic with anatomic imaging in one examination. A combination of both metabolic and anatomic imaging studies may ultimately offer better sensitivity and specificity for diagnosis, monitoring, and follow-up of AD.

Search for influence of 1.5 Tesla magnetic field on growth of yeast cells.

We have used a clinical magnetic resonance imager to search for the possible effects of a 1.5 T magnetic fields on the growth of the yeast Saccharomyces cerevisiae. Yeast samples were grown in nutrient broth contained in constant-temperature boxes, both in and out of the magnetic field of the imager. Growth was measured by using a hemocytometer and light microscope to calculate cell densities. Over the time span corresponding to approximately seven cell divisions, we find no convincing statistical evidence for an effect of magnetic field on cell density.

Magnetic resonance artifact in the postoperative cervical spine. A potential pitfall.

An magnetic resonance imaging artifact that stimulates hypertrophic bone formation is described in patients who have had an anterior cervical discectomy. The magnetic resonance images of 26 patients with anterior cervical discectomy were retrospectively reviewed. Comparison was made to the available concurrent computed tomographic scans, computed tomographic myelograms, and operative reports. A bovine spine was drilled with a drill only at one level and with a metal suction tip in close proximity to the drill at another level, and magnetic resonance images were obtained. Artifact was present in 12 patients and absent in 14; this was confirmed in the 8 patients with comparison studies. Close correlation was seen with the prospective reading of the presence of artifact and operative drill use in the seven patients with available operative reports. The bovine spine model showed no artifact at the drill-only level and significant artifact at the level where the metal suction tip was positioned next to the drill. Small metal flecks were seen grossly at the second level, but not on plain roentgenograms. The metallic magnetic resonance artifact seen in postoperative cervical spines is probably from small bits of metal from the metal suction tip as it occasionally hits the drill. Bone abnormalities seen on magnetic resonance imaging at the level of a previous anterior cervical discectomy may need a cervical computed tomogram to confirm the findings.

Flow-sensitive MR imaging of ventriculoperitoneal shunts: in vitro findings, clinical applications, and pitfalls.

To determine ventriculoperitoneal shunt patency during routine MR imaging of the head, 23 patients were studied with T1-weighted fast-field-echo scans. Without knowledge of the results of previous MR/CT studies or of the patients' clinical history, we reviewed the fast-field-echo studies and divided them according to those judged to have shunt flow (18) and those judged not to have flow (five). Fast-field-echo sequences showed high signal intensity, consistent with CSF flow and shunt patency in 17 medium-pressure systems and one high-pressure system. No signal was seen in five patients with high-pressure valve shunts. Combined clinical evaluation and MR/CT studies showed that three patients had probable shunt malfunction. One patient had true shunt malfunction; and although malfunction was thought to be present in two symptomatic patients, surgical revision showed the shunts to be patent. The possibility of temporary shunt obstruction is postulated to explain the clinical and MR findings in those two cases. The remaining two cases (9% of the patients) had no clinical evidence of shunt malfunction, and the MR findings probably reflected periodic CSF flow. One patient had an intracranial segment that was not connected and showed no flow on MR. No false-positive results (apparent flow in a nonfunctioning shunt) occurred. Using a standard medium-pressure shunt system, we constructed and imaged a phantom, which confirmed our clinical observations. T1-weighted fast-field-echo sequences may be useful in assessing patency of medium-pressure CSF shunt systems.

Manganese dipyridoxyl diphosphate. Effect of dose, time, and pulse sequence on hepatic enhancement in rats.

We used an animal model to investigate the hepatic enhancement characteristics of manganese dipyridoxyl diphosphate (MnDPDP) related to time, dose, and pulse sequence. The contrast doses selected were in the human tolerance range. Using an SE 300/15 pulse sequence, maximum mean hepatic enhancement of 45% (8 mumols/kg) and 58% (12 mumols/kg) over baseline was seen during a plateau maintained between 5 and 50 minutes postinjection in the 8 mumols/kg group, and between 10 and 90 minutes in the 12 mumols/kg group. This plateau was followed by a very gradual decline in hepatic enhancement. Using either 4 or 8 mumols/kg, there was a significant increase in postcontrast hepatic intensity on all relatively T1-weighted pulse sequences (spin echo [SE] 300/15, inversion recovery [IR] 1400/20/400, gradient echo [GE] 47/13/80 degrees, and GE 60/20/30 degrees) except GE 47/13/80 degrees at 4 mumols/kg. At 8 mumols/kg there was superior enhancement, with IR 1400/20/400 and SE 300/15, but at 4 mumols/kg there was no consistently superior sequence. None of the relatively T2-weighted pulse sequences (SE 2000/50, SE 2000/100, or GE 100/30/20 degrees) demonstrated a significant change in hepatic intensity using either dose of contrast. The data suggest that the best combination of dose, pulse sequence, and time for hepatic imaging with MnDPDP is 8 mumols/kg using heavily T1-weighted sequences 5 to 60 minutes following contrast administration.

MR measurement of intracranial CSF volume in 41 elderly normal volunteers.

A noninvasive nonplanimetric MR protocol was used to measure the total intracranial CSF volume in 41 normal subjects, aged 60-84 years, who were intensively screened to eliminate CNS disease. The protocol entailed application of MR imaging data acquired with a spin-echo sequence in a single thick slice encompassing the head. The results show a strong correlation between increased intracranial CSF volume and increasing age, and a weaker correlation between increased intracranial CSF volume and increasing total intracranial volume. The possibility of employing a CSF volume measurement as a reflection of brain atrophy to help diagnose dementia is discussed.

Direct hepatic tumor injection in rats: can it be used for analysis of MR imaging contrast agent?

With a recently described rat model technique for direct hepatic injection of tumor cells for imaging research, there were concerns that the injection itself might produce lesions detectable with magnetic resonance (MR) imaging, thereby producing false-positive results. To examine this possibility, the authors prospectively studied 14 Sprague-Dawley rats after direct hepatic injection of cells from a rat hepatoma cell line. The rats were imaged with a variety of pulse sequences before and after intravenous injection of the contrast agent manganese dipyridoxal diphosphate at a dose of 8 mumol/kg. No intrahepatic lesions could be detected with MR imaging during the first 6 days after direct hepatic injection of the tumor cells. Therefore, the direct injection technique should be accurate for evaluating various MR imaging sequences and contrast agents for early hepatic tumor detection.

Hepatic iron overload: diagnosis and quantification by noninvasive imaging.

The diagnostic efficacy of magnetic resonance (MR) and computed tomography (CT) for detection and quantification of hepatic iron was assessed in a series of patients under investigation for clinical or biochemical evidence of hepatic iron overload. Thirty patients underwent MR imaging (SE 30,60/1000 or SE 30,60/2000) at 0.5 Tesla with calculation of hepatic T2 and liver to paraspinous muscle signal intensity ratios. Twenty-nine patients also had measurement of hepatic attenuation on noncontrast CT images. Results of these imaging studies were correlated in all patients with quantitative iron determination from liver biopsy specimens. The best predictor of liver iron among parameters studied was the ratio of the signal intensities of liver and paraspinous muscle (L/M) on a SE 60/1000 sequence. Both MR using L/M ratios and CT were sensitive methods for detection of severe degrees of hepatic iron overload with 100% of patients with hepatic iron on biopsy greater than 600 micrograms/100 mg liver dry weight detected on the basis of L/M less than 0.6 or CT attenuation greater than 70 Hounsfield units (HU). The MR parameter, however, was more specific than CT (100 vs 50%) and showed a higher degree of correlation with quantitated hepatic iron from biopsy. T2 measurements showed poor correlation with hepatic iron, due to difficulty in obtaining precise T2 measurements in vivo when the signal intensity is low. None of the parameters utilized was sensitive for detecting mild or moderate degrees of hepatic iron overload. We conclude that MR and CT are sensitive techniques for noninvasive detection of severe hepatic iron overload, with MR providing greater specificity than CT.(ABSTRACT TRUNCATED AT 250 WORDS)

The bright intervertebral disk: an indirect sign of abnormal spinal bone marrow on T1-weighted MR images.

Two phantoms were constructed and imaged for the purpose of reproducing and understanding the relatively increased signal intensity of intervertebral disks on T1-weighted MR images in three patients with diffuse vertebral metastases. The first phantom simulated a normal spine and showed that the disks and vertebral bodies were of similar intensity. The second phantom simulated an abnormal spine and showed that the disks were brighter than the vertebrae. Prolonged relaxation times from the vertebral bodies as well as manipulation of the window width and level are the factors responsible for the presence of bright disks on T1-weighted images. Variations in the window width and level can accentuate the apparent increase in signal intensity from the disks but not reverse it. Although the presence of bright disks may be subtle, recognition of this sign should raise the possibility of diffuse replacement of normal fatty bone marrow in the vertebrae.

Eddy-current-induced artifacts caused by an "MR-compatible" halo device.

Traction or halo devices thought to be compatible with magnetic resonance (MR) imaging and made of nonferromagnetic metals may actually cause MR image artifacts. The authors have observed such artifacts caused by eddy currents generated in the conducting frame of the device by the radio-frequency excitation field. The severity of the artifact depends on the orientation of the device in the MR unit and can be effectively eliminated by disrupting the electrical continuity of the supporting frame of the device.

Renal corticomedullary junction. Performance of T1-weighted MR pulse sequences.

Inability to demonstrate the renal corticomedullary junction (CMJ) on magnetic resonance (MR) images has been reported in connection with several medical renal diseases. T1-weighted spin echo pulse sequences have been advocated to demonstrate a signal intensity difference between cortex and medulla. This study was undertaken to determine which of several T1-weighted spin echo (SE) and gradient echo (GE) sequences are better for delineation of the CMJ. The MR studies were performed at 0.5 Tesla on 27 normal volunteers. Multi-slice axial images of both kidneys were obtained in all subjects at each of the following five pulse sequences: SE 250/20, SE 500/30, SE 900/30, and GE 300/15 with 80 degrees and 64 degrees flip angles. Contrast/noise ratios were calculated for the signal intensity differences between cortex and medulla; the average standardized contrast/noise ratios ranked as follows: GE 300/15/80 degrees = 3.01 +/- 0.74, GE 300/15/64 degrees = 2.72 +/- 0.74, SE 250/20 = 2.02 +/- 0.33, SE 500/30 = 1.96 +/- 0.51, and SE 900/30 = 1.71 +/- 0.39. In addition, the five sequences for each patient were randomized and the images were independently ranked for delineation of CMJ by three MR radiologists. The cumulative subjective ranking for all observers from best to worst is as follows: SE 500/30, GE 300/15/80 degrees, GE 300/15/64 degrees, SE 900/30, SE 250/20. Although better contrast/noise ratios are achieved with the GE sequences and the more T1-weighted SE sequences, as a practical matter this does not seem to be the only significant factor when compared with the visual image evaluation by independent observers.(ABSTRACT TRUNCATED AT 250 WORDS)

Hand-held electronic teaching-aid for demonstrating MRI concepts.

We describe a hand-held electronic teaching-aid for magnetic resonance imaging (MRI), which can be used to demonstrate the dependence of signal intensity on changing pulse sequence parameters (TR and TE), the dependence of intensity on changing tissue parameters (T1 and T2), and the ideas of "T1-weighting" and "T2-weighting" as they relate to image contrast. The device was specifically designed to be easy to use and readily accessible to residents-in-training and MR neophytes.

Are hepatic and muscle T2 values different at 0.5 and 1.5 Tesla?

In an effort to determine whether T2 values of liver and muscle change with increasing field strength, 144 abdominal MR examinations were retrospectively evaluated. These patients were evaluated with a dual echo T2-weighted spin-echo sequence. Eighty-two of the examinations were performed at 0.5 Tesla and 72 at 1.5 Tesla (T). Eleven of the patients were evaluated with both MR systems with the same sequences. T2 values were also obtained from a Fe NH4(SO4)2 12H2O phantom. The T2 values of liver decreased from 57.8 +/- 11.3 at 0.5 T to 43.7 +/- 8.3 at 1.5 T. The T2 values of muscle decreased from 44.2 +/- 9 at 0.5 T to 35.4 +/- 7.2 at 1.5 T. Patients who were examined on both systems also demonstrated a decrease in both liver and muscle T2 values. For concentrations in the range of hepatic T2's, the phantom demonstrated a decrease in T2 values from 0.5 to 1.5 T ranging from 20.3 to 23.4%. All the T2 changes were statistically significant (p less than .05). The findings suggest that T2 values may depend on field strength, or may vary due to other hardware-related differences.

Normal SPECT thallium-201 bull's-eye display: gender differences.

The bull's-eye technique synthesizes three-dimensional information from single photon emission computed tomographic 201TI images into two dimensions so that a patient's data can be compared quantitatively against a normal file. To characterize the normal database and to clarify differences between males and females, clinical data and exercise electrocardiography were used to identify 50 males and 50 females with less than 5% probability of coronary artery disease. Results show inhomogeneity of the 201TI distributions at stress and delay: septal to lateral wall count ratios are less than 1.0 in both females and males; anterior to inferior wall count ratios are greater than 1.0 in males but are approximately equal to 1.0 in females. Washout rate is faster in females than males at the same peak exercise heart rate and systolic blood pressure, despite lower exercise time. These important differences suggest that quantitative analysis of single photon emission computed tomographic 201TI images requires gender-matched normal files.

A phantom study of intracranial CSF signal loss due to pulsatile motion.

MR imaging of the head often reveals localized areas of decreased signal intensity (flow voids) within the CSF. These flow voids are caused by turbulence within the CSF resulting from its pulsatile back-and-forth flow through the cerebral aqueduct and foramina. We describe a phantom that mimics the essential features of the CSF flow, and discuss its use in studying the dependence of the CSF flow void (CFV) on spin-echo (SE) and inversion-recovery pulse sequence parameters. The phantom had fluid-filled spaces to represent ventricles, and channels connecting these spaces to represent the aqueduct and foramina. A pump pushed the fluid in a pulsing manner through the phantom at various rates. The CFV was quantified by measuring signal loss relative to nonflowing fluid. The CFV did not appear to depend on repetition time or inversion time. The CFV was, however, strongly dependent on echo time (TE), and for single-echo SE sequences CFV became less severe as TE decreased. An even-echo rephasing effect was observed for multiecho sequences. Slice thickness and field of view also affected the appearance of the CFV, as did gating with respect to the pulsatile motion. These results imply that TE, field of view, slice thickness, and gating must be considered when using the appearance or absence of the CFV in diagnosis.

Acquisition order and motional artifact reduction in spin warp images.

Multiple averaging can be a powerful tool against motional artifacts if significant motion occurs between the redundant acquisitions taken at a given gradient strength. However, if the time delay between these redundant measurements is too short, data or images depicting the patient is exactly the same position will be combined. Pooling such identical data has no effect on motional artifacts. This problem can be solved by increasing TR, increasing the number of redundant acquisitions, or changing the order in which acquisitions are taken. Usually all acquisitions at a particular value of the warp gradient are taken before proceeding to the next gradient value. This order minimizes motion between redundant acquisitions and so maximizes artifacts. The effect of other acquisition orders on both periodic and nonrepetitive motion is discussed. Human images for breathing and phantom results for single-occurrence motions are presented.