Daniel K. Kido

MR imaging of spinal lymphoma

Fourteen patients with spinal lymphoma examined by MR imaging were reviewed. Thirteen of them also had extraspinal lymphoma. Vertebral involvement was found in 12 patients, epidural in 10, and paraspinal in 8 patients. On the basis of MR imaging at 0.3 T, spinal lymphoma may be divided into three types of growth pattern according to the main location: paraspinal, vertebral, and epidural. Most frequently, all three locations were found simultaneously on MR (7/14). In one patient the location was vertebral with epidural extension, in one paraspinal with vertebral extension, in 3 it was entirely vertebral, and in 2 entirely epidural. Multiple plane T1-weighted imaging gave complete information about the extent of spinal lymphoma. The signal intensity was lower than or equal to muscle and lower than bone marrow in paraspinal and vertebral lesions on T1-weighted images and high on T2-weighted images. Epidural lesions showed a hypo- or isointense signal relative to the cord on T1-weighted images except in one case and a hyperintense signal on T2-weighted images. Compression of the cord and cauda equina due to bulging of diseased vertebral bodies and epidural lesions was well demonstrated. MR imaging was also found useful in the follow-up of treatment.

Lumbar myelography with iohexol and metrizamide. A double-blind clinical trial.

Two non-ionic contrast media, iohexol and metrizamide, were compared in a double-blind clinical trial which included 50 patients who underwent lumbar myelography for disc herniation or spinal stenosis. The frequency of adverse reactions was lower for iohexol which is recommended for extended trials and for examination of other compartments of the subarachnoid space.

The effect of iohexol on glucose metabolism compared with metrizamide.

In a previous in vitro study we demonstrated reduced CO2 production in rat hippocampal tissue when metrizamide was added. This metabolic depression is believed to be a result of the 2-deoxy-D-glucose (2-DG) portion of the metrizamide molecule since 2-DG is a known competitive inhibitor of glucose metabolism. This competitive inhibition probably occurs at the cell membrane since it has never been shown that metrizamide penetrates neural cells. Further the inhibition is most likely related to competition for the membrane glucose carrier. A new nonionic contrast medium, iohexol, does not contain a 2-DG component and if the hypothesis for the metabolic inhibition is valid we should not expect metabolic inhibition with iohexol. This hypothesis was tested using the rat hippocampus model previously used for metrizamide. We compared iohexol with metrizamide in isotonic concentrations and also examined the effect of hypertonicity. These experiments did not demonstrate inhibition of CO2 production with iohexol at near physiologic osmolalities, however, there was a marked depressive effect with increasing osmolality. This effect from hypertonicity is, however, probably of less importance in vivo where water will rapidly diffuse toward the hypertonic areas. The apparent lack of interference of the iohexol molecule on glucose metabolism should therefore make iohexol a more suitable contrast medium, for subarachnoid investigations than metrizamide.

Lumbar Myelography with Metrizamide in Rabbits: An Investigation of Contrast Media Penetration and Resorption

Neurotoxicity from subarachnoid contrast media is probably related to their specific pharmacologic effects and to their penetration into the central nervous system. The lack of a barrier between the cerebrospinal fluid and the extracellular fluid of the brain and cord allows water-soluble contrast media to diffuse into the neural tissue. The aim of this investigation was to develop a method that allows one to quantify the neural tissue penetration for a given contrast medium in relation to the cerebrospinal fluid concentration and contact time and apply this to the use of metrizamide. The result shows a good correlation between iodine concentration in the lumbar cerebrospinal fluid and that in the lumbar cord suggestive of a simple diffusion. When time of sacrifice (contact time) is added as a covariant there is also some indication of retention of metrizamide in the neural tissue. The investigation also demonstrates that the resorption of the contrast medium in the rabbit in this experimental model is mainly in the lumbo-sacral region.

Opiate Involvement in Contrast Media-induced Blood Pressure Changes

The intravenous administration of contrast media (CM) often alters blood pressure (BP). Osmolality plays a role, but the magnitude and even direction of change varies under similar (osmotic) conditions, indicating the involvement of other mechanisms. Male Wistar rats, anesthetized with pentobarbital, received sodium/meglumine diatrizoate, iohexol, or normal saline, 4 ml/kg, via a tail vein, while blood pressure was recorded continuously. Additional groups were pretreated with the opiate antagonist, naloxone (1 mg/kg, IV), or with an equal volume of normal saline 5 minutes prior to the diatrizoate injection. Comparisons of BP change were made with the Students t-test. Diatrizoate caused a significant (P less than .0002) increase in BP relative to the saline control group, iohexol did not. Thus, the increase with diatrizoate was significantly greater than with iohexol (P less than .00006). Neither the saline nor naloxone pretreatment altered BP significantly. Saline pretreatment did not alter the significant increase in BP produced by the diatrizoate. However, the diatrizoate-induced increase in BP was prevented by the naloxone pretreatment and was significantly less than after the saline pretreatment (P less than .0001). Based on these and previous results, the authors hypothesize that release of endogenous opioids may play a role in BP changes caused by intravenous CM and that significant CM-induced changes may be prevented pharmacologically with the selective opiate blocker, naloxone.

Technical Aspects on Magnetic Resonance Imaging of the Spine at 1.5 Tesla

Technical aspects on surface coil magnetic resonance imaging of the spine using a superconducting system with a field strength of 1.5 tesla are described. By using a flat surface coil instead of the body coil the image quality was markedly improved and the signal-to-noise ratio (S/N) was increased approximately 2.6 times. Small voxels resulted in low S/N. The best image quality was achieved with a slice thickness of 5 mm, a field of view of 20 to 24 cm and a matrix of 256×256. Interleaved slices provided superior image quality compared with contiguous slices at the expense of acquisition time. For sagittal images the phase encoding gradient should be in the cranio-caudal direction to minimize motion artifacts. To obtain T1 and T2 images of high quality, spin echo pulse sequences with TR 600/TE 20 ms and TR 2000/TE 40 to 80 ms are useful.

Pharmacokinetics and excretion of iohexol after lumbar myelography in man.

Pharmacokinetics and excretion of iohexol, a new nonionic water-soluble contrast medium, were determined after lumbar myelography. Peak plasma concentrations were obtained 2 to 6 hours after injection and ranged from 29 to 177 microgram/ml. Terminal elimination half-life was 4.0 hours, and over 90% of the dose was recovered in the urine within 24 hours. In one patient with a large lumbar cauda equina tumor, absorption and excretion were delayed; but eventually 99% was recovered indicating a large capacity for reabsorption via the lumbar subarachnoid space. One mild headache of 5 minutes duration was reported in a 73-year-old woman. No significant changes in vital signs, neurologic examinations, or serum chemistries were observed.

Physiologic effects of contrast media in the rabbit.

The intravenous administration of contrast media (CM) is often associated with alterations in blood pressure (BP) and heart rate (HR). Osmolality is thought to play a role, but the magnitude and even the direction of change may vary under similar osmotic conditions indicating the involvement of other mechanisms. Conscious rabbits received sodium-meglumine diatrizoate (76%, 1 mL/kg, ear vein) every 10 minutes for 1 hour. A similar injection protocol was performed with normal saline and mannitol (36%), equiosmotic to the contrast agent. BP and HR were monitored continuously. Blood samples were collected at the midpoint between each injection for determination of hematocrit, serum osmolality, and iodine concentration. Group parameters at each time point were compared with the Students t-test. The administration of mannitol caused changes in serum osmolality, hematocrit, and HR as great or greater than the changes caused by equiosmotic diatrizoate. However, BP increased significantly in the diatrizoate group but not in the mannitol group, relative to normal saline. These results suggest that osmolality is important for certain physiologic changes induced by CM, but that BP changes involve mechanisms in addition to osmolality.

Postoperative radiographic appearance of intracranial hemostatic gelatin sponge.

Hemostatic gelatin sponges were placed in hemispheric defects created in four dogs which were then periodically scanned by computed tomography to determine the postoperative appearance of the sponges. The hemostatic sponges appeared as low attenuation regions for 7-10 days. The attenuation value of these Gelfoam cavities was intermediate between fat and air. Subsequently, clinical cases were selected in which the location of gelatin sponges were known to demonstrate the appearance of the material in patients. In addition to enhancing the accuracy of computed tomographic interpretation, we have found that the gelatin sponge can be useful as a transient computed tomography marker for localization of surgical activity.

Measurement of caudate nucleus and putamen atrophy in patients with Huntington’s disease

Direct linear measurements of caudate nucleus widths are more accurate than indirect measurements (bi-caudate distance) in detecting early atrophic changes using MRI in patients with Huntington’s disease (HD). At 95% confidence level, caudate nucleus widths of 8 mm or less were found to be abnormal, while those 9 mm or larger were normal. Caudate nuclei widths were more sensitive than similar measurements of the putamen or of bicaudate-skull ratios as correlates of functional changes in patients with early HD.