Assessment of successful incorporation of cages after cervical or lumbar intercorporal fusion with [(18)F]fluoride positron-emission tomography/computed tomography.

The purpose of this study is to assess the successful incorporation of cages in patients after cervical or lumbar intercorporal fusion with positron-emission tomography/computed tomography (PET/CT). Twenty patients (14 female and 6 male; mean age 58 years, age range 38-73 years) with 30 cervical (n = 13) or lumbar (n = 17) intercorporal fusions were prospectively enrolled in this study. Time interval between last intercorporal intervention and PET/CT ranged from 2 to 116 months (mean 63; median 77 months). IRB approval was obtained for all patients, and written informed consent was obtained from all patients. About 30 min prior to PET/CT scanning, 97-217 MBq (mean 161 MBq) 18F-fluoride were administered intravenously. Patients were imaged in supine position on a combined PET/CT system (Discovery RX/STE, 16/64 slice CT, GE Healthcare). 3D-PET emission data were acquired for 1.5 and 2 min/bed position, respectively, and reconstructed by a fully 3D iterative algorithm (VUE Point HD) using low-dose CT data for attenuation correction. A dedicated diagnostic thin-slice CT was optionally acquired covering the fused region. Areas of increased 18F-fluoride uptake around cages were determined by one double-board certified radiologist/nuclear physician and one board certified radiologist in consensus. In 12/20 (60%) patients, increased 18F-fluoride uptake around cages was observed. Of the 30 intercorporal fusions, 15 (50%) showed increased 18F-fluoride uptake. Median time between intervention and PET/CT examination in cages with increased uptake was 37 months (2-116 months), median time between intervention and PET/CT examination in those cages without increased uptake was 91 months (19-112 months), p (Wilcoxon) = 0.01 (one-sided). 14/29 (48%) cages with a time interval > 1 year between intervention and PET/CT scan showed an increased uptake. In conclusion, PET/CT frequently shows increased 18F-fluoride uptake in cervical and lumbar cages older than 1 year (up to almost 8 years in cervical cages and 10 years in lumbar cages) possibly indicating unsuccessful fusion due to increased stress/microinstability.

MR guidance of laser disc decompression: preliminary in vivo experience.

The purpose of this study was to perform percutaneous laser disc decompression (PLDD) under MR guidance in an open configuration 0. 5-T MR system. Following failed conservative treatment for 6 months, eight patients with contained disc herniations were enrolled in the study. Following MR guided introduction of the laser fiber into the targeted disc space, the laser-induced temperature distribution was visualized using a color-coded subtraction technique based on a T1-weighted GRE sequence. In seven patients PLDD could be performed. In all cases laser effects were depicted by MR. In this regard the color-coded technique was found to be superior to conventional magnitude images. Whereas no apparent decrease in the extent of herniation was discovered immediately following PLDD, T2-weighted FSE images showed signal intensity alterations in two of the seven patients. Clinical evaluation, obtained 3-4 months after PLDD, revealed a fair (n = 2) or good (n = 4) response to the treatment. One patient showed no change in symptoms. MR guidance and monitoring of PLDD is feasible within an open 0.5-T system and seems to render PLDD more safe and controllable.

Real-time monitoring of laser diskectomies with a superconducting, open-configuration MR system.

OBJECTIVE: The objective of our study was to assess the ability of a 0.5-T superconducting, open-configuration MR system to guide laser diskectomies. The study was performed ex vivo on six human cadavers as well as in vivo on three patients. CONCLUSION: The macroscopic size of necrosis correlated well with the monitored temperature spread (r2 = .76-.85). After MR-guided introduction of the laser fiber into the targeted disk space, temperature spread was visualized in all subjects.

Quantitative determination of ablation in weight of lumbar intervertebral discs with holmium: YAG laser.

BACKGROUND AND OBJECTIVE: Since 1992, the Ho:YAG 2100 nm laser has been in regular use in percutaneous lumbar disc surgery through the uniportal approach. In vitro experiments were done to find out the exact amount of ablated tissue in weight per energy used with the present beam delivery system. STUDY DESIGN MATERIALS AND METHODS: Thirty dissected human lumbar discs were treated with the Ho:YAG laser with 12 x 10(6) W/cm2 of effective power density, under 20 ml/min of continuous irrigation. The ablation amount was determined through indirect comparison, using the water content of each disc as reference, which was predetermined individually by freeze drying. RESULTS: The ablation of nucleus pulposus is 32.293 mg/kJ in dry weight and 104.719 mg/kJ in physiologic weight. The ablation capacity in annulus fibrosus is 50% of that in nucleus pulposus. CONCLUSION: With 20 kJ of energy, the average amount of energy used in actual operations, the mean ablation of nucleus pulposus is 0.556 + or - 0.06 (n = 3) grams in dry weight, and 1.89667 + or - 0.162 (n = 3) g in physiologic weight.

Percutaneous disc surgery at Balgrist since 1979--from discotomy to interbody fusion.

In 1979 percutaneous intervertebral surgery was introduced as an alternative to conventional open disc surgery. In 1982, discoscopy was developed for intraoperative monitoring of the selective removal of disc tissue at the site of herniation. The indication remains restricted to subligamentous contained herniations. In a series of 240 patients with a mean follow up of 53 months, 88% reached an at least satisfactory overall outcome. Newly developed endoscopic instrumentation demonstrate promising results for their use in the spinal canal as well as in the extradiscal spinal area. Since 1988, by means of new, specially adapted instrumentation, endoscopically controlled interbody fusion was introduced with temporary pedicular external fixation. In a series of 35 cases with monosegmental percutaneous fusion, at a mean follow-up of 25 months, the fusion rate--including initial pitfalls-- reached 29/35 (83%). The technique does not require blood transfusions, no remaining internal fixation is left. This minimally invasive approach facilitates functional rehabilitation. Some of the techniques presented in this article concerning percutaneous external fixation and percutaneous interbody fusion must be considered as experimental according to American FDA standards.

Substrate responses to acid-base alterations in dog renal proximal tubules.

Proximal tubules from dog kidney were incubated for 2-6 min with low concentrations of pyruvate, glutamine, and malate. When initial medium citrate was between 0 and 0.5 mM and alpha-ketoglutarate was between 0 and 0.1 mM, concentrations of these two substrates in tubules and media after incubation were lower with 10 than with 40 mM HCO3-. Malate levels in tubules and media changed in the opposite direction. CO2 formation from labeled citrate or alpha-ketoglutarate was greater at low than at high HCO3-. In tubules treated with digitonin to disrupt the cell membrane, differences in citrate and alpha-ketoglutarate concentrations in tubules at high and low HCO3- were eliminated. The effects of acid-base changes seen in intact tubules on malate levels and on the rate of oxidation of labeled citrate persisted after digitonin pretreatment. These results show that acute effects of acid-base changes on citrate, alpha-ketoglutarate, and malate levels observed in intact renal cortex can be reproduced in isolated tubules. They suggest that these changes are related to changes in levels of citrate and alpha-ketoglutarate in cytoplasm without corresponding changes within mitochondria.

Specific gene expression during compensatory renal hypertrophy in the rat.

The compensatory growth of the kidney which is induced by unilateral nephrectomy is a highly regulated process resulting principally in hypertrophy of the remaining kidney. The events which regulate this process are unknown. We have examined the levels of transcripts for the proto-oncogenes, myc, H-ras, K-ras, and fos, and the cellular genes, H4 histone, ornithine aminotransferase, and gamma-glutamyl transpeptidase, following unilateral nephrectomy in the rat. The pattern of expression of c-myc, c-H-ras, and c-K-ras during compensatory growth of the kidney differs from the pattern of expression of these proto-oncogenes during liver regeneration, in which, unlike the kidney, hyperplasia rather than hypertrophy predominates. The lack of change in the abundance of these proto-oncogene transcripts following unilateral nephrectomy suggests a primary relationship between the expression of these proto-oncogenes and DNA synthesis and indicates there may be separate signals for cell growth, one to double cell size and one to replicate DNA. Increased mRNA transcripts for the enzymes ornithine aminotransferase and gamma-glutamyl transpeptidase were induced in the contralateral kidney after nephrectomy. The time course of expression for these two enzymes differs. The early expression of the gamma-glutamyl transpeptidase gene may indicate an involvement of this glutathione-metabolizing enzyme during renal compensatory growth, while the function of the delayed increase in ornithine aminotransferase transcripts in the remaining kidney is not apparent.