Primary stenting for acute myocardial infarction via the transradial approach: a safe and useful alternative to the transfemoral approach

BACKGROUND

Primary stenting in acute myocardial infarction (AMI) has been demonstrated to reduce recurrent ischemic events. However, transradial stenting in AMI has not been well established. Therefore, we sought to investigate the feasibility and utility of transradial coronary stenting in patients with AMI.

METHODS

From April 1998 to April 1999, 56 patients (43 male; mean age of 57 years) who arrived within 6 hours of pain onset with culprit vessel size > 2.5 mm constituted this study. The transradial approach (Group 1) was used in 30 patients with hemodynamically stable and palpable right radial pulse. The transfemoral approach (Group 2) was used for vascular access in the remainder of patients (26) who might have required a second vascular access site for intraaortic balloon pumping (in cardiogenic shock) and/or a transvenous temporary pacemaker.

RESULTS

Overall success rate was achieved in 54 of 56 patients (96%). The success rate was 90% (27/30) in Group 1 and 96% (25/26) in Group 2. The cannulation time (from patient arrival at the catheterization room to the time of arterial cannulation) and the total procedure time (from patient arrival at the catheterization room to the completion of the procedure) were not significantly different between Group 1 and Group 2 (9.2+/-5.3 versus 8.9+/-5. 8 minutes, p>0.05; 53.7+/-19.4 versus 57.5 +/-26.8 minutes, p>0.05, respectively). In the Group 1 patients, there was no forearm ischemia or loss of radial pulse during the 30-day follow-up period.

CONCLUSION

Primary coronary stenting for acute myocardial infarction via the transradial approach is a safe and feasible alternative to the conventional transfemoral approach, and is especially useful for hemodynamically stable patients who do not require a second vascular access site.

Transcriptional inactivation of the tissue inhibitor of metalloproteinase-3 gene by dna hypermethylation of the 5'-CpG island in human gastric cancer cell lines

The tissue inhibitor of metalloproteinase-3 (TIMP-3), a recently cloned member of TIMP gene family, has been implicated in the negative regulation of tumor cell invasion and tumor growth. Down-regulation of this gene has been shown to occur in a mouse carcinogenesis model, suggesting that it might play a role in the tumor progression of some cancers. In this study, we used human gastric cancer cell lines to investigate whether TIMP-3 gene expression is suppressed in human gastric cancer. We examined whether aberrant DNA methylation of the 5'-CpG island of the TIMP-3 gene is involved in this cancer. Nine of 10 human gastric cancer cell lines completely lost TIMP-3 gene expression compared with normal samples. Southern blot analysis and bisulfite genomic sequencing revealed aberrant hypermethylation near the transcription-start site of the TIMP-3 gene in all cell lines lacking TIMP-3 expression. Treatment of these cell lines with the demethylating agent 5-aza-2'-deoxycytidine restored TIMP-3 gene expression. Our results suggest that the TIMP-3 gene is another early target of tumor-associated aberrant DNA methylation in human gastric carcinogenesis. Consequently, genetic silencing of TIMP-3 may lead to a more malignant and invasive phenotype in these cancer cells.

Induction of class alpha glutathione S-transferases by 4-methylthiazole in the rat liver: role of oxidative stress

The expression of glutathione S-transferase (GST) is a crucial factor in determining the sensitivity of cells and organs in response to a variety of toxicants. Expression of class alpha GST genes by methyl-substituted thiazoles was assessed in the rat liver. Northern blot analysis revealed that 4-methylthiazole (4-MT) elevated rGSTA2, A3, A5 and M1 mRNAs in the liver by 19-, 4-, 6- and 9-fold at 24 h after treatment, respectively, as compared to control. Consecutive 3-day treatment with 4-MT resulted in 4- to 7-fold increases in rGSTA and M1 mRNAs. Multiple treatments with 5-methylthiazole (5-MT) caused marginal increases in GST mRNAs in spite of the large increases in certain GST mRNAs at 24 h. Either 4, 5-dimethylthiazole (DT) or 2,4,5-trimethylthiazole (TT) minimally affected the rGSTA and rGSTM mRNA expression at 1-3 day(s). Western blot analysis showed that 4-MT induced rGSTA1/2, rGSTA3/5 and rGSTM1 proteins by 2.6-, 2.1- and 2.1-fold at 3 days, respectively, while other methylthiazoles failed to induce the GST subunits. Starving rats were treated with a lower dose of methylthiazoles to study the role of oxidative stress in the mRNA expression. The levels in rGSTA2/3/5 mRNAs were significantly enhanced by 4-MT in starving rats, whereas rGSTM1/2 mRNAs were not further increased. Other methylthiazoles were inactive in enhancing the mRNAs in starving animals. Pretreatment of starving rats with either cysteine or methionine completely prevented the increases in class alpha GST mRNAs by 4-MT. Data showed that 4-MT induces class alpha GSTs with the increases in the mRNAs, whereas 5-methyl-, dimethyl- and trimethyl-substituted thiazoles were minimally active. Increases in the class alpha GST mRNAs by 4-MT may be associated with the oxidative stress in hepatocytes, as supported by starvation and sulfur amino acid experiments.

In vivo MR measurements of regional arterial and venous blood volume fractions in intact rat brain

In vivo measurement of cerebral arterial and venous volume fractions is important to the understanding of brain physiology and function. By using an intravascular perfluorocarbon and 19F NMR at 4.7 T, regional arterial and venous volume fractions from an intact rat brain were resolved based on the pseudodiffusion coefficients, which were (33 +/- 7) x 10(-3) and (0.45 +/- 0.13) x 10(-3) mm(2)/sec (mean +/- SD, n = 7) for the fast- and slow-moving component, respectively. By exploiting the linear dependence of the perfluorocarbon 19F 1/T1 on the dissolved paramagnetic oxygen concentration, combined inversion-recovery and diffusion measurements were made to correlate the short T1 (high-oxygenation) component with the fast-moving component and the long T1 (low-oxygenation) component with the slow-moving component. The arterial blood volume fraction was 29 +/- 7% of the total cerebral blood volume. Finally, experiments were performed in which different oxygen concentrations were inhaled to validate this technique.

Enhanced expression of rat hepatic microsomal epoxide hydrolase by methylthiazole in conjunction with liver injury

Microsomal epoxide hydrolase (mEH) is inducible by a number of xenobiotics. Induction of mEH by certain chemopreventive agents may implicate the protective effect. In contrast, many of carcinogenic agents also induce the enzyme. The hepatotoxicity and mEH expression by methylthiazoles, which are incorporated as functional groups in a number of therapeutic agents, were assessed in the rat liver to study the structural basis for the enzyme induction and the correlative enzyme expression with hepatotoxicity. Among the methylthiazoles examined, 4-methylthiazole (MT) at the daily dose of 1.17 mmol/kg body weight caused hepatic necrosis and degeneration after 1-3 consecutive daily treatment(s), whereas 4, 5-dimethylthiazole (DT) and 2,4,5-trimethylthiazole (TT) elicited no toxicity. Treatment of rats with MT at the daily dose of 1.17 mmol/kg increased the mEH mRNA by 17- and 7-fold at day 1 and day 3, respectively, relative to control. Whereas DT caused 5- and 2-fold increases in mEH mRNA at day 1 and day 3, respectively, TT minimally affected mEH expression. The mRNA increase was consistent with the protein induction. Hence, the methylthiazole causing hepatotoxicity was more active in inducing the enzyme. Whereas treatment with MT at the dose of 0.35 mmol/kg caused no hepatotoxicity, MT caused hepatic necrosis in starving rats. Northern blot analysis showed that the mEH mRNA level was increased to a greater extent by MT in starving rats than in control animals. Conversely, treatment of starving rats with either cysteine or methionine prior to MT prevented the hepatic necrosis. Elevation of the mEH mRNA by MT in starving animals was also inhibited by either cysteine or methionine pretreatment. These results demonstrated that the methylthiazole which caused hepatotoxicity also up-regulated mEH expression, whereas other methylthiazoles showing no toxicity minimally increased the gene expression. The observation that the extent of mEH expression by MT was highly associated with that of liver injury raised the notion that mEH expression by xenobiotics may not necessarily represent the beneficial and protective effects.

Effects of cysteine on the pharmacokinetics of intravenous adriamycin in rats with protein-calorie malnutrition

In rats with protein-calorie malnutrition (PCM, 5% caseine diet for 4 weeks), hepatic cytochrome P450 levels suppressed markedly and cytochrome P450 mRNAs decreased significantly compared with those in control rats (23% caseine diet for 4 weeks), however, the values completely (or partially) returned to control levels by a week (from fourth week) of cysteine supplementation (rats with PCMC) (Cho, Kim et al., Arch. Biochem. Biophys. 1999, 372: 150-158). The formation of aglycone metabolites of adriamycin and adriamycinol, M3 and M4, respectively, seemed to be induced (Lee and Lee, Res. Commun. Mol. Pathol. Pharmacol. 1999, 105: 87-96) by pretreatment with dexamethasone (possibly by hepatic cytochrome P450 RL 33/cDEX, Komori and Oda, J. Biochem. 1994, 116: 114-120) in rats. Adriamycin, 16 mg/kg, was administered intravenously in 1-min to control rats and rats with PCM and PCMC. In rats with PCM, the plasma concentrations of adriamycin was higher (the area under the plasma concentration-time curve from time zero to 12 hr, AUC(0-12 hr), tended to be higher) and 24-hr urinary excretion of M3 (including its 'conjugates') seemed to increase than those in control rats, suggested that the formation of M3 was inhibited in rats with PCM. In rats with PCMC, the plasma concentrations of adriamycin were lower (the AUC(0-12 hr) was significantly smaller) and 24-hr urinary excretion of M3 (including its 'conjugates') were significantly greater than those in rats with PCM, suggested that the formation of M3 increased significantly by cysteine supplementation by restoring the enzyme system(s) that metabolize adriamycin to M3. The altered pharmacokinetic parameters of adriamycin mentioned above in rats with PCM returned to greater than those of control rats after cysteine supplementation (rats with PCMC). Above data suggested that other hepatic cytochrome P450 isozyme(s) which catalyze(s) the formation of M3 from adriamycin could be induced by cysteine supplementation.

Functional MRI of calcium-dependent synaptic activity: cross correlation with CBF and BOLD measurements

Spatial specificities of the calcium-dependent synaptic activity, hemodynamic-based blood oxygenation level-dependent (BOLD) and cerebral blood flow (CBF) fMRI were quantitatively compared in the same animals. Calcium-dependent synaptic activity was imaged by exploiting the manganese ion (Mn++) as a calcium analog and an MRI contrast agent at 9.4 T. Following forepaw stimulation in alpha-chloralose anesthetized rat, water T1 of the contralateral forepaw somatosensory cortex (SI) was focally and markedly reduced from 1.99 +/- 0.03 sec to 1.30 +/- 0.18 sec (mean +/- SD, N = 7), resulting from the preferential intracellular Mn++ accumulation. Based on an in vitro calibration, the estimated contralateral somatosensory cortex [Mn++] was approximately 100M, which was 2-5-fold higher than the neighboring tissue and the ipsilateral SI. Regions with the highest calcium activities were localized around cortical layer IV. Stimulus-induced BOLD and CBF changes were 3.4 +/- 1.6% and 98 +/- 33%, respectively. The T1 synaptic activity maps extended along the cortex, whereas the hemodynamic-based activation maps extended radially along the vessels. Spatial overlaps among the synaptic activity, BOLD, and CBF activation maps showed excellent co-registrations. The center-of-mass offsets between any two activation maps were less than 200 microm, suggesting that hemodynamic-based fMRI techniques (at least at high field) can be used to accurately map the spatial loci of synaptic activity.

In vivo MR measurements of regional arterial and venous blood volume fractions in intact rat brain

In vivo measurement of cerebral arterial and venous volume fractions is important to the understanding of brain physiology and function. By using an intravascular perfluorocarbon and 19F NMR at 4.7 T, regional arterial and venous volume fractions from an intact rat brain were resolved based on the pseudodiffusion coefficients, which were (33 +/- 7) x 10(-3) and (0.45 +/- 0.13) x 10(-3) mm(2)/sec (mean +/- SD, n = 7) for the fast- and slow-moving component, respectively. By exploiting the linear dependence of the perfluorocarbon 19F 1/T1 on the dissolved paramagnetic oxygen concentration, combined inversion-recovery and diffusion measurements were made to correlate the short T1 (high-oxygenation) component with the fast-moving component and the long T1 (low-oxygenation) component with the slow-moving component. The arterial blood volume fraction was 29 +/- 7% of the total cerebral blood volume. Finally, experiments were performed in which different oxygen concentrations were inhaled to validate this technique.

Motor area activity during mental rotation studied by time-resolved single-trial fMRI

The functional equivalence of overt movements and dynamic imagery is of fundamental importance in neuroscience. Here, we investigated the participation of the neocortical motor areas in a classic task of dynamic imagery, Shepard and Metzler's mental rotation task, by time-resolved single-trial functional Magnetic Resonance Imaging (fMRI). The subjects performed the mental-rotation task 16 times, each time with different object pairs. Functional images were acquired for each pair separately, and the onset times and widths of the activation peaks in each area of interest were compared to the response times. We found a bilateral involvement of the superior parietal lobule, lateral premotor area, and supplementary motor area in all subjects; we found, furthermore, that those areas likely participate in the very act of mental rotation. We also found an activation in the left primary motor cortex, which seemed to be associated with the right-hand button press at the end of the task period.

Participation of type II protein kinase A in the retinoic acid-induced growth inhibition of SH-SY5Y human neuroblastoma cells

To examine the role of protein kinase A (EC 2.7.1.37) isozymes in the retinoic acid-induced growth inhibition and neuronal differentiation, we investigated the changes of protein kinase A isozyme patterns in retinoic acid-treated SH-SY5Y human neuroblastoma cells. Retinoic acid induced growth inhibition and neuronal differentiation of SH-SY5Y cells in a dose- and time-dependent manner. Neuronal differentiation was evidenced by extensive neurite outgrowth, decrease of N-Myc oncoprotein, and increase of GAP-43 mRNA. Type II protein kinase A activity increased by 1.5-fold in differentiated SH-SY5Y cells by retinoic acid treatment. The increase of type II protein kinase A was due to the increase of RIIbeta and Calpha subunits. Since type II protein kinase A and RIIbeta have been known to play important role(s) in the growth inhibition and differentiation of cancer cells, we further investigated the role of the increased type II protein kinase A by overexpressing RIIbeta in SH-SY5Y cells. The growth of RIIbeta-overexpressing cells was slower than that of parental cells, being comparable to that of retinoic acid-treated cells. Retinoic acid treatment further increased the RIIbeta level and further inhibited the growth of RIIbeta-overexpressing cells, showing strong correlation between the level of RIIbeta and growth inhibition. However, RIIbeta-overexpressing cells did not show any sign of neuronal differentiation and responded to retinoic acid in the same way as parental cells. These data suggest that protein kinase A participates in the retinoic acid-induced growth inhibition through the up-regulation of RIIbeta/type II protein kinase A.

High-resolution mapping of iso-orientation columns by fMRI

Blood-oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is an important tool for localizing brain functions in vivo. However, the ability of BOLD fMRI to map cortical columnar structures is highly controversial, as the ultimate functional specificity of BOLD remains unknown. Here we report a biphasic BOLD response to visual stimulation in the primary visual cortex of cats. In functional imaging, the initial BOLD signal decrease accurately labeled individual iso-orientation columns. In contrast, the delayed positive BOLD changes indicated the pattern of overall activation in the visual cortex, but were less suited to discriminate active from inactive columns.

Early temporal characteristics of cerebral blood flow and deoxyhemoglobin changes during somatosensory stimulation

The close correspondence between neural activity in the brain and cerebral blood flow (CBF) forms the basis for modern functional neuroimaging methods. Yet, the temporal characteristics of hemodynamic changes induced by neuronal activity are not well understood. Recent optical imaging observations of the time course of deoxyhemoglobin (HbR) and oxyhemoglobin have suggested that increases in oxygen consumption after neuronal activation occur earlier and are more spatially localized than the delayed and more diffuse CBF response. Deoxyhemoglobin can be detected by blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI). In the present study, the temporal characteristics of CBF and BOLD changes elicited by somatosensory stimulation in rat were investigated by high-field (9.4 T) MRI. With use of high-temporal-resolution fMRI, it was found that the onset time of the CBF response in the somatosensory cortex was 0.6 +/- 0.4 seconds (n = 10). The CBF changes occurred significantly earlier than changes in HbR concentration, which responded after 1.1 +/- 0.3 seconds. Furthermore, no early increases in HbR (early negative BOLD signal changes) were observed. These findings argue against the occurrence of an early loss of hemoglobin oxygenation that precedes the rise in CBF and suggest that CBF and oxygen consumption increases may be dynamically coupled in this animal model of neural activation.

Decreased RR interval complexity and loss of circadian rhythm in patients with congestive heart failure

The present study investigated how the RR interval complexity and variability and their circadian rhythms alter for patients with congestive heart failure (CHF). Sixteen patients aged between 41 and 72 years with CHF and 20 control subjects were included. 24-h ambulatory electrocardiographic recordings were analyzed, and digitized data was partitioned into sections of 30-min duration. For each section, time- and frequency-domain indices, and complexity indices of heart rate variability were calculated. For CHF patients, 24-h average values of all indices were significantly decreased. The circadian rhythms of mean RR intervals were preserved and resembled the abnormal circadian rhythms of the low-frequency power. The circadian rhythms of high-frequency power and all complexity indices shown in the normal control were lost. Conclusively, the patients with CHF showed decreased RR interval complexity and loss of its circadian rhythm, in addition to decreased frequency-domain RR interval variability and its abnormal circadian rhythm.

Building a common feature hypothesis for thymidylate synthase inhibition

A set of 21 highly flexible competitive inhibitors of thymidylate synthase (TS; EC 2.1.1.45) covering a wide activity range (IC50 = 6 nM-100 microM) has been investigated by three-dimensional quantitative structure-activity relationship (3D-QSAR). CATALYST was used to generate three-dimensional hypotheses to study the common interaction features among a set of thymidylate synthase inhibitor. The verification of the hypothesis was achieved by using the molecules outside the training set.

New simple endoscopic operations for interstitial pregnancies

OBJECTIVES

Our aim was to report a new approach of endoscopic management (endoloop and encircling suture methods) for interstitial or cornual pregnancy and to determine the safety and effectiveness of these procedures and their effects on subsequent pregnancies.

STUDY DESIGN

This is an uncontrolled retrospective review of 24 patients treated for interstitial pregnancies through endoscopic operations with 14 to 72 months of follow-up at a large urban medical center. Blood loss, operation time, changes of serum human chorionic gonadotropin levels, the resumption of menstruation, and subsequent pregnancy after operation were analyzed.

RESULTS

Among 24 interstitial pregnancies, 3 had ruptured at the time of operation and 21 had not ruptured. Treatment consisted of either the vasopressin and electric cauterization method, the endoloop before evacuation of the conceptus method, or the encircling suture before evacuation of the conceptus method. The blood loss and operation time (mean +/- SD) for unruptured cases were 133 +/- 134 mL and 51.6 +/- 7.6 minutes in the vasopressin and electric cauterization group (n = 3), 32 +/- 22 mL and 28.5 +/- 6.4 minutes in the endoloop group (n = 15), and 40 +/- 17 mL and 35.0 +/- 5.0 minutes in the encircling suture group (n = 3). In 3 patients with ruptured pregnancy treated with the endoloop method, the blood loss and operation time (mean +/- SD) were 1100 +/- 854 mL and 82.5 +/- 51.6 minutes. Any of these operative methods resulted in rapid decline of serum human chorionic gonadotropin levels within 1 week with the exception of 1 case, in which the endoloop method was used; this patient needed additional treatment with methotrexate. Seventeen patients desired pregnancy in the future, and 15 eventually became pregnant. One of these 15 pregnancies ended in an ectopic pregnancy on the opposite side 6 months after the interstitial pregnancy. Three ended in a spontaneous abortion, and 11 were delivered by elective cesarean section at term before labor started. Operative records of cesarean section in 8 patients delivered at our institution showed little or no adhesions or defect in the cornual area of the previous operation.

CONCLUSION

The endoloop method and the encircling suture method are simple, safe, effective, and nearly bloodless. There were no uterine ruptures in the pregnancies subsequent to these methods of endoscopic management.

Phase-field model for binary alloys

We present a phase-field model (PFM) for solidification in binary alloys, which is found from the phase-field model for a pure material by direct comparison of the variables for a pure material solidification and alloy solidification. The model appears to be equivalent with the Wheeler-Boettinger-McFadden (WBM) model [A.A. Wheeler, W. J. Boettinger, and G. B. McFadden, Phys. Rev. A 45, 7424 (1992)], but has a different definition of the free energy density for interfacial region. An extra potential originated from the free energy density definition in the WBM model disappears in this model. At a dilute solution limit, the model is reduced to the Tiaden et al. model [Physica D 115, 73 (1998)] for a binary alloy. A relationship between the phase-field mobility and the interface kinetics coefficient is derived at a thin-interface limit condition under an assumption of negligible diffusivity in the solid phase. For a dilute alloy, a steady-state solution of the concentration profile across the diffuse interface is obtained as a function of the interface velocity and the resultant partition coefficient is compared with the previous solute trapping model. For one dimensional steady-state solidification, where the classical sharp-interface model is exactly soluble, we perform numerical simulations of the phase-field model: At low interface velocity, the simulated results from the thin-interface PFM are in excellent agreement with the exact solutions. As the partition coefficient becomes close to unit at high interface velocities, whereas, the sharp-interface PFM yields the correct answer.

Effects of brazilin on GLUT4 recruitment in isolated rat epididymal adipocytes

The effects of brazilin on glucose transport into isolated rat epididymal adipocytes were investigated. Brazilin increased [3H]2-deoxy-D-glucose uptake, which was characterized by an increase in Vmax with no effect on the Km value. Phenylarsine oxide, which inhibits the translocation of glucose transporters, decreased brazilin-stimulated glucose transport to the basal level. The inhibition of phosphatidylinositol 3-kinase (PI3-kinase) with wortmannin also blocked brazilin-stimulated glucose transport. Western blot analysis with an anti-GLUT4 antibody revealed that brazilin increased the translocation of GLUT4 from intracellular pools to the plasma membrane. Brazilin, in combination with phorbol ester, showed an additive effect on glucose transport. The stimulating effect of phorbol ester on glucose transport was inhibited by staurosporine, but the effect of brazilin remained unchanged. Protein kinase C activity was not influenced by brazilin treatment. The inhibition of protein synthesis showed no effect on brazilin-stimulated glucose transport, and GLUT4 content in the total membrane fraction was not altered as a result of treatment with brazilin for 4 hr. Metabolic labeling of GLUT4 with [35S]methionine showed that de novo synthesis of GLUT4 was not induced by brazilin. These data suggest that brazilin may increase glucose transport by recruitment of GLUT4 from intracellular pools to the plasma membrane of adipocytes via the activation of PI3-kinase. However, the effect of brazilin may not be mediated by GLUT4 synthesis and protein kinase C activation.

Suppression of rat hepatic cytochrome P450s by protein-calorie malnutrition: complete or partial restoration by cysteine or methionine supplementation

Pharmacokinetic profiles of therapeutic agents are altered by protein-calorie malnutrition (PCM). The current study was designed to determine the expression of hepatic cytochrome P450s in rats after protein restriction and to investigate its molecular basis. Western blot analysis revealed that rats with protein restriction for 4 weeks exhibited marked suppression in the hepatic P450 1A2, 2C11, 2E1, and 3A1/2 levels. Northern blot analysis showed that hepatic P450 1A2, 2C11, and 3A1/2 mRNAs were significantly decreased in the state of PCM. The P450 2E1 mRNA level was slightly decreased in PCM rats, suggesting the possibility that expression of P450 2E1 affected by PCM might result from the transcriptional and/or posttranscriptional regulation. PCM-induced changes in most P450 expression completely or partially returned to control levels by a week of cysteine supplementation. Cysteine also prevented decreases in P450 1A2, 2C11, 2E1, and 3A1/2 mRNA levels by PCM. Methionine was minimally active in restoring the P450 expression. A metabolic change in hepatic ethoxyresorufin dealkylase activity in PCM rats was consistent with the P450 apoprotein and mRNA levels. Although the plasma concentrations of azosemide, a loop diuretic, primarily metabolized by cytochrome P450 1A, increased in protein-deprived rats, cysteine supplementation significantly reduced the increased plasma concentrations of the drug. The altered pharmacokinetic parameters of azosemide in PCM rats returned to those of control after cysteine supplementation, corroborating the conclusion that cysteine was effective in restoring cytochrome P450 expression and metabolic activities.

Diffusion-weighted spin-echo fMRI at 9.4 T: microvascular/tissue contribution to BOLD signal changes

The nature of vascular contribution to blood oxygenation level dependent (BOLD) contrast used in functional MRI (fMRI) is poorly understood. To investigate vascular contributions at an ultrahigh magnetic field of 9.4 T, diffusion-weighted fMRI techniques were used in a rat forepaw stimulation model. Tissue and blood T(2) values were measured to optimize the echo time for fMRI. The T(2) of arterial blood was 40.8 +/- 3.4 msec (mean +/- SD; n = 5), similar to the tissue T(2) of 38.6 +/- 2.1 msec (n = 16). In comparison, the T(2) of venous blood at an oxygenation level of 79.6 +/- 6.1% was 9. 2 +/- 2.3 msec (n = 11). The optimal spin-echo time of 40 msec was confirmed from echo-time dependency fMRI studies. The intravascular contribution was examined using a graded diffusion-weighted spin-echo echo-planar imaging technique with diffusion weighting factor (b) values of up to 1200 sec/mm(2). Relative BOLD signal changes induced by forepaw stimulation showed no dependence on the strength or direction of the diffusion-sensitizing gradients, suggesting that the large vessel contribution to the BOLD signal is negligible at 9.4 T. However, gradient-echo fMRI performed with bipolar diffusion sensitizing gradients, which suppress intravascular components from large vessels, showed higher percent signal changes in the surface of the brain. This effect was attributed to the extravascular contribution from large vessels. These findings demonstrate that caution should be exercised when interpreting that higher percent changes obtained with gradient-echo BOLD fMRI are related to stronger neural activation. Magn Reson Med 42:919-928, 1999.

Cardiac memory after radiofrequency ablation of accessory pathways: the post-ablation T wave does not forget the pre-excited QRS

INTRODUCTION

Normalization of the pre-excited QRS following ablation is accompanied by repolarization changes but their directional relationship to changes in ventricular activation has not been well characterized.

METHODS

Accordingly, we measured QRS and T wave vectors and QRS-T angles from 12 lead ECG recordings immediately before and after accessory pathway (AP) radiofrequency ablation in 100 consecutive patients. Patients with bundle branch block, intraventricular conduction defect or intermittent pre-excitation were excluded, leaving a study group of 45 patients: 35 with pre-excitation and 10 with concealed APs.

RESULTS

With AP ablation, changes occurred in the QRS and T wave vectors and QRS-T angles that were essentially equal and opposite, so that the newly normalized QRS complex and QRS vector were accompanied by a T wave whose vector approximated that of the pre-ablation QRS vector. This tended to maintain a large QRS-T angle: 72 degrees +/- 50 degrees before, and 54 degrees +/- 34 degrees after QRS normalization (p = NS). A QRS-T angle >40 degrees was found before and after ablation in 22/35 patients (63%) with baseline pre-excitation; but never in patients with a concealed AP (p = 0.001). The angle between the pre-excited QRS and the post-ablation T wave was 35 degrees +/- 37 degrees, and </=40 degrees in 25/35 patients (71%). The change in T wave axis with QRS normalization correlated in magnitude with the QRS-T angle before ablation (r = 0.73, p < 0.0001). The change in QRS axis correlated with the QRS-T angle after ablation (r = 0.37, p < 0.03). Shorter AP effective refractory periods (ERPs) correlated with wider QRS-T angles after ablation (r = -0.39, p < 0.03). The ECG leads manifesting these changes depend on AP location.

CONCLUSION

T-wave changes after ablation of APs (1) are dependent on anterograde AP conduction at baseline and are not observed with concealed APs; (2) correlate in magnitude directly with the change in QRS axis and inversely with the anterograde AP-ERP; (3) are related to AP location. With termination of pre-excitation secondary repolarization changes immediately disappear and the post ablation T wave axis approximates that of the pre-excited QRS. Recognition of this sequence may prevent unnecessary clinical interventions.

Pseudo-continuous arterial spin labeling technique for measuring CBF dynamics with high temporal resolution

Cerebral blood flow (CBF) can be measured noninvasively with nuclear magnetic resonance (NMR) by using arterial water as an endogenous perfusion tracer. However, the arterial spin labeling (ASL) techniques suffer from poor temporal resolution due to the need to wait for the exchange of labeled arterial spins with tissue spins to produce contrast. In this work, a new ASL technique is introduced, which allows the measurement of CBF dynamics with high temporal and spatial resolution. This novel method was used in rats to determine the dynamics of CBF changes elicited by somatosensory stimulation with a temporal resolution of 108 ms. The onset time of the CBF response was 0.6 +/- 0.4 sec (mean +/- SD) after onset of stimulation (n = 10). The peak response was observed 4.4 +/- 3.7 sec (mean +/- SD) after stimulation began. These results are in excellent agreement with previous data obtained with invasive techniques, such as laser-Doppler flowmetry and hydrogen clearance, and suggest the appropriateness of this novel technique to probe CBF dynamics in functional and pathological studies with high temporal and spatial resolution. Magn Reson Med 42:425-429, 1999.

Comparison of matched BOLD and FAIR 4.0T-fMRI with [15O]water PET brain volumes

Valid comparisons of functional activation volumes from fMRI and PET require accurate registration, matched spatial resolution, and if possible matched noise. We coregistered 4.0T-fMRI and PET volumes, using a series of linear and nonlinear transformations applied to the PET volumes. Because of the limited number of fMRI slices that were available, PET volumes were transformed to the fMRI space. Since 4.0T-fMRI and 4.0T-MRI volumes have significant spatial distortion due to magnet inhomogeneities, high resolution 1.5T-MRI volumes were nonlinearly transformed to 4.0T-MRI volumes as part of the transformation chain. The smoothing effects of these registration transformations were measured, in order to match the spatial resolution of the coregistered fMRI and PET volumes. Spatial resolution of the transformed PET volumes in the fMRI space was degraded by up to 60% due to the transformation process. Due to both the image acquisition characteristics and the coregistration process, the transformed PET volumes had a spatial resolution that was lower than that of tMRI. Therefore, significant smoothing of fMRI volumes was necessary to match their spatial resolution with that of the transformed PET volumes. Matching the spatial resolution of the fMRI volumes to those of the transformed PET volumes was achieved by matching the shape of their point spread functions. In order to do this, Gaussian kernels were employed to smooth the fMRI volumes. We were unable to simultaneously match the resolution and noise of fMRI and PET signals in the motor cortex. Activation maps derived from transformed PET and smoothed fMRI volumes were compared. Contralateral motor cortex was active in all modalities but there were large variations in the size of the activated region and its signal to noise ratio across BOLD, FAIR, and PET images within each subject. Nevertheless, the relative CBF changes measured by FAIR were consistent with those determined by PET.

Simultaneous blood oxygenation level-dependent and cerebral blood flow functional magnetic resonance imaging during forepaw stimulation in the rat

The blood oxygenation level-dependent (BOLD) contrast mechanism can be modeled as a complex interplay between CBF, cerebral blood volume (CBV), and CMRO2. Positive BOLD signal changes are presumably caused by CBF changes in excess of increases in CMRO2. Because this uncoupling between CBF and CMRO2 may not always be present, the magnitude of BOLD changes may not be a good index of CBF changes. In this study, the relation between BOLD and CBF was investigated further. Continuous arterial spin labeling was combined with a single-shot, multislice echo-planar imaging to enable simultaneous measurements of BOLD and CBF changes in a well-established model of functional brain activation, the electrical forepaw stimulation of alpha-chloralose-anesthetized rats. The paradigm consisted of two 18- to 30-second stimulation periods separated by a 1-minute resting interval. Stimulation parameters were optimized by laser Doppler flowmetry. For the same cross-correlation threshold, the BOLD and CBF active maps were centered within the size of one pixel (470 microm). However, the BOLD map was significantly larger than the CBF map. Measurements taken from 15 rats at 9.4 T using a 10-millisecond echo-time showed 3.7 +/- 1.7% BOLD and 125.67 +/- 81.7% CBF increases in the contralateral somatosensory cortex during the first stimulation, and 2.6 +/- 1.2% BOLD and 79.3 +/- 43.6% CBF increases during the second stimulation. The correlation coefficient between BOLD and CBF changes was 0.89. The overall temporal correlation coefficient between BOLD and CBF time-courses was 0.97. These results show that under the experimental conditions of the current study, the BOLD signal changes follow the changes in CBF.

Functional mapping in the human brain using high magnetic fields

An avidly pursued new dimension in magnetic resonance imaging (MRI) research is the acquisition of physiological and biochemical information non-invasively using the nuclear spins of the water molecules in the human body. In this trial, a recent and unique accomplishment was the introduction of the ability to map human brain function non-invasively. Today, functional images with subcentimetre resolution of the entire human brain can be generated in single subjects and in data acquisition times of several minutes using 1.5 tesla (T) MRI scanners that are often used in hospitals for clinical purposes. However, there have been accomplishments beyond this type of imaging using significantly higher magnetic fields such as 4 T. Efforts for developing high magnetic field human brain imaging and functional mapping using MRI (fMRI) were undertaken at about the same time. It has been demonstrated that high magnetic fields result in improved contrast and, more importantly, in elevated sensitivity to capillary level changes coupled to neuronal activity in the blood oxygenation level dependent (BOLD) contrast mechanism used in fMRI. These advantages have been used to generate, for example, high resolution functional maps of ocular dominance columns, retinotopy within the small lateral geniculate nucleus, true single-trial fMRI and early negative signal changes in the temporal evolution of the BOLD signal. So far these have not been duplicated or have been observed as significantly weaker effects at much lower field strengths. Some of these high-field advantages and accomplishments are reviewed in this paper.

Enhancement of biliary excretion of aflatoxin B(1) and suppression of hepatic ornithine decarboxylase activity by 2-(allylthio)pyrazine in rats

2-(Allylthio)pyrazine (2-AP), a synthetic pyrazine derivative with an allylsulfur moiety, has protective effects against chemically-induced hepatic toxicity. Previous studies have shown that 2-AP significantly reduces the formation of preneoplastic foci in rats exposed to aflatoxin B(1) (AFB(1)). The present study was designed to determine whether 2-AP could increase the biliary excretion of metabolites of AFB(1) in rats treated with this carcinogen and whether the agent could alter the activity of ornithine decarboxylase (ODC), which is considered to be associated with tumor promotion. Rats were pretreated with 2-AP (p.o.) at a daily dose of 50 mg/kg for 5 consecutive days. AFB(1) (5 mg/kg) was administered intraperitoneally 2 h after the last dose of 2-AP. Amounts of principal AFB(1) metabolites, AFB(1)-glutathione and a glucuronide conjugate secreted in bile juice was increased by 56 and 50%, respectively, after the 2-AP treatment. Levels of radiolabelled AFB(1) covalently bound to calf thymus DNA catalyzed by microsomes obtained from 2-AP-treated rats (10 and 50 mg/kg, for 5 days) were reduced by 47 to 66%. ODC activity in AFB(1)-treated rats was determined by the three-step medium-term hepatocarcinogenesis assay. Rats were treated with 2-AP at the daily doses of 10, 25 and 50 mg/kg for 16 consecutive days. During this period, four repeated doses of AFB(1) (1.0 mg/kg) were given to the animals. Rats were then subjected to two-third partial hepatectomy, followed by administration of phenobarbital. 2-AP inhibited AFB(1)-induced ODC activity by 40 to 66%, as determined at the 44th day. Inhibition of AFB(1)-induced ODC activity by 2-AP in conjunction with acceleration of AFB(1) elimination through metabolic conjugation may contribute to its chemopreventive effects against this carcinogen.