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Biomedical subjects

R Floris

Publications and source records attributed to R Floris.

At least 55 records · Page 3Linked to original sources
PubMed1994

T stages of tumors of the tongue and floor of the mouth: correlation between MR with gadopentetate dimeglumine and pathologic data.

PURPOSE: To define MR accuracy in the evaluation of the T stages of tumors of the tongue and floor of the mouth. METHODS: Fifty-two patients affected by squamous cell carcinoma were studied with a superconductive system at 1.5 T. The study was performed with spin-echo T1- and T2-weighted images before contrast and short spin-echo T1-weighted and gradient-echo sequences after gadopentetate dimeglumine administration. The results obtained with MR were compared with pathologic data. RESULTS: Good correlation of T stages (TNM system) was obtained in 45 of 52 cases. MR did not show four superficial lesions. In one case, infiltration of the cortical bone of the mandible was not demonstrated (MR, T2; pathologic, T4), and in another the lesion was classified as T2 instead of T3, as it was pathologically. One lesion was classified as T4 on MR because of infiltration of the alveolar ridge but was classified as T2 at surgery. In 46 patients who underwent surgery, the accuracy of MR was excellent for predicting the relationship of tumor to midline and oral floor musculature. The results obtained with gadopentetate dimeglumine were better than those obtained in noncontrast studies in 32 (62%) of 53 cases. CONCLUSION: MR showed high accuracy in the study of tumors of the tongue and floor of the mouth.

Adolescent↗
PubMed1994

[Magnetic resonance imaging in denervated muscle. A preliminary study].

Ten patients with various forms of peripheral neuropathy and spinal radiculopathy were examined with MRI using a low-field permanent magnet (0.2 T) and spin echo (SE)/inversion recovery (IR) sequences, with an adequate inversion time to suppress healthy muscle signal. In acute denervation MR sensitivity was low on both sequences; in subacute denervation the damaged muscle was more intense than the healthy muscle only on IR sequences. MRI adequately depicted fatty infiltration in chronic denervation. In conclusion, MRI is a promising tool for mapping and noninvasively monitoring denervated motor units in skeletal muscles, whose role is currently complementary to that of electromyography.

Acute Disease↗
PubMed1994

[An introduction to fast and ultrafast sequences in magnetic resonance].

The main limitations of magnetic resonance imaging (MRI) are due to the long acquisition time needed for data sampling. Fast and ultrafast sequences, thanks to progress in hardware and software technology, allow the acquisition times to be dramatically reduced. Such improvements will definitely increase MR capabilities and make MRI a fast and dynamic technique no longer depending on patients' cooperation and limited by patients' conditions--e.g., trauma, pediatric, or claustrophobic patients--or even by the anatomic features of the region of interest. The latest experimental studies are aimed at increasing the clinical applications and the perspectives of clinical MRI and at such ambitious goals as MR-fluoroscopy, interventional MRI, total body examination in less than one minute and functional MRI. In this paper the technical principles and the main indications of this new kind of sequences are reported, with a special emphasis on Gradient-Echo (GE), Turbo Spin-Echo (turbo SE) or Fast Spin-Echo (fast SE), Turbo FLASH and Echo Planar (EP) sequence. A smaller flip angle (FA) and the substitution of the 180 degrees RF pulse with a gradient reversal are the main differences of GE from SE sequences. From GE sequences, several fast sequences are derived, such as angiographic and turbo FLASH sequences. The latter, thanks to 180 degrees preinversion RF pulse, using idoneous inversion times (IT), provide flexible contrast. Turbo SE sequences, which are directly derived from conventional SE sequence, allow the acquisition time to be markedly shortened, by acquiring several Fourier lines of K-space for each TR. The repetition of several 180 degrees pulses following the excitatory 90 degrees RF pulse does the trick through the creation of multiple echoes for a single TR. EP sequences are the fastest ones currently available: with them, an image can be acquired in 30-100 ms. However, the limited availability of the relative hardware and the need of both quality implementation and the definition of clinical indications are major obstacles to the widespread use of these sequences. The SE T2-weighted sequence, the main responsible for the long examination time, will be replaced soon. Further implementation of these sequences will make MRI a fast, flexible and adaptable method to any exam and patient disability.

Echo-Planar Imaging↗
PubMed1993

Interaction of myeloperoxidase with peroxynitrite. A comparison with lactoperoxidase, horseradish peroxidase and catalase.

Polymorphonuclear neutrophils generate both nitric oxide and superoxide and these molecules can combine to form peroxynitrite. Neutrophils also contain myeloperoxidase which reacts with peroxynitrous acid (HOONO). On mixing myeloperoxidase with HOONO compound II was formed. Compound I could not be detected as an intermediate. The apparent second-order rate constant of formation of compound II was strongly pH-dependent (2.5 x 10(5) M-1 x s-1 at pH 8.9 and 6.2 x 10(6) M-1 x s-1 at pH 7.2). The pKa of this effect is 6.9 and it was concluded that the enzyme reacts with the protonated form of the peroxide, that is peroxynitrous acid, with a pH-independent second-order rate constant of 2.0 x 10(7) M-1 x s-1 at 12 degrees C. The interaction of HOONO with lactoperoxidase was studied for comparison. As was observed for myeloperoxidase, compound I could not be detected as an intermediate. The apparent second-order rate constant of compound II formation is pH-dependent and is 3.3 x 10(5) M-1 x s-1 at pH 7.4 and 8.4 x 10(4) M-1 x s-1 at pH 9.0. In contrast, horseradish peroxidase reacts with HOONO to form compound I, which is subsequently followed by the formation of compound II. The second-order rate constant for the formation of compound I is 3.2 x 10(6) M-1 x s-1 and is pH-dependent, the pKa for this effect is 6.8. Catalase (up to 3 microM) does not affect the rate of decomposition of peroxynitrite and no compound I formation is observed. Since nitrite may be present in the peroxynitrite preparation and to discriminate between the reaction of the enzyme with nitrite or peroxynitrite, the effect of nitrite on myeloperoxidase was studied. The dissociation constant for the myeloperoxidase-nitrite complex is pH-dependent and has values of 580 microM at pH 6.0 and 55 mM at pH 8.5.

Catalase↗
PubMed1993

Lignin peroxidase L3 from Phlebia radiata. Pre-steady-state and steady-state studies with veratryl alcohol and a non-phenolic lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol.

The catalytic cycle of lignin peroxidase (LiP, ligninase) isozyme L3 from the white-rot fungus Phlebia radiata was investigated using stopped-flow techniques. Veratryl (3,4-dimethoxybenzyl) alcohol and a lignin model compound, non-phenolic beta-O-4 dimer 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol, were used as electron donors. This is the first report on the detailed kinetic analysis of a LiP-catalysed C alpha-C beta bond cleavage of the dimer, representing the major depolymerisation reaction in the lignin polymer. The native enzyme showed a typical heme peroxidase absorbance spectrum with a Soret maximum at 407 nm. Following the reaction with H2O2, the Soret band decreased in absorbance, shifted to 403 nm and then to 421 nm, demonstrating the formation of compound I followed by the formation of compound II, respectively. Similar results have been reported for the LiP from Phanerochaete chrysosporium upon reaction with H2O2. However, compound I of L3 was more stable in the absence of additional electron donors. The second-order rate constant of compound I formation by H2O2 was determined to be 6 x 10(5) M-1 s-1 and was the same at pH 3.0 and 6.0. Compound I was rapidly reduced to compound II and further to native enzyme when either veratryl alcohol or the beta-O-4 dimer was supplied as electron donor and in both cases veratraldehyde appeared as the major product. At pH 6.0, the second-order rate constant for compound II formation was similar with either veratryl alcohol or the beta-O-4 dimer (6.7 x 10(3) and 6.5 x 10(3) M-1 s-1, respectively). At pH 3.0 formation of compound II with either reductant proceeded so rapidly that determination of the respective rate constants was not possible. The results point to identical catalytic cycles of L3 with veratryl alcohol or the beta-O-4 dimer involving both compounds I and II as intermediates and participation of the same veratryl alcohol radical as the most appropriate reductant for compound II. Chemical evidence of such a radical, formed after the initial LiP-catalysed one-electron oxidation of beta-O-4 dimeric lignin models, is presented in a separate article [Lundell, T., Schoemaker, H., Hatakka, A. & Brunow, G. (1993) Holzforschung, in the press]. The catalytic redox-cycle and the oxidation mechanism presented here reconcile seemingly contradictory results obtained in previous studies on LiP kinetics during the last decade.

Benzyl Alcohols↗
PubMed1993

The role of early postoperative CT scan following surgery for herniated lumbar disc.

40 patients underwent lumbosacral microdiscectomy in a 12 months period covering the years 1988-1989 in our center. For the purpose of the present study, we considered the 30 cases who underwent CT control of the operated interspaces and of the adjacent vertebral endplates. This was routinely carried out on the 3rd post-operative day. The present study failed to show correlations between early post-operative CT data and subsequent clinical results in this unselected series of patients. In fact an image suggesting persistent disc herniation was as a rule observed in spite of satisfactory clinical results, and other CT findings that have been considered of clinical significance, such as intraspinal air and low attenuation of disc space, were commonly observed in patients with an uncomplicated post-operative course. The present study suggests that early post-operative CT appears to be of no value in the management of potential early complications of low-back surgery. The introduction of MRI appears to offer other possibilities in the evaluation and management of failed back surgery syndrome (FBSS).

Adult↗
PubMed1993

Serial determinations of leukocyte aggregation in patients with ischemic stroke.

The pattern of leukocyte aggregation and its possible relationship with the clinical outcome were evaluated in 35 untreated patients with acute cerebrovascular disease during each of the first three days of hospitalization. Although statistically significant differences were found when comparing patients and age and sex matched controls during any of the 3 days, a large overlapping of values was noted in each comparison. The overlapping was strongly reduced when the average 3-day value was compared. Similarly, when comparing subgroups of patients classified on the basis of their clinical status, the overlap of values observed during any of the 3 days dropped from 70% to 30% when considering the average 3-day levels of leukocyte aggregation. Furthermore, the level of correlation between leukocyte aggregation and size of cerebral infarction was better when considering the average 3-day value (p = .005) than the best single-day correlation (p = .01). These data suggest that the association between acute cerebrovascular ischemia and leukocyte rheology is better discovered when repeated evaluation of the latter are performed.

Age Factors↗
PubMed1992

Reaction of myeloperoxidase with its product HOCl.

The reaction of human myeloperoxidase with its product, hypochlorous acid was investigated using both rapid-scan spectrophotometry and the stopped-flow technique. In the reaction of myeloperoxidase with hypochlorous acid a primary compound is found with properties similar to that of compound I and which is converted into compound II. The primary reaction is strongly pH-dependent. At pH 7.2 the reaction is too fast to be measured but at higher pH values it is possible to determine the apparent second-order rate constant. Its value decreases to about 2 x 10(7) M-1.s-1 at pH 8.3 and to 2.3 (+/- 0.4) x 10(6) M-1.s-1 at pH 9.2, respectively. The dissociation constant for the formation of the primary compound is 25.7 (+/- 15.3) microM at pH 9.2 and about 2.5 microM at pH 8.3. The apparent second-order rate constant for the formation of compound II is hardly affected by pH and varies between 2 to 5 x 10(4) M-1.s-1 at pH 10.2 and pH 8.3, respectively. Reaction of myeloperoxidase with hypochlorous acid also resulted in irreversible partial bleaching of the chromophore. Chloride, which is a substrate of the enzyme not only protects myeloperoxidase against bleaching by hypochlorous acid but also competitively inhibits the binding of hypochlorous acid to myeloperoxidase, a process which also has been observed in the reaction with hydrogen peroxide. It is concluded that hypochlorous acid binds at the heme iron to form compound I.

Humans↗
PubMed1992

Catalytic mechanisms and regulation of lignin peroxidase.

Lignin peroxidase (LiP) is a fungal haemoprotein similar to the lignin-synthesizing plant peroxidases, but it has a higher oxidation potential and oxidizes dimethoxylated aromatic compounds to radical cations. It catalyses the degradation of lignin models but in vitro the outcome is net lignin polymerization. LiP oxidizes veratryl alcohol to radical cations which are proposed to act by charge transfer to mediate in the oxidation of lignin. Phenolic compounds are, however, preferentially oxidized, but transiently inactivate the enzyme. Analysis of the catalytic cycle of LiP shows that in the presence of veratryl alcohol the steady-state turnover intermediate is Compound II. We propose that veratryl alcohol is oxidized by the enzyme intermediate Compound I to a radical cation which now participates in charge-transfer reactions with either veratryl alcohol or another reductant, when present. Reduction of Compound II to native state may involve a radical product of veratryl alcohol or radical product of charge transfer. Phenoxy radicals, by contrast, cannot engage in charge-transfer reactions and reaction of Compound II with H2O2 ensues to form the peroxidatically inactive intermediate, Compound III. Regulation of LiP activity by phenolic compounds suggests feedback control, since many of the products of lignin degradation are phenolic. Such control would lower the concentration of phenolics relative to oxygen and favour degradative ring-opening reactions.

Benzyl Alcohols↗
PubMed1992

Migraine with aura-like syndrome due to arteriovenous malformation. The clinical value of transcranial Doppler in early diagnosis.

Arteriovenous malformations are an acknowledged cause of migraine that can long constitute the only clinical manifestation before bleeding. We describe two cases of patients suffering from symptoms like migraine with aura in whom arteriovenous malformations were detected by transcranial Doppler examination. We suggest that a screening of migraine patients to prevent bleeding from a possible underlying unruptured arteriovenous malformation could be performed by using transcranial Doppler, a non-invasive and low cost examination.

Adult↗
PubMed1992

[The use of the single-pulse RARE sequence in the study of the cerebrospinal axis].

The authors describe a fast MR sequence allowing to obtain a myelographic-like, markedly T2-weighted, image quite similar to conventional myelographies. Relative to conventional spin-echo sequences, in which echoes are encoded so as to achieve the same phase, each echo of the sequence here employed is given a different phase encoding. The sequence, called MYUR (myelography-urography) is based on the generation, after a 90 degrees pulse, of a "train" of 256 echoes, each one phase-encoded differently, by multiple 180 degrees pulses, producing a single image. The total duration of such a sequence, with 2 repetitions, is 21 seconds. The MR myelographic sequence allows to univocally study tissues with a very long T2 relaxation time; under normal conditions, only cerebrospinal fluid, urine and bile are demonstrated. A resistive MR unit operating at 0.28 T was employed in the present study. MR myelography is capable of pointing out an eventual dural sac compression or a space-occupying mass, thus allowing an effective scout-view to center the subsequent pulse sequences; all MR-myelographic exams need to be completed with other short and long TR sequences.

Brain↗
PubMed1992

[Magnetic resonance angiography in the study of abdominal neoplasms. Preliminary experience].

This study was designed to evaluate MRA imaging as a potential non-invasive method to study vascular infiltration in patients with abdominal neoplasms. Forty-three patients with abdominal tumors proven by CT and/or MRI were examined with MRA and subsequently with angiography. Of 15 cases of liver tumor, MRA allowed poor intratumoral vascularization to be demonstrated in 1 patient only, but it always provided a characteristic sign--i.e., the complete absence of flow in the hepatic segments infiltrated by the tumor and the evidence of pericapsular neovascularization. In 8 cases portal vein involvement was observed (4 cases of compression/dislocation, 2 cases of infiltration and 2 of thrombosis). In all cases MRA allowed the relationship between tumor and venous structures to be evaluated. It also demonstrated collateral vessel formations in 8 patients with cancrocirrhosis. Two cases of thrombosis and 3 infiltrations of the vena cava were demonstrated. Neither hepatic artery nor intrahepatic arterial vascularization could be correctly evaluated. Of 10 cases of renal tumors and in 3 of adrenal tumors, renal vein infiltration was seen in 4 cases and compression in 3, with only 1 false-positive finding. In these patients and in those with retroperitoneal masses, MRA provided valuable information on the relationship between tumor and vascular structures and was useful in detecting collateral vessels. In our experience, MRA is to be considered as a complementary technique to be performed after CT or MRI when additional information is needed as to the relationship between tumor and vascular structures. In the preoperative evaluation of abdominal neoplasm, angiography remains the gold standard, in spite of its invasiveness.

Abdominal Neoplasms↗
PubMed1990

Spontaneous subarachnoid hemorrhage in an HIV patient.

In an HIV-seropositive patient presenting generalized tonic-clonic seizures, magnetic resonance imaging and cerebrospinal fluid examination disclosed the signs of a previous subarachnoid bleed. No vascular malformation was observed with cerebral angiography. Laboratory tests revealed an autoimmune thrombocytopenia. A spontaneous subarachnoid hemorrhage induced by thrombocytopenia should be considered when investigating HIV patients presenting even non-specific neurological symptoms.

Adult↗
PubMed1990

Intracerebral metastasis in Ewing's sarcoma.

The evidence of CNS involvement in Ewing's sarcoma is uncommon and very often due to a direct extension of the tumor to extradural space and meninges. We report a case of a 14-year old girl with a primary ischio-pubic localization of Ewing's sarcoma. Body CT scan showed a bone lesion involving the left fronto-temporal region of the skull without affecting the brain. After chemotherapy radiological findings showed complete recovery. Ten months after treatment, the patient had neurological symptoms. Cerebral CT scan evidenced a large tumor mass localized in the right temporal lobe. Following radiotherapy the tumor mass was no longer visible. This case shows that late intraparenchymal CNS metastasis occurs independently from the previous skull lesion. Therefore these data, even through based on a single observation, lead to believe that in some cases prophylactic chemotherapy and radiotherapy of CNS may not be necessary.

Adolescent↗
PubMed1989

Sensory (VEP, BAEP, SEP) and motor-evoked potentials, liquoral and magnetic resonance findings in multiple sclerosis.

In order to define the most suitable instrumental protocol for the diagnosis of multiple sclerosis (MS), 41 patients with definite (D = 14), probable (P = 14) and suspected (S = 13) MS were examined with CSF immunology, brain MRI and multimodal evoked potentials. The central motor tracts were also tested. The following alteration rates were found: MRI = 78%, CSF = 63.6%, VEP = 70.0%, median nerve SEP = 50%, peroneal nerve SEP = 68.0%, BAEPs = 35.7%, motor-evoked potentials (MEPs) = 74.0%. Altogether, EPs were abnormal in 90% of cases. Normal MRI with altered EPs were found in 22% of cases, whilst a normal EP battery with defective CSF or MRI findings were found in 7%. Twenty-six out of 27 patients with P or S forms were reclassified into a D one when considering EPs and MRI features.

Adolescent↗