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A Constantinesco

Publications and source records attributed to A Constantinesco.

At least 19 recordsLinked to original sources
PubMed2004

Evaluation of the use of six diagnostic X-ray spectra computer codes.

A knowledge of photon energy spectra emitted from X-ray tubes in radiology is crucial for many research domains in the medical field. Since spectrometry is difficult because of high photon fluence rates, a convenient solution is to use computational models. This paper describes the use of six computer codes based on semiempirical or empirical models. The use of the codes was assessed, notably by comparing theoretical half value layers and air kerma with measurements on five different X-ray tubes used in a research hospital. It was found that three out of the six computer codes give relative spectra very close to those produced by X-ray units equipped with constant potential generators: the mean difference between measured and modelled half value layer was less than 3% with a standard deviation of 3.6% whatever the tube and the applied voltage. Absolute output is less accurate: for four computer codes, the mean difference between the measured and modelled air kerma was between 18% and 36%, with a standard deviation of 9% whatever the tube (except for the single phase generator) and the applied voltage. One of the codes gives a good output and beam quality for X-ray units equipped with 100% ripple voltage generators. The use of computational codes as described in this paper provides a means of modelling relative diagnostic X-ray spectra, the usefulness of the tube output data depending on the accuracy required by the end user.

Computers↗
PubMed2001

Myocardial flow reserve parametric map, assessed by first-pass MRI compartmental analysis at the chronic stage of infarction.

Regional myocardial flow and flow reserve (MFR) were assessed by compartmental analysis of Gd-enhanced MRI first-pass data in 7 patients with atypical chest pain, and in 15 patients with previous transmural myocardial infarction. The FE product (Flow x Extraction coefficient), derived from the modified Kety equation, was measured in regions corresponding to the Tetrofosmine-SPECT fixed defect and in remote normal regions. The FE product at rest and hyperemic FE product were similar in healed revascularized tissues (70.5 +/- 15.6 and 112.5 +/- 19.5 ml/mn/100 g, respectively) and in normal myocardium (76.2 +/- 18.3 and 142.2 +/- 33.0, respectively). In contrast, the FE index (48.8 +/- 15.2 and 60.7 +/- 18.0, respectively, P < 0.01 versus the two previous groups) and the MFR (1.27 +/- 0.20 vs. 1.91 +/- 0.29 in normal regions) were reduced in healed fibrotic tissues when the infarct-related artery remained occluded. Myocardial flow reserve maps allowed correct identification of regions corresponding to an occluded infarct-related artery.

Aged↗
PubMed2001

Xenon-129 MR imaging and spectroscopy of rat brain using arterial delivery of hyperpolarized xenon in a lipid emulsion.

Hyperpolarized (129)Xe dissolved in a lipid emulsion constitutes an NMR tracer that can be injected into the blood stream, enabling blood-flow measurement and perfusion imaging. A small volume (0.15 ml) of this tracer was injected in 1.5 s in rat carotid and (129)Xe MR spectra and images were acquired at 2.35 T to evaluate the potential of this approach for cerebral studies. Xenon spectra consistently showed two resonances, at 194.5 ppm and 199.0 ppm relative to the gas peak. The signal-to-noise ratio (SNR) obtained for the two peaks was sufficient (ranging from 12 to 90) to follow their time courses. 2D transverse-projection xenon images were obtained with an in-plane resolution of 900 microm per pixel (SNR range 8-15). Histological analysis revealed no brain damage except in two rats that had received three injections.

Animals↗
PubMed2001

Feasibility of a semiconductor dosimeter to monitor skin dose in interventional radiology.

The design and preliminary test results of a semiconductor silicon dosimeter are presented in this article. Use of this dosimeter is foreseen for real-time skin dose control in interventional radiology. The strong energy dependence of this kind of radiation detector is well overcome by filtering the silicon diode. Here, the optimal filter features have been calculated by numerical Monte Carlo simulations. A prototype has been built and tested in a radiological facility. The first experimental results show a good match between the filtered semiconductor diode response and an ionization chamber response, within 2% fluctuation in a 2.2 to 4.1 mm Al half-value layer (HVL) energy range. Moreover, the semiconductor sensor response is linear from 0.02 Gy/min to at least 6.5 Gy/min, covering the whole dose rate range found in interventional radiology. The results show that a semiconductor dosimeter could be used to monitor skin dose during the majority of procedures using x-rays below 150 keV. The use of this device may assist in avoiding radiation-induced skin injuries and lower radiation levels during interventional procedures.

Air↗
PubMed2000

[Anemia caused by vitamin B 12 deficiency in subjects aged over 75 years: new hypotheses. A study of 20 cases].

PURPOSE: New hypotheses have recently been developed on vitamin B12 deficiency and the frequently observed occurrence in the elderly subject of food cobalamin malabsorption, i.e., the non-dissociation of B12 and its carrier protein (ND B12), and the possibility of rectifying this imbalance by oral crystalline B12 supplementation. The aim of this study was therefore to confirm these hypotheses in a series of patients aged over 75 years with anemia due to B12 deficiency. METHODS: A retrospective study was carried out over a 5-year period on patients aged over 75 years presenting with megaloblastic anemia (hemoglobin [Hb] < 12 g/dL) and vitamin B12/cobalamin deficiency (B12 < 160 pg/mL). RESULTS: Twenty cases were analyzed. The average age of the patient population was 82.5 +/- 6 years, and the F/M sex ratio was 1:2. Mean Hb levels were 7.9 +/- 2.4 g/dL, mean serum B12 levels were 83 +/- 24 pg/mL, and mean homocysteinemic levels were 35 +/- 27 mumol/L. The diagnosis was as follows: food cobalamin malabsorption/ND B12 (n = 10), Biermer's disease/pernicious anemia (n = 5), malabsorption due to pancreatic insufficiency (n = 1), and low dietary B12 levels (n = 1). Disorders associated with ND B12 were: atrophic gastritis and Helicobacter pylori infection (n = 6), antacid or biguanide intake (n = 3), alcohol abuse (n = 2), or idiopathic syndrome (n = 2). In the patients who were followed up (n = 10), i.m. (n = 5) or oral (n = 5) administration of crystalline B12 resulted in the correction of hematological abnormalities. CONCLUSION: In the elderly subject, food cobalamin/ND B12 malabsorption appears to be the main cause of B12 deficiency, and is frequently associated with atrophic gastritis. In these cases, administration of oral crystalline B12 may be an efficient means of treating this disorder.

Aged↗
PubMed2000

In vivo 129Xe NMR in rat brain during intra-arterial injection of hyperpolarized 129Xe dissolved in a lipid emulsion.

Hyperpolarized 129Xe was dissolved in a lipid emulsion and administered to anaesthetized rats by manual injections into the carotid (approximately 1-1.5 mL in a maximum time of 30 s). During injection, 129Xe NMR brain spectra at 2.35 T were recorded over 51 s, with a repetition time of 253 ms. Two peaks assigned to dissolved 129Xe were observed (the larger at 194 +/- 1 ppm assigned to intravascular xenon and the smaller at 199 +/- 1 ppm to xenon dissolved in the brain tissue). Their kinetics revealed a rapid intensity increase, followed by a plateau (approximately 15 s duration) and then a decrease over 5 s. This behaviour was attributed to combined influences of the T1 relaxation of the tracer, of radiofrequency sampling, and of the tracer perfusion rate in rat brain. Similar kinetics were observed in experiments carried out on a simple micro-vessel phantom. An identical experimental set-up was used to acquire a series of 2D projection 129Xe images on the phantom and the rat brain.

Animals↗
PubMed2000

[Cartography of absolute myocardial perfusion with magnetic resonance imaging. Methods and results].

Ultra-rapid dynamic MRI (one image per heart beat) can follow the progression of the intra-myocardial signal during the first passage of diffusable gadolinium chelates injected as a bolus through a peripheral vein. A quantitative evaluation of myocardial perfusion is possible using a compartmental model of analysis. Absolute myocardial flow can be measured at rest and during hyperaemia induced by dipyridamole. It is possible to associate functional mapping, corresponding to parametric images of the flow indices, to the global evaluation. The ratio between the values obtained during hyperaemia and under basal conditions correspond to the myocardial reserve. The principles, results and limitations of this method are discussed in the light of published results, underlining the advantages of absolute flow measurement and of the differences between the results of MRI and myocardial scintigraphy.

Coronary Circulation↗
PubMed1999

Ex vivo high resolution MR imaging of the human lip with a dedicated low field system.

Histological correlations of the human lip with corresponding magnetic resonance (MR) images obtained ex vivo are presented. MR images were acquired with a dedicated low-field (0.1 T) MR system, with a resolution of 100 x 100 micron2 and a slice thickness of 1 mm using 3D-FLASH sequences. The outermost tissues visible on images are of high signal intensity, while the innermost connective tissues are of low signal intensity, both for skin and oral mucosa. It is possible to use a low-field system to obtain high resolution images of small biological samples.

Biopsy, Needle↗
PubMed1999

[Subareolar injection of 99m-Tc sulfur colloid for sentinel nodes identification in multifocal invasive breast cancer].

The objective were to study the relevance of the subareolar injection for sentinel node [SN] detection in multiple foci breast cancer. Seventy-nine patients with infiltrative breast carcinoma (diagnosed pre-operatively by core biopsy) and a mean age of 55 (31-78) years were enrolled. All patients were free of previous homolateral surgery, chemotherapy, locoregional radiotherapy or prevalent axillary lymph node. Using four 0.1 ml injections of 1.8 MBq, the technetium-99m 100 nm filtered sulfur colloid was injected by subareolar way (group I) in 16 cases of radiologically cancer with multiple invasive foci and 31 cases of radiologically unifocal cancer, and by peritumoral way (group II) in 32 cases of radiologically unifocal cancer. Scintigrams were obtained 2 to 4 hours after the injections and radioactive nodes were detected peroperatively 18 hours after the injection by intraoperative detection probe. Individual removal of all radioactive nodes was followed by axillary dissection at levels I and II of Berg including Rotter area control. All sentinel nodes were submitted to standard histopathological analysis on serial sections at 500 mu intervals completed by immunohistochemistry for cytokeratin on negative SN. SN were detected by scintigrams in 85% and 88% of the cases of group I and group II respectively, but in 98% and 97% of the cases of respectively both groups by intraoperative probe. Group I was composed of 69% ductal, 22% lobular and 9% tubular carcinomas, and group II of 87% ductal, 10% lobular and 3% tubular carcinomas. Seven and 5 radiologically unifocal tumors were in fact with multiple invasive foci at histology in groups I and II respectively. The complete scintigraphic procedure permitted the detection of a mean number of 2.7 (1-7) SN in group I and 2.3 (1-4) in group II (NS). In group I, the SN were metastatic in 22 patients (48%), 15 of them with the metastases being restricted to the SN, whereas in group II, the SN were metastatic in 9 patients (28%), 5 of them with the positivity restricted to the SN. No false negative result (SN negative and other axillary nodes positive) was observed in group I and only one false negative result in group II which was related to a cancer with histological multiple invasive foci. Sensitivities were 100% and 90%, and negative predictive values were 100% and 95%, for groups I and II respectively. Subareolar injection of radiocolloid allows identification of SN in cases of unifocal and multiple cancer. The mean number of SN detected by the subareolar method is not significantly different, although higher, to that detected by peritumoral injection.

Adenocarcinoma↗
PubMed1998

Low-field dedicated magnetic resonance imaging: a potential tool for assisting perinatal autopsy.

Although the practice of perinatal autopsy has increased in recent years, examination of the fetus and especially of the fetal brain during the first trimester or the beginning of the second trimester remains difficult. Postmortem high-resolution images of the brain of a normal and an abnormal fetus of the same gestational age (22 weeks) were obtained with a low-field (0.1 T) dedicated magnetic resonance imaging (MRI) system. We demonstrated that a small MRI machine supplemented data from classical necropsy and may help in the interpretation of in utero ultrasound and magnetic resonance images for the antenatal diagnosis of fetal malformations.

Adult↗
PubMed1997

Myocardial perfusion and function imaging at rest with simultaneous thallium-201 and technetium-99m blood-pool dual-isotope gated SPECT.

UNLABELLED: We present a simultaneous gated SPECT (G-SPECT) dual-isotope technique using 201Tl for perfusion and 99mTc blood-pool labeling for function imaging. METHODS: Seventeen patients (13 with previous myocardial infarction, MI) and a control group of three normal volunteers were investigated. They received, 15 min after a 201Tl stress/redistribution protocol with reinjection, 900-950 MBq 99mTc-HSA for blood-pool labeling. Eight frames per R-R interval were recorded in the G-SPECT mode with three windows: window A with 20% centered at 71 keV for 201Tl, window B with 10% centered at 105 keV for Tc scatter contamination and window C centered at 140 keV with 20% for 99mTc. Nongated, crosstalk-corrected 201Tl SPECT perfusion images were reconstructed according to normalized projection-by-projection subtraction from data from windows A and B. G-SPECT data from window C were reconstructed with the same reconstruction limits to allow topographic correlations of left ventricular perfusion and wall motion abnormalities. Polar maps of perfusion and function were used to divide the myocardium into 20 segments. Perfusion was expressed as the percentage of thallium uptake and function corresponding to diastolic to systolic shortening normalized by end diastolic volume. RESULTS: Segmental comparison of uncontaminated-to-contaminated and corrected 201Tl patient images demonstrated an overall agreement score of 93%, with a kappa statistic of 0.76 +/- 0.06 when normal perfused segments were excluded. Segmental matching of perfusion against function at rest showed no correlation for the 10 patients with preserved ejection fraction of 59% +/- 8% nor for the control group. For the remaining seven patients with an ejection fraction of 34% +/- 10%, there was linear correlation between perfusion and function (r2 = 0.61). CONCLUSIONS: The feasibility of dual TI-Tc G-SPECT was examined at rest and suggests low perfusion hypokinesis that matches linear dependence for CAD patients with low ejection fraction.

Adult↗
PubMed1996

Comparison between abnormalities in segmental endocardial motion and abnormalities in segmental wall thickening after anterior myocardial infarction. A cine-magnetic resonance study.

In this study, two patterns of regional contract on of the left ventricle have been studied: endocardial motion and wall thickening, in order to check which of these was the most affected after myocardial infarction. The clinical relevance of this comparison was to assess which parameter of the regional contraction abnormality would best depict the severity of the infarction. Long axis cine-magnetic resonance slices were used to assess segmental systolic left ventricular endocardial motion and segmental systolic wall thickening in 39 normal subjects and in 30 patients at the chronic stage of an anterior myocardial infarction. In the group of normal subjects, endocardial motion and wall thickening showed significant regional heterogeneity. Overall endocardial motion was greater than overall wall thickening: 9.5 +/- 2.0 mm vs 7.1 +/- 1.8 mm. P = 4 x 10(-12) (3.1 +/- 1.2 mm vs 2.0 +/- 0.7 mm, P = 9 x 10(-5) after infarction). A significant linear correlation was found between these two parameters. In the infarction group, abnormality scores for endocardial motion and for wall thickening were calculated. These scores were defined as the average values exceeding the mean minus two standard deviations of the normal range for segments corresponding to the antero-septal-apical walls. The abnormality score for endocardial motion greater than the abnormality score for wall thickening: 0.31 +/- 0.12 vs 0.20 +/- 0.07, P = 9 x 10(-4). We conclude that, in clinical practice, endocardial motion is affected to a greater degree by myocardial infarction than is wall thickening and therefore constitutes a more discriminant index in the assessment of post-infarction patients.

Adult↗
PubMed1996

[Interventional MRI. Value of low field strength and very fast 3D steady state imaging sequences for the guidance of a "non" ferromagnetic needle].

PURPOSE: The excellent tissue differenciation provided by MRI in the three directions and the lack of ionizing radiations make it ideal for interventional procedures. Many problems must still be solved: the access to the patient, the size of the artefact produced by interventional instruments and the acquisition time. In this study, we evaluated the influence of field strength for standard imaging sequences on the MRI artefact of a non ferro-magnetic biopsy needle. Then, we developed very fast sequences on a opened 0.1 T dedicated magnet to test in vitro and ex vivo the potential ability of this system in the guidance of the needle. MATERIAL AND METHODS: The biopsy needle was a new stainless steel needle made of 49% Nickel. The needle artefact's size measurements were made at 0.1 T, 0.5 T and 1 T on a bicompartmental phantom (one compartment with a long T1 and another with a long T2), with standard gradient echo (400/12/90 degrees) and spin echo (500/25) sequences. At 0.1 T, we optimized very fast steady state 3D FAST (T1 weighted) and 3D CE-FAST (T2 weighted) sequences to reduce the acquisition time, preserving good image contrasts for a field of view reaching 38 mm and 48 x 64 or 24 x 32 matrix. RESULTS: The larger needle artefact observed on gradient echo images varied from 3.6 mm at 0.1 T to 8.6 mm at 1 T. The shortest acquisition time for 4 contiguous slices of 2mm with a 1.2 mm/pixel resolution and a 24 x 32 matrix was 1.5 s for the 3D FAST (16/9/65 degrees) sequence and 3 s for the 3D CE-FAST (29/22/65 degrees) sequence. We realized a complete MRI guided abdominal puncture on a cat cadaver with 4 series of 15 s 3D FAST images (16/9/65 degrees, 4 slices, 5 excitations, 1.2 mm/pixel, FOV = 77 mm). Besides the cat positioning and the image reconstruction time, the whole puncture lasted 1 min (4 x 15 s). CONCLUSION: Low field MRI (0.1 T) combined with very fast 3D steady state sequences is adapted for the real time guidance of biopsy needles.

Biopsy, Needle↗