Filtered backprojection and spectral width of MR signal

Reconstructed images obtained by filtered backprojection are altered when the projections are distorted by an attenuation of the high frequency components of the demodulated magnetic resonance (MR) signal. This attenuation occurs if the spectral width of the MR signal is reduced by the bandwidth of the receiver radiofrequency coil as well as by the use of imperfect refocusing pulses. This signal spectrum has to be wide when the sampling bandwidth is wide, because the sampling time is very short, for instance in the case of very short interpulse delay such as 6 ms. A short interpulse delay is needed when many images are required, to enable the transverse magnetization decay of each pixel to be recorded accurately. This paper presents an analysis of backprojection reconstruction for such a case and demonstrates a contamination of each pixel by surrounding pixels. The consequence on the results of T2 measurement and biexponential decomposition of transverse magnetization decay curves are discussed. A method for correction of such artifacts is described.

[Value of nuclear magnetic resonance in dilated cardiomyopathy. Approach to intraventricular hemodynamics]

The value of magnetic resonance imaging (MRI) with multiechoes spin-echo sequences was investigated in 22 patients with dilated cardiomyopathy (group I) and 25 normal subjects serving as controls (group II). The results of MRI in group I were compared with those of echocardiography and radionuclide ventriculography. Measurements of left ventricular dimensions at echography and MRI showed a tendency, with MRI, to overestimate wall thickness and underestimate ventricular diameter. Thus, for diastolic LV we had 63.8 +/- 10.5 mm with MRI vs 70.6 +/- 7.6 mm with echography, the corresponding figures for posterior wall thickness being 112 +/- 1.4 mm vs 9.9 +/- 1.1 mm respectively. These differences seem to be due to MRI introducing a partial volume effect dependent on the thickness of slices and of their orientation in relation to the cardiac axis. MRI evaluation of left ventricular function by calculation of myocardial fibre shortening fractions correlated poorly with the echocardiographic value of the same parameter and with the radionuclide ejection fraction (r = 0.58 and 0.575 respectively; p less than 0.05). For better quantification of the cardiac pump function, planimetry of the endocardial contour during diastole and systole is required. It would seem that the value of MRI resides in the possibility it offers to explore left intraventricular haemodynamics by studying the "flow signal" obtainable from multiechoes sequences at different moments of the cardiac cycle. During systole, we found a left intraventricular signal that was reinforced on even echoes and much more intense in cardiomyopathy patients (scores = 1.61 +/- 1.06) than in controls (score = 0.77 +/- 0.7; p less than 0.01). The intensity score for this signal correlated with the ejection fraction in group I subjects (r = 0.82).

Multiple sclerosis diagnosis: magnetic resonance imaging compared with other instrumental examinations

Examination by magnetic resonance imaging (MRI), evoked potentials (EP) and cerebrospinal fluid (CSF) analyses was carried out on 97 definite, 20 probable and 40 possible multiple sclerosis (MS) patients (McAlpine's clinical criteria). MRI of only 4 transverse brain sections at the level of the ventricles and the analysis of the first 4 echoes showed periventricular or parenchymal lesions, or both, in 114 of the 117 definite and probable MS, and in 25 of the possible MS. MRI was more sensitive than the CSF analyses or EP; abnormalities more frequently appeared in known MS, and clinically asymptomatic lesions were seen. The MRI abnormalities were not, however, MS-specific; they were present in other neurological patients; none posed a question of differential diagnosis from MS. Complementary examinations, and especially MRI, should be a valuable adjunct for MS diagnosis, as long as the findings are viewed in the clinical context.

Multiple sclerosis diagnosis: magnetic resonance imaging compared with other paraclinical examinations

Examination by magnetic resonance imaging (MRI), evoked potentials (EP) and cerebrospinal fluid (CSF) analyses was carried out on 97 definite, 20 probable and 40 possible multiple sclerosis (MS) patients (McAlpine's clinical criteria). MRI of only 4 transverse brain sections at the level of the ventricles and the analysis of the first 4 echoes showed periventricular or parenchymal lesions, or both, in 114 of the 117 definite and probable MS patients and in 25 of the possible MS patients. MRI was more sensitive than the CSF analyses or EP. The MRI abnormalities were not, however, MS-specific.

[The ultrasensitive determination of TSH permits the prediction of the response to TSH in the TRH test]

A new ultrasensitive TSH immunoradiometric assay (IRMA) using two monoclonal antibodies is now able to distinguish between euthyroid and hyperthyroid patients. The aim of this study was to compare data given by ultrasensitive basal TSH (IRMA) and by the response of TSH to TRH test considered until now as the more reliable test in case of mild or atypical hyperthyroidism. Basal plasma TSH levels were determined in euthyroid (n = 80), hyperthyroid (n = 30), hypothyroid (n = 14) and pituitary deficient patients (n = 8) before and 30 minutes after a TRH test (250 micrograms i.v.). A close linear correlation was found between basal and post-stimulative TSH levels. Normal TSH response ranged from 2 to 22 uU/ml. The sensibility and the specificity of these two parameters appeared comparable in the case of primary dysthyroidism; on the contrary basal TSH levels were not sufficient for the diagnosis of central hypothyroidism. In conclusion, excepted for pituitary deficiency, basal plasma TSH (IRMA) levels are accurate and sufficient in the evaluation of the thyroid function and make the TRH-test useless.

[Importance of magnetic resonance imaging in myocardial infarct]

Imagery by magnetic resonance (IMR) represents a new modality of medical imagery based on the interaction between the magnetic fields produced by radio-frequency waves and living substance. IMR finds an interesting application in the study of different stages of myocardial infarction. In 30 cases of myocardial infarction IMR was compared with thallium tomoscintigraphy and echocardiography. In the acute stage, myomalacia appears in IMR as a superbrilliant zone, and in the chronic stage parietal thinning and dyskinesias are apparent. Intraventricular thromboses, but also hemostasis in aneurysmatic or akinetic sites are visualised as a high-intensity signal within these areas. IMR represents therefore a new means of evaluation of size and evolution of the necrosis. This procedure provides also functional informations about the contraction and flow anomalies.

Chemical and molecular exchange effects on T2 relaxation of living tissues: a pulse spacing dependence study

Contrast in magnetic resonance imaging depends principally on the longitudinal relaxation (R1) and the transverse relaxation rate (R2) of the observed nuclei, most often the protons. The spin-spin relaxation rate (R2) is the result of several mechanisms. The dependence of the interpulse delay of the Carr-Purcell-Meiboom-Gill sequence on the transverse relaxation rate of the water was studied in rat organs in vitro. It gives an insight into the exchange mechanisms involved. The increase of the interpulse delay from 0.2 ms to 5 ms gives an R2 increase of 23, 15, 3, and 2 s-1 for the heart, the liver, the spleen and the brain, respectively. These increases are compared to the R2 increases obtained in 17O-enriched water, amino acid and albumin solutions atomic exchange takes place. The concentration of these materials in organs cannot explain the R2 increase of the organs with the interpulse delay. Water exchange between intra and extracellular compartments is proposed to explain the R2 increase with interpulse delays in organs like the heart and the liver.

[Diagnostic elements of a right papyraceous ventricle. The value of nuclear magnetic resonance]

We are reporting the case of a young man presenting repeated syncopes linked to episodes of ventricular tachycardia. The rhythm disorders were due to the existence of a papyraceous right ventricle with concomitant involvement of the left ventricle disclosed during the etiological work-up. We are reporting, at this time, the usual diagnostic elements of this disease, but mostly original data provided by the nuclear magnetic resonance, as the clinical examination and the EKG are often less revealing except for late potentials always found in the arrhythmic form. The right, ventricular dysplasia and the papyraceous right ventricle represent two very close entities. Particular characteristics enable to differentiate them and also the differential diagnosis with other diseases are discussed by stressing the advantage of magnetic resonance imaging, a new method, non invasive, which lends itself well to the analysis of cardiac morphology.

[Nuclear magnetic resonance in the diagnosis of aortic diseases]

The diagnostic value of nuclear magnetic resonance imaging was assessed in a number of aortic pathologies: aneurysms of the thoracic and abdominal aorta, sinus of Valsalva aneurysms and dissection of the aorta. The imager was equipped with a resistor magnet providing a field of 0.15 Tesla. An electrocardiographic gating system was perfected. The images obtained were very satisfactory as they provided three dimensional morphological information and a qualitative assessment of blood flow. Further studies are now required with comparison with other invasive and non-invasive diagnostic methods to determine the clinical role of NMR imaging and to evaluate the diagnostic sensitivity and specificity of this new technique.

[Nuclear magnetic resonance. Our preliminary experience on the normal heart and in various cardiopathies]

Nuclear magnetic resonance imaging (NMRI) is applied in our department to the study of the normal heart and in aortic, pericardial and myocardial pathologies: aortic aneurysms, hypertrophic cardiomyopathies, myocardial infarction, pericarditis and congenital cardiopathies. The apparatus used consists of a resistive magnet which provides a field of 0.15 Tesla. Synchronisation with the electrocardiogram leads to improvement of the cardiac signals. The documents obtained are promising to the extent that information concerning cardiac structure is provided in three planes (frontal, sagittal and horizontal) and is complementary to that provided by echocardiography, isotopic techniques and contrast angiography. The future potential of the method is considerable, particularly in the area of tissue characterisation.

[Clinical value of thallium-201 myocardial scintigraphy with dipyridamole performed before and after aortocoronary bypass]

In addition to preoperative coronary angiography, 63 patients undergoing coronary bypass surgery also had myocardial scintigraphy with dipyridamole 1 to 2 days before surgery, resting scintigraphy 10 after bypass and a repeat scintigraphy with dipyridamole 3 to 6 months later. The myocardium was divided into 5 segments. In each segment the perfusion was classified as: normal, presence of a reversible defect (redistribution), presence of a permanent defect (no redistribution). A comparison of pre-and postoperative scintigraphies led to the following conclusions. Three to six months after bypass, improved perfusion was observed in 65.6% os ischaemic segments, showing that surgery was very effective. On the other hand, the immediate postoperative control (10 days) only showed improved perfusion in 42.5% of the ischaemic segments: this interval was too short to appreciate the benefits of coronary bypass. There was a good correlation between the scintigraphic improvement after surgery and the reversibility of the zones of hypofixation of Thallium before surgery. When the defect was reversible, 80% of the revascularised segments were improved. Fifty-eight per cent of non-reversible defects before surgery were unchanged by the revascularisation procedure. However, the absence of redistribution during preoperative scintigraphy was not synonymous with definitive myocardial lesions and does not represent a contra-indication to coronary bypass surgery; in fact, improved perfusion was observed in 42% of these constant defects. The quality of recovery depends on the condition of the muscle: only segments with normal motion can be improved. Degradation of the clinical condition of patients was always related to aggravation(lack of improvement in 1 case) of scintigraphy.(ABSTRACT TRUNCATED AT 250 WORDS)

NMR compartmentalization of free water in the perfused rat heart

Spin-lattice (T1) and spin-spin (T2) relaxation times have been measured on perfused rat hearts under two experimental conditions. T1 exhibits a monoexponential decay. On the other hand T2 has a decay with two components: a short one T2s and a long one T2l. These facts have been discussed according to cross-relaxation and a bicompartmentalization of tissue assuming a slow exchange model for spin-spin relaxation and a fast exchange model for spin-lattice relaxation. Increasing the osmotic pressure of the perfusion solution decreased the absolute density proton of the T2s compartment reflecting the loss of its water content. The paramagnetic ion manganese diminishes the values of T1 and those of the long component T2l without affecting its short component. Therefore the short component could be assigned to intracellular and the long component to extracellular free water. The extracellular T2 (459 ms) is approximatively 10-fold higher than the intracellular T2 (45 ms). With images of "pure T2" such a difference could be useful to enhance the contrast between organs and the surrounding liquid or between organs with different water compartmentalization.

[The spatial vectorcardiogram loop. Estimation of its planarity by the calculation of a distortion coefficient. Trial of clinical evaluation]

Automatic techniques for interpreting the electrical activity of the heart are based more and more on vectorcardiographic parameters, especially information provided by the spatial vectorcardiographic loop. This data has been shown to be a useful complement to classical electrocardiography. The aim of this study was to define a method of calculation of the planes of the vectorcardiographic loops of depolarisation and repolarisation, and to calculate a coefficient of left-sidedness obtained by the sum of squares of the distances between the points on the loop in the plane. This value is then normalised with respect to the size of the loop. Normal values of this coefficient were first defined in a healthy reference population of 70 subjects: the values are expressed in (MV/10)2 or in mm2, and are 0,28 +/- 0,05 for the QRS and 0,0026 +/- 0,0008 for the ST-T. The coefficient was then calculated in different pathological groups, the diagnosis of which had been formally confirmed: ventricular hypertrophy, valvular heart disease, conduction defects, coronary artery disease. The highest values (four times normal) were obtained in right ventricular hypertrophy, right bundle branch block and infarction associated with conduction defects. The discriminative value of the coefficient of left-sidedness is discussed with the aim of distinguishing the normal from the pathological.

[Evaluation of left ventricular function and regional kinetics following myocardial infarction. Comparative study of angiocardiography, echography and radionuclide angiography]

Left ventricular function and regional wall motion were studied three weeks after a myocardial infarction in 25 patients who had undergone L.V. monoplane cineangiography. The patients were studied by echocardiography (TM and 2D) and radionuclide angiography. Evaluation of global ejection fraction provides evidence of a close correlation between left ventricular angiography and radionuclide examination (r= 0.79). Measurement of ejection fraction by echocardiography (TM) remains clearly correlated with the same evaluation by angiography (r = 0.68). The correlations are markedly increased in the patients without significant wall motion defects (r = 0.87 for radionuclide angiography and r = 0.82 for echographic measurement). Sensitivity in the detection of L.V. aneurysms is excellent with our method of radionuclide examination (12/13) and can be compared with angiography (12/13). Two-dimensional echocardiography performed on a routine basis is less sensitive than radionuclide angiography in this diagnosis (4/13).

Fluorescence label studies of the phase transitions of T7

Optical density, fluorescence intensity, polarization and lifetime measurements were performed to analyze the temperature-induced phase transitions of phage T7 in several buffers. For labelling the intraphage DNA, ethidium bromide, proflavine and rivanol were applied for the proteins 1,6-diphenyl-1,3,5-hexatriene (DPH). In the temperature range of 20 degrees C-100 degrees C several structural changes of T7 were detected. Making corrections for light scattering by using integrating spheres and analyzing the fluorescence signals, the phase transition of intraphage DNA below 60 degrees C was interpreted as a superhelical relaxation phenomenon. The structural changes found by optical density at higher temperatures could be assigned to a change in the phage DNA or to a change in its protein part on the basis of fluorescence-melting results concerning DNA and protein labels. The effects of ionic strength and environment on the structural changes were studied.

Consequences of the chronic cutaneous application of iodinated antiseptics on the thyroid function in the guinea-pig

The effect of the chronic cutaneous application of iodine-containing substances on the thyroid function was studied in the guinea-pig. Six iodinated products were daily applied at the rate of 2 g/kg/day for 90 days. We find a quasi-abolition in the thyroid 131I-uptake (reflecting the transcutaneous absorption of free iodine) and an important transient thyroidal hyperproduction during the first month. Then, this primary hyperthyroidism induces a strong pituitary negative feed-back so that the levels of the circulating hormones T3 and T4 are normalized at the end of the experiment; a new hormonal balance is reached with a TSH level reduced by half compared to its normal value.

Evaluation of myocardial perfusion and left ventricular function by 201T1 scintigraphy after dipyridamole

201T1 myocardial imaging was performed at rest and after dipyridamole (0.44 mg/kg) on 50 patients with known or suspected ischemic heart disease. The dipyridamole had no effect in 14 patients (group Dip.0). In 17 patients (group Dip +/-) it significantly modified the contrast of the rest image (by increasing or decreasing a rest perfusion defect). In 19 patients (group Dip - Steal) the drug induced a paradoxical response interpreted as a coronary steal effect (an active region at rest becomes hypoactive after dipyridamole while an underperfused region at rest improves). All patients underwent coronary arteriography and left monoplane ventriculography; results were interpreted in relation to these angiographic data. The mean percentage of stenoses (per patient) was about the same in the three groups but it was found that, despite these stenoses, the patients of the group Dip - Steal had a good left ventricular function (EF = 0.62 +/- 0.12). On the other hand, the ejection fraction was very poor in the two other groups (0.50 +/- 0.17 and 0.48 +/- 0.17). Moreover it was found that: (1) the frequency of high grade or even complete obstruction was notably less in group Dip - Steal (P less than 0.05); (2) the frequency of angiographically visible collaterals was higher in group Dip - Steal (P less than 0.05); (3) the left anterior descending artery was less diseased than the right coronary artery in group Dip - Steal (P less than 0.05). These results have a real prognostic value for the assessment of the preserved cardiac performance in Dip - Steal patients despite severe stenoses, and are discussed in terms of compensatory collateral circulation and preservation of the coronary-flow reserve in the myocardium distal to a critical stenosis.