Streak artifact reduction in filtered backprojection using a level line-based interpolation method.

UNLABELLED: Because of the limited number of projections, the mathematic reconstruction formula of the filtered backprojection (FBP) algorithm may create an artifact that streaks reconstructed images. This artifact can be imperfectly removed by replacing the ramp filter of the FBP with an ad hoc low-pass filter, the cost being the loss of contrast and definition. In this study, a solution was proposed to increase, by computational means, the number of projections to reduce the artifact at a lower cost. The cost was a postacquisition process, which was reasonably time consuming. METHODS: The process was called interpolation of projections by contouring (IPC). First, level lines were plotted on the sinogram to delimit isocount regions; then, the regions containing the interpolated points were found, and to each point was assigned the intensity of its isocount region. Using this process, the data could be resampled, allowing an increase in the number of projections or the number of pixels by projections. A phantom study of bone scintigraphy was performed to compare the slices obtained with and without the IPC process with the true image. A clinical case was also presented. RESULTS: The phantom study showed that with the IPC process, the reconstructed slice was closer to the model, inside and outside the body, when the sinogram was resampled to multiply by 2 or 3 the number of projections, with the same number of pixels per projection. In the clinical study, the streak artifact was reduced, especially outside the body, although only a ramp filter was used. CONCLUSION: The IPC process succeeded in reducing the streak artifact. This process did not require any modification in acquisition and was not operator dependent. The increase in the number of projections is likely a necessary but not a sufficient condition to reduce the streak artifact: if not corrected, the attenuation could be a limiting factor in the removal of this artifact when the number of projections increases.

Noise removal using factor analysis of dynamic structures: application to cardiac gated studies.

UNLABELLED: Factor analysis of dynamic structures (FADS) facilitates the extraction of relevant data, usually with physiologic meaning, from a dynamic set of images. The result of this process is a set of factor images and curves plus some residual activity. The set of factor images and curves can be used to retrieve the original data with reduced noise using an inverse factor analysis process (iFADS). This improvement in image quality is expected because the inverse process does not use the residual activity, assumed to be made of noise. The goal of this work is to quantitate and assess the efficiency of this method on gated cardiac images. METHODS: A computer simulation of a planar cardiac gated study was performed. The simulated images were added with noise and processed by the FADS-iFADS program. The signal-to-noise ratios (SNRs) were compared between original and processed data. Planar gated cardiac studies from 10 patients were tested. The data processed by FADS-iFADS were subtracted to the original data. The result of the substraction was studied to evaluate its noisy nature. RESULTS: The SNR is about five times greater after the FADS-iFADS process. The difference between original and processed data is noise only, i.e., processed data equals original data minus some white noise. CONCLUSION: The FADS-iFADS process is successful in the removal of an important part of the noise and therefore is a tool to improve the image quality of cardiac images. This tool does not decrease the spatial resolution (compared with smoothing filters) and does not lose details (compared with frequential filters). Once the number of factors is chosen, this method is not operator dependent.

Regional differences and metabolic changes in normal aging of the human brain: proton MR spectroscopic imaging study.

BACKGROUND AND PURPOSE: Aging is recognized to originate from a diversity of mechanisms that blur the limits between normal and pathologic processes. The purpose of this study was to determine the early effect of normal aging on the regional distribution of brain metabolite concentrations, including N-acetylaspartate (NAA), a major neuronal marker, choline (Cho), and creatine (Cr). METHODS: Thirty-two healthy participants, ages 21 to 61 years, were examined by proton MR spectroscopic (1H MRS) imaging. 1H MRS imaging acquisitions were performed in two brain locations: the centrum semiovale and the temporal lobe. Thirty voxels were selected in four cerebral regions, cortical, semioval, temporal, and hippocampal, and 1H MR spectra were processed to determine the metabolite ratios. RESULTS: With advancing age of the participants, the ratios of %NAA, NAA:Cho, and NAA:Cr were significantly decreased, whereas the ratios of %Cho and %Cr were significantly increased in the cortical, semioval, and temporal regions. On the basis of the significant metabolic difference determined by cluster analysis, two groups of 16 participants with ages ranging from 21 to 39 years (younger group) and 40 to 61 years (older group) were compared. Repeated measures analysis of variance tests, with multiple comparison procedures between the two age groups and among the four brain region groups, showed significant decreases of the %NAA, NAA:Cho, and NAA:Cr ratios in the semioval and temporal regions of the older group compared with the younger group. When compared with other cerebral regions, %NAA and %Cho ratios were significantly decreased in the hippocampal and cortical regions, respectively. CONCLUSION: These metabolic changes suggest that brain aging is characterized by a reduction in neuronal viability or function associated with an accelerated membrane degradation and/or an increase in glial cell numbers.

Left ventricle automated detection method in gated isotopic ventriculography using fuzzy clustering.

A method that uses the fuzzy ISODATA clustering algorithm and Fourier analysis is proposed for automated detection of heart left ventricle contours. This operation is used for quantitative analysis of cardiac function. The computation begins by finding the phase image. The fuzzy ISODATA algorithm is first applied to this image to generate a number of clusters that correspond to the organ substructures (ventricles, atria). Second, the ventricles cluster is isolated and the intensities of its points are replaced by the corresponding ones from the original (end diastolic) frame. Finally, a reduced image representing the ventricular region is obtained and an additional clustering is performed to find the left ventricular boundary automatically. This algorithm is tested by application of 105 sets of 16 images each. These results are compared with the measurements obtained with two semi-automatic methods used, respectively, on the Philips and the Sopha Medical gamma cameras.

Spatial or flow velocity phase encoding gradients in NMR imaging.

We describe time modulated field gradient sequences able to selectively phase encode spatial location or flow velocity in NMR Signals. Two flow conditions are presented: constant flow velocity and simple harmonic flow superposed on steady flow. In each case we show that specific modulated gradients are available in order to discriminate between stationary and mobile protons. The methods are presented in the one dimensional case. The advantages of the phase modulation for flow analysis are the following: the method is sensitive to flow direction, unaffected by the T2, and the stationary and flow parameters are quantifiable factors.

Automated detection of the left ventricular region in gated nuclear cardiac imaging.

An approach to automated outlining the left ventricular contour and its bounded area in gated isotopic ventriculography is proposed. Its purpose is to determine the ejection fraction (EF), an important parameter for measuring cardiac function. The method uses a modified version of the fuzzy C-means (MFCM) algorithm and a labeling technique. The MFCM algorithm is applied to the end diastolic (ED) frame and then the (FCM) is applied to the remaining images in a "box" of interest. The MFCM generates a number of fuzzy clusters. Each cluster is a substructure of the heart (left ventricle,...). A cluster validity index to estimate the optimum clusters number present in image data point is used. This index takes account of the homogeneity in each cluster and is connected to the geometrical property of data set. The labeling is only performed to achieve the detection process in the ED frame. Since the left ventricle (LV) cluster has the greatest area of the cardiac images sequence in ED phase, a framing operation is performed to obtain, automatically, the "box" enclosing the LV cluster. THe EF assessed in 50 patients by the proposed method and a semi-automatic one, routinely used, are presented. A good correlation between the two methods EF values is obtained (R = 0.93). The LV contour found has been judged very satisfactory by a team of trained clinicians.

Delineation and quantitation of brain lesions by fuzzy clustering in positron emission tomography.

In this study, we investigate the application of the fuzzy clustering to the anatomical localization and quantitation of brain lesions in Positron Emission Tomography (PET) images. The method is based on the Fuzzy C-Means (FCM) algorithm. The algorithm segments the PET image data points into a given number of clusters. Each cluster is an homogeneous region of the brain (e.g. tumor). A feature vector is assigned to a cluster which has the highest membership degree. Having the label affected by the FCM algorithm to a cluster, one may easily compute the corresponding spatial localization, area and perimeter. Studies concerning the evolution of a tumor after different treatments in two patients are presented.

Regional cerebral blood flow determination using 133Xe and a standard rotating gamma-camera.

While most of the methods for quantitative regional cerebral blood flow (rCBF) determination in man requires expensive fast devices, a method is proposed using single photon emission computed tomography with a conventional rotating gamma camera and 133Xe inhalation. It is tested using a computer simulation of a cerebral exam and a simplified CBF map as a model. The results obtained show that this method is relevant and can be tested in clinical studies.

[Isotope phlebography. Value and limitations. Reliability in recent deep venous thrombosis of the lower limbs (author's transl)]. / la phlébographie isotopique. Intérêt limites. Fiabilité dans les thromboses récentes des veines profondes des membres inférieurs.

Isotope phlebography is a reliable examination in the diagnosis of deep venous thrombosis. Too complicated and expensive to be suggested for the purpose of routine detection, it nevertheless is of definite interest in three circumstances: --Suspicion of pulmonary embolism, with visualisation of any possible reservoir of peripheral clot and proof of the embolism. --Postoperatively, for repeated follow up to evaluate permeability after surgical procedures. --Finally, dynamic information by calculation of transit time of the radioactive embolus. Combined with Doppler measurement of peripheral venous pressures, it reflects the emptying capacities of a limb affected by post-phlebitis syndrome and hence plays a role in the decision to stop oral anticoagulants.

[Agenesis of the pericardium: clinical, echocardiographic and MRI aspects]. / Agénésie du péricarde: aspects clinique, échocardiographique et IRM. A propos d'un cas.

A case of agenesis of the pericardium is reported. The condition is are; a search in the literature has yielded 364 cases. It always results from an abnormal embryonic development. The agenesis is more common on the left side (70%) than on the right side (4%) or the inferior side (17%). It is more often partial than total (9%) and may be associated with other malformations, particularly malformations of the heart. The diagnosis rests on radiography of the chest and, mainly, echocardiography. CT, MRI or surgical exploration (if needed for other reasons) confirm the anatomical defect. In patients with partial pericardial agenesis the risk of cardiac entrapment makes surgery mandatory.

[Flow analysis by phase modulation of NMR signals]. / Analyse des écoulements fluides par modulation de phase des signaux RMN.

Time modulated field-gradient-sequences able to selectively phase encode spatial location or flow velocity in NMR signals are described. The specific phase modulation discriminates between stationary and mobile protons. The method is presented in the one dimensional case and has the following advantages: it is sensitive to flow direction and unaffected by the relaxation times.

An antibody purified with a lambda GT11 fusion protein precipitates enkephalinase activity.

An antiserum was raised against the neutral endopeptidase "enkephalinase" in guinea pig and used to probe a rabbit kidney cDNA expression library. A positive clone has been isolated and sequenced. The identity of the corresponding fusion protein was ascertained by its ability to select, from the crude antiserum, antibodies which specifically immunoprecipitate neutral endopeptidase enzymatic activity. This approach eliminates the uncertainty inherent to clone identification obtained from oligonucleotide probe derived from a partial sequence of the protein.

A metabolism study of human masseter muscle by 31P magnetic resonance spectroscopy during long periods of exercise and recovery.

The metabolism of the human masseter muscle was investigated using phosphorus (31p) magnetic resonance spectroscopy (MRS) during long periods of exercise and recovery. Eleven subjects aged 19 to 28 yr were examined by 31p MRS during four consecutive periods of 13 min each: rest, exercise, recovery 1 and 2. For each subject, a biting force equal to 20% of maximum voluntary biting force was applied and controlled during the exercise period to produce maximum fatigue. 31p MR spectra were localized from a 24 cm3 volume of interest using an image selected in vivo spectroscopy (ISIS) sequence and a 6 cm diameter surface coil placed on the left masseter. Compared to the resting level, the phosphocreatine (PCr) content decreased by 26% during exercise, while the inorganic phosphate (Pi) concentration increased by 65%. During the two recovery periods, the Pi content remained decreased compared with the resting level by 36% and 30%, respectively. The Pi/PCr ratio was increased from 0.30+/-0.04 at rest to 0.63+/-0.13 during exercise while the adenosine triphosphate (ATP)/Pi ratio was decreased. The pH decreased from 7.02+/-0.03 to 6.93+/-0.04 during exercise and returned to control level (7.09+/-0.08) only during the second recovery period. These results suggest that the masseter muscle is characterized by high ATP turnover and, therefore, high oxidative phosphorylative activity in agreement with its constitution of predominantly fatigue resistant type I fibers.

[Modifications, due to nutrition, of methyl and methylene 1H NMR signals in human plasma and normal serum samples]. / Etude des modifications apportées par la nutrition sur les signaux de RMN 1H méthyliques et méthyléniques d'échantillons de plasmas et sérums humains normaux.

The line width test has been realised on twelve normal healthy persons (seven men and five women). Blood was collected at different time during one day. The results obtained when blood samples was taking after eating, showed an appreciable decrease in the average methylene and methyl line width. The same test realised on clear serum samples added up with increasing quantities of triglycerids rich lipoproteins leads to the same result.