J. P. Bazin

Handling of Dynamic Sequences in Nuclear Medicine

Nuclear Medicine is one of the first domains in which the analysis of image sequences was introduced. The development of this analysis was achieved parallel to the one of the computer systems linked to the scintillation cameras. The number of works that were performed in the research laboratories and have received an application in clinical routine is however limited. The authors indicate what could be the flow chart of the processing of dynamic sequences in scintigraphy and the kind of material that would be necessary to implement it. The possibilities of using the factor and compartmental analyses in clinical routine are particularly emphasized. The authors indicate why the factors and their associated images obtained by means of the factor analysis can have a physiological meaning.

A statistical model for the determination of the optimal metric in factor analysis of medical image sequences (FAMIS)

A statistical model is added to the conventional physical model underlying factor analysis of medical image sequences (FAMIS). It allows a derivation of the optimal metric to be used for the orthogonal decomposition involved in FAMIS. The oblique analysis of FAMIS is extended to take this optimal metric into account. The case of scintigraphic image sequences is used. We derive in this case that the optimal decomposition is obtained by correspondence analysis. A scintigraphic dynamic study illustrates the practical consequences of the use of the optimal metric in FAMIS.

Famis: A software package for functional feature extraction from biomedical multidimensional images

An increased number of image sequences is acquired in all modalities of the biomedical imaging field in order to study displacement or metabolism of a tracer or a contrast agent. It requires effective processing methods to estimate the underlying physiological components. We have developed a software package based on factor analysis algorithms which can adapt to various imaging modalities and its extension to double-indexed image sequences. We describe general characteristics of the software and present the main points of the user-friendly interface. The performances of the package are discussed and the possibilities of the methodology are illustrated using an example in magnetic resonance imaging.

Factor analysis as a means of determining response to chemotherapy in patients with osteogenic sarcoma.

The prognosis of localized osteogenic sarcoma (OS) has improved considerably since the introduction of neoadjuvant chemotherapy. However, there is a subset of patients who do not show full benefit from neoadjuvant chemotherapy because of chemoresistance. The early identification of poor responders to chemotherapy during neoadjuvant therapy remains difficult. In order to evaluate the role of bone scintigraphy we report our experience of dynamic technetium-99m hydroxymethylene diphosphonate bone scintigraphy in 19 cases of paediatric osteogenic sarcomas. Before the beginning of chemotherapy, a dynamic scan was recorded during 30 min followed by static images at 3 h. The procedure was repeated halfway through the course of chemotherapy (6th week). Histological grading of the response to chemotherapy was carried out in the 12th week, showing nine good responses and ten poor responses. Factor analysis of dynamic structures (FADS) applied to dynamic scans allowed us to identify three factors termed vascular, “soft tissue” and osseous factors. The effect of chemotherapy on each factor was evaluated. Using FADS we were able to detect all the poor histological responders with the combination of vascular and osseous factors. Six out of nine good histological responders were also classified as scintigraphic responders. FADS applied to dynamic bone scans allowed us to identify at an early stage all the poor histological responders to neoadjuvant chemotherapy. This method may have clinical relevance for the therapeutic strategy in patients with OS.

Comparison between factor analysis of dynamic structures and Fourier analysis in detection of segmental wall motion abnormalities: a clinical evaluation

To evaluate Factor Analysis of Dynamic Structures (FADS) versus or in association with other methods, a protocol was set up including as ‘gold standard’ investigation the left ventricular angiography (LVA) and processing by Fourier Analysis (FA), and FADS with different variants. To refine the diagnosis of Regional Wall Motion Abnormalities (RWMA), processing was done on a sectorial basis for more accurate spatial localization and functional description.53 patients were studied (8 normal, 45 with coronary artery disease). FADS gave better results than FA on a sectorial basis. Total agreement between FADS and LVA was obtained in 208/265 (78%), while FA was in agreement with LVA in only 167/265 segments (63%). Globally, FADS was significantly better than FA (Z-test: p<0.05). When only the diagnosis of maximal abnormality was considered, FA and FADS are statistically equivalent. The superiority of FADS vs FA is more obvious in the diagnosis of hypokinesia. Most FA discrepancies corresponded to underestimation of WMA.

Foundations of factor analysis of medical image sequences: a unified approach and some practical implications

Abstract Factor Analysis of Medical Image Sequences (FAMIS) is presently conducted either in the function space or in the image space. A unified approach jointly using these two spaces is presented. First, the solution of a statistical model for scintigraphic image sequences leads to the use of correspondence analysis which is the optimal orthogonal decomposition of this data. Then, two symmetrical hypotheses concerning either the underlying fundamental functions or the underlying fundamental spatial distributions are derived. These hypotheses are merged in an original method to solve FAMIS physical model. Using this unified approach, a priori knowledge about functions and images can be jointly taken into account to improve the estimation of the underlying structures. Some practical applications of the method are illustrated on simulated data.

Early kinetics of thyroid trap in normal human patients and in thyroid diseases

A six-compartment model is proposed for the study of early iodine kinetics (150 min) in the human thyroid gland including three compartments for extrathyroidal spaces. The results were compared with those obtained with an open two-compartment thyroidal model.In six euthyroid subjects the values of the unidirectional thyroid clearance R41=86±25 ml/min and of the irreversible clearance R65=22±9 ml/min were consistent with those generally accepted. With TSH stimulation a clear increase in the thyroidal pump effectiveness was found without an increase in the irreversible clearance.In four untreated thyrotoxic patients a tenfold increase in the unidirectional thyroid clearance was found (P<0.01). The binding rate was much less increased and overlapped with the normal values; a large increase in the iodide compartment volumes was found. The unidirectional clearance remained elevated in seven patients after Carbimazole treatment and the binding rates were reduced. The six-compartment model demonstrated a rapid exit from the bound iodine compartment.In three of four goitrous patients studied, the thyroid unidirectional clearance was significantly increased (P<0.001). The volumes of the iodide compartments were much higher than those observed in the other groups.The method was applied to analyse the kinetics of different parts of the thyroid.

Diagnosis of malignancy in thyroid nodules by factor analysis of spectral and dynamic structures: a simultaneous dual-isotope dynamic study with thallium-201 and iodine-131

The aim of this study was to identify malignant thyroid nodules using iodine-123 and thallium-201 simultaneous dynamic acquisition. The image sequences acquired were processed by factor analysis of spectral and dynamic structures (FASDS). Some 49 patients were investigated, and their diagnoses were confirmed by histological examination. Data processing enables the estimation of the spectra of the two isotopes and the evaluation of the kinetics and spatial structures related to each tracer. The superimposition of thallium and iodide sum images allowed us to delineate the nodule accurately. Two groups were defined: 21 patients who had 201T1 uptake in the nodule, and 28 who had none. In the first group, 5 nodules were carcinomas, whereas all nodules in the second group were benign. The results of the 201T1 dynamic study improved the diagnosis of carcinoma as the number of false-positive cases decreased. FASDS succeeds in extracting spectral and kinetic information, proving its usefulness in clinical diagnosis.

Automated processing of first-pass radionuclide angiocardiography by factor analysis of dynamic structures.

A method for automatic processing of cardiac first-pass radionuclide study is presented. This technique, factor analysis of dynamic structures (FADS) provides an automatic separation of anatomical structures according to their different temporal behaviour, even if they are superimposed.FADS has been applied to 76 studies. A description of factor patterns obtained in various pathological categories is presented. FADS provides easy diagnosis of shunts and tricuspid insufficiency. Quantitative information derived from the factors (cardiac output and mean transit time) were compared to those obtained by the region of interest method. Using FADS, a higher correlation with cardiac catheterization was found for cardiac output calculation.Thus compared to the ROI method, FADS presents obvious advantages: a good separation of overlapping cardiac chambers is obtained; this operator independant method provides more objective and reproducible results.A number of parameters of the cardio-pulmonary function can be assessed by first-pass radionuclide angiocardiography (RNA) [1,2]. Usually, they are calculated using time-activity curves (TAC) from regions of interest (ROI) drawn on the cardiac chambers and the lungs. This method has two main drawbacks: (1) the lack of inter and intra-observers reproducibility; (2) the problem of crosstalk which affects the evaluation of the cardio-pulmonary performance. The crosstalk on planar imaging is due to anatomical superimposition of the cardiac chambers and lungs. The activity measured in any ROI is the sum of the activity in several organs and ‘decontamination’ of the TAC cannot easily be performed using the ROI method [3].

Factor analysis of 81mKr lung ventilation studies.

Factor analysis of dynamic structures (FADS) summarizes data depending on time and space in a few elementary components. Each of them associates a time-activity curve (factor) and the spatial distribution of the corresponding events. The aim was to evaluate the patterns, the number of components, and their possible link to physiology when FADS was applied to scintigraphic images representing a composite of a 81mKr ventilation cycle. In a study of 26 patients (10 normal, 16 pathologic), components were found that represent: (1) a rapid and steeply changing ventilation factor, corresponding mainly to bases in normal subjects and whole lung fields in patients, (2) a slower expiration and shorter inspiration ventilation factor distributed throughout both lung fields in all patients, (3) a constant activity curve, with an inspiratory activity peak distributed over both lung fields and the large airways, and (4) a factor including a phase shift with respect to the first; this was found significantly more often in patients with pathology.