Annie Pousse

Nouvelles techniques interventionnelles et métaboliques dans la prise en charge des métastases osseuses

Resume Les metastases osseuses sont la cause la plus frequente de douleur chez les patients atteints de cancer. Leur prise en charge sur le plan antalgique est un challenge therapeutique. La composante douloureuse ne repond pas toujours aux antalgiques majeurs, a la chimiotherapie et a la radiotherapie. Quand ces traitements sont depasses, la vertebroplastie, la cimentoplastie, la radiofrequence par voie percutanee et la radiotherapie metabolique sont des methodes elegantes et efficaces venant en complement des traitement classiques.

Compact gamma-ray probe for breast imaging based on a 5-inch PSPMT and a single NaI crystal scintillator

Scintimammography is a promising technique for breast cancer detection. Scintimammography uses radiotracer containing 99mTc that emits 140 keV gamma photons. We developed a small field of view gamma ray imaging probe called IRIS. A possible application of this probe is scintimammography. IRIS is composed by a single NaI(Tl) scintillator coupled to a 5 inch round PSPMT. In order to optimize compromise between resolution and detection efficiency, we developed a Monte Carlo code modeling light transport in NaI crystals. The thickness of the scintillator (4 mm) was optimized for 99mTc imaging. We also designed a high-resolution collimator with a 35 mm thickness and 1.7 mm hole diameter. Detection efficiency of the crystal is 65% at 140 keV. IRIS shows a 2.5 mm global spatial resolution in contact. Energy and spatial corrections allow a +/- 5% uniformity and an energy resolution better than 10% at 140 keV. IRIS has a 10 cm field of view and a 13 cm external diameter at the entrance face. The small size of the detector head allows placing the detector close to the breast, improving global spatial resolution. The high-resolution gamma ray imaging probe IRIS shows physical characteristics well suited for 99mTc breast imaging.

Modélisation tridimensionnelle des vertèbres types : Premières applications en radioanatomie et radiologie interventionnelle sous guidage tomodensitométrique

Purpose To model vertebrae in 3D to improve radioanatomic knowledge of the spine with the vascular and nerve environment and simulate CT-guided interventions.

Performances of a specific denoising wavelet process for high-resolution gamma imaging

Due to its functional capabilities, gamma imaging is an interesting tool for medical diagnosis. Recent developments lead to improved intrinsic resolution. However this gain is impaired by the poor activity detected and the Poissonian feature of gamma ray emission. High resolution gamma images are grainy. This is a real nuisance for detecting cold nodules in an emitting organ. A specific translation wavelet filter which takes into account the Poissonian feature of noise, has been developed in order to improve the diagnostic capabilities of radioisotopic high resolution images. Monte Carlo simulations of a hot thyroid phantom in which cold spheres, 3-7 mm in diameter, could be included were performed. The loss of activity induced by cold nodules was determined on filtered images by using catchment basins determination. On the original images, only 5-7 mm cold spheres were clearly visible. On filtered images, 3 and 4 mm spheres were put in prominent. The limit of the developed filter is approximately the detection of 3 mm spherical cold nodule in acquisition and activity conditions which mimic a thyroid examination. Furthermore, no disturbing artifacts are generated. It is therefore a powerful tool for detecting small cold nodules in a gamma emitting medium.

A new deconvolution method using antidiffusion for high resolution radioisotopic imaging

Radioisotopic investigations are very useful for functional diagnosis. However, visual analysis of images is lowered by blurring due to impulse response size and by their granular aspect due to low statistics. Acquired images result in the convolution between original object and detector spatial impulse response. Classical deconvolution methods used for radioisotopic image restoration fail due to bad signal to noise ratio. A new deconvolution process including two steps is designed. The first stage reduces acquired images statistical noise by applying a second order Butterworth low-pass filter. As the detector response shape may also be viewed as a 2D heat diffusion process, the deconvolution is done by running the diffusion equation into minus time. Tests were performed on physical phantom and on clinical thyroid scintigraphies acquired with IRIS (ARIES) high resolution gamma imaging probe. On physical phantom, cold spherical nodules as small as 4 mm in diameter are clearly enhanced on restored images, and diagnosis is improved.

Multiscale wavelet filter for high resolution radioisotopic images

Radioisotopic Investigations are very useful for functional diagnosis, but available gamma cameras have poor spatial resolution. Development of new PSPMT based high-resolution detectors brings new interests to this medical imaging technique. However, the Poissonian nature of emitted photon flux and low count images due to low doses administered to the patients and to collimation, lead to images with granular aspect. This noisy appearance is particularly inconvenient when looking for cold nodules as in thyroid examinations. Low-pass filters, which reduce noise, are not well suited for detecting small cold nodules. An adapted translation invariant wavelet filter is designed which takes into account the poissonian feature of noise and preserves small sized structures. The filter was tested by Monte Carlo simulations, phantom and clinical thyroid scintigraphies. Cold spherical nodules as small as 4 mm in diameter are easily detected on filtered images acquired with IRIS (ARIES) high-resolution gamma ray imaging probe. Presentation of filtered images at different scales offering enhanced visual quality and lowered noise, simultaneously with original image, allows more comfortable analysis and improves scintigraphic diagnosis ability.

Mixed wavelet-watershed method for nodule detection in high resolution scintimammography

The recent developments in gamma cameras have lead to significant improvements of intrinsic spatial resolution in radioisotopic imaging. Especially, using smaller photodetectors (PSPMT, photodiodes) enables to build more compact devices which permits to place the detector very near from the organ under study and thus to enhance the global spatial resolution. However, these improvements need to reduce image pixel size which worsens the signal to noise ratio in every pixel. Moreover, many clinical examinations, such as scintimammography will be all the more useful since small nodules can be detected. In this work, we present a method combining a denoising wavelet filtering method with watershed determination, both leading to hot nodule enhancement. This method was applied to Monte Carlo simulations of a 64 mm high volume containing hot nodules of various sizes with a tumor to background ratio equal to 5. Although nodules were not visible in raw images corresponding to 10 min acquisitions, the described process allowed the detection of 88% of 6 mm nodules and more than 97 % of nodules whose diameter was greater or equal to 8 mm. Results obtained on phantoms without hot spheres permit to assess the pertinence of the proposed method. Furthermore, the whole process runs very fast.

Mixed wavelet-watershed method for nodule detection in high resolution scintigraphy

The recent developments in gamma cameras have lead to significant improvement of intrinsic spatial resolution in radioisotopic imaging. Moreover, the use of smaller photodetectors (PSPMT, photodiodes) enables to build more compact devices which allows to place the detector very near from the organ under study and thus to enhance the global spatial resolution. However, these improvements need the use of smaller image pixel sizes which worsens signal to noise ratio in every pixel. Moreover, a lot of examinations, such as scintimammography will be all the more useful since small nodules can be detected. In this work, we present a method combining a denoising wavelet filtering method with watershed determination, both leading to hot nodule enhancement. This method was applied to Monte Carlo simulations of a 64 mm high volume containing hot nodules of various sizes with a tumor to background ratio equal to 5. Although nodules were not visible in raw images corresponding to 10 min acquisition, the described process allowed to detect 87% of 6 mm nodules and more than 97% of nodules whose diameter was greater or equal to 7 mm. Furthermore, the whole process runs very fast

Characterization of a /spl gamma/-ray detector based on square PSPMT array

Although gamma cameras have emerged in the sixties, their spatial resolution is still not sufficient to detect small tracer concentration abnormalities. Examinations like mammo-scintigraphy requires high spatial resolution and then the possibility to position the detector as close to the explored organ as possible. Diagnostic accuracy in nuclear medicine imaging can know a notable advancement with the emergence of the new position sensitive photomultiplier tube (PSPMT). This component allows to develop a compact gamma detector which fulfils these requirements. This study investigates the feasibility and the characteristics of a medium field of view high spatial resolution gamma ray detector based on an array of R8520 PSPMT coupled to a pixelated NaI(TI) crystal array. As first results, a photocathode uniformity variation of 1 to 3 was observed on the whole field of view. Energy resolution obtained is better than 10% FWHM at 140 keV in PSPMT centers. Concerning spatial linearity, it depends on the uniformity of the PSPMT used. Consequently, it will be necessary to develop linearity and energy correction methods.

Medium-sensitivity rotating collimator for high-performance radioisotopic imaging

The high-resolution radioisotopic detector allows the detection of small structures, but its sensitivity is poor. Increased parallel collimator sensitivity is obtained by enlarging the hole diameter. However, a hole diameter greater than detector intrinsic spatial resolution leads to artifacts on acquired images. Linear collimator motions can remove these artifacts. These motions consist in sampling the generic rectangle of the hexagonal collimator structure and theoretically lead to images without artifacts. However, such motions are difficult to perform. To this end, a circular translation motion is studied in this paper. Motion effectiveness was evaluated by an inhomogeneity index based on hexagon center loci. Several rotation radii optimizing image homogeneity were found. Moving collimator transparency was deterministically simulated using a uniform isotropic source and a line source. For every rotation radius that minimized homogeneity, uniform source images showed variations below 1%.. The smallest suitable motion radius is 0.32 times the structure diameter, which leads to a very small decrease in the field of view. A device performing such collimator motions was made for a high-resolution gamma imaging probe based on a photomultiplier position sensitive tube and tested using a low-energy medium-sensitivity collimator. The measured spatial impulse response was the same on the whole field of view for a given source-to-detector distance. An image restoration process allowed the improvement of spatial resolution from 3.2 to 2.6 mm. Moving a medium-sensitivity collimator allows us both to obtain good sensitivity with a high-resolution gamma detector and to restore high resolution in radioisotopic imaging. For thyroid diagnosis, this will increase the ability of cold nodule detection with low-energy isotopes. Furthermore, images obtained with /sup 131/I will be free of artifacts due to the septa size of medium-energy collimators.