X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2002-05-24
2004-10-19
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
Reexamination Certificate
active
06807249
ABSTRACT:
TECHNICAL FIELD
This invention relates to a procedure for the use of an osteodensitometry system by X-rays.
It will be remembered that osteodensitometry by X-rays is a technique for measuring bone masses and densities starting from radiographic acquisitions made at several energies.
Two energies are usually used, called “high energy” and “low energy” respectively.
Various configurations of a measurement system (X-ray source and detector) could be used to make the measurements.
A distinction is made between three families of systems depending on the type of radiation used:
pencil beam systems that use an X-ray source collimated through a hole and a X-ray monodetector that is also collimated,
fan beam systems that use an X-ray source collimated through a slit and a linear X-ray detector, and
cone beam systems that use a two-dimensional X-ray detector.
More particularly, the invention relates to the implementation of osteodensitometry systems by dual energy cone beam X-radiation.
STATE OF PRIOR ART
The methodological principles of osteodensitometry by dual energy X-radiation and the main technical solutions used at the moment are defined in the following two documents which should be referred to.
[1] Technical principles of Dual Energy X-Ray Absorptiometry”, G. M. Blake and I. Fogelman, Seminars in Nuclear Medicine, Vol XXVII, No. 3, July 1997, pages 210 to 228 and
[2] “The Evaluation of Osteoporosis: Dual Energy X-Ray Absorptiometry and Ultrasound in Clinical Practice”, Second Edition, G. M Blake, H. W Wahner and I. Fogelman, Martin Dunitz Editor, 1999, ISBN 1-85317-472-6.
In particular, refer to chapters 3, 4 and 5 in document [2] that describes principles for the measurement of bone densities using dual energies and known systems for making these measurements.
Commercially available systems for making diagnoses and therapeutic monitoring of osteoporosis in relevant sites (spinal column, hips, forearm, whole body), are of the pencil beam and fan beam type. These systems use collimators that limit parasite radiation, and particularly scattered radiation. Furthermore, the geometry of these acquisition systems limits the geometric deformations related to the size of the detector, which in particular would result from the conicity of the X-ray beam.
Furthermore, these commercially available systems use a scanning system that uses a high energy measurement and a low energy measurement in sequence, for each position of the acquisition system. This guarantees perfect consistency between the parts of the patient that are observed in the two measurements.
Commercially available cone beam systems are only designed to make bone density measurements of peripheral parts such as the fingers, toes, hands, forearms and heels. It is more difficult to implement these cone beam systems than it is to use the other two families of systems.
Scattered radiation generated by interaction between incident X-radiation and the part of the body being studied is important and cannot be ignored. Furthermore, conicity makes the measurement dependent on the position of the part of the body considered in the image field. Furthermore, during the time in which the two-dimensional sensor is being read, the patient may have moved between the high energy measurement and the low energy measurement.
“Cone beam” type systems that are commercially available at the present time are limited to an analysis of the extremities of the human body such as the hands, forearms and heels, because these areas are not very thick and their dimensions are small. Consequently, parasite radiation is limited and positioning may be consolidated, for example by using an attachment system for a forearm or a heel.
On the other hand, if this type of cone beam systems is used for larger parts of the anatomy, and particularly the spinal cord or hips, areas that are used mainly for diagnosis and monitoring of osteoporosis, it would be necessary to take account of parasite phenomena together with the significant conicity of X-radiation and adapt to potential movements of the patient.
Osteodensitometry systems for two-dimensional areas are already known, comprising a source capable of supplying X-ray flux with at least two energies, a converter screen that can transform X-rays into visible light photons, an optical image correction system and a CCD camera, and are described in the following documents which should be referred to:
[3] U.S. Pat. No. 5,150,394, Sep. 22, 1992, “Dual Energy System for Quantitative Radiographic Imaging”, (Andrew Karellas), and
[4] International application published on Nov. 14, 1996, publication No. WO 96/35372, “A System for Quantitative Radiographic Imaging”, (Andrew Karellas).
PRESENTATION OF THE INVENTION
The purpose of this invention is a process for the use of an osteodensitometry system like the system described in documents [3] and [4], this process being capable of increasing the precision and reproducibility of bone density measurements in different parts of the anatomy of a patient, starting from two-dimensional radiographies of these parts of the anatomy acquired at more than one energy.
For this purpose, the invention takes account of the patient's movements between two measurements taken at different energies.
This invention does this using matching between an image acquired at high energy and an image acquired at low energy, and also (preferably) a means of helping the patient to position himself.
Specifically, the purpose of this invention is a process for the use of an osteodensitometry system by X-rays with at least two energies, with a cone beam, this system comprising an X-ray source that can provide a cone beam of X-rays at at least one first energy called the high energy, and at a second energy called the low energy and lower than the first energy, a two dimensional X-ray detector and electronic image processor for processing images supplied by this detector, this process being characterised in that the low energy image is acquired from one part of the anatomy of a patient, and to take account of the patient's movements when making bone density measurements, the high energy image of this part of the anatomy is acquired and these images acquired at low energy and high energy are matched before creating the bone density map for the part of the anatomy.
According to one particular embodiment of the process according to the invention, the following procedure is used to match the images acquired at high and low energies respectively;
sets of contours of bone areas in the part of the anatomy are extracted from these images,
a search is made for an optimum plane transformation in order to match the set of contours for the image acquired at high energy with a set of contours for the image acquired at low energy (or vice versa according to one variant),
this transformation is used to bring the image acquired at high energy into the coordinate system of the image acquired at low energy (or vice versa according to the above variant), and
these two images are combined to determine the bone density measurement map.
According to one preferred embodiment of the process according to the invention, a radioscopy plate, in other words a plate at a low X-ray dose, is made of the part of the patient's anatomy, to help in positioning this area in the system before making the acquisitions at high and low energies.
Preferably, when the patient is examined for the first time, this low X-ray dose plate is used to retroact on the mechanics of the system in order to position the part of the anatomy with respect to the predetermined coordinate system.
Preferably, when the patient is subjected to a check-up, the plate taken at a low X-ray dose will be used to put the part of the anatomy into exactly the same position that it was in during the previous examination.
More explicitly, in the preferred embodiment, a plate with a low X-ray dose and a single energy is made of the part of the patient's anatomy before making acquisitions at low and
Dinten Jean-Marc
Robert-Coutant Christine
Church Craig E.
Commissariat a l'Energie Atomique
Hayes & Soloway P.C.
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