Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Reexamination Certificate
1999-01-11
2001-06-12
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
Reexamination Certificate
active
06246057
ABSTRACT:
FIELD OF THE INVENTION
This invention falls in the field of nuclear medicine that uses scintigraphic cameras, also called gamma cameras, to obtain very detailed images of a patient's organs. Scintigraphy is the clinical data obtained by observing the distribution of a radioactive substance administered to the patient. The observation of this distribution (utilizing an Anger camera) results in the creation of images of the organ being examined.
BACKGROUND OF THE INVENTION
On dual detector cameras, the acquisition can take place either by tomography with perpendicular or parallel detectors that revolve around the organ, or by translation of the detectors facing each other on either side of the patient's body.
The non uniformity of the attenuation due to variable attenuation coefficients, depending on the type of tissue (bone, breast, lung, muscle, . . . ) causes artifacts which alter the precision of the emission images. The conventional attenuation correction procedures are inappropriate because they presume a constant distribution of the attenuation coefficients. An acquisition by transmission, using an external radioactive source, allows for the calculation of a table of attenuation coefficients that are specific to the patient, a table that will be used to correct this emission of images. This process allows for a Transmission Attenuation Correction, better known as “TAC”.
The correction system used to implement this TAC process consists of a radioactive source that emits gamma rays of known energy that sweep the active surface of the detector through the patient's body. The attenuation of energy caused by the patient's body is measured in this detector. The result of this measuring, appropriately treated, provides data that allows for the correction of the attenuation of photon energy emitted by the irradiated organ and therefore, for the acquisition of a more precise image.
The TAC system radioactive source is a linear rod whose radiation is transmitted in the direction of the detector through a collimator; it moves parallel to itself in a plane that is parallel to the detector's surface of detection.
Over time, this radioactive source progressively loses its radiation power whereas the energy received by the detector must remain approximately constant in time. Therefore, between the source and the collimator, we have an attenuator that belongs to a series whose efficiencies are decreasing. On the other hand, when the source no longer emits rays, it must be replaced.
As it now stands in the technique, the replacement of the attenuator and of the source are delicate operations that must be performed on site with great care by specialized personnel in order not to be subject to a prolonged and therefore dangerous radiation.
The current technique represented in particular in the U.S. Pat. Nos. 5,596,197 and 5,598,003 which refer to the sweeping direction in very specific conditions does not address the problems brought up.
BRIEF DESCRIPTION OF THE INVENTION
This invention solves these inconveniences by securing the exchange of the source and the attenuators of the TAC system.
As set forth in the invention, the Transmission Attenuation Correction for scintigraphic cameras consists of a carriage that is mobile in translation, where this carriage is fitted with an articulation for a support that can fold into a box or unfold perpendicularly, characterized by the fact that it holds a removable cassette that contains a radioactive source.
In the cassette, the radioactive source is inserted in the longitudinal groove of a cylindrical rod made of material that isolates gamma rays; by rotating the rod, this groove can be placed either in front of the isolating wall, or in front of the radiation's outlet channel.
The rotation of the rod is controlled by a motorized mechanism that consists of a driving pinion integral with the motor and a driven pinion linked to the rod by a sliding assembly.
The two pinions are held apart by a first spring and the meshing, caused by a manual pulse, is maintained by an electrical part, such as an electromagnet, so that in the absence of current, the pinions are inevitably separated.
A second spring brings the rod back into the source isolation position.
When the cassette is mounted on its support, a mechanical system that immobilizes the rod in the isolation position is activated in order to authorize its rotation.
The extremity of the rod is shaped like a key that can only enter, or exit, the hole in the support if said rod is in the isolation position in the cassette.
On the double head open stand scintographic cameras, the TAC devices are included in boxes that are attached to the detectors; when unfolded, each TAC device acts on the detector facing it.
The rod consists of sectors with different attenuation coefficients that surround the source and create a cylinder that is rimmed or inserted in a tube made of material that is transparent to radiation.
As a variation, the rod that contains the source is separated into segments made of an opaque material spaced by connection bars with different attenuation coefficients.
The characteristics and advantages of the invention will appear when reading the description that follows of a concrete and non restrictive example while referring to the attached drawings where:
REFERENCES:
patent: 5576545 (1996-11-01), Stoub et al.
patent: 5596197 (1997-01-01), Jones et al.
patent: 5598003 (1997-01-01), Jones et al.
patent: 5834780 (1998-11-01), Morgan et al.
patent: 0 654 682 (1995-05-01), None
Geay Jean-Claude
Nguyen Trung
Roche François
Treillet Jean
Connolly Bove & Lodge & Hutz LLP
Hannaher Constantine
SMV International
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