X-ray or gamma ray systems or devices – Beam control
Reexamination Certificate
1999-07-19
2001-11-27
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
C378S154000, C378S146000, C250S363040, C250S363100
Reexamination Certificate
active
06324258
ABSTRACT:
This invention generally relates to the production of tomographic images of an object, normally a person, according to the preamble of claim
1
. Since the present invention is of importance in particular for tomographic images obtained by means of gamma radiation, the invention will hereinafter be discussed in particular for this type of radiation. It is noted with emphasis that the principle of the invention is also applicable to the production of images using other kinds of radiation.
In the following, a single recording will be designated by the term “projecton image” (comparable to a photograph). Further, the term “tomography image” or “sectional image” will be used for a reconstructed image of a section of the object, obtained by combining several projection images from different directions.
In principle, tomographic images can be obtained in two different ways. In the first place, it is possible to collect radiation coming from within the object itself, with a detector sensitive to such radiation (camera); such a technique is designated as emission tomography (for instance, SPECT: Single Photon Emission Computed Tomography), and the image obtained is designated as emission projection image. It can be stated in general that an emission projection image provides information about the distribution of radiation-generating matter in the object. When several emission projection images are made, in mutually different directions, it is possible to compute (reconstruct) from the obtained data the concentration distribution of that radiation-generating matter in the object; this is designated as “emission tomography image”.
In the second place, it is possible to generate radiation with a radiation source and to direct it towards the object, whereby the radiation that passes through the object is detected with the camera: such a technique is designated as transmission tomography, and the image obtained is designated as transmission projection image. With this technique, therefore, the object is located between the radiation source and the camera. It can be stated in general that a transmission image provides information about the distribution of radiation-attenuating or radiation-absorbing matter in the object. With this technique too, it is possible to combine different transmission projection images to provide a transmission tomography image.
For different reasons it is desired to make emission images and transmission images simultaneously. By this is meant that a camera is simultaneously irradiated with emission radiation coming from the object itself, and with transmission radiation which has passed through the object, while the radiation energy from the external source can be chosen to be different from the radiation energy which is generated in the object itself. An important advantage of such combined recordings is that the transmission tomogram can be used to correct the emission tomogram for attenuation of the radiation in the object.
It is desired to enable discrimination between direct radiation and scattered radiation, so as to be able to obtain better position information. To that end, use is made of a collimator placed before the camera, in combination with a predetermined spatial geometry of the radiation source. The article “Attenuation Compensation for Cardiac Single-Photon Emission Computed Tomography Imaging: Part 1. Impact of Attenuation and Methods of Estimating Attenuation Maps” by M. A. King et al in Journal of Nuclear Cardiology, volume 2, no. 6, November 1995, pp. 513-524, describes examples of this.
Furthermore, the article “A Scanning Line Source for Simultaneous Emission and Transmission Measurements in SPECT” by P. Tan et al in The Journal of Nuclear Medicine, vol. 34, No. 10, October 1993, p. 1752 discloses an apparatus according to the preamble of claim
1
. In this article an arrangement is disclosed wherein the line shaped irradiation pattern is moved over the camera. The object of the present invention is to provide a device which on the one hand provides an improved separation between transmission radiation and emission radiation and on the other hand provides an improved image strength in the transmission image, so that the images provided have an improved signal-to-noise ratio over the prior art.
It is a general object of the present invention to provide a tomography device which enables obtaining an emission and a transmission image simultaneously, whereby a good separation between emission and transmission is achieved.
It is a further object of the present invention to provide a tomography device whereby transmission and emission images can be obtained simultaneously in an efficient manner.
It is a still further object of the present invention to provide a tomography device whereby the capacity of the camera is utilized in an efficient manner. These objects are met by an apparatus as defined further in the characterizing portion of claim
1
.
EP-A-0 526 970 and U.S. Pat. No. 5,289,008 both disclose an apparatus for making transmission recording of an object during radiation. However, the irradiation pattern is not moved over the camera as required by the present invention.
REFERENCES:
patent: 2770719 (1956-11-01), Simjian
patent: 4490835 (1984-12-01), Wons
patent: 5040202 (1991-08-01), Scheid
patent: 5062129 (1991-10-01), Mulder
patent: 5448611 (1995-09-01), Kerjean
patent: 0 526 970 A2 (1992-06-01), None
patent: WO 95/14244 (1995-05-01), None
Phys. Med. Biol., 1992, vol. 37, No. 3, pp. 507-534, “Review of Convergent beam tomography in single photon emission computed tomography”.
Patrick Tan, Dale L. Bailey, Steven R. Meikle, Stefan Eberl, Rober R. Fulton and Brian F. Hutton,The Journal of Nuclear Medicine, vol. 34, No. 10, Oct. 1993, “A Scanning Line Source for Simultaneous Emission and Transmission Measurements in SPECT”.
Michael A. King, PhD, Benjamin M. W. Tsui, PhD, and Tin-Su Pan, PhD,Journal of Nuclear Cardiology, vol. 2, No. 6; 513-524 Nov./Dec. 1995 and vol. 3, No. 1; 55-63 Jan./Feb. 1996, “Attenuation compensation for cardiac singe-photon emission computed tomographic imaging: Part 1. Impact of Attenuation and Methods of Estimating Attenuation Maps”.
Academisch Ziekenhuis Utrecht
Kinney & Lange , P.A.
Porta David P.
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