Spect system with reduced radius detectors

Details Spect system with reduced radius detectors Spect system with reduced radius detectors

1998-07-31

2001-02-27

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

With or including a luminophor

C250S363080, C378S013000

Reexamination Certificate

active

06194725

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to single photon emission computed tomography (SPECT) and more particularly to a system or camera/gantry configuration which reduces the degree of patent support table motion required to position a patient adjacent to gamma cameras for imaging when cameras are positioned such that their axis essentially form an L.
SPECT examinations are carried out by injecting a radiopharmaceutical into the body of a patient to be examined. A radiopharmaceutical is a substance labeled with a radioisotope which emits photons at one or more energy levels. By choosing a compound which accumulates in an organ to be imaged, radiopharmaceutical concentration, and hence radioisotope concentration, can be substantially limited to an organ of interest. The organ to be imaged will be referred to hereinafter as an organ of interest and an energy range which approximates the known energy level will be referred to as the energy range.
While moving through a patient's blood stream the radiopharmaceutical becomes concentrated in the organ of interest. By measuring the number of photons emitted from the organ of interest which are within the marker range, organ characteristics, including irregularities, can be identified.
To measure the number of emitted photons planar gamma cameras are used. After a radiopharmaceutical has become concentrated within an organ of interest, a camera is positioned at an imaging angle with respect to the organ of interest such that the organ is positioned within the camera's field of view FOV. The camera is designed to detect photons traveling along preferred paths within the FOV.
A gamma camera consists of a collimator, a scintillation crystal, a plurality of photo multiplier tubes (PMTs) and a camera processor. The collimator typically includes a rectangular lead block having a width dimension and a length dimension which together define the FOV. Holes in the collimator block define the preferred photon paths. The preferred paths are unidirectional and perpendicular to the front face of the collimator. The collimator blocks emissions toward the crystal along non-preferred paths.
The scintillation crystal is positioned adjacent the collimator on a side opposite the FOV and has an impact surface and an oppositely facing emitter surface. The impact surface defines a two dimensional imaging area A having a length L and a width W. Photons which pass through the collimator are absorbed by the scintillation crystal. The crystal converts gamma photons to light photons each time a gamma photon is absorbed. The amount of light emitted depends on the absorbed photon's energy level.
The PMTs typically include between 37 and 91 PMTs which are arranged in a two dimensional array which is positioned adjacent the emitter surface. Light emitted by the crystal is detected by the PMTs which are in the area adjacent the emitter point. Each PMT which detects light generates an analog intensity signal. The intensity signal is proportional to the amount of light detected. When a single photon is absorbed by the crystal, the emitted light is typically absorbed by several different PMTs such that several PMTs generate intensity signals simultaneously. For the purposes of this explanation all intensity signals caused by a single photon will be collectively referred to as a signal set.
The processor receives each signal set and performs a plurality of calculations on each signal set to determine two characteristics of the corresponding photon. The processor combines the intensity signals of each signal set to identify the energy level of a corresponding photon. Photons having energies within the energy range will be referred to as events. Only signals corresponding to events are used for imaging. The processor also performs a series of calculations in an effort to determine precisely where in the crystal area A an event occurred. The processor uses these locations to create an image of the organ of interest which corresponds to the camera imaging angle.
To create a three dimensional “tomographic” image of the organ of interest, a gamma camera can be used to generate a plurality of images from different imaging angles. To this end, the camera is often mounted to an annular gantry and positioned parallel to, and at an imaging angle about, a rotation axis which passes through the organ of interest. The rotation angle is incremented between views so that the plurality of images are generated. The plurality of images are then used to construct pictures of transaxial slices of the torso section using algorithms and methods that are well known to those skilled in the tomographic arts.
To reduce the time required for generating a plurality of images many SPECT systems are equipped with two or more cameras which can be arranged at different angles with respect to the rotation axis. While many different two camera configurations can be formed, there are two configurations which are most widely used, an “H” configuration or mode and an “L” configuration or mode.
Referring to
FIG. 1
, in the H mode two cameras
10
and
12
oppose each other such that camera axis
11
and
13
are aligned and intersect an rotation axis
15
. The H mode is used to image patients efficiently by acquiring two opposing views at the same time. For example, the H mode can be used to acquire two fixed views such as anterior and posterior views simultaneously. In the alternative, the H mode can be used to acquire a series of views for SPECT over 360° by acquiring images from both detectors over a 180° rotation.
Referring to
FIG. 2
, in the L mode the two cameras
10
,
12
are positioned such that their camera axis
11
,
13
intersect at rotation axis
15
forming approximately a 90 degree angle &ggr; hence the term “L mode”. In one common L mode the axis form a 90 degree angle &ggr; while in another the axis form an essentially 101 degree angle &ggr;. For the purposes of this explanation, although the invention can be used with any L mode configuration, in the interest of simplification, the invention will be described in the context of a 90 degree L mode unless indicated otherwise.
The L mode is typically used to image the heart. During heart imaging data is typically only collected over 180 degrees of rotation about the left side of the chest. To collect 180 degrees of data using cameras configured in the L mode, the cameras are rotated about the patient through 90 degrees, each camera separately collecting 90 degrees of imaging data for a total of 180 degrees.
Because both the L and the H modes are advantageous many SPECT systems are equipped so that two cameras can be positioned in either the H or the L mode. To this end at least one of the two system cameras is mounted such that it can be independently rotated with respect to the other system camera about the gantry, the independently moveable camera lockable in either the L or the H modes. Systems in which an operator can put the detectors in either L mode or H mode are known within the industry as “variable geometry SPECT cameras”.
Because SPECT systems are expensive it is important that each system be designed such that it can be used to image virtually all patients independent of patient size. Generally, the largest section of most patients is through their chest or shoulders and is typically between 200 and 560 mm. To accommodate sections as large as 560 mm most system cameras have a field of view which is at least 540 mm. In this case, a detector enclosure or “tub” is typically over 600 mm wide.
It is well known in the industry that SPECT image quality can be improved by positioning a gamma camera as close as possible to an organ to be imaged during data gathering. To this end most SPECT systems provide some mechanism for changing the position of a patient support table relative to a gamma camera to thereby change the position of a patent on the table relative to the c

Affiliated with

Also associated with

Rating

Spect system with reduced radius detectors does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Spect system with reduced radius detectors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spect system with reduced radius detectors will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2587129