X-ray or gamma ray systems or devices – Source support – Including movable source
Reexamination Certificate
2002-02-01
2003-12-09
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Source support
Including movable source
C378S193000
Reexamination Certificate
active
06659642
ABSTRACT:
BACKGROUND OF INVENTION
At least one of the embodiments of the present invention generally relates to improvements in a medical x-ray imaging system, and more particularly relates to an improved C-arm of an x-ray imaging system.
X-ray imaging systems typically include an x-ray source, a detector, and a positioning arm, such as a C-arm, supporting the x-ray source and the detector. In operation, an imaging table, on which a patient is positioned, is located between the x-ray source and the detector. The x-ray source typically emits a conical beam of radiation, such as x-rays, toward the patient. The conical beam has a theoretical central beam. The radiation typically passes through the patient positioned on the imaging table and impinges on the detector. As the radiation passes through the patient, anatomical structures of different densities inside the patient cause intensity variances in the radiation received at the detector. The detector then translates the radiation variances into an image which may be employed for clinical evaluations. Typically, the x-ray source is directly mounted to a distal end of the C-arm while the x-ray detector is mounted to another distal end of the C-arm. The x-ray source is positioned such that emitted x-rays are received by the x-ray detector.
The C-arm is typically supported by a support structure. The support structure may be mobile or fixed. The C-arm is mounted to the support structure through a bearing assembly. The bearing assembly allows the C-arm to rotate relative to the support structure. Therefore, anatomical structures of a patient positioned between the x-ray source and the x-ray detector may be imaged from different angles and perspectives. That is, the x-ray source and the x-ray detector rotate around the patient thereby imaging anatomical structures of the patient from various angles and perspectives.
Typically, C-arms are circular, or semi-circular. That is, the radii of a C-arm are the same through every angle of rotation. A circular C-arm has a true center of rotation. However, in mobile C-arm systems, the x-ray source and the x-ray detector typically are offset from the center of rotation. The x-ray source and the x-ray detector are offset in order to balance the C-arm system. That is, the x-ray source and the x-ray detector are positioned to mechanically balance out the C-arm. However, because the x-ray source and the x-ray detector are offset from the center of rotation, the central beam is also offset from the center of rotation.
Typically, when the C-arm is rotated through an arc of 180 degrees, the central beam shifts due to the offset positioning of the x-ray source and the x-ray detector. That is, when the central beam is positioned such that a target anatomical structure is within an imaging area of the conical beam, the target anatomical structure typically is not within the imaging area throughout the entire 180 degrees of C-arm rotation. That is, the conical beam is not isocentric throughout the rotation of the C-arm. Rather, because of the offset positioning, the anatomical structure does not remain within the imaging area of the conical beam.
Isocentric C-arms have been developed. For example, some systems position the x-ray source and the x-ray detector in line with the center of rotation of the circular C-arm. In order to balance the C-arm, the C-arm structure is extended past the x-ray source and the x-ray detector. The extended portions of the C-arm structure are typically heavily weighted. The C-arm is extended to counterbalance the weight of the C-arm. When the extended C-arm is rotated, however, the extended portions typically encroach upon the space of a treating physician. That is, if the C-arm is rotated in one direction, one extended portion may hit the treating physician in the head. If, however, the C-arm is rotated in the opposite direction, the other extended portion may hit the treating physician in the shins or knees. Overall, the extended, counterbalancing portions typically are bulky and cumbersome. Further, the extended portions may hinder access to the patient positioned within the C-arm. Additionally, the extended portions increase the weight of the C-arm. The increased weight of a mobile C-arm system including extended portions typically makes movement of the mobile system more difficult than if the extended portions were not included.
Instead of extending portions of the C-arm, isocentric C-arm motion may also be achieved through the use of powerful motors. That is, the x-ray source and the x-ray detector may be positioned in line with the center of rotation of the circular C-arm. While many fixed systems include expensive, powerful motors, motors may also be used with mobile systems. Powerful motors counteract the mechanical imbalance of the C-arm. The inclusion of powerful motors on mobile systems, however, increases the overall weight of the system. As stated above, increasing the weight of mobile systems decreases the ease of mobility of the system. Further, the motors are expensive.
Typically isocentric circular C-arm systems exhibit an additional limitation. While typical isocentric systems maintain an anatomical structure within an isocentric area, or imaging area, throughout 180 degrees of rotation, the distance between an x-ray detector and a patient's body in many isocentric systems fluctuates. During x-ray imaging, a patient typically lies on his back or front side. Typical systems rotate through a semi-circular arc around the patient. Therefore, because human beings typically are not round, the x-ray detector typically is closer to the patient's skin at some positions, and further away at other positions.
For example, an x-ray detector typically is closer to a patient's skin when the patient is being imaged from the side as opposed to the top or bottom. When the x-ray detector is further away from the patient's skin, the resulting images typically are of lesser quality than when the x-ray detector is closer to the patient. As the beam of a circular isocentric C-arm is rotated around a patient, the circular area of the conical beam, and therefore the magnification of the target anatomy at the isocenter, typically remain relatively constant. Because the isocenter is circular, however, an air gap results that increases between the patient's skin and the detector as the system is rotated. In some rotated positions, the air gap creates x-ray scatter. Air scatter, in turn, reduces image contrast. The further the x-ray source and x-ray detector are from the patient, the greater the air gap is between the patient's skin and the x-ray source and detector. As the air gap increases, image contrast and magnitude of magnification decrease. That is, the greater the cross-sectional area of the conical beam, the smaller the magnification of the resulting image.
Further, the patient typically is exposed to skin intensity radiation of higher magnitude when the conical beam entering the patient is more localized. Allowing the air gap to increase results in the x-ray source being closer to the patient's skin than is necessary. The close proximity of the x-ray source causes the x-rays to enter the patient through a smaller, more localized area, thereby increasing x-ray dose to the irradiated skin. Additionally, the presence of more air between the patient and the x-ray detector causes x-ray scatter and the resulting loss of image contrast.
Some systems alleviate the problems caused by an increasing air gap and less than optimal anatomical image magnification through the use of variable source-to-image distance (SID) x-ray detectors. That is, the face of the x-ray detector moves independently of the x-ray source toward and away from the patient depending on the position of the x-ray detector through the arc of rotation. Typically, variable SID is achieved through the use of an additional motor, thereby adding weight and complexity to the system. Further, the addition of the motor, and the independent movement of the x-ray detector through the rotation of the C-a
Church Craig E.
Dellapenna Michael A.
GE Medical Systems Global Technology Company LLC
McAndrews Held & Malloy Ltd.
Thomas Courtney
LandOfFree
Non-circular C-arm for fluoroscopic imaging equipment does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Non-circular C-arm for fluoroscopic imaging equipment, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Non-circular C-arm for fluoroscopic imaging equipment will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3152956