Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-10-25
2003-09-30
Paik, Sang (Department: 3742)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06628983
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the art of nuclear medicine. It finds particular application to nuclear imaging techniques and apparatuses employing emission and transmission tomography. Although the present invention is illustrated and described herein primarily in reference to positron emission tomography (PET) and single photon emission computed tomography (SPECT), it will be appreciated that the present invention is also amenable to other noninvasive investigation techniques and other diagnostic modes in which a subject or patient is examined with transmitted radiation.
Diagnostic nuclear imaging is used to study a radionuclide distribution in a subject. Typically, one or more radiopharmaceuticals or radioisotopes are injected into a subject. The radiopharmaceuticals are commonly injected into the subject's blood stream for imaging the circulatory system or for imaging specific organs which absorb the injected radiopharmaceuticals. Gamma or scintillation camera detector heads are placed adjacent to a surface of the subject to monitor and record emitted radiation. For SPECT imaging, collimators are typically placed on the detector heads. For PET imaging, a coincidence detector detects concurrent receipt of a radiation event on two oppositely disposed heads. Often, the detector heads are rotated or indexed around the subject to monitor the emitted radiation from a plurality of directions. The monitored radiation data from the multiplicity of directions is reconstructed into a three-dimensional image representation of the radiopharmaceutical distribution within the subject. Such images typically provide functional and metabolic information.
Positron emission tomography (PET) is a branch of nuclear medicine in which a positron-emitting radiopharmaceutical such as
18
F-fluorodeoxyglucose (FDG) is introduced into the body of a subject. Each emitted positron reacts with an electron in what is known as an annihilation event, thereby generating a pair of 511 keV gamma rays. The gamma rays are emitted in directions approximately 180° apart, i.e., in opposite directions.
A pair of detectors registers the position and energy of the respective gamma rays, thereby providing information as to the position of the annihilation event and hence the positron source. Because the gamma rays travel in opposite directions, the positron annihilation is said to have occurred along a line of coincidence connecting the detected gamma rays. A number of such events are collected and used to reconstruct a clinically useful image.
The energy spectrum for clinical positron annihilation imaging is typically characterized by a photopeak at 511 keV. Similarly, Compton scattered radiation contributes to counts having energies ranging as high as the Compton edge. In coincidence imaging, a dual energy window detection scheme is sometimes used. A window around the photopeak and a window in the vicinity of the Compton region are identified. A coincidence event is counted if both detectors detect temporally simultaneous events within the photopeak window, or if one detector observes an event in the photopeak window while the other simultaneously detects an event in the Compton window. In each case, a memory location is incremented to note the event and its location such that the respective events are weighted equally. Events in which both detectors observe Compton events are discarded.
Single photon emission computed tomography (SPECT) is another nuclear imaging technique used to study the radionuclide distribution in subjects. Typically, one or more radiopharmaceuticals are injected into a subject. The radiopharmaceuticals are commonly injected into the subject's blood stream for imaging the circulatory system or for imaging specific organs which absorb the injected radiopharmaceuticals. Gamma or scintillation camera heads are placed closely adjacent to a surface of the subject to monitor and record emitted radiation. In SPECT imaging, the detector head or heads are rotated or indexed around the subject to monitor the emitted radiation from a plurality of directions. The monitored radiation emission data from the multiplicity of directions is reconstructed into a three-dimensional image representation of the radiopharmaceutical distribution within the subject.
One of the problems with nuclear imaging techniques such as PET and SPECT is that photon absorption and scatter by portions of the subject between the emitting radionuclide and the camera head(s) distort the resultant image. One solution for compensating for photon attenuation is to assume uniform photon attenuation throughout the subject. That is, the subject is assumed to be completely homogenous in terms of radiation attenuation, with no distinction made for bone, soft tissue, lung, etc. This enables attenuation estimates to be made based on the surface contour of the subject. However, human subjects do not cause uniform radiation attenuation, especially in the chest.
In order to obtain more accurate radiation attenuation measurements, a direct measurement is made using transmission computed tomography techniques. In this technique, radiation is projected from a radiation source through the subject. Radiation that is not attenuated is received by detectors at the opposite side. The source and detectors are rotated to collect transmission data concurrently or sequentially with the emission data through a multiplicity of angles. This transmission data is reconstructed into a transmission image representation using conventional tomography algorithms. The radiation attenuation properties of the subject from the transmission image representation are used to correct for radiation attenuation in the emission data.
It is desirable to precisely locate the emission images relative to other anatomical details. In so doing, the diagnostic accuracy of the nuclear medicine image is increased. This is particularly so in the area of oncology, in which precise localization of nuclear medicine images aids in surgical and/or radiotherapeutic planning and for assessment of lesion progression and treatment effectiveness.
While transmission data has largely been successful in determining attenuation correction factors for the correction of the emission image data, the transmission image data itself has generally been of less than ideal resolution. The coarseness of the images could create uncertainties when localizing the emission image with respect to anatomical features.
One method of localizing the functional information is to merge the emission image representation with an image representation generated with another imaging modality that provides anatomical or structural details, such as x-ray computed tomography (CT), magnetic resonance (MR), or ultrasound image representations. When fusing images of different modalities, image registration of the two images is required to correct for any differences in geometric relations between the two images. Any misalignment of the two images impairs the diagnostic value of the fused images. Image registration can be performed by a number of techniques, such as using discrete extrinsic or intrinsic landmarks known to bear a constant relationship to the subject's anatomy during the two studies, and using three-dimensional surface identification algorithms to construct numerical models of the external surface of the images. Such techniques allow the images to be aligned and oriented with respect to each other by translating, rotating, and descaling one or both of the image representations to allow the images to be superimposed or fused. However, given the lack of structural detail in nuclear medicine emission images and the low resolution of typical transmission images, significant uncertainties can remain when combining a nuclear medicine image with an image from a different modality. Moreover, inconvenience, cost, and multiple scans are generally required when obtaining scans from multiple modalities.
Imaging devices which combine a CT-like device with a gamma camera are known
Fay Sharpe Fagan Minnich & McKee LLP
Koninklijke Philips Electronics , N.V.
Paik Sang
LandOfFree
Nuclear imaging systems and methods with feature-enhanced... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nuclear imaging systems and methods with feature-enhanced..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nuclear imaging systems and methods with feature-enhanced... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3109060