This invention relates to a stereotactic device for use with an imaging apparatus (such as magnetic resonance, CT imaging, and fluoroscopy) useful in the visualization and analysis of organic tissues and bodies, and to research into the cause and symptoms of disease, its diagnosis and treatment.
It is often necessary to sample or test a portion of tissue from humans and other animals, particularly in diagnosing and treating patients with tumors. When a physician establishes that suspicious circumstances exist, a biopsy is typically performed to determine whether the cells are cancerous. A biopsy may be accomplished by an open or percutaneous technique. Open biopsy removes part or all of the potentially cancerous mass. Percutaneous biopsy is usually done with a needle-like instrument and may be either a fine needle aspiration (FNA) or a core biopsy. In FNA biopsy, individual cells or cell clusters are obtained for cytologic examination. In core biopsy, a core or fragment of tissue may be obtained for histologic examination that may be accomplished utilizing a frozen section or paraffin section.
The biopsy done depends a lot on the surrounding circumstances. No single procedure is ideal for all cases.
To properly diagnose a questionable mass, tissue is needed from an organ or lesion within the body. Usually only part of the organ or lesion needs to be examined. The sample extracted must, however, be representative of the organ or lesion as a whole. In the past, surgery was necessary to locate, identify and remove the sample. With the advent of medical imaging equipment such as x-rays, fluoroscopy, ultrasound, and magnetic resonance imaging, it became possible to identify tiny abnormalities embedded deep within the body. Definitive characterization, though, still requires adequate sampling to characterize the histology of the organ or lesion.
As an example, mammography can often identify non-palpable breast abnormalities earlier than they could be diagnosed by physical examination. Although most non-palpable breast abnormalities are benign, some may be malignant. If breast cancer can be diagnosed before it becomes palpable, the subsequent mortality rate can be reduced. However, it is often difficult to determine whether or not pre-palpable breast abnormalities are malignant, as some benign lesions have mammographic features which mimic malignant lesions and some have features which mimic benign lesions.
To reach a definitive diagnosis, tissue from within the breast must be removed and examined under a microscope. Prior to the late 1980's, reaching a definitive tissue diagnosis for non-palpable breast disease required a mammographically-guided localization, either with a wire device, visible dye, or carbon particles, followed by an open, surgical biopsy utilizing one of these methods to guide the surgeon to the non-palpable lesion within the breast.
In one open method of the prior art, a breast is pierced with a localization wire to position the large diameter section of the wire through the center of the lesion, acting as a temporary marker. Tissue is then removed around the area marked by the localization wire. The tissue is prepared and sectioned for evaluation. Such an open surgical breast biopsy can have many drawbacks. Open biopsies can be disfiguring, expensive, and are imperfect. Any of a number of possible errors may lead to an incorrect diagnosis of a lesion. Open surgical biopsies also carry a small mortality risk due to the risk of anesthesia, and a moderate morbidity rate including bleeding, infection, and fracture or migration of the localizing wire. In cases where multiple lesions are present, a surgeon may be reluctant to biopsy each lesion due to the large tissue mass that must be extracted from the breast. The most convenient lesion is typically taken which results in an incomplete diagnosis. Finally, surgical breast biopsies are extremely common. In the United States alone it is estimated that open, surgical breast biopsies are performed on over 500,000 women annually. A less invasive alternative has long been sought.
In 1988, two stereotactic guidance systems were modified to allow the guiding portion of each system to accommodate spring powered devices. In 1989, free-hand ultrasound guidance techniques were developed to guide the stereotactic guidance systems to breast lesions seen by ultrasound. With the introduction of stereotactic and ultrasound guided percutaneous breast biopsies, an alternative to open, surgical breast biopsy was obtained.
In the use of magnetic resonance imaging ("MRI") for breast biopsies, there is a serious problem with the interventional procedures. The problem is that the probe cannot be seen, and therefore its location is unknown at the moment before it is to enter the patient. This is one of the most important reasons why MRI has not been used extensively for interventional procedures.
There are many imaging stereotactic devices currently available. Despite the incredible power of existing imaging technologies however, very few procedures are actually done using the existing technology in a routine clinical setting. There are several reasons for the lack of general acceptance of these devices in existing markets.
Most of the systems are expensive, and normally this expense cannot be justified in terms of usage or benefit for the large capital investment required. Physicians and hospitals are generally not prepared in today's economic climate to make a large investment for a system that may only be used intermittently and may become quickly outdated.
Most existing systems are electronic and use optical and computer interfaces. The majority of these systems do not function in a real-time setting, but rather use special post-processed acquired image information. This information is then used to direct the procedure at a different time and place.
Many of the systems are imager proprietary or dependent, so it is possible that only a few units may be able to use a specific technology. Though these systems claim to have very high real-space accuracy, in reality, they have only limited real-space correlation since there is no live (real-time) imaging to confirm the progress of the procedure.
Most stereotactic units are complex and have multiple components. Some of the systems envelop the patient, for example, through the use of head frames that are bolted directly to the skull. If there is any change in the components of such a rigid system at the time and place of the actual intervention, the previously obtained information that forms the basis for the intervention is no longer valid. These systems also rely on gathering many images to direct the operation, rather than needing only a few. Because of this, the process can be very slow, since a large amount of data needs to be acquired to direct the process.
A number of existing stereotactic systems utilize fiducials that are placed on the patient or the stereotactic frame. These are image-conspicuous markers that are seen in the image space and real-space. Utilizing this information, the virtual reality space depicted on the images is fused with the real-space.
There are a number of devices that attach directly to the scanner, but these are generally cumbersome and have not been used extensively.
There are also a few systems that use very limited vector trajectories (of only a few angles). These are of little value since the limited number of approaches they provide to the target may not be enough to address the complicated anatomy, therapeutic devices and goals of a variety of procedures.
Currently there are a number of rapid CT or MRI data acquisition systems available, but they have the disadvantages of being proprietary and of exposing the patient and operator to increased radiation dosage. These CT systems are analogous to fluoroscopy.
There are a few combined CT and fluoroscopic stereotactic systems. These have the potential to be very versatile, but they are complex proprietary systems. There are also a number of open magnet designs, but these are limited by vendor design. Critical information used to direct the procedure or intervention is based on artifacts from the needle or probe rather than on accurate real-time real-space information. The inherent imaging problems created by these artifacts limit the accuracy of these devices. The image quality of the fast imaging systems in general is not as good as routine imaging techniques.
FIG. 1 is a schematic of an enveloping frame that is used for head stereotactic systems of the prior art. The vertical lines 1 of the box represent the vertical struts, the horizontal lines 2 are crossing members used to define the section plane, the angled lines 3 represent cross-members and the sphere 4 is the target. This frame is bolted or rigidly fixed to the patient and then imaged with many sections. The information gathered is used at a later time and place. Without real-time real-space confirmation during the intervention, there is no absolute confirmation that the previously determined plan is actually being correctly implemented.
FIG. 2 is a schematic of an image obtained from such a fixed frame rigid system. The vertical members 1 are seen at the corners of the square, and the cross-members 3 are used to define the slice location and the target 4. There is no intuitive information that an operator can use to confirm that the information is accurate. Typically, a second system is used to actually execute the procedure at a later time with no real-time real-space confirmation of the previously obtained plan.
FIG. 3 shows an example of an MRI image 5 showing the use of a fixed frame stereotactic unit used for head imaging. The head 6 appears in the center of the image, with the target labeled in the left temporal bone. Also visible are the rods 7 (such as horizontal, vertical and cross-members 1, 2 and 3 shown in FIG. 2) surrounding the skull of the patient as a fixed device. The information is acquired by taking multiple images that must be post-processed.
There are a number of limitations to this type of device. The constituent support tubes are necessarily relatively large (in order to support the static arrangement), and thus cause a certain degree of inherent error in the system. The image shown is a single image that provides no real-time information that an operator might use during an image-monitored procedure. Also, a further error factor arises because the tubes are relatively distant from the target site, and the image itself is not without distortion, making the system distortion sensitive. Also, if the subject is moved, the system cannot be readily realigned.
A number of computer-based systems' disadvantages have been mentioned. The most important of these is that they provide no real-time confirmation at the actual time of intervention. All of these systems use specially acquired post-processed images that assume that the virtual reality of the previously obtained imaging information and the true reality at the time of the actual intervention are identical. These systems are expensive, large, and can only be used in select locations.
There remain problems associated with fast, open, and combined technology systems. All are expensive, vendor specific and, as such, are limited to only a few sites. They are such complicated systems that any minor problem can render them useless, for example, if the batteries on an LED stop working. They have limited real-space accuracy since they have problems with partial volume averaging and other imaging artifacts. Using these systems it may be difficult to track more than one device being used at a time.
Accordingly, the criteria for an improved stereotactic device includes:
1. Accuracy in the form of mm level control and live image confirmation. PA1 2. Ability to make rapid adjustments (preferably by remote control), and the use of a single image. PA1 3.Flexibility in the form of multiple dimension adjustability, and the accommodation of a wide variety of probes. PA1 4. Intuitive use through clear, non-computer-generated interpretation of electronic image information. PA1 5. Simple construction; a device that may be compact enough to fit within the imaging system next to the patient and inexpensively constructed, and may be of disposable materials. PA1 6. Applicability independent of site and imaging device.
Accordingly, there remains a need for relatively inexpensive stereotactic devices that may be used with a wide variety of imaging systems for the performance of varied procedures, and that may be used with any number of invasive devices and techniques.
Although the present invention is presented against the backdrop of certain imaging techniques and devices, and the problems faced in using them, the present invention is not limited to use with these techniques and devices. Rather, the present invention may find application in other health care, research, and industrial applications.