Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-07-17
2001-06-19
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C324S309000
Reexamination Certificate
active
06249694
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention disclosed and claimed herein generally pertains to magnetic resonance (MR) angiography, i.e., to MR imaging of an artery or like vessel carrying blood or other fluid. More particularly, the invention pertains to a method of the above type wherein MR data are acquired at each of a number of scan locations or stations, which are spaced along a vessel of comparatively great length. Even more particularly, the invention pertains to a method of the above type wherein an amount of contrast agent, or bolus, moves along the vessel or other conduit, from station-to-station, and measures are taken to ensure that MR data is acquired at a particular station only or substantially when the bolus is located there.
It is now a well known practice in MR angiography to insert a volume of contrast agent, such as gadolinium chelate, into blood flowing along a vessel. The volume or mass of contrast agent is referred to as a bolus, and has the effect of shortening the T
1
time of the blood. Thus, an MR image of the blood, acquired by a fast gradient echo or like technique, will show up very well with respect to adjacent stationary tissue of the vessel structure.
It is also well known that certain clinical assessments require imaging a vascular territory of comparatively great length. Using MR for these evaluations, therefore, necessitates the acquisition of MR data over several stations or scan locations, which are located at intervals along the vessel path of flow. To acquire data at a particular station, the patient is selectively positioned with respect to an MR scanner, typically by movement of a table supporting the patient. Data are then acquired from a series of slices taken through a region or section of the patient, which comprises the particular scan location or station. Thereafter, the patient is shifted, relative to the scanner, so that data may be acquired from another section of the patient, comprising another scan location or station. MR angiography employing this procedure in conjunction with an injection of a contrast bolus may be referred to as bolus chasing peripheral MR angiography.
At present, when a contrast agent is used in connection with a peripheral MR angiography exam, the first scan station is selected to be the section of the patient, along a vessel of interest, at which the bolus arrives first. When the scan at the first station is completed, the acquisition normally moves to the next scan station. However, the most appropriate time to move to the next station is not precisely known. For example, in the case of slow blood flow, the distal vasculature at the next scan station may not have had adequate time to fill with contrast material. On the other hand, if flow rate is greater than anticipated, the contrast agent may tend to move into stationary tissue adjacent to the next scan station, before data acquisition commences. In either case, contrast between moving fluid and stationary tissue may be significantly reduced at the next scan station. Moreover, undesirable effects, resulting either from flow rate which is too slow or too great, may tend to become progressively worse as imaging proceeds to subsequent scan stations, and as the total number of scan stations increases.
SUMMARY OF THE INVENTION
The invention is generally directed to a method of peripheral MR angiography for imaging structure associated with a vessel, such as a comparatively long artery within a patient, wherein MR data are to be acquired at each of a plurality of scan stations positioned along the vessel. The method includes the step of inserting a contrast agent into blood via intravenous injection, to provide a bolus which flows to first and second stations, in succession. The method further comprises acquiring an initial portion of a first MR data set associated with the first station, and monitoring the second station to determine whether the bolus has arrived there. If it is determined from the monitoring step that the bolus has in fact arrived at the second station, at least some of the MR data of a second data set associated therewith are then acquired. However, if it is determined that the bolus has not yet arrived at the second station, acquisition of further data at the first station is continued.
In a preferred embodiment of the invention, the portion of MR data initially acquired at the first scan location comprises central k-space data, and the vessel comprises an artery residing in an imaging subject. Moreover, an MR scanning device and a table supporting the imaging subject are associated with the MR method, the table being operated to selectively position the imaging subject with respect to the scanning device, in order to acquire the MR data sets respectively associated with the first and second scan stations.
In a useful embodiment of the invention, the monitoring step comprises placing an NMR monitoring means which is responsive to the contrast agent in closely spaced relationship with the vessel and proximal to the second station, and setting the monitoring means to generate a signal when the amount of contrast agent at the second station exceeds a specified threshold.
In another useful embodiment of the invention, the monitoring step comprises rapidly acquiring MR data from a region which is proximal to the vessel and also to the second scan station, and then rapidly re-constructing an image from the rapidly acquired data. An operator may then readily determine the amount of contrast agent at the second scan station simply by visual inspection of the rapidly acquired image.
OBJECTS OF THE INVENTION
An object of the invention is to provide a more optimum method for peripheral MR angiography, which is directed to an artery or other vessel of substantial length.
Another object is to provide a method of the above type, wherein data acquisition at each scan station, in a succession of scan stations spaced along the vessel, is substantially synchronized in time with arrival at the scan station of a bolus of contrast agent.
Another object is to provide a method of the above type which tracks arrival of the bolus at successive scan station along the vessel path of flow.
Another object is to provide a method of the above type, wherein an assessment is made as to whether the bolus has or has not moved from the current scan station to a subsequent scan station, and data acquisition either shifts to the subsequent station, or continues at the current station, in accordance with the assessment.
REFERENCES:
patent: 5417213 (1995-05-01), Prince
patent: 5422576 (1995-06-01), Kao et al.
patent: 5590654 (1997-01-01), Prince
patent: 5928148 (1999-07-01), Wang et al.
Bernstein Matthew A.
Foo Thomas K. F.
Ho Vincent B.
Cabou Christian G.
General Electric Company
Imam Ali M.
Lateef Marvin M.
Price Phyllis Y.
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