Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2001-04-11
2003-03-18
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S309000
Reexamination Certificate
active
06534981
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an MR imaging method and an MRI (Magnetic Resonance Imaging) apparatus, and more particularly to an MR imaging method and an MRI apparatus capable of improving picture quality without increasing the number of times of data collection and restraining artifacts resulting from differences in noise structure between parts differing in the number of times of addition.
In an MR imaging method, it is usual to configure k spaces out of views from the first view through a Vth view which differ in the quantity of phase encoding, repeatedly collect data by Xn times of addition in an nth (n=1~V) view, and use data An resulting from arithmetic averaging as the data of the nth view for image reconfiguration.
According to the related art, the number of times of addition Xn may be constant all the time as illustrated in
FIG. 1
, varied linearly to become greater as the absolute value of the quantity of phase encoding decreases as illustrated in
FIG. 2
, or varied stepwise to become greater as the absolute value of the quantity of phase encoding decreases as illustrated in FIG.
3
.
By an MR imaging method according to the related art, whereby the number of times of addition Xn is to be kept constant all the time as shown in
FIG. 1
, there is a problem that picture quality is little improved relative to an increase in the overall number of times of data collection because parts where the absolute value of the quantity of phase encoding is large, which little contribute to picture quality, and parts where the absolute value of the quantity of phase encoding is small, which greatly contribute to picture quality, are added the same number of times.
On the other hand, where the number of times of addition is varied to become greater as the absolute value of the quantity of phase encoding decreases as shown in
FIG. 2
or
FIG. 3
, picture quality can be improved without increasing the overall number of times of data collection because parts where the absolute value of the quantity of phase encoding is large, which little contribute to picture quality, are added a fewer number of times and because parts where the absolute value of the quantity of phase encoding is small, which greatly contribute to picture quality, are added a greater number of times.
However, where the variation is linear as shown in
FIG. 2
, there is a problem that the advantage of improving picture quality without increasing the overall number of times of data collection is not sufficient because, although the number of times of addition is maximized in the view where the absolute value of the quantity of phase encoding is “0”, the number of times of addition linearly decreases in a part away from that view even by a minimal distance.
On the other hand, where the variation is stepwise as shown in
FIG. 3
, the advantage of improving picture quality without increasing the overall number of times of data collection is increased because the number of times of addition is maximized not only in the view where the absolute value of the quantity of phase encoding is “0” but also in neighboring views.
However, since the variation in the number of times of addition is not continuous, there is a problem that differences in noise structure between parts differing in the number of times of addition are apt to invite the emergence of artifacts.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an MR imaging method and an MRI apparatus capable of improving picture quality without increasing the overall number of times of data collection and restraining artifacts resulting from differences in noise structure between parts differing in the number of times of addition.
In its first aspect, the invention provides an MR imaging method whereby k spaces are configured out of views from the first view, where the quantity of phase encoding takes on the largest negative (or positive) value, through a Vth view, where the quantity of phase encoding takes on the largest positive (or negative) value, and data An resulting from arithmetic averaging as the data of the nth view resulting from repeated collection of data by Xn times of addition in an nth (n−1~V) view are used for image reconfiguration, characterized in that the number of times of addition Xn is varied to become greater as the absolute value of the quantity of phase encoding decreases and to cause all or part of it to follow either a Hamming function or a Hanning function.
The above-described MR imaging method according to the first aspect can improve picture quality without increasing the overall number of times of data collection because the number of times of addition Xn is varied to become greater as the absolute value of the quantity of phase encoding decreases and to cause all or part of it to follow either a Hamming function or a Hanning function, and accordingly the number of times of addition is increased not only in the view where the absolute value of the quantity of phase encoding is “0” but also in neighboring views. Moreover, since the variation in the number of times of addition is continuous, artifacts resulting from differences in noise structure between parts differing in the number of times of addition can be restrained.
In its second aspect, the invention provides an MR imaging method whereby k spaces are configured out of views from the first view, where the quantity of phase encoding takes on the largest negative (or positive) value, through a Vth view, where the quantity of phase encoding takes on the largest positive (or negative) value, and data An resulting from arithmetic averaging as the data of the nth view resulting from repeated collection of data by Xn times of addition in an nth (n=1~V) view are used for image reconfiguration, characterized in that, where the reference number of times of addition is N:
(1) the number of times of addition from the first view till the (V/8)-th view is (N−N/2);
(2) the number of times of addition from the (V−V/8+1)-th view till the Vth view is (N−N/2);
(3) the number of times of addition from the (V/8+1)-th view till the (V−V/8)-th view is (N+N/2); and
(4) the number of times of addition from the (V/8+1)-th view till the (V−V/8)-th is a value resulting from the subtraction of (N−N/2) from the earlier calculated number of times of addition, multiplication of the balance by either a Hamming function or a Hanning function, addition of (N−N/2) to the product, and discrete processing of the sum.
By the above-described MR imaging method according to the second aspect, the total number of views V is equally divided into eight, and the areas of the two ends of each V/8, where the absolute value of the quantity of phase encoding is the greatest, are reduced in the number of times of addition by ½ of the reference number of times N, because their contributions to picture quality is small. On the other hand, the remaining middle 6V/8 areas are increased in the number of times of addition by ½ of the reference number of times N, because their contributions to picture quality are great, and further to alleviate the non-continuity of the variations of the number of times of addition, the number of times of addition is varied so as to follow either a Hamming function or a Hanning function. This makes possible improvement of picture quality without increasing the overall number of times of data collection because the number of times of addition is increased not only in the view where the absolute value of the quantity of phase encoding is “0” but also in neighboring views. Furthermore, as the variation in the number of times of addition is continuous in the part from the (V/8+1)-th view till the (V−V/8)-th view, whose contributions to picture quality are great, artifacts resulting from differences in noise structure between parts differing in the number of times of addition can be restrained.
In its third aspect, the invention provides an MR i
Kosugi Susumu
Uetake Nozomu
GE Medical Systems Global Technology Company LLC
Kojima Moonray
Lefkowitz Edward
Vargas Dixomara
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