Method and apparatus to automatically determine the relationship between data
A method is provided that determines velocity encoding direction of volumetric image data sets comprising three-directional velocity information (V 0 , V 1 , V 2 ) of a target volume, which involves: a) defining a coordinate system (X, Y, Z); b) determining all the possible arrangements of the three velocity components (V 0 , V 1 , V 2 ) along the three coordinate axes (X, Y, Z); c) determining reference point or points in the target volume either automatically or upon user input; d) determining streamlines for each point for all possible combinations of velocity components as determined in b); and e) considering as velocity encoding direction the arrangement of the three velocity components corresponding to the streamlines having the longest length or a length above a threshold. A corresponding apparatus and computer program are also disclosed.
1. A method for determining velocity encoding direction of volumetric image data sets comprising three-directional velocity information comprising three velocity components (V 0 , V 1 , V 2 ) of a target volume, the method comprising:
a) defining a coordinate system comprising three coordinate axes (X, Y, Z);
b) determining all the possible arrangements of the three velocity components (V 0 , V 1 , V 2 ) along the three coordinate axes (X, Y, Z);
c) determining reference point or points in the target volume either automatically or upon user input;
d) determining streamlines for each reference point for all of the possible arrangements of the three velocity components as determined in b); and
e) considering, as the velocity encoding direction, the arrangement of the three velocity components corresponding to the streamline having the longest length or a length above a threshold.
2. The method of claim 1 , wherein:
flow direction is used to determine the orientation of the velocity encoding direction, such flow direction being user input or automatically calculated.
3. The method of claim 2 , wherein:
the arrangement of the three velocity components is inverted in orientation if the corresponding flow line doesn't follow the flow direction.
4. The method of claim 1 , wherein: at least one reference point is determined by selecting velocity voxels having velocity module above a velocity threshold.
5. The method of claim 1 , wherein:
the volumetric image data sets comprise structural magnitude information and three-directional velocity information of the target volume; and
at least one reference point is being determined by selecting magnitude voxels having magnitude data above a magnitude threshold.
6. The method of claim 1 , wherein:
temporal velocity curves in a point upstream (A) and in a point downstream (B) are used to determine the flow direction, the flow direction being considered downstream if the curve at point upstream (A) is delayed in time with reference to the curve at point downstream (B), and the flow direction being considered upstream if the curve at point downstream (B) is delayed in time with reference to the curve at point upstream (A).
7. The method of claim 6 , wherein:
delay between the curves is searched by identifying the peak in the curves and comparing temporal position among such peaks.
8. The method of claim 6 , wherein:
delay between the curves is searched by calculating a correlation function among the upstream and downstream curves.
9. The method of claim 8 , wherein:
the correlation function is given as:
CC
(
T
)
=
∑
t
=
0
N
phases
-
1
S
A
(
t
)
·
S
B
(
mod
(
t
+
T
,
N
phases
)
)
where S A , S B are, respectively, velocity curves at upstream point A and at downstream point B,
T is a temporal lag between the velocity curves,
t is a phase index identifying a 3D volume within a 4D flow data set, and
N phases is a number of phases corresponding to a number of 3D volumes within the 4D flow data set, the correlation function being calculated at least for three lags comprising −1, 0, +1, wherein upstream condition is determined if
CC (−1)<( C (0)< CC (+1)
or downstream condition is determined if
CC (−1)> CC (0)> CC (+1).
10. The method of claim 1 , further comprising:
performing quantitative flow analysis using the velocity information and/or showing streamlines, vector fields, cross sectional flow or similar parameters.
11. The method of claim 1 , wherein:
the image data sets are sequences of 4D MR flow data sets.
12. The method of claim 1 , wherein:
volumetric image data sets are related to one or more cardiac cycles, streamlines and/or velocity curves being determined in the peak systolic phase of such cycle or cycles.
13. A computer product directly loadable into the memory of a digital computer and comprising a non-transitory computer readable medium storing software code portions for performing the method according to claim 1 when the computer product is run on a computer.
14. An MR apparatus for acquiring volumetric images, the apparatus comprising an acquisition system for obtaining a cine of consecutive image volumes of a target organ, the apparatus further comprising a processing module programmed for performing the method according to claim 1 .
15. The MR apparatus of claim 14 , wherein:
the acquisition system is configured to acquire 4D flow images of a volume containing a vessel; and
the processing module is programmed to determine the direction and orientation of the velocity vectors related to the flow within such vessel with reference to a coordinate system.
16. The MR apparatus of claim 15 , wherein:
the orientation of velocity vectors is determined by the processing module by calculating pulse wave velocity curves in at least two points of the vessel and determining the temporal shift between such curves.