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Fix for bug in ray tracing projection which produced axial artifacts due to flipped theta angle #1231

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Aug 17, 2023
Merged

Fix for bug in ray tracing projection which produced axial artifacts due to flipped theta angle #1231

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729dee2
Added functionality to invert theta value when obtained from LOR that…
Aug 7, 2023
3ebd273
Simplifications of the changes.
Aug 17, 2023
4aa69f2
Updated release notes.
Aug 17, 2023
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3 changes: 3 additions & 0 deletions documentation/release_5.2.htm
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Expand Up @@ -125,6 +125,9 @@ <h3>Minor (?) bug fixes</h3>
<li><code>sample_function_on_regular_grid</code> did not handle offset correctly in all places <br /><a href="https://github.com/UCL/STIR/issues/1178/">issue #1178</a>.
<br /><a href="https://github.com/UCL/STIR/pull/1172/">PR #1172</a>.
</li>
<li>Ray tracing projection for BlocksOnCylindrical scanner geometries contained a bug where some bins were swapped across oblique segments <br /><a href="https://github.com/UCL/STIR/issues/1223/">issue #1223</a>. This sometimes lead to large artifacts in reconstructions.
<br /><a href="https://github.com/UCL/STIR/pull/1231/">PR #1231</a>.
</li>
</ul>

<h3>Documentation changes</h3>
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9 changes: 4 additions & 5 deletions src/include/stir/LORCoordinates.inl
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Expand Up @@ -342,12 +342,11 @@ find_LOR_intersections_with_cylinder(LORAs2Points<coordT1>& intersection_coords,
}
const coordT2 root = static_cast<coordT2>(sqrt(argsqrt));

auto l1 = static_cast<coordT2>((-b + root) / a);
auto l2 = static_cast<coordT2>((-b - root) / a);
auto l1 = static_cast<coordT2>((-b - root) / a);
auto l2 = static_cast<coordT2>((-b + root) / a);

// TODO won't work when coordT1!=coordT2
intersection_coords.p1() = d*l1 + c1;
intersection_coords.p2() = d*l2 + c1;
intersection_coords.p1() = d * l1 + c1;
intersection_coords.p2() = d * l2 + c1;
assert(fabs(square(intersection_coords.p1().x())+square(intersection_coords.p1().y())
- square(radius))
<square(radius)*10.E-5);
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9 changes: 4 additions & 5 deletions src/include/stir/ProjDataInfoGeneric.inl
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Expand Up @@ -80,11 +80,10 @@ ProjDataInfoGeneric::get_t(const Bin& bin) const
float
ProjDataInfoGeneric::get_tantheta(const Bin& bin) const
{
CartesianCoordinate3D<float> _p1;
CartesianCoordinate3D<float> _p2;
find_cartesian_coordinates_of_detection(_p1, _p2, bin);
CartesianCoordinate3D<float> p2_minus_p1 = _p2 - _p1;
return p2_minus_p1.z() / (sqrt(square(p2_minus_p1.x())+square(p2_minus_p1.y())));
LORInAxialAndNoArcCorrSinogramCoordinates<float> lor;
get_LOR(lor, bin);

return (lor.z2() - lor.z1()) / (2 * lor.radius());
}

float
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38 changes: 1 addition & 37 deletions src/include/stir/ProjDataInfoGenericNoArcCorr.inl
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Expand Up @@ -88,43 +88,7 @@ get_s(const Bin& bin) const
{
LORInAxialAndNoArcCorrSinogramCoordinates<float> lor;
get_LOR(lor, bin);
// REQUIREMENT: Euclidean coordinate of 3 points, a,b and c.
// CALCULATION: // Equation of a line, in parametric form, given two point a, b: p(t) = a + (b-a)*t
// // Let a,b,c be points in 2D and let a,b form a line then shortest distance between c and line ab is:
// // || (p0-p1) - [(p0-p1)*(p2-p1)/||p2-p1||^2]*(p2-p1) ||
// p1 = _p1, p2=_p2 and p0=(0,0,0)
// OUTPUT: replace the ring_radius*sin(lor.beta()) with distance from o to ab.

// Can't access coordinate of detection from this class so we have to recalculate where it is:

CartesianCoordinate3D<float> _p1;
CartesianCoordinate3D<float> _p2;
find_cartesian_coordinates_of_detection(_p1, _p2, bin);

// // Get p1-p0 and p2-p1 vector.
CartesianCoordinate3D<float> p2_minus_p1 = _p2 - _p1;
CartesianCoordinate3D<float> p0_minus_p1 = CartesianCoordinate3D<float>(0,0,0) - _p1;
float p0_minus_p1_dot_p2_minus_p1 = p0_minus_p1.x()* p2_minus_p1.x() + p0_minus_p1.y()*p2_minus_p1.y();
float p2_minus_p1_magitude = square(p2_minus_p1.x()) + square(p2_minus_p1.y());
float x = 0;
float y = 0;
float sign = sin(lor.beta());
if (p2_minus_p1_magitude > 0.01)
{
x = p0_minus_p1.x() - (p0_minus_p1_dot_p2_minus_p1/p2_minus_p1_magitude)*p2_minus_p1.x();
y = p0_minus_p1.y() - (p0_minus_p1_dot_p2_minus_p1/p2_minus_p1_magitude)*p2_minus_p1.y();
}
else
{
error("get_s(): 2 detection points are too close to each other. This indicates an internal error.");
}
float s = sqrt(square(x) + square(y));

if(sign < 0.0){
return -s;
}else{
return s;
}
return lor.s();
}

void
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20 changes: 13 additions & 7 deletions src/test/test_proj_data_info.cxx
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Expand Up @@ -148,7 +148,7 @@ ProjDataInfoTests::test_generic_proj_data_info(ProjDataInfo& proj_data_info)
#endif
for (int segment_num = proj_data_info.get_min_segment_num(); segment_num <= proj_data_info.get_max_segment_num(); ++segment_num)
{
for (int view_num = proj_data_info.get_min_view_num(); view_num <= proj_data_info.get_max_view_num(); view_num += 3)
for (int view_num = proj_data_info.get_min_view_num(); view_num <= proj_data_info.get_max_view_num(); view_num += 1)
{
// loop over axial_positions. Avoid using first and last positions, as
// if there is axial compression, the central LOR of a bin might actually not
Expand Down Expand Up @@ -176,10 +176,13 @@ ProjDataInfoTests::test_generic_proj_data_info(ProjDataInfo& proj_data_info)
{
const Bin new_bin = proj_data_info.get_bin(lor);
#if 1
const int diff_segment_num = intabs(org_bin.segment_num() - new_bin.segment_num());
const int diff_view_num = intabs(org_bin.view_num() - new_bin.view_num());
// the differences need to also consider wrap-around in views, which would flip tangential pos and segment
const int diff_segment_num = intabs(org_bin.view_num() - new_bin.view_num()) < proj_data_info.get_num_views() - intabs(org_bin.view_num() - new_bin.view_num()) ?
intabs(org_bin.segment_num() - new_bin.segment_num()) : intabs(org_bin.segment_num() + new_bin.segment_num());
const int diff_view_num = min(intabs(org_bin.view_num() - new_bin.view_num()), proj_data_info.get_num_views() - intabs(org_bin.view_num() - new_bin.view_num()));
const int diff_axial_pos_num = intabs(org_bin.axial_pos_num() - new_bin.axial_pos_num());
const int diff_tangential_pos_num = intabs(org_bin.tangential_pos_num() - new_bin.tangential_pos_num());
const int diff_tangential_pos_num = intabs(org_bin.view_num() - new_bin.view_num()) < proj_data_info.get_num_views() - intabs(org_bin.view_num() - new_bin.view_num()) ?
intabs(org_bin.tangential_pos_num() - new_bin.tangential_pos_num()) : intabs(org_bin.tangential_pos_num() + new_bin.tangential_pos_num());
if (new_bin.get_bin_value() > 0)
{
if (diff_segment_num > max_diff_segment_num)
Expand Down Expand Up @@ -220,10 +223,13 @@ ProjDataInfoTests::test_generic_proj_data_info(ProjDataInfo& proj_data_info)
lor.get_intersections_with_cylinder(lor_as_points, lor.radius());
const Bin new_bin = proj_data_info.get_bin(lor_as_points);
#if 1
const int diff_segment_num = intabs(org_bin.segment_num() - new_bin.segment_num());
const int diff_view_num = intabs(org_bin.view_num() - new_bin.view_num());
// the differences need to also consider wrap-around in views, which would flip tangential pos and segment
const int diff_segment_num = intabs(org_bin.view_num() - new_bin.view_num()) < proj_data_info.get_num_views() - intabs(org_bin.view_num() - new_bin.view_num()) ?
intabs(org_bin.segment_num() - new_bin.segment_num()) : intabs(org_bin.segment_num() + new_bin.segment_num());
const int diff_view_num = min(intabs(org_bin.view_num() - new_bin.view_num()), proj_data_info.get_num_views() - intabs(org_bin.view_num() - new_bin.view_num()));
const int diff_axial_pos_num = intabs(org_bin.axial_pos_num() - new_bin.axial_pos_num());
const int diff_tangential_pos_num = intabs(org_bin.tangential_pos_num() - new_bin.tangential_pos_num());
const int diff_tangential_pos_num = intabs(org_bin.view_num() - new_bin.view_num()) < proj_data_info.get_num_views() - intabs(org_bin.view_num() - new_bin.view_num()) ?
intabs(org_bin.tangential_pos_num() - new_bin.tangential_pos_num()) : intabs(org_bin.tangential_pos_num() + new_bin.tangential_pos_num());
if (new_bin.get_bin_value() > 0)
{
if (diff_segment_num > max_diff_segment_num)
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