切片（Slice）或切面是三维图像比较常用的概念，尤其在医学图像中。通过提取切面可以方便地浏览和分析图像内部组织结构。VTK中vtkImageReSlice类可以实现图像切面的提取。在实际开发中，四视图中冠状视面、矢状面和横断面（显示过图像内部一点且平行于XY、YZ、XZ平面的平面），需要用到此类。
#include <vtkSmartPointer.h>
#include <vtkImageReader2.h>
#include <vtkMatrix4x4.h>
#include <vtkImageReslice.h>
#include <vtkLookupTable.h>
#include <vtkImageMapToColors.h>
#include <vtkImageActor.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleImage.h>
#include <vtkCommand.h>
#include <vtkImageData.h>
#include <vtkMetaImageReader.h>
#include <vtkImageCast.h>
class vtkImageInteractionCallback : public vtkCommand
{
public:
static vtkImageInteractionCallback *New()
{
return new vtkImageInteractionCallback;
}
vtkImageInteractionCallback()
{
this->Slicing = 0;
this->ImageReslice = 0;
this->Interactor = 0;
}
void SetImageReslice(vtkImageReslice *reslice)
{
this->ImageReslice = reslice;
}
void SetImageMapToColors(vtkImageMapToColors *mapToColors)
{
this->mapToColors = mapToColors;
}
vtkImageReslice *GetImageReslice()
{
return this->ImageReslice;
}
void SetInteractor(vtkRenderWindowInteractor *interactor)
{
this->Interactor = interactor;
}
vtkRenderWindowInteractor *GetInteractor()
{
return this->Interactor;
}
virtual void Execute(vtkObject *, unsigned long event, void *)
{
vtkRenderWindowInteractor *interactor = this->GetInteractor();
int lastPos[2];
interactor->GetLastEventPosition(lastPos);
int currPos[2];
interactor->GetEventPosition(currPos);
if (event == vtkCommand::LeftButtonPressEvent)
{
this->Slicing = 1;
}
else if (event == vtkCommand::LeftButtonReleaseEvent)
{
this->Slicing = 0;
}
else if (event == vtkCommand::MouseMoveEvent)
{
if (this->Slicing)
{
vtkImageReslice *reslice = this->ImageReslice;
// Increment slice position by deltaY of mouse
int deltaY = lastPos[1] - currPos[1];
reslice->Update();
double sliceSpacing = reslice->GetOutput()->GetSpacing()[2];
vtkMatrix4x4 *matrix = reslice->GetResliceAxes();
// move the center point that we are slicing through
double point[4];
double center[4];
point[0] = 0.0;
point[1] = 0.0;
point[2] = sliceSpacing * deltaY;
point[3] = 1.0;
matrix->MultiplyPoint(point, center);
matrix->SetElement(0, 3, center[0]);
matrix->SetElement(1, 3, center[1]);
matrix->SetElement(2, 3, center[2]);
mapToColors->Update();
interactor->Render();
}
else
{
vtkInteractorStyle *style = vtkInteractorStyle::SafeDownCast(
interactor->GetInteractorStyle());
if (style)
{
style->OnMouseMove();
}
}
}
}
private:
int Slicing;
vtkImageReslice *ImageReslice;
vtkRenderWindowInteractor *Interactor;
vtkImageMapToColors *mapToColors;
};
int main()
{
vtkSmartPointer<vtkMetaImageReader> reader =
vtkSmartPointer<vtkMetaImageReader>::New();
reader->SetFileName ( "../data/brain.mhd" );//.mhd和.raw要放在一起
reader->Update();
int extent[6];
double spacing[3];
double origin[3];
reader->GetOutput()->GetExtent(extent);
reader->GetOutput()->GetSpacing(spacing);
reader->GetOutput()->GetOrigin(origin);
double center[3];
center[0] = origin[0] + spacing[0] * 0.5 * (extent[0] + extent[1]);
center[1] = origin[1] + spacing[1] * 0.5 * (extent[2] + extent[3]);
center[2] = origin[2] + spacing[2] * 0.5 * (extent[4] + extent[5]);
static double axialElements[16] = {
1, 0, 0, 0,
0, 1, 0, 0,
0, 0, 1, 0,
0, 0, 0, 1
};
vtkSmartPointer<vtkMatrix4x4> resliceAxes =
vtkSmartPointer<vtkMatrix4x4>::New();
resliceAxes->DeepCopy(axialElements);
resliceAxes->SetElement(0, 3, center[0]);
resliceAxes->SetElement(1, 3, center[1]);
resliceAxes->SetElement(2, 3, center[2]);
vtkSmartPointer<vtkImageReslice> reslice =
vtkSmartPointer<vtkImageReslice>::New();
reslice->SetInputConnection(reader->GetOutputPort());
reslice->SetOutputDimensionality(2);
reslice->SetResliceAxes(resliceAxes);
reslice->SetInterpolationModeToLinear();
vtkSmartPointer<vtkLookupTable> colorTable =
vtkSmartPointer<vtkLookupTable>::New();
colorTable->SetRange(0, 1000);
colorTable->SetValueRange(0.0, 1.0);
colorTable->SetSaturationRange(0.0, 0.0);
colorTable->SetRampToLinear();
colorTable->Build();
vtkSmartPointer<vtkImageMapToColors> colorMap =
vtkSmartPointer<vtkImageMapToColors>::New();
colorMap->SetLookupTable(colorTable);
colorMap->SetInputConnection(reslice->GetOutputPort());
colorMap->Update();
vtkSmartPointer<vtkImageActor> imgActor =
vtkSmartPointer<vtkImageActor>::New();
imgActor->SetInputData(colorMap->GetOutput());
vtkSmartPointer<vtkRenderer> renderer =
vtkSmartPointer<vtkRenderer>::New();
renderer->AddActor(imgActor);
renderer->SetBackground(1, 1, 1);
vtkSmartPointer<vtkRenderWindow> renderWindow =
vtkSmartPointer<vtkRenderWindow>::New();
renderWindow->SetSize(500, 500);
renderWindow->AddRenderer(renderer);
vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
vtkSmartPointer<vtkRenderWindowInteractor>::New();
vtkSmartPointer<vtkInteractorStyleImage> imagestyle =
vtkSmartPointer<vtkInteractorStyleImage>::New();
renderWindowInteractor->SetInteractorStyle(imagestyle);
renderWindowInteractor->SetRenderWindow(renderWindow);
renderWindowInteractor->Initialize();
vtkSmartPointer<vtkImageInteractionCallback> callback =
vtkSmartPointer<vtkImageInteractionCallback>::New();
callback->SetImageReslice(reslice);
callback->SetInteractor(renderWindowInteractor);
callback->SetImageMapToColors(colorMap);
imagestyle->AddObserver(vtkCommand::MouseMoveEvent, callback);
imagestyle->AddObserver(vtkCommand::LeftButtonPressEvent, callback);
imagestyle->AddObserver(vtkCommand::LeftButtonReleaseEvent, callback);
renderWindowInteractor->Start();
return EXIT_SUCCESS;
}
效果图：
代码解释：
先通过vtkMetaImageReader读取一副三维图像，获取图像范围、原点和像素间隔，由这三个参数可以计算图像的中心位置。
接下来定义了切面的变换矩阵axialElements，该矩阵的前三列分别表示X、Y和Z方向矢量，第四列为切面坐标系原点。通过修改切面坐标系原点，可以得到不同位置的切面图像。
然后将读取的图像作为vtkImageReslice的输入，通过函数SetResliceAxes()设置变换矩阵resliceAxis。