三维图像切面提取

           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。

程序说明：

1. 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。
2. 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。
3. 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。

注意：

         一定要把.mhd文件和.zraw文件放在同一个文件夹下。

程序代码实现;

#include 
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#include 


#include "vtkAutoInit.h"
VTK_MODULE_INIT(vtkRenderingOpenGL2);
VTK_MODULE_INIT(vtkInteractionStyle);


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 reader =
		vtkSmartPointer::New();
	reader->SetFileName("D:\\pictures\\brain.mhd");
	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 resliceAxes =
		vtkSmartPointer::New();
	resliceAxes->DeepCopy(axialElements);

	resliceAxes->SetElement(0, 3, center[0]);
	resliceAxes->SetElement(1, 3, center[1]);
	resliceAxes->SetElement(2, 3, center[2]);

	vtkSmartPointer reslice =
		vtkSmartPointer::New();
	reslice->SetInputConnection(reader->GetOutputPort());
	reslice->SetOutputDimensionality(2);
	reslice->SetResliceAxes(resliceAxes);
	reslice->SetInterpolationModeToLinear();

	vtkSmartPointer colorTable =
		vtkSmartPointer::New();
	colorTable->SetRange(0, 1000);
	colorTable->SetValueRange(0.0, 1.0);
	colorTable->SetSaturationRange(0.0, 0.0);
	colorTable->SetRampToLinear();
	colorTable->Build();

	vtkSmartPointer colorMap =
		vtkSmartPointer::New();
	colorMap->SetLookupTable(colorTable);
	colorMap->SetInputConnection(reslice->GetOutputPort());
	colorMap->Update();

	vtkSmartPointer imgActor =
		vtkSmartPointer::New();
	imgActor->SetInputData(colorMap->GetOutput());

	vtkSmartPointer renderer =
		vtkSmartPointer::New();
	renderer->AddActor(imgActor);
	renderer->SetBackground(1, 1, 1);

	vtkSmartPointer renderWindow =
		vtkSmartPointer::New();
	renderWindow->SetSize(500, 500);
	renderWindow->AddRenderer(renderer);

	vtkSmartPointer renderWindowInteractor =
		vtkSmartPointer::New();
	vtkSmartPointer imagestyle =
		vtkSmartPointer::New();

	renderWindowInteractor->SetInteractorStyle(imagestyle);
	renderWindowInteractor->SetRenderWindow(renderWindow);
	renderWindowInteractor->Initialize();

	vtkSmartPointer callback =
		vtkSmartPointer::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;
}