CT Image Post Processing – 0.25 CE Credits

A free, ASRT-approved CE course for CT technologists that covers CT post-processing techniques


CT Image Post Processing
CT Image Post Processing

The application of imaging techniques to the original axial images of a CT scan in order to derive additional information or hide unwanted information that distracts from the clinical findings is called image post-processing. CT image post-processing requires the modification of a 3D image volume, which in most cases consists of a stack of individual axial images. There are many CT post-processing methods and techniques. The most commonly used techniques are maximum intensity projection (MIP), Minimum intensity projection (MinIP), volume rendering (VR), multiplanar reconstruction (MPR) or curved planar reconstruction. We will cover all of these CT image post-processing methods in this article and show examples of many of them through CT images, such as images of nodes within the Barety lodge revealed by a multiplanar reconstruction. This article is approved by the ASRT for 0.25 Category A CE Credits.

CE Credits
0.25 Category A
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Expiry date: July 1, 2022
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Meets ARRT ® CE reporting requirements
Approved by the American Society of Radiologic Technologists (ASRT) for 0.25 Category A CE credits
License duration: 180 days from purchase date
Meets the CE requirements of the following states: California, Texas, Florida, Kentucky, Massachusetts, and New Mexico
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  • Understand the concept of post-processing
  • Explain volume rendering
  • Compare maximum intensity projection (MIP) and minimum intensity projection (MinIP)
  • Discuss image fusion
Discipline Major content category & subcategories CE Credits provided
CT-2016 Image Production
Physics and Instrumentation 0.25
CT-2017 Image Production
Image Formation 0.25
RA-2017 Procedures
Abdominal Section 0.25
RA-2018 Procedures
Abdominal Section 0.25

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CHAPTER 1
Post-Processing

Rendering Modes

There are three main methods, the minimum intensity projection, the average intensity projection, and the maximum intensity projection.

CT Image Post Processing

Maximum Intensity Projection: MIP

The maximum intensity projection consists of projecting the voxel with the highest attenuation value on every view throughout the volume onto a 2D image. An image that displays the maximum intensity for each pixel point on a thickened reformat plane.

Maximum Intensity Projection

Vascular

Here an example of shows where the maximum intensity projection is used to search for vascular diseases or anomalies.

Maximum Intensity Projection

MIP Vascular: Renal Artery

This image shows us dysplastic renal artery stenosis. Notice the contour of the renal artery.

Maximum Intensity Projection

Nodules

The image shows where the maximum intensity projection is used to search for parenchyma solid nodule lesions. Notice the many metastatic lesions shown in both lung fields.

Maximum Intensity Projection

Pulmonary Nodules

The image shows where the maximum intensity projection is used to search for parenchyma solid nodular lesions. Notice the pulmonary lesion in the lung field.

Maximum Intensity Projection

Lithiasis

You can see on this image an example of maximum intensity projection which is used to search for ureter stenosis caused by perivesical lithiasis.

Maximum Intensity Projection

Minimum Intensity Projection: MinIP

The minimum intensity projection is a data visualization method that enables the detection of low-density structures in a given volume.

Minimum Intensity Projection

Chest

Both of these images show how the minimum intensity projection technique is used for the diagnosis of emphysema. Notice the bullae in the image on the left and the pneumothorax in the left lung on the image on the right.

Minimum Intensity Projection

Inner Ear

On these images, we can see an example of how the minimum intensity projection is used in the diagnosis of the semicircular canal. Abnormalities such as cholesteatomas can be easily seen.

Minimum Intensity Projection

Heart

The minimum intensity algorithm is particularly useful in highlighting hypo or low dense regions within the heart.

Minimum Intensity Projection

Biliary Tract

This example shows us the presence of air in the biliary tract known as pneumobilia. Notice the white arrows pointing out the air.

Minimum Intensity Projection

Average

In the average intensity algorithm (AIP), the visualization is averaged. The AIP technique is an algorithm that is intended to create a thick MPR image by using the average of the attenuation through the tissues of interest to calculate the pixel viewed on the computer.

Minimum Intensity Projection

Images

In the image on the left, we see the polycystic disease of both kidneys while the image on the left shows the presence of ascites in the abdomen.

Multiplanar Reconstructions

Both images show the presence of nodes in the Barety lodge, or Barety space (or right pre-tracheal space). The Barety lodge is an anatomical space located in the middle mediastinum of the human thorax which is formed of a cellulo-lymphatic tissue running along the trachea.

barety lodge

Curved

Multiplanar

The curved multiplanar axis allows the draw of a central axis inside a structure independently from its origin. (vascular or other). Visualization of sagittal and coronal vertebrae in the same plan. Also a visualization of the coast in the same plan.

barety lodge

Mandible

It allows the visualization of the mandibular canal as well as the visualization of the pre implanted bony space.

barety lodge

Bronchial Tree

This image shows us the visualization of the bronchial lumen and its caliber.

barety lodge

Post Processing

The curved post-processing algorithm allows for:

  • Better visualization of a tract
  • Better localization of a pathological element
  • Better distance measurement (example: stenosis)
  • This study can be done automatically through vascular HU or manually point by point

Images

The image on the left shows us the facial nerve while the image on the right shows renal artery dysplastic stenosis.

barety lodge

Aneurysm

The image post-processed with a curved technique shows a carotid aneurysm in the upper third of the image on the right.

barety lodge

Stenosis

Stenosis Measurement

For stenosis quantification, you have to place the reference on the curvilinear or the stretched vessel image. Once positioned, verify the vessel’s contour for the reference and the lesion.

barety lodge

Stenosis Percentages

Stenosis percentages, maximum and minimum diameter and the surface are displayed in the following table.

barety lodge

Endoprosthesis

Endoprosthesis Planning

In this step, you can choose and import the type of prosthesis you want. To do so, you have only to click on the list of prosthesis models and select your choice.

barety lodge

Once the model is selected, you have to adjust the measurements as indicated on the template. For each measurement, check the light contour automatically created by the software.

barety lodge

Volume Rendering

Volume rendering (VR) will allow us to use predefined protocols to adjust the amount of opacity and color applied to the model. Then you can display the table of results referring to the necessary measurements for prosthesis fabrication.

barety lodge

Density

Each density range has a very specific opacity coefficient (or transparency coefficient).

barety lodge

Volume Rendering and MIP

Volumetric MIP and ANGIO

The image on the left is post-processed using a volumetric maximum intensity projection technique.

CT Image Post Processing

Endoscopy

Colonic Endoscopy

The lowest Hounsfield units voxels (near air) have a maximum transparency effect. The voxels with great HU present a significant opacity which materializes the wall of the colon. This is a 3D visualization of the interior of a hollow organ.

CT Image Post Processing

Bronchial Endoscopy

Bronchial endoscopy allows the visualization of the bronchial lumen filled with an inhalant object or invasive cancer. This is a 3D visualization of the interior of a hollow organ.

CT Image Post Processing

Image Fusion

After fixing three landmarks (or points) in the anatomy, the system readjusts the plans with a maximum tolerance of 20*.

CT Image Post Processing

PET CT

A PET/CT combines the nuclear medicine sensitivity with the anatomical location of the CT scanner.

CT Image Post Processing

Emphysema Measurement

The automated application called “lung density” provides the physician with quantitative data on the volume of pulmonary emphysema, as well as gives us a visual representation of its diffusion.

CT Image Post Processing

Damaged Alveoli

This image shows us an example of images where the damaged alveoli are highlighted in blue.

CT Image Post Processing

Percentage of Lung Parenchyma

Here, we can see the percentage of lung parenchyma in function of Hounsfield densities.

CT Image Post Processing

HU Measurements

This image shows the average density measurements in Hounsfield Units of 25%, 50 %, 75%, and 100%.

This concludes the CT Image Post-Processing course. If you choose to take the post-test to earn your CE credits and CE certificate for this course, you have 3 attempts to earn a passing score of at least 75%, as per ARRT ® regulations. If you just enjoyed reading about CT post-processing techniques and found it useful and helpful for your clinical practice but do not wish to take the post-test, you can access the content again at any time, completely free.

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