Interventional Radiology: Digital Subtraction Techniques

Temporal Subtraction in Interventional Radiology

• Temporal subtraction is a technique used in interventional radiology to enhance the visualization of contrast media by subtracting images taken before and after the injection of contrast.

Variables for Temporal Subtraction

• Pre-contrast image: an image taken before the injection of contrast.
• Post-contrast image: an image taken after the injection of contrast.
• Mask: the pre-contrast image used to subtract from the post-contrast image.

Purpose of Temporal Subtraction

• To improve the visualization of blood vessels and other structures by reducing background noise and enhancing the contrast of the injected contrast media.

The Mask in Temporal Subtraction

• The mask is a digital image of the anatomy before the injection of contrast.
• The mask is subtracted from the post-contrast image to remove the background anatomy.

Enhancing Visualization Through Subtraction

• The subtraction process removes the background anatomy, leaving only the contrast-enhanced structures visible.
• This improves the visibility of subtle details within the vessels and surrounding structures.

Types of Digital Subtraction

• Temporal subtraction: involves subtracting images taken at different times.
• Energy subtraction: involves subtracting images acquired at different energy levels (kVp).
• Hybrid subtraction: a combination of temporal and energy subtraction.

Diapositive Mask

• A diapositive mask is a positive image generated from the pre-contrast image, used in subtraction techniques to obtain a sharper subtraction image.

Theory Behind Subtraction Methods

• All subtraction methods in radiography utilize the difference in density between the contrast media and the background anatomy.
• The pre-contrast image is used as a reference to subtract from the post-contrast image, highlighting the contrast-enhanced structures.

Final Subtraction Print

• The final subtraction print is the image that remains after the subtraction process.
• It is created by subtracting the pre-contrast image (mask) from the post-contrast image.

Generator Requirements for Temporal Subtraction

• The X-ray generator must be capable of producing multiple images in rapid succession to capture pre-contrast and post-contrast images.

Advantage of Using Diapositive Mask

• Diapositive mask in subtraction methods promotes sharper subtracted images, as it enhances edges and details within the contrast-filled structures.

Purpose of Creating Contrast Films at Different Energy Levels (kVp)

• Creating contrast films at varying kVp levels is a technique used in the shortcut method of subtraction.
• This method allows for the creation of contrast subtraction images without acquiring a pre-contrast image.

One Density Film and Image Visibility

• A film with only one density will not show an image because there is no difference in density to create contrast.

Modes of Temporal Subtraction

• Continuous subtraction: subtracts images continuously as the contrast flows through the vessels.
• Single-shot subtraction: subtracts a single pre-contrast image from a single post-contrast image.

Contrast in Radiography

• In radiography, contrast refers to the difference in density between two adjacent areas on a radiographic image.

Role of Contrast Films in Shortcut Method

• Contrast films play a crucial role in the shortcut method of subtraction.
• By creating images at different kVp levels, the method allows for image subtraction without acquiring a pre-contrast image.

Learn about digital subtraction techniques in interventional radiology, including temporal subtraction, energy subtraction, and hybrid subtraction. Understand how these techniques enhance the visualization of angiogram information by removing non-essential structures and highlighting the pattern of contrast media.