Digital Subtraction Angiography (DSA)

Digital Subtraction Angiography (DSA) Overview

• DSA is an advanced CT imaging technique
• DSA visualizes blood vessels
• DSA subtracts pre-contrast images from post-contrast images
• Enhances vascular structure visualization
• Eliminates background noise from bones and soft tissues

The Imaging Chain in DSA

• X-ray Generator: Produces X-ray beams for imaging
• X-ray Tube: Emits X-rays toward the area of interest
• Image Intensifier: Enhances/amplifies the X-ray signal for better visualization
• TV Lens System: Transmits the intensified image to a TV camera
• TV Camera: Converts the optical image into an electronic signal
• Video Signal: Carries image data for digital processing

Manual Subtraction Technique

• Involves comparing two images
• First-Order Subtraction: Direct subtraction of pre-contrast and post-contrast images
• Second-Order Subtraction: Further enhancement by removing residual noise and artifacts

Digital Angiography

• Analog-to-Digital Converter (ADC): Converts continuous image signals into digital form
• Pixel Formation: Defines image resolution and clarity
• TV Monitor: Displays the processed images in real-time for analysis

Digital Subtraction Techniques

• Energy Subtraction: Uses different X-ray energy levels to differentiate tissues
• Temporal Subtraction: Removes stationary structures by comparing images over time
• Time Interval Difference (TID): Highlights rapid blood flow changes
• Dual Energy Subtraction: Uses two different energy levels to separate soft tissues from vessels
• Hybrid Subtraction: Combines multiple subtraction techniques for better visualization

Intra-arterial vs. Intravenous Angiography

• Percutaneous (Intra-arterial): Direct injection into an artery for high-resolution imaging
• Cut-down (Intravenous): Injection into a vein for systemic contrast distribution

Patient Care in Angiographies

• Pre-procedure preparation involves fasting, allergy check, and IV line placement
• Monitoring during the procedure includes vital signs and contrast reaction management
• Post-procedure care involves hydration, puncture site monitoring, and patient recovery instructions

Clinical Applications of DSA

• Intracranial Angiography: Detects aneurysms and vascular malformations in the brain
• Pulmonary Angiography: Assesses pulmonary embolism
• Thoracic Aortography: Evaluates the aorta for aneurysms or dissections
• Abdominal Angiography: Visualizes abdominal vessels and organs
• Angiography of the Limbs: Diagnoses peripheral arterial disease
• Interventional Angiography: Guides minimally invasive procedures

Interventional Radiology (IR) Overview

• Uses imaging techniques like CT, fluoroscopy, and ultrasound
• Performs minimally invasive procedures for diagnosis and treatment
• IR procedures can be diagnostic, such as biopsy
• IR procedures can be therapeutic, like angioplasty and embolization

Patient Management and Care in IR

• Pre-procedure assessment and consent
• Intra-procedure monitoring
• Post-procedure observation and follow-up

Integral Processes in IR

• Medical aspects of procedures, including indications, contraindications, and risks
• Fluoroscopy and radiography as imaging guidance techniques

Contrast Media in IR

• Iodinated contrast agents are used
• Precautions include allergy screening and hydration to prevent nephrotoxicity

Equipment and Techniques in IR

• Catheters, guidewires, needles, and imaging systems are used for procedures

Role of the Radiologic Technologist in IR

• Assist in patient positioning and contrast administration
• Operate imaging equipment
• Ensure patient safety and comfort

Common Interventional Procedures

• Percutaneous Transluminal Angioplasty (PTA): Expands narrowed arteries
• Transcatheter Embolization: Blocks abnormal blood flow to tumors or aneurysms
• Percutaneous Nephrostomy Tube Placement: Drains kidney obstructions
• Inferior Vena Cava (IVC) Filter Placement: Prevents pulmonary embolism

Other Interventional Procedures

• Lymphography: Imaging the lymphatic system
• Lymphatic Injection of Feet and Hands: Evaluates lymphatic drainage

Scanning Program in CT Imaging - Introduction

• Computed Tomography (CT) imaging is a crucial diagnostic tool for detailed cross-sectional imaging
• A structured scanning program ensures high-quality images and prioritizes patient safety and comfort
• Essential steps include patient preparation, scan parameter selection, imaging techniques, and contrast administration

Setting Up the Patient

• Proper patient preparation and positioning are key to obtaining high-quality CT images and minimizing motion artifacts
• Patients should be positioned according to the specific examination being performed
• Common positions include supine (lying on the back), prone (lying on the stomach), and decubitus (lying on the side)

Ensuring Patient Comfort and Safety

• Explain the procedure clearly to alleviate anxiety
• Remove metallic objects (jewelry, eyeglasses, etc.) that may cause artifacts
• Verify patient identity and check for contraindications (e.g., pregnancy, allergies to contrast agents, implanted devices)
• Give lead shielding if needed, especially for radiation-sensitive areas

Setting Examination Parameters

• Adjusting scan parameters ensures optimal image quality while minimizing radiation dose
• Slice Thickness: Determines the thickness of each CT slice, typically 1-5 mm, depending on the study
• Field of View (FOV): Defines the area covered in the scan; adjust to include only the region of interest
• Exposure Time and Tube Current (mA): Controls radiation dose; adjusted based on patient size and clinical need
• kVp (Kilovoltage Peak): Determines the energy of X-rays; typically set between 100-140 kVp for body imaging

Selecting Scan Series

• CT scans consist of multiple sequences tailored to specific clinical indications
• Axial Scans: Standard cross-sectional images
• Coronal and Sagittal Reconstructions: Reformatted images to enhance diagnostic interpretation
• High-Resolution CT (HRCT): Used for lung imaging, providing fine detail
• Angiographic Studies (CTA): Specialized sequences for vascular imaging
• The appropriate scan series is selected based on the suspected pathology and referring physician’s request

Scout Scans

• A scout scan (topogram or localizer) is an initial X-ray image taken before the main CT scan
• Scout scans help define the anatomical area to be scanned
• Assist in positioning the patient correctly
• Allow the technologist to adjust parameters before initiating the full scan

Patient Protocol, Positioning, and Techniques

• Standardized protocols ensure consistency in imaging quality and diagnostic accuracy
• Abdominal CT: Patient lies supine with arms above the head to minimize artifacts
• Brain CT: Patient head positioned in a headrest to reduce movement
• Chest CT: Patient instructed to hold their breath during scanning to minimize motion blur
• Helical (spiral) scanning and multi-phase imaging are used based on clinical needs

Photography

• Photography in CT refers to capturing, processing, and archiving images for diagnostic purposes
• Images are acquired in axial, coronal, and sagittal planes
• Post-Processing: Includes multi-planar reconstruction (MPR), 3D rendering, and volume imaging
• Images are stored in PACS (Picture Archiving and Communication System) for retrieval and review by radiologists

Plain and Contrast Examinations

• CT scans can be performed with or without contrast depending on the clinical indication
• Non-Contrast Studies: Used for initial evaluation of the brain, lungs, and bones
• Plain Scans: Detect calcifications, hemorrhages, fractures, and acute strokes
• Plain Scans: Avoid interference from contrast agents

Contrast-Enhanced Studies

• Contrast media improves visualization of blood vessels, organs, and tumors
• Contrast helps detect infections, tumors, vascular diseases, and inflammatory processes
• Contrast agents enhance the visibility of structures by altering their radiodensity

Contrast Types

• Intravenous (IV) Contrast: Highlights blood vessels and soft tissues
• Oral Contrast: Used for gastrointestinal imaging
• Rectal Contrast: Occasionally used for rectal or colon imaging
• Iodinated Contrast: Most commonly used for IV and intra-arterial injection
• Gadolinium-Based Contrast: Used in MRI but not for CT

Precautions for Contrast Administration

• Check for Allergies: Pre-medicate patients with iodine allergies or prior contrast reactions
• Monitor Renal Function: Assess patients with kidney disease; contrast can be nephrotoxic
• Hydration: Adequate hydration helps excrete contrast
• Adverse Reactions: Mild (nausea, warmth), moderate (hives, bronchospasm), or severe (anaphylaxis, hypotension) reactions may occur, requiring immediate intervention