Lesson 1: Principles of Computed Tomography (CT) Physics

CT imaging relies on X-ray attenuation principles, where multiple projections acquired from different angles are reconstructed into cross-sectional images using mathematical algorithms.

• CT Scanner Components:
  • X-ray Tube: Emits photons that traverse the patient and reach detectors.
  • Detectors: Convert X-ray photons into electrical signals for image reconstruction.
  • Gantry: Houses the X-ray tube and detectors; rotates around the patient.
  • Control Console & Workstation: Adjusts scan parameters and processes images.
• Helical vs. Axial Scanning:
  • Axial (Step-and-Shoot) scanning involves image acquisition in discrete slices.
  • Helical (Spiral) scanning continuously moves the table through the gantry for volumetric data acquisition.
• Hounsfield Units (HU): Quantify tissue density based on X-ray attenuation (-1000 HU for air, 0 HU for water, +1000 HU for dense bone).
• Beam Hardening & Artifacts: Beam hardening artifacts arise due to preferential absorption of low-energy photons, necessitating correction techniques.

Lesson 2: CT Image Formation & Reconstruction Algorithms

CT images are generated through complex computational processes that reconstruct X-ray attenuation data into interpretable images.

• Raw Data to Image Conversion:
  • Filtered Back Projection (FBP): Traditional method, uses mathematical filters to enhance edges.
  • Iterative Reconstruction (IR): Reduces noise and radiation dose while improving image quality.
  • Deep Learning-Based Reconstruction: Emerging technique using AI for enhanced clarity and reduced artifacts.
• Spatial & Temporal Resolution:
  • Spatial resolution depends on detector size, focal spot, and reconstruction kernel.
  • Temporal resolution is critical in cardiac imaging; multi-segment reconstruction reduces motion artifacts.
• Multiplanar Reformation (MPR): Allows visualization in coronal, sagittal, and oblique planes.
• Volume Rendering Techniques (VRT) & Maximum Intensity Projection (MIP): 3D visualization tools aiding in vascular and structural assessment.
  
  

Lesson 3: Radiation Dose Optimization & Safety in CT

Minimizing radiation exposure while maintaining diagnostic accuracy is crucial in CT imaging.

• Dose Metrics:
  • CT Dose Index (CTDIvol): Represents the radiation dose for a single slice.
  • Dose-Length Product (DLP): Accounts for total scan length, giving an estimate of total radiation exposure.
• ALARA Principle:
  • Optimize kVp and mAs based on patient size and diagnostic need.
  • Utilize automatic exposure control (AEC) for dose modulation.
• Pediatric Considerations:
  • Lower radiation doses should be used in children.
  • Justification and optimization strategies must be strictly adhered to.
• Protective Measures:
  • Lead shielding of radiosensitive organs.
  • Avoiding unnecessary repeat scans.
    
    

Lesson 4: Contrast Media in CT Imaging

Iodinated contrast agents enhance soft tissue differentiation and vascular assessment in CT.

• Types of Contrast Media:
  • Non-ionic low-osmolar contrast media (LOCM): Reduces adverse reactions.
  • High-osmolar contrast media (HOCM): Historically used but with increased risk of nephrotoxicity.
• Phases of Enhancement:
  • Non-contrast phase: Baseline attenuation values.
  • Arterial phase: 20-30 sec post-injection, assesses arteries.
  • Venous phase: 60-70 sec post-injection, evaluates venous structures.
  • Delayed phase: Identifies pathologies like tumors or fibrosis.
• Contrast-Induced Nephropathy (CIN):
  • Preventative strategies include hydration and using lower contrast doses in at-risk patients.
    
    

Lesson 5: Systematic Approach to CT Interpretation

A structured analysis ensures accurate diagnosis and prevents errors.

• General Interpretation Principles:
  • Evaluate image quality, patient positioning, and scan parameters.
  • Compare with prior imaging studies if available.
• Organ-Specific Review:
  • Brain: Identify infarcts, hemorrhage, mass lesions, hydrocephalus.
  • Chest: Evaluate lung parenchyma, mediastinum, pleura, airways.
  • Abdomen: Assess solid organs, bowel, vascular structures.
  • MSK: Detect fractures, soft tissue pathology, osteomyelitis.
• Common Pitfalls:
  • Motion artifacts, improper contrast timing, beam hardening effects.
    
    

Lesson 6: Advanced CT Applications

CT is essential in various specialized imaging applications.

• CT Angiography (CTA): Evaluates vascular pathology (aneurysms, stenosis, embolism).
• Cardiac CT: Coronary artery calcium scoring and CT coronary angiography (CTCA) for CAD.
• Dual-Energy CT (DECT): Uses two energy levels to differentiate materials like iodine, calcium, and uric acid.
• CT Perfusion: Measures cerebral blood flow, aiding stroke assessment.
• Virtual Colonoscopy & Endoscopy: Non-invasive techniques for gastrointestinal imaging.

Lesson 7: Emergency CT Imaging

CT plays a critical role in acute settings for rapid diagnosis and intervention.

• Stroke Imaging:
  • Non-contrast CT (NCCT) for hemorrhage detection.
  • CT perfusion & CTA for ischemic stroke workup.
• Trauma CT (Whole-Body CT):
  • Identifies life-threatening injuries in polytrauma patients.
• Acute Chest Pain:
  • Triple rule-out CT (TRO-CT) evaluates for PE, aortic dissection, and coronary pathology.
• Acute Abdominal Pain:
  • CT is the modality of choice for appendicitis, bowel obstruction, and perforation.

Lesson 8: Future Directions & Emerging Trends in CT Imaging

Technological advancements continue to refine CT imaging capabilities.

• Photon-Counting CT: Provides improved spatial resolution and spectral imaging capabilities.
• AI in CT Imaging: Machine learning algorithms assist in image interpretation and workflow optimization.
• Low-Dose CT Screening: Lung cancer screening and coronary CT angiography advancements.
• Portable CT Systems: Facilitating imaging in critical care and intraoperative settings.
• Nanoparticle-Based Contrast Agents: Under research for improved lesion detection and functional imaging.