Imaging MSK Y1 Lecture 24-25 Student version

Imaging the Skeleton and Soft Tissues

  • Presenter: Dr. Clara Duncan (Clinical Teaching Fellow)

  • Adapted from: Dr. Lesley Robson and Dr. Zoltan Kiraly

Learning Objectives

  • Describe the role of CT and MRI in imaging soft tissues.

  • Be aware of other imaging modalities for assessing muscle and soft tissue.

X-Ray

Overview

  • X-rays pass through the body; different body parts allow varying amounts of electrons to pass.

  • A detector converts the emitted x-rays into visible images on a screen.

  • X-rays are ionizing radiation that can alter atoms.

  • They provide a 2D representation of a 3D image, necessitating both anteroposterior (AP) and lateral views for full pathology visualization.

Case Studies

  1. Case 1: 45-year-old man falls; severe pain and wrist drop present, indicating possible fracture.

  2. Case 2: 25-year-old man twisted ankle; shows severe pain and deformity, but intact foot pulses.

  3. Case 3: 20-year-old man with shoulder pain; exhibits classic symptoms of a shoulder dislocation.

  4. Case 4: 13-year-old girl with intermittent ankle pain; no significant findings on examination.

Ionising Radiation

Definition

  • Ionising radiation breaks electrons from atoms, altering the chemical composition, potentially damaging DNA.

Effects

  • Deterministic Effects: Occur only if a threshold dose is exceeded (e.g., skin burns).

  • Stochastic Effects: Increased risk of harmful outcomes, especially with higher doses (e.g., cancer).

Effective Doses of Common Procedures

  • Chest X-ray: 0.1 mSv (24 days background)

  • Wrist X-ray: 0.001 mSv (6 hours)

  • Abdominal X-ray: 1.2 mSv (292 days)

  • Chest CT: 7 mSv (4.6 years)

  • Head CT: 2 mSv (1.3 years)

  • CT coronary angiogram: 12 mSv (8 years)

  • Combined PET-CT: 25 mSv (16.6 years)

Advantages vs Disadvantages of X-Rays

Advantages

  • Good for imaging bones.

  • Cost-effective and readily available.

  • Low radiation doses.

Disadvantages

  • Limited soft tissue imaging; poor nerve and organ visualization.

  • Not suitable for complex bone abnormalities; requires significant mass loss to detect changes.

Computed Tomography (CT)

Definition

  • CT scans provide detailed internal images non-invasively using rotating X-ray tubes.

  • Multiple angles processed into tomographic (cross-sectional) images via computer algorithms.

Indications

  • Head: Stroke, tumor, hemorrhage, dementia.

  • Chest: Tumor, metastasis, coronary angiography.

  • Abdomen/Pelvis: Liver, Crohn’s disease, inflammatory bowel disease.

  • Complex fractures, metastatic workups are key applications.

Sequence and Processing

  • Image acquisition in transverse plane, can be reconstructed into coronal and sagittal planes.

Contrast CT Imaging

Purpose

  • - Enhances differentiation between biological tissues via IV or oral contrast.

Risks

  • Allergic reactions, kidney injury from contrast exposure.

MRI Overview

Definition

  • Uses non-ionizing radiation, providing high soft tissue contrast.

  • Acquires images in transverse plane; can reconstruct in any plane.

Indications

  • Neuroimaging, cardiovascular applications, musculoskeletal imaging, abdominal conditions.

Contraindications

  • Cardiac pacemakers, metallic foreign bodies, cochlear implants, early pregnancy.

MRI Imaging Types

T1 vs T2-weighted Images

  • T1: Shows normal anatomy and good grey/white matter contrast.

  • T2: Indicates pathology, highlighting areas with higher water content, such as inflammation or edema.

Summary of Imaging Modalities

Ultrasound

  • Non-invasive, no radiation exposure, excellent for soft tissues. Used for various diagnostic procedures across multiple specializations.

PET Scans

  • Use radiotracers to identify cancerous cells; provide metabolic information about body tissues.

Final Notes

  • Review the advantages and disadvantages of each imaging modality to guide appropriate clinical decision-making.

  • Consider techniques based on patient-specific factors and desired clinical outcomes.