Imaging in Orthopaedics

Imaging in Orthopaedics

Prepared by Dr. Alper DUNKI

Spot Knowledge

Radiography

• Principle: X-ray transmission → high density = white
• + Cheap, fast, widely available, good for bones/interventions
• – Poor soft tissue contrast, radiation, magnification, pregnancy risk

Computed Tomography (CT)

• Principle: X-rays, Hounsfield units, cross-sectional, 3D
• + High resolution, bone detail, biopsy guidance
• – High dose radiation, metal artifact, not safe in pregnancy

Magnetic Resonance Imaging (MRI)

• Principle: Protons in magnetic field, RF pulses
• + Best for soft tissues (ligaments, tendons, cartilage, marrow)
• – Long scan time, motion/metal artifact, not safe with pacemaker, gadolinium risk in renal failure

Ultrasonography

• Principle: High-frequency sound waves ± Doppler
• + Portable, cheap, safe (pregnancy, children), dynamic, interventional guidance
• – Operator-dependent, poor for bone & deep joints

Nuclear Medicine (Scintigraphy, PET)

• Principle: Radioisotopes (Tc-99m, FDG) → metabolic activity
• + Detects osteomyelitis, metastasis, stress & occult fractures
• – Low resolution, delayed acute detection, contraindicated in breastfeeding

Radiography

Radiography is based on obtaining images by transmitting x-ray beams through tissues. Structures with high radiodensity (bone, metal) appear white. Today, digital radiography is widely used; with the PACS system, images can be easily stored and transferred.

• Advantages:     Inexpensive, widely available, rapid, and effective in guiding      interventional procedures.
• Disadvantages:     Limited soft tissue contrast, involves radiation, images are magnified.      Requires caution during pregnancy.

Computed Tomography (CT)
CT produces cross-sectional images using x-rays. Densities are measured in Hounsfield units. Multidetector CT scanners provide high resolution in a short time.

• Advantages:     High contrast resolution, 3D reconstruction, ease of measurement. Cortical      bone and trabecular structures are demonstrated in detail. Provides      guidance for biopsy and interventions.
• Disadvantages:     Artifacts with metallic implants, motion sensitivity, limitations related      to obesity. Radiation dose is high, contraindicated during pregnancy.

Magnetic Resonance Imaging (MRI)
MRI generates images using the motion of protons within a strong magnetic field and radiofrequency waves. It does not involve ionizing radiation. The most commonly used sequences are T1 and T2.

• Advantages:     Optimal visualization of soft tissues (ligament, tendon, cartilage,      muscle, bone marrow). Tomographic structure, relative safety of gadolinium      contrast, and absence of radiation.
• Disadvantages:     Long acquisition time, motion artifacts, image distortion due to metallic      implants. Sedation may be required in young children.
• Risks:     The magnetic field may be hazardous for devices such as pacemakers or      cochlear implants. Gadolinium is contraindicated in renal failure (risk of      NSF). Its safety during pregnancy is uncertain.

Ultrasonography
Ultrasound operates with high-frequency sound waves. Superficial tissues are imaged with high frequency, deep tissues with low frequency. With Doppler technique, vascular flow can be demonstrated.

• Advantages:     Portable, inexpensive, radiation-free, safe for pregnant women and      children. Enables dynamic evaluation (tendon and nerve subluxation).      Serves as guidance for needle placement and interventions.
• Disadvantages:     Image quality is operator-dependent. Cortical bone and deep      intra-articular structures are imaged with limitations.

Nuclear Medicine
Biological agents labeled with radioactive isotopes are used. Bone scintigraphy is performed with Tc-99m and demonstrates bone metabolism. PET uses FDG to reveal metabolic activity; it is particularly common in oncology.

• Advantages:     Evaluation of metabolic processes, detection of osteomyelitis, metastases,      stress fractures, and occult fractures.
• Disadvantages:     Low spatial resolution, delayed sensitivity in acute lesions, limited      efficacy in lytic lesions. Contraindicated in breastfeeding women.

Radiation Safety
Children and fetuses are sensitive to ionizing radiation. CT exposes patients to the highest dose (5–15 mSv). Low-dose principles and the ALARA (“as low as reasonably achievable”) approach are essential.

• Risks:     DNA damage, cancer development, fetal malformation, and childhood      leukemia.
• Protection:     Shielding of gonads and radiosensitive organs, reduction of dose through      distance, and the obligatory use of protective equipment.

Conclusion
Medical imaging modalities are indispensable in diagnostic and therapeutic processes.

• Radiography      and CT demonstrate osseous structures.
• MRI      provides superior visualization of soft tissues.
• Ultrasonography      enables dynamic evaluation and safe use.
• Nuclear      medicine offers insight into metabolic processes.

Each modality’s advantages and limitations should be considered, and radiation safety principles must be observed. Appropriately selected imaging methods enhance patient safety and diagnostic accuracy.

References

1. Islam SKM, Nasim MA, Hossain I, Ullah MA, Gupta KD, Bhuiyan MM. Introduction of medical imaging modalities. arXiv. 2023 Jun 1;2306.01022. doi:10.48550/arXiv.2306.01022

2. Huang Y, Li Y, Li J, Hua T, Liu Y. Advances in medical imaging techniques. BMC Methods. 2024; doi:10.1186/s44330-024-00010-7