Human Anatomy
Radiodiagnosis
Radiodiagnosis for MBBS: radiographic densities, plain radiograph, ultrasound, CT and MRI and normal radiological anatomy, mapped to NMC codes AN54.1 to AN54.3.
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Radiodiagnosis
Radiodiagnosis for MBBS: radiographic densities, plain radiograph, ultrasound, CT and MRI and normal radiological anatomy, mapped to NMC codes AN54.1 to AN54.3.
The radiodiagnosis chapter introduces the imaging methods used to study anatomy and detect disease, from plain radiographs to CT, MRI and ultrasound. It teaches the normal appearances that clinical radiology depends upon.
High-yield: Radiodiagnosis
- Radiodiagnosis uses imaging to study normal anatomy and to detect disease without dissection.
- A plain radiograph shows dense bone as white, air-filled lung as black, and soft tissue in shades of grey.
- The five basic radiographic densities from black to white are air, fat, water or soft tissue, bone and metal.
- A chest radiograph shows the heart, lungs, ribs and the diaphragm and is one of the most common investigations.
- The cardiothoracic ratio on a chest radiograph is normally less than half the width of the chest.
- A barium study uses a contrast medium to outline the lumen of the gastrointestinal tract.
- Ultrasound uses sound waves and is safe in pregnancy, making it the first choice for imaging the fetus.
- CT gives detailed cross-sectional images and is excellent for bone and acute bleeding.
- MRI gives excellent soft tissue detail and uses no ionising radiation.
- Contrast media outline vessels in angiography and highlight the urinary tract in an intravenous urogram.
- Ionising radiation carries a small risk, so imaging is chosen to give the most information for the least dose.
- The as low as reasonably achievable principle guides the safe use of radiation in imaging.
- Recognising the normal appearance of structures on each modality is the basis for detecting the abnormal.
- Radiographs of the growing skeleton show epiphyseal plates that must not be mistaken for fractures.
Imaging modalities at a glance
- **Plain radiograph:** Uses X-rays. Bone white, air black. Good first look at chest, abdomen and bones.
- **Ultrasound:** Uses sound waves, no radiation. First choice in pregnancy and for soft tissue and vessels.
- **CT:** Cross-sectional X-ray images. Excellent for bone, trauma and acute bleeding.
- **MRI:** Uses magnetic fields, no ionising radiation. Best for soft tissue such as brain and cord.
NMC competencies in this chapter
- **AN54.1:** Principles of radiodiagnosis and radiographic densities
- **AN54.2:** Imaging modalities: radiograph, ultrasound, CT and MRI
- **AN54.3:** Normal radiological anatomy and applied aspects
Frequently Asked Questions
Why is ultrasound preferred in pregnancy?
Ultrasound uses sound waves rather than ionising radiation, so it is safe for the fetus and is the first choice for imaging during pregnancy.
What are the basic radiographic densities?
From black to white they are air, fat, water or soft tissue, bone and metal. Recognising these shades is the basis for reading any plain radiograph.
When is CT chosen over MRI?
CT is fast and shows bone and acute bleeding well, so it suits emergencies and trauma, whereas MRI is chosen for detailed soft tissue such as the brain and spinal cord.
How does this chapter help in NEET-PG?
Understanding imaging modalities and normal appearances underlies radiology across all specialties, so radiodiagnosis is directly high-yield for PG preparation.
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