Diagnostic Imaging and Therapeutic Radiology Essentials

Posted on Sep 28, 2025 in Biology

Musculoskeletal Radiology and Trauma Imaging

Imaging Methods in Musculoskeletal Radiology

Musculoskeletal radiology utilizes various methods to assess bone lesions and fractures.

  • Plain Film Radiography: Used primarily for assessing bone lesions and fractures. For small bones and children, single emulsion films are often used.
  • Computed Tomography (CT): Provides good visualization for sclerotic lesions of the spine, pelvis, wrist, ankle, foot, or when soft tissue tumors are present on normal film.
  • Magnetic Resonance Imaging (MRI): Cannot image cortical bone but provides better definition of soft tissue and bone marrow. Muscle, fat, fluid, tendons, ligaments, and cartilage can be clearly distinguished. In trauma, tumor, or inflammatory lesions of the skeleton or soft tissues, intravenous Gadolinium is administered to obtain clearer images.
  • Ultrasound (US): Used to evaluate soft tissues of the musculoskeletal system. Can assess joints, tendons, ligaments, foreign bodies, and guide procedures such as needle aspiration.

Osseous System: Normal Anatomy

There are five types of bones:

  1. Long bones: Longer than they are wide, major bones of the limbs (e.g., femur, tibia, fibula, metatarsals, phalanges). They contain a hollow medullary cavity that stores bone marrow.
  2. Short bones
  3. Flat bones
  4. Irregular bones
  5. Sesamoid bones

Bone structure consists of an outer cortex and an inner medulla. The difference in density allows for differentiation on X-rays, with the cortex being denser and therefore appearing whiter.

Skeletal Trauma and Physeal Injuries

Imaging modalities such as radiographs, sonography, CT, MRI, and bone scintigraphy demonstrate the extent of injury within the soft tissues or bone marrow.

  • Fracture: A break in the continuity of bone, cartilage, or both. Fractures are classified as:
    • Closed fracture: Skin intact.
    • Open fracture: Skin pierced.
    • Complete fracture: The whole tubular shaft circumference is broken.
    • Incomplete fracture.
  • Bone Bruising: Seen as bone contusion, often due to stress fractures.
  • Compression Fracture and Depression Fracture.
  • Fat released from marrow after trauma can be detected on radiographic examination using the horizontal beam technique.

Physeal Injuries (Growth Plate)

Physeal injuries occur at the growth plate in children. The five types of Salter-Harris fractures are seen on radiographs:

  1. S = Separated (separates the growth plate apart)
  2. A = Above (fracture line extends above the physeal plate)
  3. L = Lower (fracture line extends lower than the physeal plate)
  4. T = Through (fracture line goes through the growth plate)
  5. R = Rammed or Crushed (crushes the physeal plate)

Thoracic Imaging: Pleura and Mediastinum

Pleural Lesions and Fluid Accumulation

The pleura has two layers: visceral and parietal. They produce pleural fluid, which is resorbed through lymph channels. Increased production or decreased resorption leads to pathological accumulation (effusion) in the pleural cavity.

Pleural fluid types:

  • Clear Transudate: Clear, yellow, typically bilateral. Associated with cardiac failure, renal failure, or hypoproteinemia.
  • Serofibrinous Exudate: Yellow-brown or purulent. Associated with TB, subphrenic abscess, lung cancer, or connective tissue diseases (e.g., lupus erythematosus).
  • Blood Effusion (Hemothorax): Due to open or closed trauma, or hemorrhagic diseases with increased bleeding time.
  • Chylous Exudate: Due to thoracic trauma or obstruction of the thoracic duct (e.g., filariasis, which affects lymph nodes).

Plain chest X-ray cannot differentiate between these types, so Pleurocentesis is performed. In the upright position, fluid accumulates first in the costophrenic angle (posteriorly, then laterally), appearing as opacity on the film.

Lying in the lateral decubitus position helps distinguish pleural fluid from pleural thickening, as gravity causes fluid to collect between the lateral chest wall and the lung.

Unilateral accumulation of fluid causes mediastinal deviation towards the side that is normal. This is helpful in the differential diagnosis of a collapsed lung (atelectasis), where mediastinal deviation occurs towards the affected side.

Mediastinal Lesions and Localization

A lateral view can be used to localize an anterior, superior, or middle mediastinum mass seen on the frontal view.

Mediastinal Compartments:

  • Anterior Mediastinum: Retrosternal space and heart.
  • Middle Mediastinum: Structures along the trachea, esophagus, and between hilar shadows.
  • Posterior Mediastinum: Areas on both sides of the thoracic column.

Masses by Location:

  • Anterior Mediastinum Masses: Caused by retrosternal goiter, tumor/cyst in the thymus, or dermoid cyst. A goiter causes deviation and compression of the trachea. Near the diaphragm, anterior masses are usually a pericardial fat pad, pericardial cyst, or Morgagni hernia.
  • Middle Mediastinum Masses: Aortic arch aneurysm, bronchogenic cyst, lesions in the esophagus, or enlarged lymph nodes.
  • Posterior Mediastinum Masses: Neurogenic tumors, paravertebral soft tissue enlargement, or hematomas due to fractures of the vertebral column.

CT scans can precisely define the location of mediastinal masses. MRI is favored as it can characterize the nature of the mass.

Mediastinitis: Arises after perforation of the esophagus or thoracotomy, which increases the width of the mediastinum.

Gastrointestinal and Abdominal Radiology

GI Tract Examination Techniques

  • Double-Contrast Barium Meal (DCBM): The aim is to visualize all parts of the esophagus, stomach, and proximal duodenum in double contrast with good mucosal barium coating. Gastrografin is the most common contrast agent used.
  • CT Scanning: Useful in gastroduodenal disease for staging of neoplasms and assessment of extramural disease. Also useful in gastroduodenal perforation. CT scanning is the method of choice for imaging extramural colorectal disease. Limitation: Bowel thickening is non-specific.
  • MR Imaging: Useful in detecting fistulas and abscesses in Inflammatory Bowel Disease (IBD).
  • Other techniques include Endoscopic Ultrasound, Enteroclysis examination, and Double Contrast Barium Enema.
  • Esophageal Manometry: Used for esophageal motility disorders.

Gastrointestinal Tract: Normal Anatomy

The GI tract consists of a hollow muscular tube starting from the oral cavity, continuing through the pharynx, esophagus, stomach, and intestines to the rectum and anus.

  • Salivary Glands: Three pairs of glands communicate with the oral cavity.
  • Oesophagus: Muscular tube, approximately 25 cm in length and 5 cm in diameter. Made up of inner circular and outer longitudinal layers. A nerve plexus surrounds the lower portion.
  • Stomach: J-shaped expanded bag, consisting of the fundus, body, pylorus, etc. Contains stomach acid used for digestion.
  • Small Intestine: Duodenum, jejunum, and ileum.
  • Large Intestine: Horseshoe-shaped, consisting of the cecum, ascending, transverse, descending, sigmoid colon, and rectum.
  • Liver: Organ used for detoxification, metabolism, and bile production.
  • Gallbladder: Pear-shaped organ for storage and concentration of bile.
  • Pancreas: Has both exocrine (numerous acini) and endocrine (Islets of Langerhans) functions.

Pancreas Disease Imaging

Techniques for imaging include simple X-ray, Endoscopic Retrograde Cholangiopancreatography (ERCP), CT, and MRI.

CT Findings:

  • Focal or diffuse enlargement of the pancreas.
  • Infiltration of the peripancreatic fat.
  • Fluid collections in the peripancreatic and anterior pararenal spaces.

ERCP is performed by cannulating the ampulla of Vater under radiological control. Contrast medium is injected into the common bile duct and pancreatic duct, allowing visualization of biliary obstruction due to stones or neoplasm.

Spleen Disease Imaging

Ultrasonography (US) is frequently the first imaging modality used to evaluate the spleen. Color Doppler is useful in the evaluation of vascular pathology in the splenic hilum.

  • Unenhanced CT images are mainly used for the detection of splenic calcifications.
  • MRI shows the characteristic findings of a cyst: a well-defined round mass with a thin or imperceptible wall, homogeneous hypointense on T1-weighted images, and hyperintense on T2-weighted images.

Splenomegaly is a radiologic and clinical sign, classically described when the craniocaudal splenic length is more than 12 cm. This may result from congestion.

Congenital Abnormalities: The congenital absence of the spleen is known as asplenia, and the presence of one or more accessory spleens is known as polysplenia. Both are very rare and usually associated with other congenital abnormalities.

Urogenital System Imaging

Bladder and Urethra Disease Imaging

Bladder Imaging Techniques

  • Intravenous Pyelogram (IVP) / Intravenous Urogram (IVU): An X-ray of the urinary system taken after injecting a special dye into a vein. The dye outlines the kidneys, ureters, and bladder, helping to show urinary tract tumors.
  • Retrograde Pyelogram: A catheter is placed through the urethra up into the bladder or ureter. Dye is injected through the catheter to make the lining of the bladder, ureters, and kidneys easier to see on X-rays.
  • MRI: Particularly useful in showing if cancer has spread outside of the bladder into nearby tissues or lymph nodes. An MRI Urogram (special MRI of the kidneys, ureters, and bladder) can be used instead of an IVP.
  • CT Urogram: A CT scan of the kidney, ureters, and bladder. It provides detailed information about the size, shape, and position of any tumors in the urinary tract.
  • Ultrasound: Useful in determining the size of a bladder cancer and whether it has spread beyond the bladder to nearby organs or tissues.

Specific Bladder Conditions

Bladder Calculi (Stones):

  • Plain Radiograph: Usually densely radiopaque. Calculi may be single or multiple and are often large. Frequently, lamination is observed internally, like the skin of an onion.
  • Ultrasound: Sonographically, they are mobile, echogenic, and shadow distally. They may be associated with bladder wall thickening due to inflammation.

Bladder Exstrophy (Ectopia Vesicae): Refers to a herniation of the urinary bladder through an anterior abdominal wall defect. Imaging findings include a soft-tissue mass extending from a large infraumbilical anterior wall defect, the absence of a normal urinary bladder, and a low-lying umbilical cord insertion.

Neurogenic Bladder: A dysfunctional urinary bladder resulting from injury to the central or peripheral nerves that control urination. Ultrasound often demonstrates a thick wall with a small contracted or large atonic bladder. A large post-void residual is frequently noted.

Urethra Imaging Techniques

  • Retrograde Urethrography (RUG): Considered the standard study for urethral and periurethral imaging in men. Indicated for evaluating urethral injuries, strictures, and fistulas. The patient is placed in a supine 45° oblique position. 20–30 mL of 60% iodinated contrast material is injected under fluoroscopic guidance to fill the anterior urethra.
  • Voiding Cystourethrography (VCUG): The most commonly used imaging method in the evaluation of the female urethra and male posterior urethra. Performed after the bladder is filled with contrast material (via transurethral or suprapubic catheterization, typically using a 14 French Foley catheter).

Urethra Diseases:

  • Strictures of the Urethra: Use Sonourethrography, CT, or X-ray.
  • Urethral Diverticula: Use VCUG, an examination in which fluoroscopy of the bladder and urethra is performed during voiding.

Nuclear Medicine Principles and Applications

Cardiac Radionuclide Studies

Myocardial Perfusion Imaging (MPI): Used for the diagnosis and management of Coronary Heart Disease (CHD). Radiopharmaceuticals used include Thallium-201 and 99mTc-labeled agents.

  • A normal heart receives increased blood flow during exercise. Since the amount of thallium extracted by the heart is proportional to blood flow, thallium uptake is also increased.
  • In ischemic or infarcted heart tissue, blood flow and therefore thallium uptake are decreased. The image appears as an area of relatively decreased thallium uptake. Thallium uptake in the heart should be uniform.
  • To distinguish between ischemic and infarcted heart tissue, delayed images are taken after 3–4 hours:
    • In ischemic heart, the abnormality returns to normal on delayed images (reversible defect).
    • A fixed defect is present in infarction.
  • SPECT imaging is commonly performed.

Myocardial Infarct Imaging: Radiopharmaceutical (RP) is 99mTc stannous pyrophosphate. It localizes in areas of acute Myocardial Infarction (MI). Calcium accumulation in the peripheral zones of MI correlates with sites of maximum pyrophosphate deposition. Indications include identifying MI several days after the acute event.

Equilibrium Gated Radionuclide Ventriculogram (EGRV): Widely used for monitoring left ventricular function. RP involves injecting stannous pyrophosphate IV to sensitize the RBC membrane, followed by injection of 99mTc-pertechnetate, which enters the sensitized RBCs. Gated imaging is synchronized with the ECG.

In Hypertrophic Cardiomyopathy, the R-R interval increases from 50 ms to 90–200 ms as the heavy wall stays contracted before the beginning of fast filling. Wall motion is categorized by the observer using a special color-translation table:

  • Normal: Converging vigorously on the center of the blood pool during systole.
  • Hypokinetic: Not moving enough.
  • Akinetic: Not moving at all.
  • Dyskinetic: Moving in the wrong way.

Pulmonology: Ventilation/Perfusion Scanning

Radionuclide Ventilation/Perfusion (V/Q) scanning is divided into two parts:

1. Perfusion Scan: Performed with radioactive particles (99mTc) injected intravenously. Distribution is proportional to blood flow. If an embolus occludes a vessel, a perfusion defect will be found. It is a sensitive test for Pulmonary Embolism (PE). In PE, defects are segmental, peripheral, wedge-shaped, and often found in the lower lobes. The lung may appear smaller than normal. Perfusion scans are not specific, hence ventilation scans are always performed as part of a lung scan.

2. Ventilation Scan: Performed with radioactive gas (133Xe) inhaled before the perfusion scan.

  • V/Q Mismatches: Good ventilation with decreased perfusion. Highly indicative of PE.
  • V/Q Matches: Decreased perfusion with decreased ventilation. Consistent with non-embolic pulmonary disease (e.g., COPD, asthma, pneumonia, tumors).

Principles of Radioimmunoassay (RIA)

RIA is a very sensitive in vitro assay technique used to measure concentrations of antigens (e.g., hormone levels in blood) by using antibodies. RIA is extremely sensitive and specific; for example, it can distinguish the difference between T3 and T4, even though they only differ by one iodide atom.

Competitive ligand binding is the basis of RIA.

Components of RIA: IgG specific antibody (Ab), radiolabeled antigen (Ag), and an unknown sample containing the same Ag that is to be measured.

Method Example (Measuring Patient Insulin Levels):

  1. Antibodies are placed in wells on a dish.
  2. Radiolabeled Ag (Insulin Ag tagged with a radioactive dye, usually iodine) is added, which binds to the Ab.
  3. The patient’s blood is added. If the patient’s blood has the same Ag being measured (insulin), the Ag in the blood will displace the radiolabeled Ag.

Increased patient Ag concentration leads to a decreased percentage of radiolabeled Ag bound to the Ab. Radioactivity in the two Ag fractions (bound or free) may be measured in a gamma counter.

Clinical Uses: Measuring ACTH, ADH, aldosterone, cortisol, estradiol, estrogen, LH, FSH, PTH, insulin, gastrin, glucagon, thyroid function tests (free T3, T4, TBG, TSH), dosage of drugs (digoxin, methotrexate), IgE, and Ag or Ab for hepatitis.

Radiotherapy: Physics and Clinical Use

Ionizing Radiation: Attributes and Interactions

Ionizing Radiation: When an X-ray or gamma ray passes through a medium, interaction between photons and matter transfers energy to the medium.

  • Electrons transfer energy by producing ionization and excitation of atoms along their path.
  • Ionization: The process where neutral atoms acquire a positive or negative charge (stripping electrons from atoms).
  • Charged particles are known as directly ionizing radiation. Uncharged particles are indirectly ionizing radiation.

Interactions of Photons with Matter:

  1. Coherent Scattering: No energy is changed into motion, and none is absorbed in the medium.
  2. Photoelectric Effect.
  3. Compton Effect: A photon interacts with an atomic electron; the electron receives energy from the photon and is emitted.

Dosimetric Quantities and Measurements

Exposure (X): A measure of ionization produced in air by photons. $X = dQ/dm$. Unit: Coulomb per kilogram (C/kg) or Roentgen (R). $dQ$ is the absolute value of the total charge; $dm$ is the mass.

Absorbed Dose (D): Describes the quantity of radiation for all types of ionizing radiation. Not used over 3 MeV.

  • $D = dE/dm$. $dE$ is the mean energy imparted by ionizing radiation.
  • Old unit: rad.
  • SI unit: Gray (Gy). 1 Gy = 1 J/Kg.

Power of Dose ($P_d$): The quotient of dose by the time. $P_d = D/t$. Unit: Gy/h.

Radiotherapy for Specific Cancers

Nasopharynx Cancer Radiotherapy

Radiation doses typically range from 66–70 Gy (2.0 Gy/fraction; daily).

  • External-Beam Radiation Therapy (EBRT)
  • Proton Therapy
  • Brachytherapy: When radiation treatment is given using implants, it is called internal radiation therapy.

Lymphoma Radiotherapy

Lymphomas are cancers of the cells of the lymphatic system (B cell lymphoma is more common in adults). The two main types are Hodgkin’s and Non-Hodgkin’s (10 types).

Radiation Therapy (EBRT):

  • Mantle Field: Radiation given to the lymph node area in the neck, chest, and under the arms. The treated area is a T shape that runs across the shoulders, neck, and sternum.
  • Inverted Y: Radiation given to lymph nodes in the upper abdomen, spleen, and pelvis (an upside-down Y treating the spine and groins).
  • Total Nodal Irradiation (TNI): Radiation given to both the mantle field and inverted Y.

Total dose is typically 30–40 Gy. Chemotherapy can also be used.

Skin Cancer Radiotherapy

Two types: malignant melanoma and non-malignant (Basal Cell and Squamous Carcinoma).

Etiology: Ultraviolet light, skin type and color, dysplastic nevus, burns.

Diagnosis: Biopsy.

Treatment:

  • For malignant melanoma, surgical treatment is primary. Radiotherapy is rarely used after surgery.
  • For palliative care, doses are typically 400 Gy daily for 5 days or 300 Gy daily for 7 days.

Radiotherapy of Non-Oncological Diseases

Non-tumor diseases can be treated by radiotherapy for its benefits:

  • Anti-irritative
  • Analgesic
  • Antihyperemic

Most Popular Diseases Treated:

  • Orthopedics: Arthrosis deformans, spondylosis, osteochondrosis, bursitis, tendinitis. Daily dose 50–100 Gy, total dose 200–400 Gy. Treatment can be repeated after 6–8 months.
  • Surgery: Furunculosis, hidradenitis axillaris, abscesses. Daily dose 50–100 Gy, total dose 150–300 Gy.
  • Neurology: Syringomyelia, neuralgia, neuritis chronica.
  • Ophthalmology: Blepharitis, ulcus corneae, iritis, uveitis (use caution as the retina is vulnerable).
  • Dermatology: Mycosis fungoides, hemangioma cutis and ossarum.