Radiology facts

Best investigation for the detection of bone metastases

  • Radioisotope bone scan is the preferred method for the detection of bone metastases
  • It is more sensitive than radiography for the detection of most metastases
  • Technetium-99m is the commonly used radioisotope
  • It accumulates in reactive new bone that is formed in the metastases resulting in a ‘hot spot‘ in the scan
  • The amount of accumulation depends on the level of blood flow
  • In some cases, ‘cold spots‘ are also noted due to the absence of bone formation within the lesion
  • The results from a bone scan are not specific as the tracer can accumulate in other areas with increased bone formation such as sites of fracture healing / infection
  • So a bone scan should be followed by other radiological modalities such as CT scan to confirm the lesion

Threshold radiation dose for acute radiation syndromes:

  • Haematologic / haematopoietic syndrome – 1 Gy
  • Gastrointestinal syndrome – 5 Gy
  • Central nervous system syndrome – 20 Gy

Prevention of contrast nephropathy

  • Non ionic low osmolar contrast agents are preferred in patients with decreased renal function to prevent contrast nephropathy
  • Ionic contrast media have a higher risk for contrast nephropathy, and hence should be avoided
  • The amount of contrast media used should be limited
  • The patient should be well hydrated before the procedure
  • Supplementary interventions include use of N-acetylcysteine, fenoldopam, theophylline, prostaglandins and magnesium

Egg on side’ or ‘Egg on string’ appearance is characteristic of transposition of great arteries.

Alpha rays have the highest ionization power, whereas gamma rays have the highest penetration power.

Both meningioma and ependymoma show calcification. But it is more common in meningioma

Transfemoral route most preferred route to perform cerebral angiography

Nuchal oedema ultrasound marker is associated with greatest increased risk for Trisomy 21 in fetus

Non-contrast CT scan of abdomen is most sensitive imaging modality for diagnosis of ureteric stones in a patient with acute colic

Dual energy X-ray absorptiometry is the gold standard for the diagnosis of osteoporosis

At t=0 there are 6 x 10^23 radioactive atoms of a substance, which decay with a disintegration constant equal to 0.01/sec. What would be the initial decay rate?

Rate of decay = Disintegration constant X Number of radioactive atoms
= 0.01 X 6 x 10^23
= 6 X 10^21

Respiratory gating is a technique in radiotherapy in which the radiation is applied during that phase of respiratory cycle in which the tumour is in the best range. This is to prevent unnecessary radiation exposure to normal structures.

Permanent implants for brachytherapy

  • Iodine-125
  • Palladium-103
  • Gold-198
  • Caesium-131

Technetium—99m linked to Methylene disphosphonate is the most useful radio pharamaceutical for skeletal imaging

Gamma camera in Nuclear Medicine is used for Measuring the radioactivity.

Multiple sclerosis is a demyelinating disorder. Hence the lesions in MR imaging will be seen in the white matter (due to loss of myelin).

Presence of collaterals in an angiogram indicate that there is significant renal artery stenosis.

Diameter of the descending right pulmonary artery > 16 mm is the objective sign of identifying pulmonary plethora in a chest radiograph

Causes of rib notching:

  • Superior rib notching
    • Polio
    • Restrictive lung disease
    • Neurofibromatosis
    • Connective tissue disease
    • Osteogenesis imperfecta
    • Hyperparathyroidism
  • Inferior rib notching
    • Thrombosis of aorta
    • Coarctation of arota
    • Blalock Taussig shunt
    • Occlusion of subclavian artery
    • Pulmonary AV malformation

Radiotherapy is to be started within 10 days post surgery. Delay in starting radiotherapy for Wilm’s tumour can result in an increase in relapse rate.

Typical effective dose (mSv) for various investigations:

  • Chest X-ray: 0.02
    CT Head: 2.3
    CT Chest: 8
    CT Abdomen / Pelvis: 10
    Bone scan (Tc-99m): 4

Phosphorus 32 emits Beta particles

Radioisotopes used as systemic radionuclide: phosphorus, strontium, samarium

Alpha ray (helium ion) has the most ionization potential. Gamma ray has the most penetration power.

Plethoric lung fields are seen in conditions which increase pulmonary blood flow. They are:

  • Left to right shunt – ASD, VSD, PDA, Coronary artery fistula into right heart, Aortopulmonary window
  • Transposition of great arteries with ASD or VSD
  • Truncus arteriosus
  • Total anomalous pulmonary venous connection

Areas of spiculated microcalcifications on mammogram would suggest malignancy

On MRI the differential diagnosis of spinal cord edema is Myelomalacia

Most sensitive sonological indicator for aneuploidy is Nuchal translucency

One of the most chemoresistant tumors is Malignant fibrous histiocytoma

Bone scan of a patient with Multiple Myeloma shows cold spots

Spongy appearance with central sunburst calcification is seen in serous cystadenoma

Most common hormone deficiency seen after intracranial radiation therapy is growth hormone

FNAC is not done in a suspected case of pheochromocytoma

Osteosarcoma is one of the least radiosensitive tumors

Diffuse axonal injuries, It is associated with unconsciousness and CT scan shows multiple petechial haemorrhages.

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