MedicoNotebook

0 X-ray photon interaction with matter

X-ray photon interaction with matter can occur in various forms:

Photoelectric effect {low energy photon (energy just greater than binding energy of electron) interacts with innermost shell electron}- MCQ

directly proportional to atomic number of matter
inversely proportional to cube of incident photon energy
maximum with tightly bound electrons (i.e. innermost shell - K)

Compton scattering/effect

is the cause of scatter radiation and thus increase radiation dose
does not depend on atomic number
inversely proportional to photon energy

Coherent scattering
Pair production (not important in diagnostic radiology)

Author: Dr Ayush Goel

0 Stroke

Author: Dr Ayush Goel

Stroke (cerebrovascular accident) is a neurological deficit that can occur due to:

ischemia (ischaemic stroke)
haemorrhage (haemorrhagic stroke)

lobar haemorrhage
hypertensive haemorrhage

Imaging

CT scan

First investigation to be undertaken is CT scan, to rule out haemorrhage. It is thus the investigation of choice for haemorrhagic stroke.

Axial Non contrast CT image showing left capsuloganglionic haemorrhage as hyperdense area
Image courtesy: Dr Ayush Goel

Hyperacute/early Ischaemic stroke is best evaluated on MRI (see below), however, there are subtle signs that may be present on CT to help make a diagnosis:

Hyperdense MCA sign: shows clot in MCA (earliest sign on CT)
Loss if Insular ribbon
Loss of grey-white matter differenciation

Red - loss of insular ribbon and grey-white matter differentiation; green - normal insular ribbon, blue - normal deep grey matter.
Image courtesy: Dr Ayush Goel

Later, even CT can demonstrate the infarcted area very well as wedge shaped hypodensity in the particular vascular territory.

Chronic infarct in left MCA terriotory
Image courtesy: Dr Ayush Goel

MRI

It is the investigation of choice for ischaemic stroke.

Diffusion weighted MR imaging is the earliest to detect ischaemic region as hyperintense on DWI and hypointense on ADC maps.

ADC (Red circle) and DWI (Blue circle)
Image courtesy: Dr Garima Goel

MedicoNotebook - Founder : DrShiviMudgal (Goel) , Co-Founder : DrAyushGoel

0 Medical One Liners 411-420

411. Bulging fissure sign: Klebsiella pneumonia

412. Venous sinus thrombosis CT:

Non contrast - dense delta sign
Contrast CT - empty delta sign

413. Worst headache of life: Subarachnoid haemorrhage

414. Investigation of choice for

aneurysm - angiography
aortic aneurysm - CT scan as there may be intraluminal thrombus
aortic dissection - MRI

415. Basal exudates on CT seen in: Tuberculous meningitis and cryptococcal meningitis.

416. Contrast of X-ray image is inversely related to kVp.

417. Radiation intensity is inversely proportional to square of distance from the radiation.

418. Chest X-ray PA view is taken with film to focus distance of 180 cm. Chest AP view and other X-rays are taken at 100 cm.

419. Golden S sign: Right upper lobe collapse due to hilar mass.

420. Most common lung carcinoma with cavitation: Squamous cell carcinoma

MedicoNotebook - Founder : DrShiviMudgal (Goel) , Co-Founder : DrAyushGoel

0 Myocardial perfusion and viability

Author: Dr Ayush Goel

Myocardial perfusion and viability assessment is important for many reasons:

to diagnose, locate and grade the severity of coronary artery disease
to identify candidates who would benefit from re-vascularization
to evaluate response of re-vascularization

Terminology

Stunned myocardium

It refers to a state in which there is wall dysfunction but the perfusion (resting and stress) is normal.

Myocardial ischemia

It refers to a state in which there is decreased perfusion on stress but normal during rest (seen as reversible perfusion defect). These patients will significantly benefit with treatment.

Hibernating myocardium

In this the myocardium shows decreased perfusion on both stress and resting phase (seen as fixed defect) but the myocytes are viable and will benefit from revascularization.

Myocardial infarct

In this there is absent perfusion on both stress and resting phase (seen as fixed defect) and the myocytes are not viable. There will be no benefit from revascularization.

Imaging techniques

thallium-201 SPECT
- excessive radiation dose (c.f. 99mTc-MIBI)
- redistribution may occur
- single injection for stress and resting phase
99mTc-Sestamibi SPECT
- less radiation dose
- no redistribution
- separate injections for stress and resting phase
FDG-PET (for viability)
- based on the fact that myocardium utilizes glucose for metabolism when under effect of ischemia (hence the ischemic myocardium will show greater uptake than normal cells)
- under normal circumstances, it utilizes fatty acids for energy
- non-viable myocardium will not show any uptake
Cardiac MR perfusion imaging