Medical One Liners 421-430

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421. For lung investigation - CT scan is best, except in Pancoast tumour/Superior sulcus tumour where MRI is investigation of choice to look for brachial plexus involvement.

422. Silhouette's sign or more correctly loss of silhouette sign:

• Middle lobe pathology: obscures right heart border
• Lower lobe pathology: obscures diaphragm
• Lingular pathology: left heart border
• Posterior segment of left upper lobe: aortic knuckle
• Also see this MCQ: here

423. Lordotic chest X-ray view is used for:

• Middle lobe examination (best view)
• Lung apex pathology
• Interlobar fissural effusion

424. Mammography:

• screening in >40 yr females - once yearly
• to detect DCIS - MRI is best (done in 2nd week of menstruation)
• in young female, mammography is not useful as there is a lot of glandular tissue that makes the breast very dense
• Most common sign of malignancy seen on mammogram: microcalcification
• Popcorn calcification in breast: Fibroadenoma {Note: Popcorn calcification in lungs - pulmonary hamartoma, it also has fat in the lesion}

425. Radiation doses: 

• Extremity X-ray = DEXA < Chest X-ray < Mammography < CT head < CT chest < CT Abdomen and pelvis < Coronary CT angiography < PET/CT
• Barium studies have doses close to CT head, except Barium enema which has dose just less than CT chest.

426. HRCT Lung - uses bone algorithm for image reconstruction, useful for:

• interstitial lung diseases and bronchiectasis

--> HRCT in Alveolar proteinosis: Crazy pavement appearance (see also: MCQ)

--> HRCT is also used in temporal bone imaging.

• for Bony labyrinth: do CT
• Membranous labyrinth: do MRI

427. All fractures are well visualized on CT except stress fracture which is best seen on MRI due to edema.

428. MRI uses free induction decay to receive signals.

Absolute contraindication:

• Pacemaker
• Metallic (ferromagnetic) implant/foreign body

429. Substances that are white/hyperintense on T1 Weighted MRI:

• fat
• subacute haemorrhage
• posterior pituitary
• melanoma and its metastases

430. CSF is white on T2 weighted image and dark on T1 weighted image. 

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