<prompt> Investigation of choice for Interstitial Lung Disease?Plain chest X-rayHRCTMRIUltrasonography  <response>: Ans. b HRCT Ref. Harrison 18th p 1554High Resolution Computerized Tomography BASIC PRINCIPLE:- Bone algorithm Basic Principle0- Narrow beam collmation- 1 mm sections- Small field of view- Large matrix size INDICATIONS Investigation of choice for:- LUNGS: Interstitial Lung Disease ILD Bronchiectasis Signet-ring sign Emphysema- PETROUS TEMPORAL BONE: Cholesteatoma Mastoiditis Petrositis Ossicular chain disruption Congenital ear malformations Facial canal fracture Some Patterns of ILDs on HRCT:- Groundglass haziness is the earliest sign of almost all ILDs.0- Honeycombing correlates with end-stage disease.- Tree in bud apperance is seen in atypical mycobacterial infectionendobronchial TB.deg- Crazy paving is seen in several ILDs but is a distinct feature of Pulmonary Alveolar Proteiniosis.- Multiple discrete lung cysts and chylous pleural effusion in a postmenopausal women is chracteristic of lymphangioleomyomatosis.- Mosaic perfusion is also a feature of ILD.Also KnowDiseases with Predeliction for Upper Lung ZonesDiseases with Predeliction for Lower Lung ZonesExtrinsic allergic alveolitis chronic hypersensitivity pneumonitisFibrosing alveolitisCWPAsbestosisLCHInterstitial pulmonary edemaAnkylosing spondylitisLymphangitis carcinomatosaSilicosis Sarcoidosis 