<prompt> HRCT is investigation of choice for?Mediastinal lesionsChest traumaLung cancerInterstitial lung disease  <response>: Ans. D. Interstitial lung disease.HRCT Lungs: BASIC PRINCIPLE- Bone algorithm Basic Principle6- 1 mm sections 6- Narrow beam collumation 6- Small field of view6- Large matrix size INDICATIONS Investigation of choice for- LUNGS: Interstitial Lung Disease ILD6 Bronchiectasis Signet-ring sign 6 EmphysemaILD: Radiologic patterns of INTERSTITIAL LUNG DISEASES ILD Reticular patternNodular patternReticulonodularSeptal GroundglasspatTree-in-bud Fibrosing alveolitis Asbestosis Sarcoidosis Chro allergic alveolitis LCH LAM Silicosis CWP Sarcoidosis TB Subacute EAA LCH Sarcoidosis Lymphangitis Ca Interst pulm edema Lymphangitic Ca P. jerovecii Atyp TB NSIP Pulm hge Alveolar proteiniosis Eosinophilic pneumoEndo TB Collagen vas ds Ex. Allergic alveolitis HRCTDisease1. Reticular pattern Many ILDs2. Multiple cysts Lymphangioleomyomatosis LAM Pulmonary Histiocytosis3. Lepidote growth Bronchoalveolar cancer4. Crazy paving Alveolar proteinosis silocosis5. Tree-in-bud appearance Endobronchial TB and Atypical mycobacterial TB6. Ground glass hazzinessEarliest radiological finding of any ILD7. Bilateral perihitar ground glass haziness, especially in a immunocompromised individualPCP ILDs primarily affecting UZs ILDs primarily affecting LZs Extrensic ellergic alveolitis Coal workers pneumoconiosis Langerhans disease Ankylosing spondylitis Sarcoidosis Silicosis Mnemonic: E-CLASS Fibrosing alveolitis Asbestosis bilat basal affection Interstitial pulmonary edema Lymphangitis carcinomatosa Mnemonic: FAILAdditional Educational points:Role of CT, PET scan, Bronchoscopy and Image guided biopsy in Pulmonary Nodule evaluation: Investigation for SPNSensitivitySpecificityAccuracyComment1.Transthoracic FNAB95-10091-- Gives tissue diagnosis; Best for evaluating SPN.2.PET FDG scan92-10052-10094 Best non-invasive tool for evaluating SPN.3.CECT987385 If a chest x-ray shows a lung nodule, usually CECT is best to roughly know whether it is infectivecongenital neoplasm. And main advantage of CT is it maps the lesion, apart from characterizing the lesion. Further CT is best to guide lung mediastinal biopsies.4.HRCT--- Not primarily useful for solitary lung nodule evaluation. It is for diffuse or interstitial lung diseases.5.MRI--- Not much preferred for chest imaging except for pathologies like Pancoast tumor; Vascular lesions, Neurogenic tumors, etc.6.Bronchoscopy--- Should be used for central lesions if at all and endobronchial lesions. Can be used if CT chest is normal.SPNSolitary Pulmonary Nodule. 