The term ‘‘interstitial lung disease’’ is synonymous with ‘‘diffuse parenchymal lung disease’’^[1]. Interstitial lung diseases are a group of diffuse parenchymal lung disorders associated with substantial morbidity and mortality.^[2]The American Thoracic Society and European Respiratory Society define ILD as a heterogeneous group of non-neoplastic disorders resulting from damage to the lung parenchyma by inflammation and fibrosis that diminish the lung’s capacity for alveolar gas diffusion.^[3]

CLASSIFICATION OF ILD ^[4,5]

ROLE OF IMAGING IN DIAGNOSIS:

                Imaging plays a key role in the diagnosis and assessment of interstitial lung disease (ILD). Multidisciplinary team with expertise in ILD can often reach a reliable diagnosis based on clinical finding and radiology alone, as exemplified by the Join Consensus International Societies Statement on the classification of idiopathic interstitial pneumonias.^[6]

CHEST RADIOGRAPHS:

• Chest radiography is typically the first radiological investigation requested and is frequently the initial indicator of ILD.
• It can be crucial to compare a patient's current chest radiograph with their prior ones in order to detect radiological anomalies and validate the existence of a progressing lung disease.
• Chest radiography may help exclude oedema or infection and can screen for complications, including malignancy. Typical findings in idiopathic pulmonary fibrosis include reticulations and reduced lung volumes.

HIGH RESOLUTION COMPUTED TOMOGRAPHY:

• The latest clinical guidelines from the American Thoracic Society and European Respiratory Society recommend HRCT as a more sensitive tool for detecting ILD compared to chest radiography or conventional chest CT, making it essential for diagnosing ILD. ^[7,8]
• High resolution computed tomography is now a standard investigation in patients with suspected interstitial lung disease.
• HRCT plays a key role in identification of the pathological phenotype of ILD, and typical imaging features are well recognised in international consensus guidelines.^[3]
• HRCT can also aid in distinguishing between various types of ILDs, including subclassifying CTD-ILDs and differentiating between early and progressive stages of the disease. ^[9-11]

HRCT IN PROGNOSIS:

• Beyond diagnosis, HRCT is valuable for assessing prognosis in ILDs. The extent of honeycombing and reticulation can help predict mortality risk in IPF patients.
• Assessing fibrosis extent can suggest a poor prognosis for patients with fibrotic ILDs, even in cases of fibrotic IIP with minimal honeycombing. ^[12,13]

MAGNETIC RESONANCE IMAGING:

• Combining functional and morphological information, MRI has been arising as a radiation-free alternative, comparable to CT in many instances.^[14,15]
• The presence of high signal intensity lesions has been reported as a helpful predictor of treatment response and prognosis.^[16]
• Drawbacks with MRI is that it has a poor signal-to-noise ratio in the lung and are currently overshadowed by HRCT as the imaging technique of choice for ILD diagnostic and prognostic purposes.^[17]

TRANSTHORACIC ULTRASOUND:

• While international guidelines do not define a specific role for TUS (transthoracic ultrasound) in evaluating ILDs (interstitial lung diseases), this imaging technique offers several advantages. It is non-invasive, safe, enables rapid real-time assessment, and is accessible for clinicians across all hospital wards.
• TUS can be valuable in identifying early lung involvement and monitoring ILD progression, serving as a timely prompt for follow-up chest CT scans when necessary.

Study Design- Cross-Sectional Observational Study Study Duration- 24 months from the approval of Ethical Committee. Study Population- 100 patients. Method A prospective study was carried out at Parul Sevashram Hospital. Consecutive patients presenting with respiratory symptoms like cough, fever, difficulty in breathing, dyspnea on exertion, tachypnea and seeking medical advice for the same or have medical conditions due to such affliction will be included in the study after taking consent. 100 patients meeting the inclusion criteria were enrolled in the study. Written Informed consent was obtained from each patient. Inclusion Criteria • Patients of all ages were included. • No gender bias. • Patients presenting with signs and symptoms suggestive of Collagen Vascular Diseases like SLE, rheumatoid disease, systemic sclerosis, MCTD, UCTD, poly-derma. • Patients of Pulmonary / Systemic vasculities like Wegener’s granulomatosis, Churgg-Strauss syndrome, Microscopic polyangitis, Diffuse alveolar haemorrhage, etc. • Patients with history of occupational exposure to asbestos, silica, coal dust, heavy metal exposure, aluminium, organic dust etc. • Patients on pneumato-toxic drugs. • Patients with exposure to radiotherapy. • Patients with history of allergy. Exclusion Criteria • Known cases of pulmonary infections, pneumocystis carinii pneumonia, viral pneumonias. • Known cases of pulmonary metastasis. • Known cases of tuberculosis (except silico-tuberculosis). • Known cases of lung masses. • Known cases of lymphangitic carcinomatosis. • Pregnant females. • Those who didn’t gave consent. TECHNIQUE: All patients were subjected to chest X ray & followed by HRCT thorax, at the same time using: 1. X ray machine – GE X Ray Machine 2. Toshiba Alexion 16 slice CT scan machine. CHEST X RAY TECHNIQUE: PA view was taken in full inspiration. SCANNING PARAMETERS: • POSITION: Supine, Prone • SCANNER SETTINGS: kV (p)-120, mAs (effective)-100-200 or dynamic • COLLIMATION: 1 mm • SCAN TIME: 60-90 sec • MATRIX SIZE: 512 x 512 • SUPERIOR EXTENT: Lung apices. • WINDOW SETTINGS: Lung window and Mediastinal window. • SLICE THICKNESS: 0.625-1.25 mm • FOV: 35 cm • RECONSTRUCTION ALGORITHM: High spatial frequency HRCT THORAX TECHNIQUE: • 1 mm collimation sections were obtained. Five to eight slices with thincollimation were obtained at different anatomic levels of the lung. 2 cm or 3 cm intersection gap was used. Scanning was performed using a field of view large enoughto encompass both lungs (35-40cm). • Retrospective targeting of the imagereconstruction to a single lung or an even smaller portion of the lung parenchyma was done for spatial resolution. • Inspiratory and expiratory scans were taken in all patients.