The Added Value of Minimum Intensity Projection in Cases of Hypersensitivity Pneumonitis

Abstract Background: HRCT is the most sensitive examination to characterize the findings of hypersensitivity pneumonitis. High resolution computed tomography scanning is frequently carried out as part of the initial diagnostic assessment of HP. MinIP images aided in the visualization of some character-istics CT features of HP such as mosaic attenuation, and ground glass opacities by delineating low attenuating areas within mosaic attenuation. It also demonstrated areas of air trapping. MinIP images also showed better visualization of traction bron-chiectasis & and bronchiolectasis as well as cysts. However, visualization of other features of HP as ill-defined centrilob-ular nodules, reticulations, and honeycombing was not aided by MinIP. Aim of Study: To highlight the key role of high-resolution computed tomography scanning (HRCT scan) with the use of minimum intensity projection (MinIP) reformation in diagnosis of hypersensitivity pneumonitis (HP). Material and Methods: • The cross sectional prospective study involved 47 patients (40 female and 7 male) diagnosed as cases of hypersensitivity pneumonitis. Cases were referred from outpatient department of Pulmonology Unit of Kasr Al-Ainy Hospital for follow-up HRCTover a over a period of 10 month from January 2023 to October 2023. • All patients underwent HRCT chest using 16 channels mul-ti-slice computed tomography (MSCT) scanner in Kasr Al-Ainy hospital. Results: In this study out of total cases (47), 44.7% of cas-es showed features of non-fibrotic HP, while 55.3% of cases showed features of fibrotic HP. 
The most common HRCT finding seen in this study were mosaic attenuation & ground glass opacities both were seen in 93.6% of cases each. Similarly reticulations which included interlobular & intralobular interstitial thickening was seen in 55.3% of cases. Tractional bronchiectasis & tractional bronchi-olectasis was seen in 36.2% of cases and centrilobular nodules was seen in 27.7% of the cases. The least common findings seen were lung cysts and honey combing, both of them were seen in 17% cases each. Conclusions: • MinIP clearly delineates the difference in lung attenuation pattern within mosaic attenuation by delineating high attenu-ating areas such as ground glass opacity with areas of low at-tenuation such as air trapping. MinIP can be used as alternate for visualization of air trapping, where it’s difficult to acquire an expiratory study or when it’s unavailable. Similarly, as it can aid in better visualization of the airways, it is very help-ful in visualization of tractional bronchiectasis and tractional bronchiolectasis which indicates fibrotic nature of disease. • However, MinIP is unable to visualize other HRCT findings of HP such as centrilobular nodules & other fibrotic changes such as reticulations & honeycombing. Thus, MinIP should be used as an addition to conventional HRCT images in reaching diagnosis of HP.