High-resolution computed tomography (HRCT) of the lung is well established in its role in formulating an initial diagnosis in patients with diffuse lung disease (DLD); however, its ability to monitor patients with serial examinations may be equally important. Patients with DLD often undergo multiple HRCT examinations at various stages in their disease. This longitudinal imaging data often provides significant additional information compared with a single time point and may be used in a variety of ways, including: 1) increasing the accuracy of initial diagnosis; 2) assisting in the estimation of prognosis; 3) identifyingprogression of disease; 4) detecting new processes in patients with acute or worsening symptoms; and 5) detecting other abnormalities or complications, such as lung cancer. In the future, quantitative imaging techniques that can more accurately characterize and measure the extent of lung affected by disease may routinely complement visual assessment by radiologists. Clinicians and radiologists should be aware of the role of serial imaging and understand the expected progression of DLDs over time. The goal of this paper is to define the role that longitudinal HRCT plays in patients with DLD.Diffuse lung diseases are those in which the disease process is widespread involving both the lungs but need not affect all lung regions uniformly. Plain chest radiograph though inexpensive, excellent modality of choice, the pattern of diffuse lung disease on radiography is often nonspecific. HRCT can detect normal and abnormal lung interstitium and morphological characteristics of both localized and diffuse lung diseases.HRCT technique There are several issues specific to longitudinal imaging in patients with DLD that may affect the selection of a preferred HRCT technique. The most important of these is the decision to use volumetric or spaced axial scans. Spaced axial imaging performed at 0.5–2 cm intervals imparts a lower radiation dose and usually provides adequate sampling of the lung parenchyma that is representative of the overall process when compared to volumetric computed tomography [1] and histopathology obtained from lung biopsy [2]. As several series (supine, prone, expiratory) are often obtained contemporaneously in patients with DLD, spaced axial imaging provides an incremental reduction in overall radiation dose compared with multiple volumetric acquisitions. On the other hand, volumetric imaging is superior in its ability to image the entirety of the lung parenchyma. This may be particularly advantageous in the serial follow-up of DLD. Subtle changes in disease extent may be easier to appreciate when the whole lung is imaged, whereas the sampling error intrinsic to spaced axial images may significantly limit the assessment of longitudinal changes. In the near future, quantitative lung imaging may be used routinely in the evaluation of DLD. Quantitative computed tomography is not only able to evaluate extent of lung affected by disease, but is also able to distinguish different computed tomography findings based upon computerized textural analysis. Utilizing these techniques, quantitative computed tomography may contribute to estimating prognosis on initial imaging and determining progression of disease on serial imaging. This represents another significant advantage of volumetric imaging over spaced axial scans, given that quantitative computed tomography has been studied primarily in the context of volumetric datasets. Last, spaced axial scans may miss focal abnormalities such as pneumonia or lung cancer. Patients with DLD have reduced pulmonary reserve, thus the detection of active lung processes, such as pneumonia, is important so that early treatment may be instituted. The incidence of lung cancer is significantly higher in patients with DLD. Lung cancer may have a significant impact on mortality and transplant candidacy in these patients. The advantage of spaced axial scans over volumetric acquisitions has diminished as radiation reduction techniques have become more sophisticated. Model-based iterative reconstruction techniques can reduce effective dose by as much as 80% compared to older reconstruction techniques, without an associated reduction of diagnostic accuracy [3]. Additionally, the risks and benefits of higher-dose volumetric computed tomography techniques should be considered in the context of each individual patient. Given the delay between radiation exposure and the onset of most adverse effects, radiation is less of a concern in older patients or patients whose lifespan is reduced by their DLD. For all of the reasons detailed above, volumetric acquisitions have become the standard protocol at many institutions except for selected patient subgroups in which radiation exposure is a significant concern. Prone and expiratory images are often helpful in establishing an initial diagnosis, but may be less important on follow-up imaging. Prone imaging may provide a superior assessment of findings in the posterior sub-pleural lung, particularly in early DLD, whereas expiratory imaging is important in detecting airways obstruction. For many diseases, however, these series are not required after an initial diagnosis has been established. Expected evolution of findings over time on HRCT Longitudinal imaging of DLD may be helpful in both establishing an initial diagnosis and in the follow-up of patients after a diagnosis has been established. Before discussing the role of serial HRCT in these contexts, it is important to have a fundamental understanding of the expected temporal evolution of findings for specific diseases. Data on serial HRCT changes are sparse in the literature. For this reason, conclusions regarding the evolution of diseases over time are often based on small series or inferred from serial clinical and pulmonary function test (PFT) data. Temporal evolution of DLD varies greatly and is affected by the complex relationship between the nature of the inciting insult, the resulting immune reaction, and the treatment that is administered. Certain diseases, such as cryptogenic organizing pneumonia, may resolve completely without significant residual abnormalities while other diseases, such as idiopathic pulmonary fibrosis (IPF), are irreversible and typically progress despite treatment.

The initial imaging tool for the lung parenchyma remains the chest radiograph. It is unsurpassed in the amount of information it yields in relation to its cost, radiation dose, availability, and ease of performance. However, the chest radiograph has its limitations. It is normal in 10 to 15 percent of symptomatic patients with proven infiltrative lung disease, in up to 30 percent of those with bronchiectasis, and in close to 60 percent of patients with emphysema [4]. In several studies, the chest radiograph has been shown to have an overall sensitivity of 80 percent and a specificity of 82 percent for detection of diffuse lung disease [5]. Chest radiography could provide a confident diagnosis in only 23 percent of cases, and those confident diagnoses proved correct only in 77 percent of cases.For these reasons, high resolution computed tomography (HRCT, also called thin-section CT scanning), is frequently used to help clarify specific problems. Typical features of the lung parenchyma and of the small airways correlate with obstructive or restrictive pulmonary function tests [6].

AIMS AND OBJECTIVE:  The aims and objectives was to evaluate the importance of high resolution computed tomography in the diagnosis of diffuse lung diseases; to detect diffuse lung diseases in patients who had normal or questionable radiographic abnormalities with symptoms or pulmonary function tests suggestive of diffuse lung disease; to determine the site of CT guided lung biopsy for  confirmation of diagnosis in suspicious diseases and to study the various patterns of diffuse lung diseases on HRCT.

MATERIAL AND METHODS:

The study was carried out in the Department of Radiology, Madhubani Medical College, Madhubani, Bihar.A total number of 60 patients with suspected or known interstitial lung disease were studied by high-resolution computed tomography (HRCT) over a period of 12 months from April 2023 to March 2024.The age group of patients varied from 18 years to 60 years.

Inclusion criteria:

Patients were selected on the basis of the following.

1. Clinical history suggestive    of    interstitial    lung disease.
2. Known cases of interstitial lung disease.
3. Abnormal chest radiographs   (with   an   interstitial pattern)
4. Abnormal restrictive pulmonary function tests

Exclusion criteria:

1. Known cases of lung malignancies and previously treatedcases of diffuse parenchymal lung disease are excluded from the study.
2. Patients who are pregnant or lactating at the time of study.
3. Patients who are unwilling to give informed consent. .

Study design:Prospective and Observational study.

METHODOLOGY:

A prospective hospital-based study was undertaken attending outpatient departments and inpatient admissions. After obtaining informed consent from selected patients, the relevant data such as age, parity, menstrual symptoms, and other associated findings in clinical examination were recorded. In all these women, findings were correlated and results were analyzed.

Technique

The total  number  of  patients  with  suspected  or  known interstitial  lung  disease  were  studied  by  high-resolution computed   tomography   (HRCT)   over   a   period   of   24 months.The study group consisted of 60 patients, of this 32 were males (53.33%) and 28 were females (46.66%). 

The CT machine used  was SiemensSomatomspiritdual slice CT scanner.

1.Patient  was  placed  on  gantry  table  in  the  supine position  with  both  arms  above  the  head  and  no gantry tilt.

2.A    digitized    AP    scanogram    was    obtained    in suspended full inspiration.The  patients  were  taught  prior  to  procedures  to  hold breath  in  deep  inspiration  and  expiration  wherever required.

3. Axial sequential scans   of   1mm   thickness   were obtained at 10 mm intervals fromlung  apices  to bases in suspended full inspiration.

4.Modifications in the above technique were done if indicated as;

(1) prone  scan were  taken to determine whether opacities in the dependent lung are abnormal or  not  and  (2) scans  were  also  taken  at  the  end  of deep expiration to detect any air trapping.

Permission from the Institutional ethical committee was obtained prior to the study and informed consent of study objects was taken before HRCT chest was done.

Scanning parameters

Sample size: 60 Patients.

Period of Study: 1 year.

Equipment- GE Bright Speed Elite 16 Slice CT scanner

HRCT chest protocol:

Slice thickness: 1.25 mm

Reconstruction slice thickness: 0.625mm

Scan time: 0.8 second.

KVp: 120-140.

mAs: 100-200

Collimation: 1.5-3 mm

Matrix size: 512x512

FOV: 35 cm

Reconstruction algorithm: High spatial frequency (Bonealgorithm).

Window: Lung window

Position: Usually supine, but prone scans were obtainedwherever needed.

Level of respiration: Suspended full inspiration. When air trapping was suspected, expiratory images were also taken.

Superior extent: Lung apices.

Inferior extent: Domes of diaphragm.

Scanner settings:KV(p): 120 –140; mAs:129 –150

Collimation: 1mmScan time:1second.Matrix size: 512 x 512

Reconstruction: High spatial frequency algorithm.

Windows setting:

Window width    : 1200 to 1600 HU.

Window level      : 600 to -800 HU.

STATISTICAL ANALYSIS:

Collected data were entered in the Microsoft excel spreadsheet, coded appropriately and later cleaned for any possible errors. Analysis was carried out using Statistical Package for the Social Sciences (SPSS) for windows version 21.0. Statistical analyses were performed using the chi-square test and student’s t-test and results were analysed.

OBSERVATION AND RESULT:

sixtycases  of  diffuse  lung  disease were  studied  by high  resolution  computed  tomography  scanning  of  lungs in  the  department  of  radiology,  Madhubani Medical  College & hospital, Madhubani, Bihar, India.

Age and sex

The  age  group  in  which  maximum  number  of  patients presented  was  41-50,51-60  and  61-70  years  each, which   included  34 (56.66%)   males   and   26(43.33%) females. Diffuse lung diseases are slightly more common in males than in females.Out of 60 cases 38(63.3%) were males and 22(36.66%) are females.

Location and morphology

Ground glass opacity (48%) was most commonly observed morphological finding followed by reticular (52%), bronchiectasis (39%) and honey combing (24%).

Fig:1- Silicotuberculosis in a 52-year-old stoneworker. Axial HRCT scan       (C:-600, W: 1600) shows an irregular thick-walled cavitary lesion (arrow) in the upper lobe of right lung, suggestive of pulmonary tuberculosis. Multiple ill-defined nodular lesions seen in both lungs, with areas of para-cicatricial emphysema.

Fig:2- Honeycomb LungHRCT findings: (A) Pattern of involvement: multiple areas of honeycombing noted in B/L lung fields predominantly in lower zones and peripherally.

A  total  number  of  60  patients  with  suspected  or  known interstitial  lung  disease  were  studied  by  high  resolution computed   tomography   (HRCT)   over   a   period   of   12 months.HRCT scans were done by obtaining 1 mm thick section atevery 10mmintervals from  thoracic  inlet  to diaphragmusing high spatial frequency (bone) algorithm.TuberculosisStudy  included  fourteen  (28%)  cases  of  tuberculosis  out ofwhich   seven   were   old   patients with   symptoms suggestive  of  reactivation  of  the  disease.  Cavities wereseen in all 7 patients.Other findings such as pleural thickening   were   seen   in   4   patients   and   mediastinal lymphadenopathy   in   2   patients   wasdescribed   as explained by Im JG et al. [7]. Four of the seven new cases,diagnosed as military TB onHRCT  showed  randomly  distributed  nodules(1-3)mm commonly   involving   the   perivascular   and   sub pleural regions-consistent  with  findings.

Idiopathic pulmonary fibrosis

In  the  present  studywe  came  across  12  cases  of  IPF. chest  radiograph  taken  prior  to  CT  of  all  the  patients showed  reticular  pattern  in  the  lower  zones  and  had probable diagnosis of ILD . On HRCT posterior basal and sub  pleuralareas  were  commonly  affected  in  all  patients (100%).Middle  lobes  and  anterior  segments  of  upper lobe  involvement  were  seen  in  4  patients  suggesting disease    process    begins    in    posterior    basal    regions progressively involving the upper regions. These findings were  correlated  with  findings  of  Lim  MK  et  aland Battista G et al.[8.9]. Finding of honeycombing found as thick walled small air containing  cystic  spaces  sharing  walls  and  lying  in  the layers   in   posterior   basal   regionscorrespond   to   the findings of Nishiyama O et al[10].

HRCT is 16% more sensitive in detection of diffuse lung disease abnormalities than chest radiograph in our study.Eleven cases which appeared normal on chest radiographs were detected as abnormal on HRCT whereas all cases abnormal on chest radiograph were also abnormal on HRCT.HRCT is the most accurate noninvasive imagingmodality for evaluation of lung parenchyma. The cross sectional perspective and high spatial resolution makes HRCT superior to other imaging modalities like chest X- ray, lung tomography and conventional CT Scanning. Clinical evaluation, chest radiography and HRCT examination should be regarded as integral components of the investigation protocol in patients with various interstitial lung diseases. Hence high resolution computed tomography is a standard investigation to identify and quantify anatomic pattern and distribution of various interstitial lung diseases and also evaluates activeness and progression of disease in relation to prognosis and therapy.

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