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Case of hot tub lung showing a shadow distribution consistent with unequal ventilation
  1. Takefumi Nikaido1,
  2. Yoshinori Tanino1,
  3. Kojiro Ono2,
  4. Riko Sato1,
  5. Yoko Shibata1
  1. 1Pulmonary Medicine, Fukushima Medical University School of Medicine, Fukushima, Japan
  2. 2Medical Imaging R&D Center, Konica Minolta Inc, Chiyoda, Tokyo, Japan
  1. Correspondence to Dr Takefumi Nikaido; taken@fmu.ac.jp

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Case presentation

A 76-year-old woman, who had undergone right upper lobectomy for lung cancer, was found to have newly developed diffuse, submillimetre ground-glass nodular opacities with an airway-centred distribution on chest CT after 6-year follow-up (figure 1B). These opacities were absent in the middle lobe, and expiratory CT showed a low-absorption area showing a decrease in ventilation in the middle lobe as well (figure 1B,C). This decrease in ventilation was considered to be due to the compensatory upward shift of the middle lobe following right upper lobectomy.1

Figure 1

(A) Chest radiograph was almost normal. (B, C) Chest CT scan showed a low-absorption area in the right upper lung field in both the inspiratory (B) and expiratory (C) phases, indicating reduced ventilation in this area.

It was revealed that the patient had been using a 24-hour circulation type bathtub for years. Mycobacterium avium was detected in both home bathwater and sputum cultures, leading to a diagnosis of hot tub lung, a form of hypersensitivity pneumonitis. Evaluation of CT images based on the pathophysiology of the disease revealed an opacities distribution corresponding to ventilation and trans-bronchial M. avium exposure as the antigen. Chest X-ray was almost normal (figure 1A). Images processed using a postprocessing workstation (DIX1, KONICAMINOLTA, Japan) from dynamic chest radiography (DCR) revealed reduced ventilation and circulation in the right upper lung area corresponding to the middle lobe (figure 2A,C and online supplemental files 1–4). Pulmonary ventilation and perfusion scintigraphy revealed similar findings (figure 2B,D). The reduced pulmonary circulation likely resulted from hypoxic pulmonary vasoconstriction caused by decreased ventilation.

Figure 2

(A) DCR-based ventilation evaluation using image subtraction and colour-mapping techniques with the patient in the resting supine position with an anteroposterior view during tidal breathing. (B) The colour defect area (arrow head) indicates decreased ventilation, in line with the ventilation scintigraphy findings. (C) DCR-based circulation evaluation using image subtraction and colour-mapping techniques with the patient in the resting supine position with an anteroposterior view during breath holding. (D) The colour defect area (arrow head) indicates decreased circulation, consistent with perfusion scintigraphy findings. DCR, dynamic chest radiography.

DCR is a functional imaging technique that provides real-time visualisation of both the entire lung and diaphragmatic movement using a flat-panel detector and a portable or stationary pulsed X-ray generator. It also enables pulmonary function assessment by measuring temporal changes in X-ray translucency due to respiration or cardiac pumping. Postprocessing with image subtraction and colour mapping allows DCR to detect ventilatory and circulatory impairments as reduced changes in X-ray translucency.2 The imaging protocol for our case was conducted with the patient in the resting supine position with an anteroposterior view, employing two distinct sequences: tidal breathing for ventilation analysis and breath-holding for circulatory assessment. Scan parameters were 80 kV tube voltage, 56 mA tube current, 5.6 ms pulsed X-ray duration, 15 fps frame rate, 1.2 m source-to-image distance and 10–20 s total scan time. The total entrance surface dose to the detector was approximately 2.8 mGy. The total patient dose is adjustable by changing the imaging time, imaging rate and source to image distance and can be less than the dose limit for two conventional images (frontal and lateral views) recommended by the International Atomic Energy Agency (1.9 mGy). In the present case, although the dose for each evaluation (ventilation and circulation) using DCR was below the dose limit (1.9 mGy), the total dose (2.8 mGy) was higher than 1.9 mGy. However, the total dose was significantly lower compared with chest CT (~20 mGy for both inspiratory and expiratory images) and ventilation perfusion scan (~60 mGy).

The advantages of DCR are as follows: (1) Imaging can be performed in a manner similar to conventional chest radiography in both upright and supine positions, (2) The total patient dose can be significantly reduced compared with chest CT and pulmonary ventilation perfusion scan and (3) Pulmonary function can be assessed even without the use of contrast media. In our case, the DCR findings for pulmonary ventilation and circulation were consistent with scintigraphy results, suggesting DCR’s usefulness. Although DCR does not directly measure alveolar gas exchange or actual perfusion, it provides relative functional information related to pulmonary ventilation and circulation. Given the advantages of DCR, it may be a useful tool for identifying disease characteristics where ventilation (or air trapping) plays a role in the pathology, as shown in the present case.3

The present report is the first to demonstrate low absorption areas like air trapping with DCR, a condition typically diagnosed using dynamic CT or scintigraphy. Our findings highlight the potential of DCR to visualise a poorly ventilated area manifested as an opacities defect in hypersensitivity pneumonitis, where ventilation and perfusion dynamics are critical.

Ethics statements

Patient consent for publication

Ethics approval

This study involves human participants. The Research Ethics Committee of Fukushima Medical University approved this study (reference number: 3661). Participants gave informed consent to participate in the study before taking part.

References

Footnotes

  • Contributors TN conceptualised and designed the report. RS collected the data. KO developed the data acquisition sequence and postprocessing software. TN drafted the manuscript, while YT, KO and YS contributed to its revision. YS serves as the guarantor of this manuscript.

  • Funding This work was supported by JSPS KAKENHI (Grant Number JP20K20226).

  • Competing interests The dynamic flat-panel imaging system was loaned from Konica Minolta. TN, YT, RS and YS have no other conflicts of interest to declare. KO is an employee of Konica Minolta.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.