Clinical Utility of Portable Dynamic Chest X Ray (DDR) in the ICU

Chest radiography was introduced to medical practice over a century ago, shortly after the discovery of X-rays by Roentgen. Since then, it has been a key component of the health, screening, clinical evaluation, and the assessments of therapy for billions of people. To this day, chest radiography remains the most frequently ordered imaging test. In this 700-bed tertiary care hospital, over 100,000 chest radiographs are obtained annually. The technique of chest radiography has remained largely unchanged and is seen as a mostly qualitative rather than quantitative tool. Chest dynamic X-ray (DDR) is a new advanced version of chest radiography that provides important quantitative parameters such as lung motion, ventilation, and perfusion. With a dynamic scan of 20-30 seconds, sequential images of both lungs are obtained with high temporal resolution during breathing (7.5-30 frames per second), without increasing radiation dose. DDR utilizes a dynamic digital radiography (DDR) technique with a flat-panel detector (2-6) and generates images with a field-of-view (FOV) that can cover both lungs. DDR utilizes detectors with higher sensitivity than those typically used in conventional radiography, enabling multiple dynamic time frames to be obtained despite keeping the dose mostly unchanged. Compared to conventional radiography, computer analysis and image processing of the DDR sequential time frames provide additional valuable metrics that capture motion and other key functions of the lungs, while high-quality chest radiographs can also be generated from the recombined frames. Chest DDR can be performed in essentially any patient position, including standing or sitting, to capture lung physiology in a manner representative of daily life. Furthermore, DDR is inexpensive, requires minimal space, and enables high throughput, which can help reduce medical costs. While area-detector CT can provide a higher temporal resolution, its FOV cannot entirely cover both lungs and its radiation dose can be prohibitively high. Chest DDR offers a unique opportunity to provide dynamic imaging parameters for lung motion and function in a safe, practical, and cost-effective manner.

Recently, the portable DDR technology has become available. This portable DDR scanner enables applications for non-mobile patients, like ICU patients. It allows the semi-quantitative or quantitative evaluation of pulmonary perfusion, ventilation, and diaphragmatic motion. ICU patients may have limited access to CT or MRI scanners due to the severity of their condition and/or to difficulties associated with support their devices (ECMO, LVAD, etc.), hence, why the portable DDR technology could have an especially meaningful impact on their care. The current Radiology team consists of Drs. Nishino, Wada, Valtchinov and Madore. The PI's group from Radiology will work in close collaboration with Dr. Frendl's research team in the BWH ICUs, as well as their biostatistician as multidisciplinary team of experts. They will also continue cooperation with Mr. Tsunomori and Mr. Yoneyama. These team members already have an established track record of successful collaboration with the PI.

The investigators will use the observational study design where two diagnostic imaging modalities will be compared for their ability to best diagnose lung pathologies (i.e., diaphragmatic motion and lung aeration/ventilation, pulmonary perfusion, and lung water content). These imaging modalities are: (i) the current portable AP chest x-ray (CXR)-based diagnostic technique and (ii) the recently developed portable dynamic chest XR (DDR) technique.

The DDR technology has yet to be proven to provide specific benefits for the care of the patients through the improved diagnosis of their pulmonary issues. Its ability to provide clinically meaningful additional information on aspects of lung pathologies (diaphragmatic motion and lung aeration/ventilation, pulmonary perfusion, and lung water content), that cannot be clearly discerned from the current portable CXR-based diagnostic technique, need to be documented; hence, the aims.

This study design will compare the ability to diagnose those lung pathologies (atelectasis, pulmonary embolus, and pulmonary edema) as determined by either the DDR technology or the traditional qualitative portable routine AP CXR (the current standards of diagnosis) through images obtained via the two techniques at the same time points for each patient. The DDR imaging and analysis will provide both qualitative and semi-quantitative data for each patient at all time points.

For this study, the patient's routine portable CXR will serve as the control image when applicable, and DDR images will serve as study images for each timepoint. For certain clinical conditions, the applicable gold standards will be used as controls, i.e. CT angiogram for pulmonary embolus, V-Q scans for lung ventilation and perfusion, and fluorographic swallowing studies for speech and swallow evaluation.

Data derived from these studies will be expected to provide novel and clinically crucial (quantitative or semi-quantitative) information on the degree of diaphragmatic excursion when the patient is spontaneously ventilating vs. when ventilator support is provided. This would be crucial for decision making regarding the patient's readiness for extubation, or, inversely, when poor excursion of the diaphragms is detected for non-ventilated patients, it would support the decision for early implementation of ventilator support. Data on lung aeration would also factor into this decision-making process.

Currently, quantitative or semi-quantitative data regarding these physiologic functions of the lungs are not available. Hence, why the investigators will focus on validating these novel metrics against clinical scenarios and outcomes. The investigators anticipate that this novel technology will better guide clinical decision making like the need for (or inversely, the safe removal of) ongoing ventilator support for our patients.

Furthermore, the perfusion (blood flow assessment) component of the image analysis would provide invaluable (currently unavailable) diagnostic options for those patients for whom CT angiogram is not available to rule out/confirm pulmonary embolism (PE). CT angiogram is not available for patients who suffer from hemodynamic instability, or when it is clinically contraindicated, like patients with impending renal failure. The added value of the DDR technology for the diagnosis of larger PEs will be assessed in the later stages of this study.