-Substantially contributed to the statistical analyses -Substantially contributed to the writing and revision of the manuscript -Approved the final version of the manuscript -Accountable for the manuscript's contents Disclosure statement: Dr. Boltyenkov reports personal fees from Siemens Medical Solutions USA, Inc., outside the submitted work, and is a shareholder of Siemens Healthineers.
Jason J. Wang, PhD, academic affiliation non-partnership track employee -Substantially contributed to the design of the study -Substantially contributed to the data curation and organization -Substantially contributed to the statistical analyses -Substantially contributed to the revision of the manuscript -Approved the final version of the manuscript -Accountable for the manuscript's contents Disclosure statement: Dr. Wang has nothing to disclose.
Jesse Chusid, MD, MBA, academic affiliation non-partnership track employee, Senior Vice President of Imaging Services, Northwell Health -Substantially contributed to the design of the study -Substantially contributed to the data supervision -Substantially contributed to the revision of the manuscript -Approved the final version of the manuscript -Accountable for the manuscript's contents Disclosure statement: Dr. Chusid has nothing to disclose.
Danny Hughes, PhD, academic affiliation non-partnership track employee -Substantially contributed to the conception and design of the study -Substantially contributed to the revision of the manuscript -Approved the final version of the manuscript -Accountable for the manuscript's contents Disclosure statement: Dr. Hughes reports grants from Harvey L. Neiman Health Policy Institute, outside the submitted work.
Pina C. Sanelli, MD, MPH, FACR, academic affiliation non-partnership track employee, Vice Chair of Research, Department of Radiology, Donald and Barbara Zucker School of Medicine at Hofstra/Northwell -Substantially contributed to the conception and design of the study -Substantially contributed to the data curation and organization -Substantially contributed to the statistical analyses -Substantially contributed to the writing and revision of the manuscript -Approved the final version of the manuscript -Accountable for the manuscript's contents Disclosure statement: Dr. Sanelli reports grants from Harvey L. Neiman Health Policy Institute, during the conduct of the study; grants and non-financial support from Siemens Healthineers, Inc, outside the submitted work.
Statement of Data Access and Integrity: The authors declare that they had full access to all of the data in this study and the authors take complete responsibility for the integrity of the data and the accuracy of the data analysis.
Sources of support: Funding support received from the Harvey L. Neiman Health Policy Institute through a research partnership.
The COVID-19 pandemic continues to significantly impact the health of the population affecting a total of 1,859,693 people in the United States with 106,927 deaths as of June 2, 2020 [1] . New York State has quickly become the U.S. epicenter of COVID-19 disease with 380,825 cases and 29,988 deaths [1] occurring in a short period of time. Hospitals had to become flexible to quickly expand inpatient units and provide appropriate resources for this rapidly growing cohort. Additionally, this novel disease population posed a challenge for healthcare providers to anticipate the necessary resources as new information about disease progression and complications was continually becoming available.
As medical resources shifted away from elective and non-urgent procedures toward emergent and critical care of COVID-19 patients, departments were forced to reconfigure their personnel and resources. In particular, many Radiology practices rescheduled non-urgent and routine imaging according to recommendations from the American College of Radiology (ACR) [2] . Hence, Radiology practices experienced significant declines in imaging volumes, especially in the outpatient setting [3, 4] .
Although, the inpatient setting was not as severely affected by declines in imaging volumes, a shift in the composition mix of imaging modality types with increased use of radiography relative to cross-sectional imaging was observed [4] . These findings suggest a potential impact on the resource utilization, staffing needs, and reimbursement for Radiology practices.
The purpose of this study was to evaluate the change in the inpatient imaging volumes and composition mix during the COVID-19 pandemic. We analyzed the weekly imaging volumes stratified by the imaging modality types and CPT-coded exam groups during the COVID-19 pandemic in a large healthcare system.
A retrospective review of the inpatient imaging case volumes in a large integrated healthcare system [4] was performed from January 1, 2019 -April 18, 2020 to evaluate the change in the imaging volumes and composition mix according to imaging modality types and CPT-coded exam groups during the COVID-19 pandemic. Similar to our prior methods [4] , the weekly aggregated imaging volumes were provided in 2020 and 2019 for the inpatient service stratified by the imaging modality types (radiography, ultrasound, computed tomography [CT], magnetic resonance imaging [MRI], nuclear medicine, and interventional radiology). Individual CPT-coded data within each modality type was also provided as weekly aggregated data to further evaluate the case volumes for specific types of imaging exams. Overall, there was no significant decline in the number of imaging scanners in our healthcare system between 2020 and 2019 that could have potentially affected the expected imaging exam volumes during the COVID-19 pandemic. Institutional Review Board (IRB) approved a waiver to utilize the retrospective aggregate data.
At our institution, the first positive-tested COVID-19 patient was confirmed on March 8, 2020 (week 11, day 1). However, the first positive-tested COVID-19 patient was confirmed on March 1, 2020 (week 10, day 1) in New York City (NYC). On March 27, 2020 (week 13, day 6), the Radiology department released guidelines for inpatient imaging utilization to limit the spread of the coronavirus (SARS-CoV-2) to healthcare providers, staff, and patients, as well as reduce contamination of imaging equipment from scanning COVID-19 patients [4] .
The 2020 and 2019 aggregated weekly (weeks 1-16) imaging case volumes were stratified by imaging modality types (radiography, ultrasound, CT, MRI, nuclear medicine, and interventional radiology) and by individual CPT-codes. For the analysis of the CPT-coded data, CPT groups were primarily assigned by anatomic regions, such as head, orbit/face/neck, chest, abdomen/pelvis, and extremities, within each modality type. Non-invasive vascular imaging was assigned as separate CPT-coded groups according to the modality types and anatomic regions, such as CT angiography (CTA) 
In year 2020, the total inpatient imaging volume performed at our institution for weeks 1-16 was 162,470 exams, compared to 175,511 exams in year 2019, representing an overall 7.4% decline. Table 1 
In a short time, the COVID-19 pandemic has had a substantial economic impact on healthcare institutions. Many Radiology practices have experienced a rapid decline in imaging case volumes [3, 4] as a consequence of public policy, financial hardship, and patient fear. In particular, outpatient imaging was expected to have the greatest decline in imaging volumes across all modality types [4] . Even though inpatient imaging has been less affected by the declines in imaging volume during the post-COVID-19 (weeks 10-16) period, it is important to be aware that there was a significant shift in the composition mix of the imaging modality types and specific CPT-coded exams.
The results from this study have revealed an overall 13.6% decline in the total imaging volume in the inpatient setting over the first 7 week-period during the COVID-19 pandemic, compared to 2019, including all imaging modality types. For further analysis of the post-COVID-19 (weeks 10-16) period, the dataset was split to represent the early post-COVID-19 (weeks 10-13) and late post-COVID-19 (weeks 14-16) periods. There was a greater decline of 16.6% in the total inpatient imaging volume during the early post-COVID-19 period immediately following the first confirmed positive-tested COVID-19 patient in NYC (week 10, day 1). This may be partly explained by the preemptive response to lower the overall inpatient census by delaying elective procedures in order to increase capacity for the expected influx of COVID-19 patients. However, the inpatient imaging volume increased in the late post-COVID-19 (weeks 14-16) period, resulting in only a 9.6% decline in year over year imaging volume, likely due to the surge of COVID-19 patients requiring hospitalization. By week 16, the inpatient imaging volume was down only 4.2% compared to the same period in 2019.
Despite the relatively modest level of inpatient imaging volume decline compared to the outpatient and emergency settings [4] , this study revealed that the 2020 imaging volume composition mix changed significantly (p<0.0001) during the COVID-19 pandemic. A significant shift in the imaging modality types was observed in the 2020 late post-COVID-19 (weeks 14-16) period with the greatest percentage comprised of radiography (74.3%), followed in descending order by CT (12.7%), ultrasound (8.0%), MRI (2.4%), interventional radiology (2.3%), and nuclear medicine (0.4%). This may be partly explained by the departmental guidelines recommending judicious use of crosssectional imaging, ultrasound and interventional radiology in order to prevent spread of COVID-19 disease to patients and healthcare providers.
When we further examined the specific CPT-coded groups within imaging modality types during the 2020 late post-COVID-19 (weeks 14-16) period, the mean weekly imaging volumes had statistically declined for all CPT-coded groups in CT and radiography modality types, except for CTA Chest and Radiography Chest, compared to 2019. The imaging volumes actually increased for CTA Chest and Radiography Chest in the late post-COVID-19 period, although this change was not statistically significant.
In addition, the 2020 trend data revealed an increase in the imaging volumes in the late post-COVID-19 (weeks 14-16) period for CTA Chest, Radiography Chest and Ultrasound Venous Duplex, relative to the early post-COVID-19 (weeks 10-13) period.
From the growing literature in this area, we are now aware that changes in the prothrombotic factors occur in severe COVID-19 infection inducing a hypercoagulable state [8, 9] . These patients have been reported with elevated D-dimer, fibrinogen, and factor VIII [8, 9] with marked increased frequency of venous thromboembolism and pulmonary embolism seen in up to one-third of COVID-19 patients in the intensive care unit [10, 11] . The imaging work-up for the diagnosis of these clinical manifestations includes Radiography Chest, CTA Chest and Ultrasound Venous Duplex, likely explaining the shift in the imaging composition mix observed in this study.
To our knowledge, there are no prior publications that evaluated the change in the inpatient imaging volumes and composition mix during the COVID-19 pandemic stratified by imaging modality types and CPT-coded groups. The results from this study may have significant implications for leaders preparing for a potential resurgence of the COVID-19 crisis. This real-world data should be useful in preparing for potential resource utilization and staffing requirements. In particular, these results may be helpful in developing new imaging utilization guidelines and departmental policies aimed at optimally accommodating the unique imaging needs for COVID-19 patients. Radiology practices can plan in advance for adequate staffing, as well as develop safe and efficient decontamination procedures in specific imaging modalities (radiography, ultrasound and CT). Additionally, Radiologists with clinical expertise for the specific CPT-coded imaging exams (Radiography Chest, CTA Chest and Ultrasound Venous Duplex) will be valuable in providing high quality care.
The main limitations of this study are similar to our prior work [4] using a retrospective study design analyzing aggregated and anonymized data. However, this study provided more detailed analyses of individual CPT-coded groups within each modality type. Within the ultrasound modality, point-of-care ultrasound was excluded in the aggregated volume data. Although another limitation affecting the generalizability of these findings is that our healthcare system is located in the epicenter of the COVID-19 pandemic [4] , these results may be helpful in establishing a worst-case scenario. Further studies evaluating the inpatient imaging volumes and composition mix in Radiology practices located outside the epicenter would also be a valuable addition to the literature.
In summary, the results from this study provide real-world data to inform Radiology practices regarding not only the decline in inpatient imaging volumes, but more importantly the significant shift in the imaging composition mix during the COVID-19 pandemic. This study may assist in guiding inpatient practice decisions based on the shift in the imaging volumes across different modality types and specific CPT-coded groups in order to provide optimal access and availability of the imaging resources necessary during the COVID-19 pandemic. 
-This study revealed an overall 13.6% decline in the inpatient imaging volume during the COVID-19 pandemic (7 weeks) including all imaging modality types.
-Imaging volume deterioration varied in the post-COVID-19 (weeks 10-16) period with the greatest decline (16.6%) observed in the early post-COVID-19 (weeks 10-13) period. Inpatient imaging volume started to increase in the late post-COVID-19 (weeks 14-16) period. By week 16, the inpatient imaging volume only declined by 4.2%.
-A statistically significant shift in the 2020 imaging volume composition mix was observed in the late post-COVID-19 (weeks 14-16) period, largely comprised of radiography (74.3%), followed by CT (12.7%), ultrasound (8%), MRI (2.4%), interventional radiology (2.3%) and nuclear medicine (0.4%).
-The trend data revealed increased imaging volumes for specific CPT-coded groups in the late post-COVID-19 (weeks 14-16) period for CTA Chest, Radiography Chest and Ultrasound Venous Duplex.
-This data may be useful to Radiology practices in preparing for the possibility of a second wave of the COVID-19 pandemic.