Value of minimum intensity projections for chest CT in COVID-19 patients

Abstract

Purpose: To investigate whether minimum intensity projection (MinIP) reconstructions enable more accurate depiction of pulmonary ground-glass opacity (GGO) compared to standard transverse sections and multiplanar reformat (MPR) series in patients with suspected coronavirus disease 2019 (COVID-19).

Method: In this multinational study, chest CT scans of 185 patients were retrospectively analyzed. Diagnostic accuracy, diagnostic confidence, image quality regarding the assessment of GGO, as well as subjective time-efficiency of MinIP and standard MPR series were analyzed based on the assessment of six radiologists. In addition, the suitability for COVID-19 evaluation, image quality regarding GGO and subjective time-efficiency in clinical routine was assessed by five clinicians.

Results: The reference standard revealed a total of 149 CT scans with pulmonary GGO. MinIP reconstructions yielded significantly higher sensitivity (99.9 % vs 95.6 %), specificity (95.8 % vs 86.1 %) and accuracy (99.1 % vs 93.8 %) for assessing of GGO compared with standard MPR series. MinIP reconstructions achieved significantly higher ratings by radiologists concerning diagnostic confidence (medians, 5.00 vs 4.00), image quality (medians, 4.00 vs 4.00), contrast between GGO and unaffected lung parenchyma (medians, 5.00 vs 4.00) as well as subjective time-efficiency (medians, 5.00 vs 4.00) compared with MPR-series (all P < .001). Clinicians preferred MinIP reconstructions for COVID-19 assessment (medians, 5.00 vs 3.00), image quality regarding GGO (medians, 5.00 vs 3.00) and subjective time-efficiency in clinical routine (medians, 5.00 vs 3.00).

Conclusions: MinIP reconstructions improve the assessment of COVID-19 in chest CT compared to standard images and may be suitable for routine application.

Keywords: COVID-19; Multidetector computed tomography; Pneumonia; Spiral computed; Tomography; Viral infection.

Fig. 1

Flow chart of patient inclusion. COVID-19: coronavirus disease 2019; RT-PCR: real-time reverse transcription polymerase chain reaction; SARS-CoV-2:severe acute respiratory syndrome coronavirus 2.

Fig. 2

A 37-years-old man, who presented to the emergency department with cough and fever. An immediate CT scan was performed due to suspected pulmonary coronavirus disease 2019 (COVID-19) manifestation. The axial minimum intensity projection (MinIP) reconstruction (left side) shows focal subtle ground-glass opacity (GGO) in the left lower lung lobe (arrowhead) suspicious for early stage pulmonary COVID-19, which was missed on axial multiplanar reformat (MPR) series (right side) by 6/6 readers in this study. Real-time reverse transcription polymerase chain reaction (RT-PCR) confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Fig. 3

A 46-years-old woman presenting to the emergency department with fever and cough. The CT scan reveals subtle ground-glass opacity (GGO) (arrows) in the right paramediastinal upper lung lobe suspicious for early stage coronavirus disease 2019 (COVID-19) exclusively on axial minimum intensity projection (MinIP) reconstruction (left side). On axial standard multiplanar reformat (MPR) series (right side), the GGO was missed by 3/6 readers in this study due to a masking vessel (arrowhead).

Fig. 4

Box and Whisker plots show the results of subjective image ratings by radiologists regarding the diagnostic reader confidence while assessing ground-glass opacity (GGO), general image quality, the contrast between GGO and unaffected lung parenchyma, and subjective time-efficiency of minimum intensity projection (MinIP) reconstructions and multiplanar reformat (MPR) series. Medians are displayed as horizontal bold black lines. MinIP reconstructions were rated as distinctly better than standard MPR images with regards to diagnostic confidence, contrast and subjective time-efficiency (average difference in scores, 0.33, 0.67 and 0.77, respectively, all comparisons P < .001), while ratings for general image quality were only slightly better for MinIP reconstructions compared to MPR series (average difference in scores, 0.14, P < .001).

Fig. 5

CT scan of a 72-years-old man with fever, cough, shortness of breath and real-time reverse transcription polymerase chain reaction (RT-PCR) confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The axial minimum intensity projection (MinIP) reconstruction (left side) enables improved contrast between diffuse ground-glass opacity (GGO) and unaffected normal lung parenchyma in the right lower lung lobe compared to standard multiplanar reformat (MPR) series (right side).

Fig. 6

Box and Whisker plots show the results of subjective image ratings by clinicians regarding the general suitability for ground-glass opacity (GGO) assessment, image quality, and subjective time-efficiency for clinical routine of minimum intensity projection (MinIP) reconstructions and multiplanar reformat (MPR) series. Medians are displayed as horizontal bold black lines. MinIP reconstructions were rated as distinctly better than standard MPR images for all categories (average difference in scores, 1.61, 1.50 and 1.50, respectively, all comparisons P < .001).