Continuous quantitative measurement of the main bronchial dimensions and lung density in the lateral position by four-dimensional dynamic-ventilation CT in smokers and COPD patients

Figures & data

Table 1 Patient characteristics

Characteristics	Total (n=42)	Right lateral position (n=15)	Left lateral position (n=27)	P-valuea
Age (years)	69.8±8.4	71.4±5.8	69.3±10.0	0.673
Gender (F:M)	10:32	4:11	6:21	0.748
BMI (kg/m^2)	22.5±2.6	23.8±3.8	22.2±3.3	0.217
FEV1/FVC (%)	70.1±10.5	68.5±12.4	70.8±8.1	0.742
FEV1 predicted (%)	90.7±15.9	86.6±18.9	94.1±11.9	0.145
Smoking index (pack-year)	42.4±28.7	57.9±30.9	36.8±25	0.181
Tumor size (mm)	21.2±15.2	21.7±15.8	21.0±15.1	0.487

Note:

a Comparisons are estimated between the right and left lateral positions.

Abbreviation: BMI, body mass index.

Figure 1 Example of continuous measurements of MLD and Ai in the dependent lung field.

Notes: Both MLD and Ai values are plotted in each of the 15 frames (0.35 seconds/frame). In this patient, the peak inspiratory Ai is 146.1 mm², and the peak expiratory Ai is 94.3 mm². The ΔAi_1.05 value is 16.5% (24.2 mm²/146.1 mm²), which was calculated between the peak inspiratory frame and the third frame after (1.05 seconds later) and adjusted by the peak inspiratory Ai as an Ai change in the early expiratory phase. The peak inspiratory MLD is −777 HU, and the peak expiratory MLD is −653 HU. The ΔMLD_1.05 value is 10.2% (−79 HU/−777 HU), which was calculated between the peak inspiratory frame and the third frame after (1.05 seconds later) and adjusted by the peak inspiratory MLD as a density change in the early expiratory phase.
Abbreviations: Ai, luminal area; MLD, mean lung density.

Figure 2 Example image of continuous airway measurement using the “4D Airways Analysis” software.

Notes: The corresponding measurement points in all 14 frames are shown at the bottom. On this image, a measurement point is set in the right main bronchus in the dependent lung field. A measured Ai of frame No. 8 (blue arrow) is shown in the center square (surrounded by a orange rectangle). Continuous changes in Ai are shown in the upper right square (blue dashed oval).
Abbreviation: Ai, luminal area.

Table 2 Lung density measurements and correlations to clinical indices

	Measured value	Correlation to FEV1/FVC	Correlation to FEV1 predicted	Correlation to smoking index
	Mean±SD (range)	r (P-value)	r (P-value)	r (P-value)
Nondependent lung
End-inspiratory MLD (HU)	−850.9±24.0 ([−930]–[−804])	0.272 (0.082)	−0.074 (0.640)	0.036 (0.822)
End-expiratory MLD (HU)	−818.5±35.3 ([−909]–[−700])	0.031 (0.844)	−0.046 (0.774)	0.023 (0.885)
ΔMLD EI (%)	3.8±2.2 (0.2–13.6)	−0.344 (0.026a)	−0.036 (0.822)	−0.07 (0.661)
ΔMLD1.05 (%)	1.9±1.1 (0.1–5.1)	−0.417 (0.006a)	−0.089 (0.574)	−0.023 (0.885)
%LAA−950 at end inspiration	6.5±11.1 (0.0–61.1)	−0.552 (<0.001a)	−0.103 (0.517)	0.130 (0.414)
Dependent lung
End-inspiratory MLD (HU)	−811.3±31.0 ([−877]–[−740])	0.448 (0.003a)	0.010 (0.948)	−0.042 (0.790)
End-expiratory MLD (HU)	−723.4±45.2 ([−819]–[−628])	0.254 (0.104)	0.166 (0.293)	−0.017 (0.915)
ΔMLD EI (%)	10.9±3.8 (2.2–18.5)	0.043 (0.785)	0.242 (0.123)	−0.039 (0.804)
ΔMLD1.05 (%)	6.1±2.7 (1.9–14.1)	−0.056 (0.723)	0.122 (0.442)	0.137 (0.387)
%LAA−950 at end inspiration	3.3±7.0 (0–32.7)	−0.551 (<0.001a)	−0.148 (0.351)	0.007 (0.963)
Nondependent/dependent ratio in ΔMLD1.05	0.31±0.19 (0.06–1.01)	−0.476 (0.001a)	−0.293 (0.060)	0.163 (0.313)

Note:

a Significant.

Abbreviations: MLD, mean lung density; ΔMLD_EI, the subtracted value of the peak expiratory MLD from the peak inspiratory MLD divided by the peak inspiratory MLD; ΔMLD_1.05, the subtracted value of the MLD at the third frame (1.05 seconds) after the peak inspiration divided by the peak inspiratory MLD; %LAA₋₉₅₀, the ratio of low attenuation area (under -950 HU) to the total lung field; HU, Hounsfield unit.

Table 3 Airway dimension measurements and correlations to clinical indices

	Measured value	Correlation to FEV1/FVC	Correlation to FEV1 predicted	Correlation to smoking index
	Mean±SD (range)	r (P-value)	r (P-value)	r (P-value)
Nondependent main bronchus
End-inspiratory Ai (mm^2)	148.6±51.4 (73.3–302.7)	0.004 (0.98)	−0.031 (0.847)	0.047 (0.769)
End-expiratory Ai (mm^2)	125.6±44.5 (57.5–237.6)	0.102 (0.52)	0.096 (0.547)	−0.006 (0.970)
ΔAi EI (%)	10.5±10.6 ([−13.7]–38.5)	−0.431 (0.004a)	−0.300 (0.054)	0.041 (0.797)
ΔAi1.05 (%)	6.8±7.9 ([−7.0]–30.0)	−0.465 (0.002a)	−0.290 (0.063)	0.099 (0.535)
Dependent main bronchus
End-inspiratory Ai (mm^2)	132.3±45.1 (66.9–273.3)	−0.050 (0.755)	−0.078 (0.623)	0.310 (0.046a)
End-expiratory Ai (mm^2)	105.2±31.8 (41.5–166.9)	0.037 (0.817)	0.062 (0.698)	0.192 (0.224)
ΔAi EI (%)	18.5±10.9 ([−8.5]–44.4)	−0.232 (0.140)	−0.276 (0.077)	0.256 (0.102)
ΔAi1.05 (%)	14.1±10.5 (1.9–44.9)	−0.311 (0.045a)	−0.523 (<0.001a)	0.291 (0.062)

Note:

a Significant.

Abbreviations: Ai, luminal area; ΔAi_EI, the subtracted value of the peak expiratory Ai from the peak inspiratory Ai divided by the peak inspiratory Ai; ΔAi_1.05, the subtracted value of the Ai at the third frame (1.05 seconds) after the peak inspiration divided by the peak inspiratory Ai.

Figure 3 Measurements of cross-correlation coefficients between the two time curves from the MLD and the airway Ai in the dependent lung (A) and nondependent lung (B) of a male smoker without COPD (FEV₁/FVC=0.70).

Notes: The two time curves of the MLD and the main bronchial Ai movement in the right dependent lung are in almost opposite directions, suggesting that the tracheal dilation and the lung inflation occurred simultaneously. The cross-correlation coefficient between the two time curves was large and negative (−0.84) (A). The two time curves of the MLD and the main bronchial Ai movement in the left nondependent lung moved independently of each other (cross-correlation coefficient=−0.14) (B). Change in the main bronchial Ai in the left nondependent lung (B) was much smaller than that in the right dependent lung (A). The nondependent/dependent ratio in the ΔMLD_1.05 value was 0.264.

Abbreviations: Ai, luminal area; MLD, mean lung density; HU, Hounsfield unit.

Figure 4 Measurements of cross-correlation coefficients between the two time curves from the MLD and the airway Ai in the dependent lung (A) and nondependent lung (B) of a male smoker with COPD (FEV₁/FVC=0.544).

Notes: It was unclear that the two time curves of the MLD and the main bronchial Ai movement in the right dependent lung moved in opposite directions (cross-correlation coefficient=−0.46) (A). Furthermore, the main bronchial Ai decreased rapidly in the early expiratory phase (white arrows) followed by a strange increase during the middle-to late-expiratory phases (black arrows), suggesting the presence of paradoxical airway movement (A). The two time curves of the MLD and the main bronchial Ai movement in the left nondependent lung are in relatively opposite directions (cross-correlation coefficient=−0.601) (B). The nondependent/dependent ratio in the ΔMLD_1.05 value was relatively large (0.389), due to mild increase in MLD during expiration caused by COPD.
Abbreviations: Ai, luminal area; MLD, mean lung density; HU, Hounsfield unit.

Table 4 CCCs (between main bronchial Ai and MLD) and correlations to clinical indices

	CCC between airway Ai and MLD	Correlation to FEV1/FVC	Correlation to FEV1 predicted	Correlation to smoking index
	Mean±SD (range)	r (P-value)	r (P-value)	r (P-value)
Total (n=42)
Nondependent main bronchus	[−0.581]±0.389 ([−0.951]–0.451)	0.229 (0.145)	0.024 (0.882)	0.006 (0.97)
Dependent main bronchus	[−0.721]±0.162 ([−0.912]–[−0.258])	−0.474 (0.002a)	−0.232 (0.139)	0.183 (0.246)
Right lateral position (n=15)
Nondependent main bronchus	[−0.567]±0.353 ([−0.904]–0.451)	0.279 (0.315)	0.559 (0.030a)	−0.333 (0.147)
Dependent main bronchus	[−0.712]±0.187 ([−0.857]–[−0.258])	−0.657 (0.008a)	−0.545 (0.036a)	0.254 (0.362)
Left lateral position (n=27)
Nondependent main bronchus	[−0.588]±0.406 ([−0.951]–0.419)	0.230 (0.249)	−0.266 (0.18)	0.155 (0.441)
Dependent main bronchus	[−0.727]±0.147 ([−0.912]–[−0.321])	−0.400 (0.038a)	−0.032 (0.874)	0.207 (0.3)

Note:

a Significant.

Abbreviations: Ai, luminal area; CCC, cross-correlation coefficient; MLD, mean lung density.

Figure 5 Scatter plots of the cross-correlation coefficient between two time curves of MLD and the main bronchial Ai movement in the dependent lung for the total study population (n=42) with FEV₁/FVC.

Abbreviations: Ai, luminal area; MLD, mean lung density.

Video S1 The dynamic-ventilation computed tomography of a non-COPD smoker. It is clear that the dependent (downside) right lung mainly respires, comparing with the nondependent (upside) left lung.

Video S2 The dynamic-ventilation computed tomography of a COPD patient. The dependent (downside) right lung and nondependent (upside) left lung move similarly, suggesting that the nondependent lung respires largely comparing with the non-COPD smoker in Video 1.