The Effects of Radiation Dose and CT Manufacturer on Measurements of Lung Densitometry

doi:10.1378/chest.06-2325

Chest

Volume 132, Issue 2, August 2007, Pages 617-623

https://doi.org/10.1378/chest.06-2325 Get rights and content

Background

To evaluate the effect of radiation dose and scanner manufacturer on quantitative CT scan measurements of lung morphology in smokers.

Methods

Low-dose and high-dose, inspiratory, multislice CT scans were obtained in 50 subjects at intervals of approximately 6 months (mean [± SD] interval, 0.5 ± 0.2 years). In another 30 subjects, multislice CT scans were acquired first using a GE LightSpeed Ultra (General Electric Healthcare; Milwaukee, WI), followed a mean time of 1.2 ± 0.4 years later by using a Siemens Sensation 16 scanner (Siemens Medical Solutions; Erlangen, Germany). Custom software was used to measure lung volume, mass, mean density, and the extent of emphysema using threshold cutoffs of −950, −910, and −856 Hounsfield units (HU) and the lowest 15th and 5th percentile points.

Results

The change in radiograph dose significantly affected measurements of emphysema assessed using mean lung density, threshold, or percentile methods. There were also interactions between dose and total lung volume for all of the measurements except the −950-HU threshold and the lowest fifth percentile point. These two emphysema measurements suggest that there was more emphysema found in the CT scans obtained using a lower radiograph dose. Only the mean lung density and −856-HU threshold showed significant effects between CT scanner manufacturers and interactions between total lung volume and scanner. All other measures of lung structure were not different between the two CT scanners.

Conclusion

CT scan measurements of very low density lung structures are significantly affected by radiation dose but are less sensitive to the lung volume. Image acquisition parameters including radiation dose, scanner type, and the subject's breath size should be standardized to estimate emphysema severity in longitudinal studies.

Section snippets

Subject Selection

Subjects for this study were selected from the British Columbia Cancer Agency Lung Health Study.²⁰ The study was approved by the clinical ethics review boards of the British Columbia Cancer Agency and the University of British Columbia. All subjects signed informed consent forms to allow their spirometry and CT scan images to be used for research. This study comprises a cohort of heavy smokers who have been screened for the presence of lung nodules using “low-dose” CT scans. If suspicious

Subjects

The subjects' demographic data are summarized in Table 1 . There were more men in the CT dose study than in the CT scanner manufacture study, and there were more current smokers than former smokers in each study group. There were no significant differences (p > 0.05) in the spirometry measurements between study groups.

Radiation Dose Study

A summary of the measurements of total lung volume, total lung mass, mean lung density, %Emphysema, and percentile points obtained using the low-dose and high-dose CT scan images

Discussion

Quantitative CT scan imaging has become a very important tool for quantifying the extent of emphysema in subjects with COPD. However, most published studies arise from a single institution scanning small numbers of subjects using a single CT scanner and a site-specific scanning protocol. It is now apparent that to advance the knowledge of how the lung changes with time, either in a diseased state or with an intervention, quantitative CT scanning must be applied to larger cohorts acquired from

ACKNOWLEDGMENT

The authors wish to acknowledge Dr. Elizabeth Tench for statistical analysis; Anh-Toan Tran and Ida Chan, MD, for technical assistance in developing and supporting the lung analysis application; and Claudine Storness-Bliss, Dianna Louie, and Sukhinder Khattra for logistical assistance.

References (35)

M Kinsella et al.
Quantitation of emphysema by computed tomography using a “density mask” program and correlation with pulmonary function test
Chest
(1990)
A Heremans et al.
Measurement of lung density by means of quantitative CT scanning: a study of correlations with pulmonary function test
Chest
(1992)
Y Watanuki et al.
Correlation of quantitative CT with selective alveolobronchogram and pulmonary function tests in emphysema
Chest
(1994)
MD Hayhurst et al.
Diagnosis of pulmonary emphysema by computerised tomography
Lancet
(1984)
NL Muller et al.
“Density mask”: an objective method to quantitate emphysema using computed tomography
Chest
(1988)
N Sakai et al.
An automated method to assess the distribution of low attenuation areas on chest CT scans in chronic pulmonary emphysema patients
Chest
(1994)
A Madani et al.
Quantitative computed tomography assessment of lung structure and function in pulmonary emphysema
Eur Respir J
(2001)
EJ Stern et al.
CT of the lung in patients with pulmonary emphysema: diagnosis, quantification, and correlation with pathologic and physiologic findings
AJR Am J Roentgenol
(1994)
WM Thurlbeck et al.
Emphysema: definition, imaging, and quantification
AJR Am J Roentgenol
(1994)
BC Stoel et al.
Optimization and standardization of lung densitometry in the assessment of pulmonary emphysema
Invest Radiol
(2004)

I Orlandi et al.

Spirometric-gated computed tomography quantitative evaluation of lung emphysema in chronic obstructive pulmonary disease: a comparison of 3 techniques

J Comput Assist Tomogr

(2004)

DS Gierada et al.

Repeatability of quantitative CT indexes of emphysema in patients evaluated for lung volume reduction surgery

Radiology

(2001)

RJ Lamers et al.

Chronic obstructive pulmonary disease: evaluation with spirometrically controlled CT lung densitometry

Radiology

(1994)

GA Gould et al.

Parenchymal emphysema measures by CT lung density correlates with lung function in patients with bullous disease

Eur Respir J

(1993)

PA Gevenois et al.

Comparison of computed density and macroscopic morphometry in pulmonary emphysema

Am J Respir Crit Care Med

(1995)

PA Gevenois et al.

Comparison of computed density and microscopic morphometry in pulmonary emphysema

Am J Respir Crit Care Med

(1996)

GA Gould et al.

CT measurements of lung density in life can quantitate distal airspace enlargement-an essential defining feature of human emphysema

Am Rev Respir Dis

(1988)

Cited by (119)

Chest computed tomography in severe bronchopulmonary dysplasia: Comparing quantitative scoring methods
2023, European Journal of Radiology
Bronchopulmonary dysplasia (BPD) is the most common complication of extreme preterm birth and structural lung abnormalities are frequently found in children with BPD. To quantify lung damage in BPD, three new Hounsfield units (HU) based chest-CT scoring methods were evaluated in terms of 1) intra- and inter-observer variability, 2) correlation with the validated Perth-Rotterdam-Annotated-Grid-Morphometric-Analysis (PRAGMA)-BPD score, and 3) correlation with clinical data.
Chest CT scans of children with severe BPD were performed at a median of 7 months corrected age. Hyper- and hypo-attenuated regions were quantified using PRAGMA-BPD and three new HU based scoring methods (automated, semi-automated, and manual). Intra- and inter-observer variability was measured using intraclass correlation coefficients (ICC) and Bland-Altman plots. The correlation between the 4 scoring methods and clinical data was assessed using Spearman rank correlation.
Thirty-five patients (median gestational age 26.1 weeks) were included. Intra- and inter-observer variability was excellent for hyper- and hypo-attenuation regions for the manual HU method and PRAGMA-BPD (ICCs range 0.80–0.97). ICC values for the semi-automated HU method were poorer, in particular for the inter-observer variability of hypo- (0.22–0.71) and hyper-attenuation (-0.06–0.89). The manual HU method was highly correlated with PRAGMA-BPD score for both hyper- (ρs0.92, p < 0.001) and hypo-attenuation (ρs0.79, p < 0.001), while automated and semi-automated HU methods showed poor correlation for hypo- (ρs < 0.22) and good correlation for hyper-attenuation (ρs0.72–0.74, p < 0.001). Several scores of hyperattenuation correlated with the use of inhaled bronchodilators in the first year of life; two hypoattenuation scores correlated with birth weight.
PRAGMA-BPD and the manual HU method have the best reproducibility for quantification of CT abnormalities in BPD.
Emphysema Quantifications With CT Scan: Assessing the Effects of Acquisition Protocols and Imaging Parameters Using Virtual Imaging Trials
2023, Chest
CT scan has notable potential to quantify the severity and progression of emphysema in patients. Such quantification should ideally reflect the true attributes and pathologic conditions of subjects, not scanner parameters. To achieve such an objective, the effects of the scanner conditions need to be understood so the influence can be mitigated.
How do CT scan imaging parameters affect the accuracy of emphysema-based quantifications and biomarkers?
Twenty anthropomorphic digital phantoms were developed with diverse anatomic attributes and emphysema abnormalities informed by a real COPD cohort. The phantoms were input to a validated CT scan simulator (DukeSim), modeling a commercial scanner (Siemens Flash). Virtual images were acquired under various clinical conditions of dose levels, tube current modulations (TCM), and reconstruction techniques and kernels. The images were analyzed to evaluate the effects of imaging parameters on the accuracy of density-based quantifications (percent of lung voxels with HU < −950 [LAA-950] and 15^th percentile of lung histogram HU [Perc15]) across varied subjects. Paired t tests were performed to explore statistical differences between any two imaging conditions.
The most accurate imaging condition corresponded to the highest acquired dose (100 mAs) and iterative reconstruction (SAFIRE) with the smooth kernel of I31, where the measurement errors (difference between measurement and ground truth) were 35 ± 3 Hounsfield Units (HU), −4% ± 5%, and 26 ± 10 HU (average ± SD), for the mean lung HU, LAA-950, and Perc15, respectively. Without TCM and at the I31 kernel, increase of dose (20 to 100 mAs) improved the lung mean absolute error (MAE) by 4.2 ± 2.3 HU (average ± SD). TCM did not contribute to a systematic improvement of lung MAE.
The results highlight that although CT scan quantification is possible, its reliability is impacted by the choice of imaging parameters. The developed virtual imaging trial platform in this study enables comprehensive evaluation of CT scan methods in reliable quantifications, an effort that cannot be readily made with patient images or simplistic physical phantoms.
Optimal threshold in low-dose CT quantification of emphysema
2020, European Journal of Radiology
Low–dose CT is now widely used in the screening of lung cancer and the detection of pulmonary nodules. There has also been increasing interest in using Low–dose CT for evaluating emphysema. In conventional dose CT, the threshold of −950HU is a common threshold for density-based emphysema quantification for worldwide population. However, the optimal threshold for assessing emphysema at low-dose CT has not been determined. The purpose of this study is to determine the optimal threshold for low-dose CT quantification of emphysema for Chinese population.
In this study, 548 low-dose chest CT examinations acquired from different subjects (119 none, 49 mild, 163 moderate, 152 severe, and 65 very severe obstruction) are collected. At the level of the entire lung and individual lobes, the extent of emphysema was quantified by the percentage of the low attenuation area (LAA%) at a wide range of thresholds from −850HU to −1000HU. Both Pearson and Spearman’s rank correlation coefficients were used to assess the correlations between 1) LAA% and pulmonary functions and 2) LAA% and the five-category classification. The statistical significance of the difference between correlation coefficients were evaluated using Steiger’Z test.
LAA% had a good correlation with both pulmonary function (|r| = 0.1–0.600, p < 0.001) and the five-category classification (r = 0.163–0.602, p < 0.001) in both the entire lung and individual lobes under different thresholds. The highest correlation coefficient is obtained at −940HU instead of -950HU.
Low-dose CT can be used for quantitative assessment of emphysema, and the threshold of -940HU is a suitable threshold for quantifying emphysema in low-dose CT images for Chinese population.
Automated measurement of liver attenuation to identify moderate-to-severe hepatic steatosis from chest CT scans
2020, European Journal of Radiology
Develop and validate an automated method for measuring liver attenuation in non-contrast low-dose chest CT (LDCT) scans and compare it to the standard manual method for identifying moderate-to-severe hepatic steatosis (HS).
The automated method identifies a region below the right lung within the liver and uses statistical sampling techniques to exclude non-liver parenchyma. The method was used to assess moderate-to-severe HS on two IRB-approved cohorts: 1) 24 patients with liver disease examined between 1/2013–1/2017 with non-contrast chest CT and abdominal MRI scans obtained within three months of liver biopsy, and 2) 319 lung screening participants with baseline LDCT performed between 8/2011–1/2017. Agreement between the manual and automated CT methods, the manual MRI method, and pathology for determining moderate-to-severe HS was assessed using Cohen’s Kappa by applying a 40 HU threshold to the CT method and 17.4% fat fraction to MRI. Agreement between the manual and automated CT methods was assessed using the intraclass correlation coefficient (ICC). Variability was assessed using Bland-Altman limits of agreement (LoA).
In the first cohort, the manual and automated CT methods had almost perfect agreement (ICC = 0.97, κ = 1.00) with LoA of −7.6 to 4.7 HU. Both manual and automated CT methods had almost perfect agreement with MRI (κ = 0.90) and substantial agreement with pathology (κ = 0.77). In the second cohort, the manual and automated CT methods had almost perfect agreement (ICC = 0.94, κ = 0.87). LoA were −10.6 to 5.2 HU.
Automated measurements of liver attenuation from LDCT scans can be used to identify moderate-to-severe HS on LDCT.
Quantitative CT of Interstitial Lung Disease
2019, Seminars in Roentgenology
Citation Excerpt :
However, there are many important CT protocol issues common to both VCT and QCT imaging of the lungs including instructing the patient to breathe to the proper lung volume and having the patient remains entirely still, while holding their breath in order for the CT scanner to obtain all of the projection data to accurately reconstruct the images.5 The patient dose, lung volume, and CT scanner type can affect the accuracy of the CT lung density measurements.6 The patient should be positioned in the center of the CT gantry and their arms should be above their heads.
To investigate dose reduction and comparability of standard dose CT vs Ultra low dose CT in evaluating pulmonary emphysema
2019, Clinical Imaging
The aim of this study was to investigate the extent of dose reduction and comparability of standard dose CT vs Ultra low dose CT in evaluating pulmonary emphysema.
Forty-nine patients with emphysema were recruited from a tertiary referral respiratory clinic. Each patient had a non-contrast Standard Dose (SD) and Ultra Low Dose (ULD) thoracic CT. The images were reconstructed using contemporary iterative reconstruction with a standard lung kernel. Lung volumes and emphysema severity was calculated using a commercially available automated densitometry segmentation package. The effective dose was calculated for both CT protocols.
Automated densitometry calculated the total lung volume and percentage lung area of emphysema. The findings were highly comparable between ULD and SD protocols. A strong correlation was seen between ULD and SD images in measurement of total lung volume (R = 0.925, p < 0.001) and percentage lung involvement by densitometry (R = 0.940, p < 0.001). There is a 95% dose reduction with the ULD protocol, the mean effective dose is 0.12 ± 0.09 mSv versus 2.33 ± 1.54 mSv for the SD protocol.
ULD thoracic CT is a comparable protocol for the assessment of emphysema severity relative to standard dose CT. ULD CT is performed at a 95% dose reduction compared to SD CT.

View all citing articles on Scopus

This work was supported by National Cancer Institute grants N01-CN-85188, 1U01-CA-96109 and P01–96964 (to Dr. Lam); a Canadian Institutes of Health Research-Industry Partnership Grant (GlaxoSmithKline) No. DOP#76813 (PDP), and a British Columbia Lung Association/Canadian Institutes of Health Research New Investigator Award (to Dr. Coxson).

Dr. Coxson has received honoraria, consultant fees, and contract service agreements from GlaxoSmithKline for research studiesinvolving quantitative CT scanning and COPD. A percentage of his salary between 2003 and 2006 derived from contract funds provided to a colleague (Dr. Paré) by GlaxoSmithKline for the development of validated methods to measure emphysema and airway disease using CT scanning. There is no financial relationship between any industry and the current study. Dr. Paré is the principal investigator of a project jointly funded by the Canadian Institute of Health Research (CIHR) and GlaxoSmithKline (one third by the CIHR and two thirds by industry). This grant application was funded after peer review by the regular CIHR mechanism, and the funds received from industry are directly related to the operating costs of the study. Dr. Paré is also principal investigator of a Merck Frosst-supported research program to investigate gene expression in the lungs of patients who have COPD. These funds have supported the technical personnel and expendables involved in the project. Dr. Hogg served as a consultant to Altana Pharmaceuticals in 2003, 2004, and 2005, and also served on the Canadian advisory board for GlaxoSmithKline for 1 year in 2003. He has participated as a speaker in scientific meetings and courses organized and financed by various pharmaceutical companies including AstraZeneca, Altana Pharmaceuticals, and GlaxoSmithKline. He serves as the principal investigator on a grant jointly funded by the CIHR and GlaxoSmithKline (one third by the CIHR and two thirds by industry). This grant application was funded after peer review by the regular CIHR mechanism, and the funds received from industry are directly related to the operating costs of the study. Drs. Yuan, Mayo, Lam, and McWilliams have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

View full text

Chest

Original ResearchChest ImagingThe Effects of Radiation Dose and CT Manufacturer on Measurements of Lung Densitometry

Background

Methods

Results

Conclusion

Section snippets

Subject Selection

Subjects

Radiation Dose Study

Discussion

ACKNOWLEDGMENT

Chest

Chest

Chest

Lancet

Chest

Chest

Quantitative computed tomography assessment of lung structure and function in pulmonary emphysema

Eur Respir J

CT of the lung in patients with pulmonary emphysema: diagnosis, quantification, and correlation with pathologic and physiologic findings

AJR Am J Roentgenol

Emphysema: definition, imaging, and quantification

AJR Am J Roentgenol

Optimization and standardization of lung densitometry in the assessment of pulmonary emphysema

Invest Radiol

Spirometric-gated computed tomography quantitative evaluation of lung emphysema in chronic obstructive pulmonary disease: a comparison of 3 techniques

J Comput Assist Tomogr

Repeatability of quantitative CT indexes of emphysema in patients evaluated for lung volume reduction surgery

Radiology

Chronic obstructive pulmonary disease: evaluation with spirometrically controlled CT lung densitometry

Radiology

Parenchymal emphysema measures by CT lung density correlates with lung function in patients with bullous disease

Eur Respir J

Comparison of computed density and macroscopic morphometry in pulmonary emphysema

Am J Respir Crit Care Med

Comparison of computed density and microscopic morphometry in pulmonary emphysema

Am J Respir Crit Care Med

CT measurements of lung density in life can quantitate distal airspace enlargement-an essential defining feature of human emphysema

Am Rev Respir Dis

Original Research
Chest Imaging
The Effects of Radiation Dose and CT Manufacturer on Measurements of Lung Densitometry