Pulmonary ventilation and perfusion imaging with dual-energy CT

Pulmonary emphysema: the assessment of lung perfusion with Dual-Energy CT and pulmonary scintigraphy

AIM

To assess the correlation of quantitative data of pulmonary Perfused Blood Volume (PBV) on Dual-Energy CT (DECT) datasets in patients with moderate - severe Pulmonary Emphysema (PE) with Lung Perfusion Scintigraphy (LPS) as the reference standard. The secondary endpoints are the correlation between the CT densitometric analysis and the visual assessment of parenchymal destruction with PBV.

MATERIALS AND METHODS

Patients with moderate - severe PE candidate to Lung Volumetric Reduction (LVR), with available a pre-procedural LS and a contrast-enhanced DECT were retrospectively included. DECT studies were performed with a 3rd generation Dual-Source CT and the PBV was obtained with a 3-material decomposition algorithm. The CT densitometric analysis was performed with a dedicated commercial software (Pulmo3D). The Goddard Score was used for visual assessment. The perfusion LS were performed after the administration of albumin macroaggregates labeled with 99mTechnetium. The image revision was performed by two radiologists or nuclear medicine physicians blinded, respectively, to LS and DECT data. The statistical analysis was performed with nonparametric tests.

RESULTS

Thirty-one patients (18 males, median age 69 y.o., interquartile range 62-71 y.o.) with moderate - severe PE (Median Goddard Score 14/20 and 31% of emphysematous parenchyma at quantitative CT) candidate to LVR were retrospectively included. The median enhancement on PBV was 17 HU. Significant correlation coefficients were demonstrated between lung PBV and LS, poor in apical regions (Rho = 0.1-0.2) and fair (Rho = 0.3-0.5) in middle and lower regions. No significant correlations were recorded between the CT densitometric analysis, the visual score, and the PBV.

CONCLUSIONS

Lung perfusion with PBV on DECT is feasible in patients with moderate - severe PE candidate to LVR, and has a poor to fair agreement with LPS.

Utility of Dual-Energy Computed Tomography in Clinical Conundra

Advancing medical technology revolutionizes our ability to diagnose various disease processes. Conventional Single-Energy Computed Tomography (SECT) has multiple inherent limitations for providing definite diagnoses in certain clinical contexts. Dual-Energy Computed Tomography (DECT) has been in use since 2006 and has constantly evolved providing various applications to assist radiologists in reaching certain diagnoses SECT is rather unable to identify. DECT may also complement the role of SECT by supporting radiologists to confidently make diagnoses in certain clinically challenging scenarios. In this review article, we briefly describe the principles of X-ray attenuation. We detail principles for DECT and describe multiple systems associated with this technology. We describe various DECT techniques and algorithms including virtual monoenergetic imaging (VMI), virtual non-contrast (VNC) imaging, Iodine quantification techniques including Iodine overlay map (IOM), and two- and three-material decomposition algorithms that can be utilized to demonstrate a multitude of pathologies. Lastly, we provide our readers commentary on examples pertaining to the practical implementation of DECT's diverse techniques in the Gastrointestinal, Genitourinary, Biliary, Musculoskeletal, and Neuroradiology systems.

Dual Energy Computed Tomography Collagen Material Decomposition for Detection of Lumbar Spine Disc Extrusion and Sequestration: A Comparative Study With Greyscale Computed Tomography

Purpose: To assess value of dual energy computed tomography (DECT) collagen material decomposition algorithm when combined with standard computed tomography (CT) in detection of lumbar disc extrusion and sequestration. Materials and Methods: Retrospective analysis of all patients with acute low back pain who had a diagnosis of lumbar spine disc extrusion and/or sequestration on Magnetic Resonance Imaging (MRI) (reference standard), and had undergone non-contrast DECT of the lumbar spine within 60 days of the MRI. Age and sex-matched control patients (n = 42) were included. Patients were grouped into standard, grey-scale CT only group and standard CT + DECT tendon images group. Two double-blinded radiologists reviewed both groups for presence of extrusion or sequestration. They also rated their diagnostic confidence on Likert 5-point scale. McNemar Chi-square test was used to compare diagnostic accuracy, unpaired t-test to compare reviewers diagnostic confidence, and Cohen's k (kappa) test for interobserver agreement. Results: The combined group showed higher overall sensitivity (96.6% vs 87.2%), specificity (99% vs 95.4%), and diagnostic accuracy (98.7% vs 94.5%) with a lower false positive rate (1.1% vs 4.6%). McNemar Chi-square test confirmed statistical significance (P = .03 and P = .02 for Reviewers R1 and R2, respectively). The mean diagnostic confidence was also significantly higher on combined group (R1: 3.74 ± 1.1 vs 3.47 ± 1.15 (P < .01) and R2: 3.91 ± 1.15 vs 3.72 ± 1.16 [mean ± SD] (P = .02)). Conclusion: Utilizing MRI as a reference standard, DECT tendon application combined with standard CT increases the sensitivity, specificity, and accuracy of detection of lumbar spine disc extrusion and sequestration, when compared to standard CT alone.

Functional lung imaging in thoracic tumor radiotherapy: Application and progress

Radiotherapy plays an irreplaceable and unique role in treating thoracic tumors, but the occurrence of radiation-induced lung injury has limited the increase in tumor target doses and has influenced patients' quality of life. However, the introduction of functional lung imaging has been incorporating functional lungs into radiotherapy planning. The design of the functional lung protection plan, while meeting the target dose requirements and dose limitations of the organs at risk (OARs), minimizes the radiation dose to the functional lung, thus reducing the occurrence of radiation-induced lung injury. In this manuscript, we mainly reviewed the lung ventilation or/and perfusion functional imaging modalities, application, and progress, as well as the results based on the functional lung protection planning in thoracic tumors. In addition, we also discussed the problems that should be explored and further studied in the practical application based on functional lung radiotherapy planning.

Dual-Energy CT for Pulmonary Embolism: Current and Evolving Clinical Applications

Pulmonary embolism (PE) is a potentially fatal disease if the diagnosis or treatment is delayed. Currently, multidetector computed tomography (MDCT) is considered the standard imaging method for diagnosing PE. Dual-energy CT (DECT) has the advantages of MDCT and can provide functional information for patients with PE. The aim of this review is to present the potential clinical applications of DECT in PE, focusing on the diagnosis and risk stratification of PE.

Diagnostic Impact of Quantitative Dual-Energy Computed Tomography Perfusion Imaging for the Assessment of Subsegmental Pulmonary Embolism

OBJECTIVE

The aim of this study was to investigate the quantitative differences of dual-energy computed tomography perfusion imaging measurements in subsegmental pulmonary embolism (SSPE), between normal lung parenchyma (NLP) and hypoperfused segments (HPS) with and without thrombus on computed tomography angiography (CTA).

METHODS

Lung attenuation, iodine density, and normalized uptake values were measured from HPS and NLP on iodine maps of 43 patients with SSPE. Presence of pulmonary embolism (PE) on CTA was recorded. One-way repeated-measures analysis of variance and Kruskal-Wallis analyses with post hoc comparisons were conducted.

RESULTS

The numbers of HPS with and without SSPE on CTA were 45 (55.6%) and 36 (44.4%), respectively. Lung attenuation of NLP was significantly different from HPS (P < 0.001). Iodine density and normalized uptake values of HPS with PE were significantly lower than those of HPS without PE, which is significantly lower than NLP (P < 0.001).

CONCLUSIONS

Subsegmental pulmonary embolism causes HPS on dual-energy computed tomography perfusion imaging, which demonstrates different iodine density and normalized uptake values depending on the presence of thrombus.

Mechanical Ventilation Redistributes Blood to Poorly Ventilated Areas in Experimental Lung Injury

Supplemental Digital Content is available in the text.

Determine the intra-tidal regional gas and blood volume distributions at different levels of atelectasis in experimental lung injury. Test the hypotheses that pulmonary aeration and blood volume matching is reduced during inspiration in the setting of minimal tidal recruitment/derecruitment and that this mismatching is an important determinant of hypoxemia.

Imaging Pulmonary Blood Flow Using Pseudocontinuous Arterial Spin Labeling (PCASL) With Balanced Steady-State Free-Precession (bSSFP) Readout at 1.5T

BACKGROUND

Quantitative assessment of pulmonary blood flow and visualization of its temporal and spatial distribution without contrast media is of clinical significance.

PURPOSE

To assess the potential of electrocardiogram (ECG)-triggered pseudocontinuous arterial spin labeling (PCASL) imaging with balanced steady-state free-precession (bSSFP) readout to measure lung perfusion under free-breathing (FB) conditions and to study temporal and spatial characteristics of pulmonary blood flow.

STUDY TYPE

Prospective, observational.

SUBJECTS

Fourteen volunteers; three patients with pulmonary embolism.

FIELD STRENGTH/SEQUENCES

1.5T, PCASL-bSSFP.

ASSESSMENT

The pulmonary trunk was labeled during systole. The following examinations were performed: 1) FB and timed breath-hold (TBH) examinations with a postlabeling delay (PLD) of 1000 msec, and 2) TBH examinations with multiple PLDs (100-1500 msec). Scan-rescan measurements were performed in four volunteers and one patient. Images were registered and the perfusion was evaluated in large vessels, small vessels, and parenchyma. Mean structural similarity indices (MSSIM) was computed and time-to-peak (TTP) of parenchymal perfusion in multiple PLDs was evaluated. Image quality reading was performed with three independent blinded readers.

STATISTICAL TESTS

Wilcoxon test to compare MSSIM, perfusion, and Likert scores. Spearman's correlation to correlate TTP and cardiac cycle duration. The repeatability coefficient (RC) and within-subject coefficient of variation (wCV) for scan-rescan measurements. Intraclass correlation coefficient (ICC) for interreader agreement.

RESULTS

Image registration resulted in a significant (P < 0.05) increase of MSSIM. FB perfusion values were 6% higher than TBH (3.28 ± 1.09 vs. 3.10 ± 0.99 mL/min/mL). TTP was highly correlated with individuals' cardiac cycle duration (Spearman = 0.89, P < 0.001). RC and wCV were better for TBH than FB (0.13-0.19 vs. 0.47-1.54 mL/min/mL; 6-7 vs. 19-60%). Image quality was rated very good, with ICCs 0.71-0.89.

DATA CONCLUSION

ECG-triggered PCASL-bSSFP imaging of the lung at 1.5T can provide very good image quality and quantitative perfusion maps even under FB. The course of labeled blood through the lung shows a strong dependence on the individuals' cardiac cycle duration.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 2 J. MAGN. RESON. IMAGING 2020;52:1767-1782.

State of the art: utility of multi-energy CT in the evaluation of pulmonary vasculature

Multi-energy computed tomography (MECT) refers to acquisition of CT data at multiple energy levels (typically two levels) using different technologies such as dual-source, dual-layer and rapid tube voltage switching. In addition to conventional/routine diagnostic images, MECT provides additional image sets including iodine maps, virtual non-contrast images, and virtual monoenergetic images. These image sets provide tissue/material characterization beyond what is possible with conventional CT. MECT provides invaluable additional information in the evaluation of pulmonary vasculature, primarily by the assessment of pulmonary perfusion. This functional information provided by the MECT is complementary to the morphological information from a conventional CT angiography. In this article, we review the technique and applications of MECT in the evaluation of pulmonary vasculature.

A Feasibility Study of Single-inhalation, Single-energy Xenon-enhanced CT for High-resolution Imaging of Regional Lung Ventilation in Humans

RATIONALE AND OBJECTIVES

The objective of this study was to assess the feasibility of single-inhalation xenon-enhanced computed tomography (XeCT) to provide clinically practical, high-resolution pulmonary ventilation imaging to clinics with access to only a single-energy computed tomography scanner, and to reduce the subject's overall exposure to xenon by utilizing a higher (70%) concentration for a much shorter time than has been employed in prior studies.

MATERIALS AND METHODS

We conducted an institutional review board-approved prospective feasibility study of XeCT for 15 patients undergoing thoracic radiotherapy. For XeCT, we acquired two breath-hold single-energy computed tomography images of the entire lung with a single inhalation each of 100% oxygen and a mixture of 70% xenon and 30% oxygen, respectively. A video biofeedback system for coached patient breathing was used to achieve reproducible breath holds. We assessed the technical success of XeCT acquisition and side effects. We then used deformable image registration to align the breath-hold images with each other to accurately subtract them, producing a map of lung xenon distribution. Additionally, we acquired ventilation single-photon emission computed tomography-computed tomography (V-SPECT-CT) images for 11 of the 15 patients. For a comparative analysis, we partitioned each lung into 12 sectors, calculated the xenon concentration from the Hounsfield unit enhancement in each sector, and then correlated this with the corresponding V-SPECT-CT counts.

RESULTS

XeCT scans were tolerated well overall, with a mild (grade 1) dizziness as the only side effect in 5 of the 15 patients. Technical failures in five patients occurred because of inaccurate breathing synchronization with xenon gas delivery, leaving seven patients analyzable for XeCT and single-photon emission computed tomography correlation. Sector-wise correlations were strong (Spearman coefficient >0.75, Pearson coefficient >0.65, P value <.002) for two patients for whom ventilation deficits were visibly pronounced in both scans. Correlations were nonsignificant for the remaining five who had more homogeneous XeCT ventilation maps, as well as strong V-SPECT-CT imaging artifacts attributable to airway deposition of the aerosolized imaging agent. Qualitatively, XeCT demonstrated higher resolution and no central airway deposition artifacts compared to V-SPECT-CT.

CONCLUSIONS

In this pilot study, single-breath XeCT ventilation imaging was generally feasible for patients undergoing thoracic radiotherapy, using an imaging protocol that is clinically practical and potentially widely available. In the future, the xenon delivery failures can be addressed by straightforward technical improvements to the patient biofeedback coaching system.

UTE-SENCEFUL: first results for 3D high-resolution lung ventilation imaging

PURPOSE

This study aimed to develop a 3D MRI technique to assess lung ventilation in free-breathing and without the administration of contrast agent.

METHODS

A 3D-UTE sequence with a koosh ball trajectory was developed for a 3 Tesla scanner. An oversampled k-space was acquired, and the direct current signal from the k-space center was used as a navigator to sort the acquired data into 8 individual breathing phases. Gradient delays were corrected, and iterative SENSE was used to reconstruct the individual timeframes. Subsequently, the signal changes caused by motion were eliminated using a 3D image registration technique, and ventilation-weighted maps were created by analyzing the signal changes in the lung tissue. Six healthy volunteers and 1 patient with lung cancer were scanned with the new 3D-UTE and the standard 2D technique. Image quality and quantitative ventilation values were compared between both methods.

RESULTS

UTE-based self-gated noncontrast-enhanced functional lung (SENCEFUL) MRI provided a time-resolved reconstruction of the breathing motion, with a 49% increase of the SNR. Ventilation quantification for healthy subjects was in statistical agreement with 2D-SENCEFUL and the literature, with a mean value of 0.11 ± 0.08 mL/mL for the whole lung. UTE-SENCEFUL was able to visualize and quantify ventilation deficits in a patient with lung tumor that were not properly depicted by 2D-SENCEFUL.

CONCLUSION

UTE-SENCEFUL represents a robust MRI method to assess both morphological and functional information of the lungs in 3D. When compared to the 2D approach, 3D-UTE offered ventilation maps with higher resolution, improved SNR, and reduced ventilation artifacts.

Signal enhancement ratio imaging of the lung parenchyma with ultra-fast steady-state free precession MRI at 1.5T

BACKGROUND

Lung perfusion MRI after i.v. gadolinium (Gd) contrast administration is commonly based on spoiled gradient-echo acquisitions, such as volume-interpolated breath-hold examinations (VIBE), suffering from low signal-to-noise in the parenchyma.

PURPOSE

To investigate the lung signal enhancement ratio (SER) with ultra-fast steady-state free precession (ufSSFP) after Gd-administration.

STUDY TYPE

Retrospective.

SUBJECTS

Ten subjects with healthy lungs; nine patients with pulmonary diseases (chronic obstructive pulmonary disease [COPD], lung cancer, pulmonary fibrosis, lung contusion).

FIELD STRENGTH/SEQUENCE

VIBE and ufSSFP imaging of the chest was performed at 1.5T before and 3 minutes after i.v. gadobenate dimeglumine.

ASSESSMENT

A workflow including deformable image registration and median filtering was used to compute 3D SER maps. SER was analyzed in the lung, blood pool, liver, muscles, and fat. The artifacts were assessed by a radiologist. In the COPD patients, ufSSFP-SER was compared to ^99m Tc-MAA-SPECT/CT by visual scoring of lung enhancement deficits.

STATISTICAL TESTS

Mean signal, standard deviation (SD), intersubject SD, and coefficient of variation (CV) were calculated for SER. Statistical significance of differences in signal and artifacts were determined using Wilcoxon signed-rank paired test. Intermodality agreement between ufSSFP-SER and SPECT/CT was calculated by Cohen's kappa (κ_q ).

RESULTS

In healthy lungs, ufSSFP-SER (99% ± 23%, mean ± pooled intrasubject SD, CV = 23%) was significantly higher (P < 10^-3 ) and more homogeneous (P < 10^-3 ) than VIBE (47% ± 26%, CV = 57%). UfSSFP-SER was significantly higher (P < 10^-3 ) for the lungs (99% ± 9%, mean ± intersubject SD) than for the blood (81% ± 7%) and other tissues (liver 33% ± 8%, muscle 26% ± 5%, fat 2% ± 1%). In the lung ufSSFP-SER exhibits homogeneity on iso-gravitational planes, and an anterior-posterior gradient. In COPD patients, ufSSFP-SER was reduced and less homogeneous compared to the control group (73% ± 33%, mean ± pooled intrasubject SD, CV = 42%). ufSSFP-SER had moderate intermodality agreement with SPECT/CT (κ_q  = 0.64).

DATA CONCLUSION

UfSSFP-SER of the lung is a rapid and simple method. Our preliminary data show plausible results in different pulmonary diseases, motivating further evaluation in larger cohorts.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.

Imaging in Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is one of the potentially curable causes of pulmonary hypertension and is definitively treated with pulmonary thromboendartectomy. CTEPH can be overlooked, as its symptoms are nonspecific and can be mimicked by a wide range of diseases that can cause pulmonary hypertension. Early diagnosis of CTEPH and prompt evaluation for surgical candidacy are paramount factors in determining future outcomes. Imaging plays a central role in the diagnosis of CTEPH and patient selection for pulmonary thromboendartectomy and balloon pulmonary angioplasty. Currently, various imaging tools are used in concert, with techniques such as computed tomography (CT) and conventional pulmonary angiography providing detailed structural information, tests such as ventilation-perfusion (V/Q) scanning providing functional data, and magnetic resonance imaging providing a combination of morphologic and functional information. Emerging techniques such as dual-energy CT and single photon emission computed tomography-CT V/Q scanning promise to provide both anatomic and functional information in a single test and may change the way we image these patients in the near future. In this review, we discuss the roles of various imaging techniques and discuss their merits, limitations, and relative strengths in depicting the structural and functional changes of CTEPH. We also explore newer imaging techniques and the potential value they may offer.

Improvement in Ventilation-Perfusion Mismatch after Bronchoscopic Lung Volume Reduction: Quantitative Image Analysis

Purpose To evaluate whether bronchoscopic lung volume reduction (BLVR) increases ventilation and therefore improves ventilation-perfusion (V/Q) mismatch. Materials and Methods All patients provided written informed consent to be included in this study, which was approved by the Institutional Review Board (2013-0368) of Asan Medical Center. The physiologic changes that occurred after BLVR were measured by using xenon-enhanced ventilation and iodine-enhanced perfusion dual-energy computed tomography (CT). Patients with severe emphysema plus hyperinflation who did not respond to usual treatments were eligible. Pulmonary function tests, the 6-minute walking distance (6MWD) test, quality of life assessment, and dual-energy CT were performed at baseline and 3 months after BLVR. The effect of BLVR was assessed with repeated-measures analysis of variance. Results Twenty-one patients were enrolled in this study (median age, 68 years; mean forced expiratory volume in 1 second [FEV₁], 0.75 L ± 0.29). After BLVR, FEV₁ (P < .001) and 6MWD (P = .002) improved significantly. Despite the reduction in lung volume (-0.39 L ± 0.44), both ventilation per voxel (P < .001) and total ventilation (P = .01) improved after BLVR. However, neither perfusion per voxel (P = .16) nor total perfusion changed significantly (P = .49). Patients with lung volume reduction of 50% or greater had significantly better improvement in FEV₁ (P = .02) and ventilation per voxel (P = .03) than patients with lung volume reduction of less than 50%. V/Q mismatch also improved after BLVR (P = .005), mainly owing to the improvement in ventilation. Conclusion The dual-energy CT analyses showed that BLVR improved ventilation and V/Q mismatch. This increased lung efficiency may be the primary mechanism of improvement after BLVR, despite the reduction in lung volume. ^© RSNA, 2017 Online supplemental material is available for this article.

Predictive value of perfusion defects on dual energy CTA in the absence of thromboembolic clots

BACKGROUND

To determine the predictive value of volumetrically measured lung perfusion defects (PDvol) and right ventricular dysfunction on dual-energy computed tomography angiography (DE-CTA) for predicting all cause mortality in patients suspected of pulmonary embolism (PE) but without evident thromboembolic clot on CTA.

METHODS

448 patients underwent DE-CTA on a 64-channel DSCT system between January 2007 and December 2012 for suspected PE, of which 115 were without detectable thromboembolic clot on CTA. Diagnostic performance for identifying patients at risk of dying was evaluated using ROC analysis. All-cause mortality was assessed via the hospital electronic medical records and/or consultation of the patient or the patient's primary care physician via phone call interviews. Sensitivity, specificity, positive likelihood ratio, negative likelihood ratio and area under the curve (AUC) were determined for PDvol (volume of perfusion defects/total lung volume), transverse right ventricular to left ventricular diameter ratios (RV/LV) and for the combination of both tests.

RESULTS

Mortality was 38% within the investigated time period of 6 months. Patients who died had significantly higher PDvol (PDvol 28 ± 13% vs. 19 ± 12%, p < 0.001) and a non-significant difference in transverse RV/LV ratio (1.14 ± 0.37 vs. 1.06 ± 0.22, p = 0.159). The AUC was 0.71 for PDvol, 0.53 for RV/LV ratio, and 0.67 for the combination of PDvol and RV/LV ratio. PDvol remained a significant predictor after correcting for age.

CONCLUSIONS

In the absence of thromboembolic clots, PDvol at DE-CTA appears to be predictive for all cause mortality.

[MRI methods for pulmonary ventilation and perfusion imaging]

CLINICAL/METHODICAL ISSUE

Separate assessment of respiratory mechanics, gas exchange and pulmonary circulation is essential for the diagnosis and therapy of pulmonary diseases. Due to the global character of the information obtained clinical lung function tests are often not sufficiently specific in the differential diagnosis or have a limited sensitivity in the detection of early pathological changes.

STANDARD RADIOLOGICAL METHODS

The standard procedures of pulmonary imaging are computed tomography (CT) for depiction of the morphology as well as perfusion/ventilation scintigraphy and single photon emission computed tomography (SPECT) for functional assessment.

METHODICAL INNOVATIONS

Magnetic resonance imaging (MRI) with hyperpolarized gases, O2-enhanced MRI, MRI with fluorinated gases and Fourier decomposition MRI (FD-MRI) are available for assessment of pulmonary ventilation. For assessment of pulmonary perfusion dynamic contrast-enhanced MRI (DCE-MRI), arterial spin labeling (ASL) and FD-MRI can be used.

PERFORMANCE

Imaging provides a more precise insight into the pathophysiology of pulmonary function on a regional level. The advantages of MRI are a lack of ionizing radiation, which allows a protective acquisition of dynamic data as well as the high number of available contrasts and therefore accessible lung function parameters.

ACHIEVEMENTS

Sufficient clinical data exist only for certain applications of DCE-MRI. For the other techniques, only feasibility studies and case series of different sizes are available. The clinical applicability of hyperpolarized gases is limited for technical reasons.

PRACTICAL RECOMMENDATIONS

The clinical application of the techniques described, except for DCE-MRI, should be restricted to scientific studies.

The role of dual-energy computed tomography in the assessment of pulmonary function

The assessment of pulmonary function, including ventilation and perfusion status, is important in addition to the evaluation of structural changes of the lung parenchyma in various pulmonary diseases. The dual-energy computed tomography (DECT) technique can provide the pulmonary functional information and high resolution anatomic information simultaneously. The application of DECT for the evaluation of pulmonary function has been investigated in various pulmonary diseases, such as pulmonary embolism, asthma and chronic obstructive lung disease and so on. In this review article, we will present principles and technical aspects of DECT, along with clinical applications for the assessment pulmonary function in various lung diseases.

Feasibility of Single Scan for Simultaneous Evaluation of Regional Krypton and Iodine Concentrations with Dual-Energy CT: An Experimental Study

Purpose To evaluate the feasibility of a simultaneous single scan of regional krypton and iodine concentrations by using dual-energy computed tomography (CT). Materials and Methods The study was approved by the institutional animal experimental committee. An airway obstruction model was first made in 10 beagle dogs, and a pulmonary arterial occlusion was induced in each animal after 1 week. For each model, three sessions of dual-energy CT (80% krypton ventilation [krypton CT], 80% krypton ventilation with iodine enhancement [mixed-contrast agent CT], and iodine enhancement [iodine CT]) were performed. Krypton maps were made from krypton and mixed-contrast agent CT, and iodine maps were made from iodine and mixed-contrast agent CT. Observers measured overlay Hounsfield units of the diseased and contralateral segments on each map. Values were compared by using the Wilcoxon signed-rank test. Results In krypton maps of airway obstruction, overlay Hounsfield units of diseased segments were significantly decreased compared with those of contralateral segments in both krypton and mixed-contrast agent CT (P = .005 for both). However, the values of mixed-contrast agent CT were significantly higher than those of krypton CT for both segments (P = .005 and .007, respectively). In iodine maps of pulmonary arterial occlusion, values were significantly lower in diseased segments than in contralateral segments for both iodine and mixed-contrast agent CT (P = .005 for both), without significant difference between iodine and mixed-contrast agent CT for both segments (P = .126 and .307, respectively). Conclusion Although some limitations may exist, it might be feasible to analyze regional krypton and iodine concentrations simultaneously by using dual-energy CT. ^© RSNA, 2016.

Dual-energy CT for imaging of pulmonary hypertension: challenges and opportunities

Computed tomography (CT) is routinely used in the evaluation of patients with pulmonary hypertension (PH) to assess vascular anatomy and parenchymal morphology. The introduction of dual-energy CT (DECT) enables additional qualitative and quantitative insights into pulmonary hemodynamics and the extent and variability of parenchymal enhancement. Lung perfusion assessed at pulmonary blood volume imaging correlates well with findings at scintigraphy, and pulmonary blood volume defects seen in pulmonary embolism studies infer occlusive disease with increased risk of right heart dysfunction. Similarly, perfusion inhomogeneities seen in patients with PH closely reflect mosaic lung changes and may be useful for severity assessment and prognostication. The use of DECT may increase detection of peripheral thromboembolic disease, which is of particular prognostic importance in patients with chronic thromboembolic PH with microvascular involvement. Other DECT applications for imaging of PH include low-kilovoltage images with greater inherent iodine conspicuity and iodine-selective color-coded maps of vascular perfusion (both of which can improve visualization of vascular enhancement), virtual nonenhanced imaging (which better depicts vascular calcification), and, potentially, ventricular perfusion maps (to assess myocardial ischemia). In addition, quantitative assessment of central vascular and parenchymal enhancement can be used to evaluate pulmonary hemodynamics in patients with PH. The current status and potential advantages and limitations of DECT for imaging of PH are reviewed, and current evidence is supplemented with data from a tertiary referral center for PH.

Novel imaging approaches in adult asthma and their clinical potential

Currently, imaging in asthma is confined to chest radiography and CT. The emergence of new imaging techniques and tremendous improvement of existing imaging methods, primarily due to technological advancement, has completely changed its research and clinical prospects. In research, imaging in asthma is now being employed to provide quantitative assessment of morphology, function and pathogenic processes at the molecular level. The unique ability of imaging for non-invasive, repeated, quantitative, and in vivo assessment of structure and function in asthma could lead to identification of 'imaging biomarkers' with potential as outcome measures in future clinical trials. Emerging imaging techniques and their utility in the research and clinical setting is discussed in this review.

Optimization of dual-energy xenon-computed tomography for quantitative assessment of regional pulmonary ventilation

OBJECTIVE

Dual-energy x-ray computed tomography (DECT) offers visualization of the airways and quantitation of regional pulmonary ventilation using a single breath of inhaled xenon gas. In this study, we sought to optimize scanning protocols for DECT xenon gas ventilation imaging of the airways and lung parenchyma and to characterize the quantitative nature of the developed protocols through a series of test-object and animal studies.

MATERIALS AND METHODS

The Institutional Animal Care and Use Committee approved all animal studies reported here. A range of xenon/oxygen gas mixtures (0%, 20%, 25%, 33%, 50%, 66%, 100%; balance oxygen) were scanned in syringes and balloon test-objects to optimize the delivered gas mixture for assessment of regional ventilation while allowing for the development of improved 3-material decomposition calibration parameters. In addition, to alleviate gravitational effects on xenon gas distribution, we replaced a portion of the oxygen in the xenon/oxygen gas mixture with helium and compared gas distributions in a rapid-prototyped human central-airway test-object. Additional syringe tests were performed to determine if the introduction of helium had any effect on xenon quantitation. Xenon gas mixtures were delivered to anesthetized swine to assess airway and lung parenchymal opacification while evaluating various DECT scan acquisition settings.

RESULTS

Attenuation curves for xenon were obtained from the syringe test-objects and were used to develop improved 3-material decomposition parameters (Hounsfield unit enhancement per percentage xenon: within the chest phantom, 2.25 at 80 kVp, 1.7 at 100 kVp, and 0.76 at 140 kVp with tin filtration; in open air, 2.5 at 80 kVp, 1.95 at 100 kVp, and 0.81 at 140 kVp with tin filtration). The addition of helium improved the distribution of xenon gas to the gravitationally nondependent portion of the airway tree test-object, while not affecting the quantitation of xenon in the 3-material decomposition DECT. The mixture 40% Xe/40% He/20% O2 provided good signal-to-noise ratio (SNR), greater than the Rose criterion (SNR > 5), while avoiding gravitational effects of similar concentrations of xenon in a 60% O2 mixture. Compared with 100/140 Sn kVp, 80/140 Sn kVp (Sn = tin filtered) provided improved SNR in a swine with an equivalent thoracic transverse density to a human subject with a body mass index of 33 kg/m. Airways were brighter in the 80/140 Sn kVp scan (80/140 Sn, 31.6%; 100/140 Sn, 25.1%) with considerably lower noise (80/140 Sn, coefficient of variation of 0.140; 100/140 Sn, coefficient of variation of 0.216).

CONCLUSION

To provide a truly quantitative measure of regional lung function with xenon-DECT, the basic protocols and parameter calibrations need to be better understood and quantified. It is critically important to understand the fundamentals of new techniques to allow for proper implementation and interpretation of their results before widespread usage. With the use of an in-house derived xenon calibration curve for 3-material decomposition rather than the scanner supplied calibration and a xenon/helium/oxygen mixture, we demonstrate highly accurate quantitation of xenon gas volumes and avoid gravitational effects on gas distribution. This study provides a foundation for other researchers to use and test these methods with the goal of clinical translation.

Spectral CT imaging as a new quantitative tool? Assessment of perfusion defects of pulmonary parenchyma in patients with lung cancer

OBJECTIVE

This study investigated the capability of dual-energy spectral computed tomography (CT) to quantitatively evaluate lung perfusion defects that are induced by central lung cancer.

METHODS

Thirty-two patients with central lung cancer underwent CT angiography using spectral imaging. A univariate general linear model was conducted to analyze the variance of iodine concentration/CT value with three factors of lung fields. A paired t-test was used to compare iodine concentrations and CT values between the distal end of lung cancer and the corresponding area in the contralateral normal lung.

RESULTS

Iodine concentrations increased progressively in the far, intermediate and near ground sides in the normal lung fields at 0.60±0.28, 0.93±0.27 and 1.25±0.38 mg/mL, respectively (P<0.001). The same trend was observed for the CT values [-(840.64±49.08), -(812.66±50.85) and -(760.83±89.17) HU, P<0.001]. The iodine concentration (0.70±0.42 mg/mL) of the lung field in the distal end of lung cancer was significantly lower than the corresponding area in the contralateral normal lung (1.19±0.62 mg/mL) (t=-7.23, P<0.001). However, the CT value of lung field in the distal end of lung cancer was significantly higher than the corresponding area in the contralateral normal lung [-(765.29±93.34) HU vs. -(800.07±76.18) HU, t=3.564, P=0.001].

CONCLUSIONS

Spectral CT imaging based on the spectral differentiation of iodine is feasible and can quantitatively evaluate pulmonary perfusion and identify perfusion defects that are induced by central lung cancer. Spectral CT seems to be a promising technique for the simultaneous evaluation of both morphological and functional lung information.

SPECT/CT and pulmonary embolism

Acute pulmonary embolism (PE) is diagnosed either by ventilation/perfusion (V/P) scintigraphy or pulmonary CT angiography (CTPA). In recent years both techniques have improved. Many nuclear medicine centres have adopted the single photon emission CT (SPECT) technique as opposed to the planar technique for diagnosing PE. SPECT has been shown to have fewer indeterminate results and a higher diagnostic value. The latest improvement is the combination of a low-dose CT scan with a V/P SPECT scan in a hybrid tomograph. In a study comparing CTPA, planar scintigraphy and SPECT alone, SPECT/CT had the best diagnostic accuracy for PE. In addition, recent developments in the CTPA technique have made it possible to image the pulmonary arteries of the lungs in one breath-hold. This development is based on the change from a single-detector to multidetector CT technology with an increase in volume coverage per rotation and faster rotation. Furthermore, the dual energy CT technique is a promising modality that can provide functional imaging in combination with anatomical information. Newer high-end CT scanners and SPECT systems are able to visualize smaller subsegmental emboli. However, consensus is lacking regarding the clinical impact and treatment. In the present review, SPECT and SPECT in combination with low-dose CT, CTPA and dual energy CT are discussed in the context of diagnosing PE.

Non-contrast-enhanced preoperative assessment of lung perfusion in patients with non-small-cell lung cancer using Fourier decomposition magnetic resonance imaging

OBJECTIVE

To investigate non-contrast-enhanced Fourier decomposition MRI (FD MRI) for assessment of regional lung perfusion in patients with Non-Small-Cell Lung Cancer (NSCLC) in comparison to dynamic contrast-enhanced MRI (DCE MRI).

METHODS

Time-resolved non-contrast-enhanced images of the lungs were acquired prospectively in 15 patients using a 2D balanced steady-state free precession (b-SSFP) sequence. After non-rigid registration of the native image data, perfusion-weighted images were calculated by separating periodic changes of lung proton density at the cardiac frequency using FD. DCE MRI subtraction datasets were acquired as standard of reference. Both datasets were analyzed visually for perfusion defects. Then segmentation analyses were performed to describe perfusion of pulmonary lobes semi-quantitatively as percentages of total lung perfusion. Overall FD MRI perfusion signal was compared to velocity-encoded flow measurements in the pulmonary trunk as an additional fully quantitative reference.

RESULTS

Image quality ratings of FD MRI were significantly inferior to those of DCE MRI (P<0.0001). Sensitivity, specificity, and accuracy of FD MRI for visual detection of perfusion defects were 84%, 92%, and 91%. Semi-quantitative evaluation of lobar perfusion provided high agreement between FD MRI and DCE MRI for both entire lungs and upper lobes, but less agreement in the lower parts of both lungs. FD perfusion signal showed high linear correlation with pulmonary arterial blood flow.

CONCLUSION

FD MRI is a promising technique that allows for assessing regional lung perfusion in NSCLC patients without contrast media or ionizing radiation. However, for being applied in clinical routine, image quality and robustness of the technique need to be further improved.

New insight into the assessment of asthma using xenon ventilation computed tomography

BACKGROUND

Image analyses include computed tomography (CT), magnetic resonance imaging, and xenon ventilation CT, which is new modality to evaluate pulmonary functional imaging.

OBJECTIVE

To examine the usefulness of dual-energy xenon ventilation CT in asthmatic patients.

METHODS

A total of 43 patients 18 years or older who were nonsmokers were included in the study. Xenon CT images in wash-in and wash-out phases were obtained at baseline and after inhalation of methacholine and salbutamol. The degrees of ventilation defects and xenon trappings were evaluated through visual analysis.

RESULTS

Ventilation defects and xenon trapping were significantly increased and decreased after methacholine challenge and salbutamol inhalation, respectively (P < .005). The ventilation abnormalities were not significantly related to the percentage of forced expiratory volume in 1 second (FEV1) or the ratio of FEV1 to forced vital capacity. Xenon trappings after salbutamol inhalation were negatively related to the scores of the asthma control test, wheezing, or night symptoms, with statistical significance (P < .05), whereas, FEV1 showed no significant correlation with symptom scores. Baseline FEV1 was significantly lower and dyspnea and wheezing were more severe in the non-full reversal group than in the full reversal group after salbutamol inhalation in xenon CT (P < .05). The degree of ventilation defects were positively correlated with FEV1 improvement after 3 months of treatment (P = .02).

CONCLUSION

The results of this study suggest that xenon ventilation CT can be used as a new method to assess ventilation abnormalities in asthma, and these ventilation abnormalities can be used as novel parameters that reflect the status of asthma control and symptom severity.

[Imaging for diagnostics of urolithiasis including dual-energy CT]

Patients with stone disease usually present to the urologist with acute colic pain. For the right choice of therapy the diagnosis needs to be confirmed using one of many imaging methods, including ultrasonography, abdominal radiography, intravenous urography, non-contrast-enhanced computed tomography (CT), CT and magnetic resonance imaging (MRI) urography and dual-energy CT. The techniques differ in the availability, diagnostic sensitivity and specificity and level of radiation exposure. Compared to the others dual-energy CT allows distinction between different stone compositions with high accuracy and can affect the choice of therapy. This article on imaging and diagnosis of urolithiasis discusses the different imaging methods and highlights dual-energy CT and its distinctive features.

Dual-energy CT imaging of thoracic malignancies

Computed tomography (CT) plays a pivotal role in the detection, characterization, and staging of lung cancer and other thoracic malignancies. Since the introduction of clinically viable dual-energy CT techniques, substantial evidence has accumulated on the use of this modality for imaging chest malignancies. This article describes the principles of dual-energy CT along with suitable image acquisition, reconstruction, and postprocessing strategies for oncologic applications in the chest. The potential of dual-energy CT techniques for the detection, characterization, staging, and surveillance of chest malignancy, as well as the limitations of this modality are discussed.

Dual-energy lung perfusion and ventilation CT in children

Dual-energy thoracic CT provides two key insights into lung physiology, i.e. regional perfusion and ventilation, and has been actively investigated to find clinically relevant applications since the introduction of dual-source CT. This functional information provided by dual-energy thoracic CT is supplementary because high-resolution thoracic anatomy is entirely preserved on dual-energy thoracic CT. In addition, virtual non-contrast imaging can omit pre-contrast scanning. In this respect, dual-energy CT imaging technique is at least dose-neutral, which is a critical requirement for paediatric imaging. In this review, imaging protocols, analysis methods, clinical applications and diagnostic pitfalls of dual-energy thoracic CT for evaluating lung perfusion and ventilation in children are described.

Dual-energy CT of the lung

OBJECTIVE

The introduction of dual-energy CT (DECT) has ushered in the ability of material differentiation and tissue characterization beyond the traditional CT attenuation scale. This quality has been exploited for visualizing and quantifying the specific tissue content using radiographic contrast agents, such as iodine-based contrast media or inhaled xenon gas. Applications of this paradigm in the thorax include characterization of the pulmonary blood pool in the setting of acute or chronic pulmonary embolism (PE) and characterization of diseases of the lung parenchyma. Selective xenon detection is being explored for imaging of lung ventilation. In addition, the usefulness of DECT-based selective iodine uptake measurements has been described for the diagnosis and surveillance of thoracic malignancies. This article reviews the current applications of DECT-based imaging techniques in the chest with an emphasis on the diagnosis and characterization of pulmonary thromboembolic disorders.

CONCLUSION

DECT can provide both anatomic and functional information about the lungs in a variety of pulmonary disease states based on a single contrast-enhanced CT examination. This quality has been shown to improve the diagnosis of acute and chronic PEs, other vascular disorders, lung malignancies, and parenchymal diseases. Further developments in DECT techniques and CT scanner technology will further foster and enhance the utility of this application and open new avenues in lung imaging.

Worsening respiratory function in mechanically ventilated intensive care patients: feasibility and value of xenon-enhanced dual energy CT

OBJECTIVES

To evaluate the feasibility and incremental diagnostic value of xenon-enhanced dual-energy CT in mechanically ventilated intensive care patients with worsening respiratory function.

METHODS

The study was performed in 13 mechanically ventilated patients with severe pulmonary conditions (acute respiratory distress syndrome (ARDS), n=5; status post lung transplantation, n=5; other, n=3) and declining respiratory function. CT scans were performed using a dual-source CT scanner at an expiratory xenon concentration of 30%. Both ventilation images (Xe-DECT) and standard CT images were reconstructed from a single CT scan. Findings were recorded for Xe-DECT and standard CT images separately. Ventilation defects on xenon images were matched to morphological findings on standard CT images and incremental diagnostic information of xenon ventilation images was recorded if present.

RESULTS

Mean xenon consumption was 2.95 l per patient. No adverse events occurred under xenon inhalation. In the visual CT analysis, the Xe-DECT ventilation defects matched with pathologic changes in lung parenchyma seen in the standard CT images in all patients. Xe-DECT provided additional diagnostic findings in 4/13 patients. These included preserved ventilation despite early pneumonia (n=1), more confident discrimination between a large bulla and pneumothorax (n=1), detection of an airway-to-pneumothorax fistula (n=1) and exclusion of a suspected airway-to-mediastinum fistula (n=1). In all 4 patients, the additional findings had a substantial impact on patients' management.

CONCLUSIONS

Xenon-enhanced DECT is safely feasible and can add relevant diagnostic information in mechanically ventilated intensive care patients with worsening respiratory function.

Pulmonary perfused blood volume with dual-energy CT as surrogate for pulmonary perfusion assessed with dynamic multidetector CT

PURPOSE

To compare measurements of regional pulmonary perfused blood volume (PBV) and pulmonary blood flow (PBF) obtained with computed tomography (CT) in two pig models.

MATERIALS AND METHODS

The institutional animal care and use committee approved all animal studies. CT-derived PBF and PBV were determined in four anesthetized, mechanically ventilated, supine swine by using two methods for creating pulmonary parenchymal perfusion heterogeneity. Two animals were examined after sequentially moving a pulmonary arterial balloon catheter from a distal to a central location, and two others were examined over a range of static airway pressures, which varied the extents of regional PBF. Lung sections were divided into blocks and Pearson correlation coefficients calculated to compare matching regions between the two methods.

RESULTS

CT-derived PBF, CT-derived PBV, and their associated coefficients of variation (CV) were closely correlated on a region-by-region basis in both the balloon occlusion (Pearson R = 0.91 and 0.73 for animals 1 and 2, respectively; Pearson R = 0.98 and 0.87 for comparison of normalized mean and CV for animals 1 and 2, respectively) and lung inflation studies (Pearson R = 0.94 and 0.74 for animals 3 and 4, respectively; Pearson R = 0.94 and 0.69 for normalized mean and CV for animals 3 and 4, respectively). When accounting for region-based effects, correlations remained highly significant at the P < .001 level.

CONCLUSION

CT-derived PBV heterogeneity is a suitable surrogate for CT-derived PBF heterogeneity.

Metal artifact reduction by dual-energy computed tomography using energetic extrapolation: a systematically optimized protocol

OBJECTIVES

Energetic extrapolation is a promising strategy to reduce metal artifacts in dual-source computed tomography (DSCT). We performed this study to systematically optimize image acquisition parameters for this approach in a hip phantom and assess its value in a clinical study.

MATERIALS AND METHODS

Titanium and steel hip prostheses were placed in a standard hip phantom and a water tank and scanned on a DSCT scanner. Tube spectra, tube current ratio, collimation, pitch, and rotation time were optimized in a stepwise process. Artifacts were quantified by measuring the standard deviation of the computed tomography density in a doughnut-shaped region of interest placed around the prosthesis. A total of 22 adult individuals with metallic implants referred for computed tomography for a musculoskeletal indication were scanned using the optimized protocol. Degree of artifacts and diagnostic image quality were rated visually (0-10) and maximum streak intensity was measured.

RESULTS

Sn140/100 kVp proved superior to Sn140/80 kVp. There was a benefit for increasing tube current ratio from 1:1 to 3:1, but not beyond, in favor of the Sn140 kVp spectrum. Artifacts were less severe for a collimation of 32 × 0.6 mm as compared with 40 × 0.6 mm. A pitch of 0.5 at a rotation time of 0.5 seconds per rotation was preferable to other combinations with comparable scanning times. In the clinical study, increasing the extrapolated photon energy from 64 to 120 keV decreased the severity of artifacts from 8.0 to 2.0 (P < 0.001) and decreased streak intensity from 871 to 153 HU (P < 0.001). The median diagnostic image quality rating improved from 2.5 to 8.0 (P < 0.001). The median energy level visually perceived as optimal for diagnostic evaluation was 113 keV (range, 100-130 keV).

CONCLUSIONS

Sn140/100 kVp with a tube current ratio of 3:1, a collimation of 32 × 0.6 mm, and extrapolated energies of 105 to 120 keV are optimal parameters for a dedicated DSCT protocol that effectively reduces metal artifacts by energetic extrapolation. The protocol effectively reduces metal artifacts in all types of metal implants. The optimized reconstructions yielded relevant additional findings.

Ventilation and perfusion magnetic resonance imaging of the lung

A close interaction between the respiratory pump, pulmonary parenchyma and blood circulation is essential for a normal lung function. Many pulmonary diseases present, especially in their initial phase, a variable regional impairment of ventilation and perfusion. In the last decades various techniques have been established to measure the lung function. Besides the global pulmonary function tests (PFTs) imaging techniques gained increasing importance to detect local variations in lung function, especially for ventilation and perfusion assessment. Imaging modalities allow for a deeper regional insight into pathophysiological processes and enable improved planning of invasive procedures. In contrast to computed tomography (CT) and the nuclear medicine techniques, magnetic resonance imaging (MRI), as a radiation free imaging modality gained increasing importance since the early 1990 for the assessment of pulmonary function. The major inherent problems of lung tissue, namely the low proton density and the pulmonary and cardiac motion, were overcome in the last years by a constant progress in MR technology. Some MR techniques are still under development, a process which is driven by scientific questions regarding the physiology and pathophysiology of pulmonary diseases, as well as by the need for fast and robust clinically applicable imaging techniques as safe therapy monitoring tools. MRI can be considered a promising ionizing-free alternative to techniques like CT or nuclear medicine techniques for the evaluation of lung function. The goal of this article is to provide an overview on selected MRI techniques for the assessment of pulmonary ventilation and perfusion.

Lung imaging in rodents using dual energy micro-CT

Dual energy CT imaging is expected to play a major role in the diagnostic arena as it provides material decomposition on an elemental basis. The purpose of this work is to investigate the use of dual energy micro-CT for the estimation of vascular, tissue, and air fractions in rodent lungs using a post-reconstruction three-material decomposition method. We have tested our method using both simulations and experimental work. Using simulations, we have estimated the accuracy limits of the decomposition for realistic micro-CT noise levels. Next, we performed experiments involving ex vivo lung imaging in which intact lungs were carefully removed from the thorax, were injected with an iodine-based contrast agent and inflated with air at different volume levels. Finally, we performed in vivo imaging studies in (n=5) C57BL/6 mice using fast prospective respiratory gating in end-inspiration and end-expiration for three different levels of positive end-expiratory pressure (PEEP). Prior to imaging, mice were injected with a liposomal blood pool contrast agent. The mean accuracy values were for Air (95.5%), Blood (96%), and Tissue (92.4%). The absolute accuracy in determining all fraction materials was 94.6%. The minimum difference that we could detect in material fractions was 15%. As expected, an increase in PEEP levels for the living mouse resulted in statistically significant increases in air fractions at end-expiration, but no significant changes in end-inspiration. Our method has applicability in preclinical pulmonary studies where various physiological changes can occur as a result of genetic changes, lung disease, or drug effects.

Dual-energy micro-CT of the rodent lung

The purpose of this work is to investigate the use of dual-energy micro-computed tomography (CT) for the estimation of vascular, tissue, and air fractions in rodent lungs using a postreconstruction three material decomposition method. Using simulations, we have estimated the accuracy limits of the decomposition for realistic micro-CT noise levels. Next, we performed experiments involving ex vivo lung imaging in which intact rat lungs were carefully removed from the thorax, injected with an iodine-based contrast agent, and then inflated with different volumes of air (n = 2). Finally, we performed in vivo imaging studies in C57BL/6 mice (n = 5) using fast prospective respiratory gating in end inspiration and end expiration for three different levels of positive end expiratory pressure (PEEP). Before imaging, mice were injected with a liposomal blood pool contrast agent. The three-dimensional air, tissue, and blood fraction maps were computed and analyzed. The results indicate that separation and volume estimation of the three material components of the lungs are possible. The mean accuracy values for air, blood, and tissue were 93, 93, and 90%, respectively. The absolute accuracy in determining all fraction materials was 91.6%. The coefficient of variation was small (2.5%) indicating good repeatability. The minimum difference that we could detect in material fractions was 15%. As expected, an increase in PEEP levels for the living mouse resulted in statistically significant increases in air fractions at end expiration but no significant changes at end inspiration. Our method has applicability in preclinical pulmonary studies where changes in lung structure and gas volume as a result of lung injury, environmental exposures, or drug bioactivity would have important physiological implications.