Differences in CT density between dependent and nondependent portions of the lung: influence of lung volume.

Verschakelen, Johny; Fraeyenhoven, L Van; Laureys, Geneviève; Demedts, Maurice; Baert, A L

doi:10.2214/ajr.161.4.8372744

Cited by 107 publications

(58 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…For instance, Verschakelen et al (22) found gradients in computed tomography (CT) lung density between dependent and nondependent lung regions that were most marked at low lung volumes, without, however, observing any difference in density gradients between supine and prone postures. Because the observed regional differences in CT lung densities were explained by gravity-dependent differences in perfusion and lung inflation, the similar pattern observed supine and prone would suggest either that perfusion and ventilation gradients between dependent and nondependent were similar prone and supine, or that both the perfusion and ventilation gradients are reduced in the prone vs. supine posture.…”

Section: Discussionmentioning

confidence: 99%

Similar ventilation distribution in normal subjects prone and supine during tidal breathing

Rodríguez-Nieto

Peces-Barba

Mangado

et al. 2002

Journal of Applied Physiology

View full text Add to dashboard Cite

Rodríguez-Nieto, M. J., G. Peces-Barba, N. Gonzá lez Mangado, M. Paiva, and S. Verbanck. Similar ventilation distribution in normal subjects prone and supine during tidal breathing. J Appl Physiol 92: 622-626, 2002; 10.1152/japplphysiol.00574.2001.-Multiple-breath washout (MBW) tests, with end-expiratory lung volume at functional residual capacity (FRC) and 90% O2, 5% He, and 5% SF6 as an inspired gas mixture, were performed in healthy volunteers in supine and prone postures. The semilog plot of MBW N2 concentrations was evaluated in terms of its curvilinearity. The MBW N2 normalized slope analysis yielded indexes of acinar and conductive ventilation heterogeneity (Verbanck S, Schuermans D, Van Muylem A, Paiva M, Noppen M, and Vincken W. J App Physiol 83: 1907Physiol 83: -1916Physiol 83: , 1997. Also, the difference between SF6 and He normalized phase III slopes was computed in the first MBW expiration. Only MBW tests with similar FRC in the prone and supine postures (P Ͼ 0.1; n ϭ 8) were considered. Prone and supine postures did not reveal any significant differences in curvilinearity, N2 normalized slope-derived indexes of conductive or acinar ventilation heterogeneity, nor SF6-He normalized phase III slope difference in the first MBW expiration (P Ͼ 0.1 for all). The absence of significant changes in any of the MBW indexes suggests that ventilation heterogeneity is similar in the supine and prone postures of normal subjects breathing near FRC. ventilation heterogeneity; tidal breathing; posture; phase III slope SINCE THE WORK of Piehl and Brown (15), showing improved gas exchange in patients when they are positioned in the prone posture, several authors have confirmed these findings (5). The exact reason for improved gas exchange remains uncertain, but it is most often sought in the redistribution of lung ventilation, perfusion, or both. Research into the actual beneficial effect of prone ventilation is hampered by the many confounding factors that can affect the study outcomes. For instance, Tokics et al. (19) have shown that, in supine, anaesthetized, mechanically ventilated patients, nondependent lung regions receive a larger fraction of the inhaled volume, in contrast to what is observed in awake normal subjects. Also, the lung volume at which measurements of perfusion and/or ventilation are done in supine and prone postures will affect the results, yet the actual lung volumes with the test subjects supine and prone are rarely reported.Whereas Kaneko et al. (9) had suggested that the pleural pressure gradient does not change between prone and supine postures, a recent study by Mayo et al. (11), using magnetic resonance imaging in humans, estimated that the pleural pressure gradient is three times smaller prone than supine. Potential differences of top-to-bottom ventilation distribution could also be linked to the different location of the heart with respect to the portion of the dependent lung regions that it is compressing (1). In the prone posture, the heart is seen to be mainly resting on the sternu...

show abstract

Section: Discussionmentioning

confidence: 99%

Similar ventilation distribution in normal subjects prone and supine during tidal breathing

Rodríguez-Nieto

Peces-Barba

Mangado

et al. 2002

Journal of Applied Physiology

View full text Add to dashboard Cite

show abstract

“…Another complication is that respiration occurs throughout the PET acquisition whereas a single phase of respiration (10) 23 (11) 17 (11) 13 (9) 12 (7) 13 (9) 17 (13) 23 (17) 31 (19) 40 (21) 50 (22) 13 (11) 10 (8)…”

Section: Discussionmentioning

confidence: 99%

“…Nevertheless, these errors are separate from those induced by assigning erroneous m-coefficients to the lungs and do not alter the conclusions of this study. On the contrary, without a means to account for the changing lung m-coefficients with respiration (16,17,19), optimal correction of the transmission to emission mismatch (via a time-varying m-map) would be flawed. The principal reason that this study was performed using a large-animal model was that it allowed for precise control of their ventilation; the lungs could be held at the same respiratory state during the CT and MR image acquisitions.…”

Section: (3)mentioning

confidence: 99%

See 1 more Smart Citation

Variable Lung Density Consideration in Attenuation Correction of Whole-Body PET/MRI

Marshall

Prato²,

Deans³

et al. 2012

J Nucl Med

View full text Add to dashboard Cite

Present attenuation-correction algorithms in whole-body PET/ MRI do not consider variations in lung density, either within or between patients; this may adversely affect accurate quantification. In this work, a technique to incorporate patient-specific lung density information into MRI-based attenuation maps is developed and compared with an approach that assumes uniform lung density. Methods: Five beagles were scanned with 18 F-FDG PET/CT and MRI. The relationship between MRI and CT signal in the lungs was established, allowing the prediction of attenuation coefficients from MRI. MR images were segmented into air, lung, and soft tissue and converted into attenuation maps, some with constant lung density and some with patient-specific lung densities. The resulting PET images were compared by both global metrics of quantitative fidelity (accuracy, precision, and root mean squared error) and locally with relative error in volumes of interest. Results: A linear relationship was established between MRI and CT signal in the lungs. Constant lung density attenuation maps did not perform as well as patient-specific lung density attenuation maps, regardless of what constant density was chosen. In particular, when attenuation maps with patient-specific lung density were used, precision, accuracy, and root mean square error improved in lung tissue. In volumes of interest placed in the lungs, relative error was significantly reduced from a minimum of 12% to less than 5%. The benefit extended to tissues adjacent to the lungs but became less important as distance from the lungs increased. Conclusion: A means of using MRI to infer patient-specific attenuation coefficients in the lungs was developed and applied to augment whole-body MRI-based attenuation maps. This technique has been shown to improve the quantitative fidelity of PET images in the lungs and nearby tissues, compared with an approach that assumes uniform lung density.Key Words: PET/MRI; attenuation correction; lung density; segmentation; whole-body imaging Aft er a decade and a half of development, human whole-body PET/MRI systems are now a reality (1). It has been widely speculated that PET/MRI will prove useful in several clinical disciplines (2-4), a prediction that is in the nascent stages of realization (5,6). However, without a means of attenuation correction (AC), accurate quantification in PET is not possible.Multiple approaches have been proposed to create MRIbased attenuation maps (m-maps) (7-15). However, none of these approaches measures the attenuation coefficients (m-coefficients) of the lungs, which vary both between individuals (16) and within a given individual (17,18) and are influenced by inflation (16,17,19), gravitational dependency (18,19), and pathology (18,20,21).Visualizing lung parenchyma with MRI is challenging. The lungs have a low proton density (22) and short transverse relaxation time (T 2 *) (23,24), compromising available MRI signal. Also, the lungs are mobile and highly vascular, generating motion and flow artifacts, respectively...

show abstract

“…The characterization of the disease severity was mainly done by looking at different gray scaling densities interpreted as infiltrates, consolidation or atelectasis during the acute phase [15] and after the resolution of ARDS [23]. The measurement of lung and intrathoracic gas volumes by CT has been validated previously [24,25], but has not been used for as a routine procedure due to complicated and time-consuming exposure and analysis techniques. More recently, from the distribution of frequencies distributions it was attempted to describe changes within the lung induced by certain interventions [7] with regard to the distribution of ventilation.…”

Section: Discussionmentioning

confidence: 99%

Multislice spiral computed tomography to determine the effects of a recruitment maneuver in experimental lung injury

et al. 2005

View full text Add to dashboard Cite

Although recruitment of atelectatic lung is a common aim in acute respiratory distress syndrome (ARDS), the effects of a recruitment maneuver have not been assessed quantitatively. By multislice spiral CT (MSCT), we analyzed the changes in lung volumes calculated from the changes in the CT values of hyperinflated (V(HYP)), normally (V(NORM)), poorly (V(POOR)) and nonaerated (V(NON)) lung in eight mechanically ventilated pigs with saline lavage-induced acute lung injury before and after a recruitment maneuver. This was compared to single slice analysis near the diaphragm. The increase in aerated lung was mainly for V(POOR) and the less in V(NORM). Total lung volume and intrathoracic gas increased. No differences were found for tidal volumes measured by spirometry or determined by CT. The inspiratory-expiratory volume differences were not different after the recruitment maneuver in V(NON) (from 62+/-18 ml to 43+/-26 ml, P = 0.114), and in V(NORM) (from 216+/-51 ml to 251+/-37 ml, P = 0.102). Single slice analysis significantly underestimated the increase in normally and poorly aerated lung. Quantitative analysis of lung volumes by whole lung MSCT revealed the increase of poorly aerated lung as the main mechanism of a standard recruitment maneuver. MSCT can provide additional information as compared to single slice CT.

show abstract

Differences in CT density between dependent and nondependent portions of the lung: influence of lung volume.

Abstract: OBJECTIVE.Lung tissue, blood, and air determine the physical density of the lung and hence the attenuation measured on CT scans.

Cited by 107 publications

References 20 publications

Similar ventilation distribution in normal subjects prone and supine during tidal breathing

Similar ventilation distribution in normal subjects prone and supine during tidal breathing

Variable Lung Density Consideration in Attenuation Correction of Whole-Body PET/MRI

Multislice spiral computed tomography to determine the effects of a recruitment maneuver in experimental lung injury

Contact Info

Product

Resources

About