Chest Fat Quantification via CT Based on Standardized Anatomy Space in Adult Lung Transplant Candidates

Abstract

PurposeOverweight and underweight conditions are considered relative contraindications to lung transplantation due to their association with excess mortality. Yet, recent work suggests that body mass index (BMI) does not accurately reflect adipose tissue mass in adults with advanced lung diseases. Alternative and more accurate measures of adiposity are needed. Chest fat estimation by routine computed tomography (CT) imaging may therefore be important for identifying high-risk lung transplant candidates. In this paper, an approach to chest fat quantification and quality assessment based on a recently formulated concept of standardized anatomic space (SAS) is presented. The goal of the paper is to seek answers to several key questions related to chest fat quantity and quality assessment based on a single slice CT (whether in the chest, abdomen, or thigh) versus a volumetric CT, which have not been addressed in the literature.MethodsUnenhanced chest CT image data sets from 40 adult lung transplant candidates (age 58 ± 12 yrs and BMI 26.4 ± 4.3 kg/m2), 16 with chronic obstructive pulmonary disease (COPD), 16 with idiopathic pulmonary fibrosis (IPF), and the remainder with other conditions were analyzed together with a single slice acquired for each patient at the L5 vertebral level and mid-thigh level. The thoracic body region and the interface between subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) in the chest were consistently defined in all patients and delineated using Live Wire tools. The SAT and VAT components of chest were then segmented guided by this interface. The SAS approach was used to identify the corresponding anatomic slices in each chest CT study, and SAT and VAT areas in each slice as well as their whole volumes were quantified. Similarly, the SAT and VAT components were segmented in the abdomen and thigh slices. Key parameters of the attenuation (Hounsfield unit (HU) distributions) were determined from each chest slice and from the whole chest volume separately for SAT and VAT components. The same parameters were also computed from the single abdominal and thigh slices. The ability of the slice at each anatomic location in the chest (and abdomen and thigh) to act as a marker of the measures derived from the whole chest volume was assessed via Pearson correlation coefficient (PCC) analysis.ResultsThe SAS approach correctly identified slice locations in different subjects in terms of vertebral levels. PCC between chest fat volume and chest slice fat area was maximal at the T8 level for SAT (0.97) and at the T7 level for VAT (0.86), and was modest between chest fat volume and abdominal slice fat area for SAT and VAT (0.73 and 0.75, respectively). However, correlation was weak for chest fat volume and thigh slice fat area for SAT and VAT (0.52 and 0.37, respectively), and for chest fat volume for SAT and VAT and BMI (0.65 and 0.28, respectively). These same single slice locations with maximal PCC were found for SAT and VAT within both COPD and IPF groups. Most of the attenuation pr...

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“…The adipose tissue volume was calculated to assess obesity as a comorbidity and as a crude estimate of patient size (height and weight were not available). Adipose tissue volume and was estimated by density interval between -170HU and -40HU on a single slice at level of T7-T8 [16].…”

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“…Fourth, the measurement of single slice cross-sectional area of adipose may not entirely reflect the total adiposity. Prior work has demonstrated a significant correlation between single slice cross-sectional area and total volume of adipose 37,38 ; additionally, our measures of adipose were highly correlated with traditional measures of body composition suggesting that we are measuring the tissue of interest. Fifth, the divergent findings in abdominal and thoracic subcutaneous adipose could also reflect either (1) different populations rather than the differential effects of the 2 distinct anatomical adipose depots or (2) differences in adipose measurement related to the use of clinically indicated rather than protocolized research thoracic CT scans.…”

“…Using a standardized anatomical space approach, 37,38 our group previously identified that the maximum correlation between the total volume of thoracic SAT and single slice area of thoracic SAT is found at the mid-T8 vertebral level (Pearson's r = 0.97), and maximum correlation between the total volume of thoracic VAT and single slice area of thoracic VAT is found at the mid-T7 vertebral level (Pearson's r = 0.86). 37 Using this technique, we identified the single slice cross-sectional area of thoracic VAT and thoracic SAT ( Figure 1C-D). There was high interrater reliability with an intraclass correlation coefficient of 0.98 for the thoracic SAT and 0.97 for the thoracic VAT (Supplementary Figure S1A-B).…”

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“…For example, without a precise definition of the boundaries of the thoracic body region and intrathoracic adipose tissue region, standardized quantification of intrathoracic fat becomes impossible. [1][2][3] Standardized object definitions can also facilitate enriching and sharpening prior knowledge that is encoded into and utilized in methods for localizing objects body-wide 4,5 and distinguishing different patient groups. 6,7 In this spirit, body region definition becomes just as important as or even more important than objects contained in the body region.…”

“…For developing generalizable methods that operate body‐wide, for meaningful use of quantitative information, and for standardized clinical operation, standardized definitions of these objects become essential. For example, without a precise definition of the boundaries of the thoracic body region and intrathoracic adipose tissue region, standardized quantification of intrathoracic fat becomes impossible . Standardized object definitions can also facilitate enriching and sharpening prior knowledge that is encoded into and utilized in methods for localizing objects body‐wide and distinguishing different patient groups .…”