Mini thoracic CT adequately determines Haller index and decreases radiation exposure in children with pectus excavatum

INTRODUCTION

The preoperative assessment of Pectus Excavatum (PE) is resource intensive. CT chest for the purpose of calculating a Haller index (HI) remains a central component and is necessary for third-party reimbursment for surgical correction. With the goal of minimizing radiation exposure, a strategy was introduced to perform a mini-Thoracic CT (mini-CT) for the calculation of HI.

OPERATIVE TECHNIQUE

The mini-CT was performed as follows: a radio-opaque marker (ROM) was placed at the clinical deepest point of the deformity. The CT was then columnated to scan 3 cm above and 3 cm below the ROM. HI was calculated according to previously described technique. Seven children with PE who underwent mini-CT were age and weight matched to 7 children with PE who underwent standard low dose CT chest during the same time period. Radiation doses were evaluated using dose length product (DLP) and effective dose (mSv) between the two groups. Significance of differences was determined using the students t-test. The DLP of mini-CT compared to chest-CT was 17.9 vs 48.9,mGycm respectively. (p< 0.001) The mSv of the mini-CT compared to chest-CT was 0.32 vs 0.88, sMV respectively. (p<0.001) Both DLP and mSv were reduced by 63% in children who received a mini-CT. All children obtained insurance authorization and underwent uncomplicated Nuss repair.

CONCLUSION

For children with pectus excavatum deformities the mini-Thoracic CT is an effective method to calculate the HI. Compard to the conventional low dose chest CT, the mini-CT strategy significantly reduces radiation exposure to the child by 63% with no impact on third-party authorizations or Nuss repair.

Fiber orientation measurements by diffusion tensor imaging improve hydrogen-1 magnetic resonance spectroscopy of intramyocellular lipids in human leg muscles

Twelve healthy subjects underwent hydrogen-1 magnetic resonance spectroscopy ([Formula: see text]) acquisition ([Formula: see text]), diffusion tensor imaging (DTI) with a [Formula: see text]-value of [Formula: see text], and fat-water magnetic resonance imaging (MRI) using the Dixon method. Subject-specific muscle fiber orientation, derived from DTI, was used to estimate the lipid proton spectral chemical shift. Pennation angles were measured as 23.78 deg in vastus lateralis (VL), 17.06 deg in soleus (SO), and 8.49 deg in tibialis anterior (TA) resulting in a chemical shift between extramyocellular lipids (EMCL) and intramyocellular lipids (IMCL) of 0.15, 0.17, and 0.19 ppm, respectively. IMCL concentrations were [Formula: see text], [Formula: see text], and [Formula: see text] in SO, VL, and TA, respectively. Significant differences were observed in IMCL and EMCL pairwise comparisons in SO, VL, and TA ([Formula: see text]). Strong correlations were observed between total fat fractions from [Formula: see text] and Dixon MRI for VL ([Formula: see text]), SO ([Formula: see text]), and TA ([Formula: see text]). Bland-Altman analysis between fat fractions (FFMRS and FFMRI) showed good agreement with small limits of agreement (LoA): [Formula: see text] (LoA: [Formula: see text] to 0.69%) in VL, [Formula: see text] (LoA: [Formula: see text] to 1.33%) in SO, and [Formula: see text] (LoA: [Formula: see text] to 0.47%) in TA. The results of this study demonstrate the variation in muscle fiber orientation and lipid concentrations in these three skeletal muscle types.