Emphysema quantification using chest CT: influence of radiation dose reduction and reconstruction technique.

BACKGROUND: Computed tomography (CT) emphysema quantification is affected by both radiation dose (i.e. image noise) and reconstruction technique. At reduced dose, filtered back projection (FBP) results in an overestimation of the amount of emphysema due to higher noise levels, while the use of iterative reconstruction (IR) can result in an underestimation due to reduced noise. The objective of this study was to determine the influence of dose reduction and hybrid IR (HIR) or model-based IR (MIR) on CT emphysema quantification. METHODS: Twenty-two patients underwent inspiratory chest CT scan at routine radiation dose and at 45%, 60% and 75% reduced radiation dose. Acquisitions were reconstructed with FBP, HIR and MIR. Emphysema was quantified using the 15th percentile of the attenuation curve and the percentage of voxels below -950 HU. To determine whether the use of a different percentile or HU threshold is more accurate at reduced dose levels and with IR, additional measurements were performed using different percentiles and HU thresholds to determine the optimal combination. RESULTS: Dose reduction resulted in a significant overestimation of emphysema, while HIR and MIR resulted in an underestimation. Lower HU thresholds with FBP at reduced dose and higher HU thresholds with HIR and MIR resulted in emphysema percentages comparable to the reference. The 15th percentile quantification method showed similar results as the HU threshold method. CONCLUSIONS: This within-patients study showed that CT emphysema quantification is significantly affected by dose reduction and IR. This can potentially be solved by adapting commonly used thresholds.

Etidronate for Prevention of Ectopic Mineralization in Patients With Pseudoxanthoma Elasticum.

BACKGROUND: In pseudoxanthoma elasticum (PXE), low pyrophosphate levels may cause ectopic mineralization, leading to skin changes, visual impairment, and peripheral arterial disease. OBJECTIVES: The authors hypothesized that etidronate, a pyrophosphate analog, might reduce ectopic mineralization in PXE. METHODS: In the Treatment of Ectopic Mineralization in Pseudoxanthoma Elasticum trial, adults with PXE and leg arterial calcifications (n = 74) were randomly assigned to etidronate or placebo (cyclical 20 mg/kg for 2 weeks every 12 weeks). The primary outcome was ectopic mineralization, quantified with 18fluoride positron emission tomography scans as femoral arterial wall target-to-background ratios (TBRfemoral). Secondary outcomes were computed tomography arterial calcification and ophthalmological changes. Safety outcomes were bone density, serum calcium, and phosphate. RESULTS: During 12 months of follow-up, the TBRfemoral increased 6% (interquartile range [IQR]: -12% to 25%) in the etidronate group and 7% (IQR: -9% to 32%) in the placebo group (p = 0.465). Arterial calcification decreased 4% (IQR: -11% to 7%) in the etidronate group and increased 8% (IQR: -1% to 20%) in the placebo group (p = 0.001). Etidronate treatment was associated with significantly fewer subretinal neovascularization events (1 vs. 9, p = 0.007). Bone density decreased 4% ± 12% in the etidronate group and 6% ± 9% in the placebo group (p = 0.374). Hypocalcemia (<2.20 mmol/l) occurred in 3 versus 1 patient (8.1% vs. 2.7%, p = 0.304). Eighteen patients (48.6%) treated with etidronate, compared with 0 patients treated with placebo (p < 0.001), experienced hyperphosphatemia (>1.5 mmol/l) and recovered spontaneously. CONCLUSIONS: In patients with PXE, etidronate reduced arterial calcification and subretinal neovascularization events but did not lower femoral 18fluoride sodium positron emission tomography activity compared with placebo, without important safety issues. (Treatment of Ectopic Mineralization in Pseudoxanthoma elasticum; NTR5180).