Echo Time‐Dependence of Observed Lung T₁ in Patients With Cystic Fibrosis and Correlation With Clinical Metrics

Abstract

Background: Noninvasive monitoring of early abnormalities and therapeutic intervention in cystic fibrosis (CF) lung disease using MRI is important. Lung T 1 mapping has shown potential for local functional imaging without contrast material. Recently, it was discovered that observed lung T 1 depends on the measurement echo time (TE). Purpose: To examine TE-dependence of observed T 1 in patients with CF and its correlation with clinical metrics. Study Type: Prospective. Population: In all, 75 pediatric patients with CF (8.6 AE 6.1 years, range 0.1-23 years), with 32 reexamined after 1 year. Field Strength/Sequence: Patients were examined at 1.5T using an established MRI protocol and a multiecho inversion recovery 2D ultrashort echo time (UTE) sequence for T 1 (TE) mapping at five TEs including TE 1 = 70 μs. Assessment: Morphological and perfusion MRI were assessed by a radiologist (M.W.) with 11 years of experience using an established CF-MRI scoring system. T 1 (TE) was quantified automatically. Clinical data including spirometry (FEV1pred%) and lung clearance index (LCI) were collected. Statistical Tests: T 1 (TE) was correlated with the CF-MRI score, clinical data, and LCI. Results: T 1 (TE) showed a different curvature in CF than in healthy adults: T 1 at TE 1 was shorter in CF (1157 ms AE 73 ms vs. 1047 ms AE 70 ms, P < 0.001), but longer at TE 3 (1214 ms AE 72 ms vs. 1314 ms AE 68 ms, P < 0.001) and later TEs. The correlations of T 1 (TE) with patient age (ρ TE1-TE5 = −0.55, −0.44, −0.24, −0.30, −0.22), and LCI (ρ TE1-TE5 = −0.43, −0.42, −0.33, 0.27, −0.22) were moderate at ultra-short to short TE (P < 0.001) but decreased for longer TE. Moderate but similar correlations at all TE were found with MRI perfusion score (ρ TE1-TE5 = −0.43, −0.51, −0.47, −0.46, −0.44) and FEV1pred% (ρ TE1-TE5 = +0.44, +0.44, +0.43, +0.40, +0.39) (P < 0.05). Data Conclusion: TE should be considered when measuring lung T 1 , since observed differences between CF and healthy subjects strongly depend on TE. The different variation of correlation coefficients with TE for structural vs. functional metrics implies that TE-dependence holds additional information which may help to discern effects of tissue structural abnormalities and abnormal perfusion. Level of Evidence: 2 Technical Efficacy Stage: 1

Practical protocol for lung magnetic resonance imaging and common clinical indications

“…Lung ventilation can be assessed with hyperpolarized gas MRI and oxygen-enhanced MRI. Alternatively, lung ventilation can also be assessed without gaseous contrast using Fourier decomposition [ 22 ]. Although hyperpolarized gas MRI can provide higher image quality and resolution than Fourier decomposition, the high cost of the gases and the need of dedicated hardware have limited its clinical implementation.…”

“…The morphological sequences of the protocol were shown to be efficient in imaging bronchial wall thickening, bronchiectasis, mucus plugging, air-fluid levels, consolidation/infiltration, mosaic pattern and lobar or segmental destruction, with reasonable quality compared to CT [ 14 , 48 , 49 , 51 , 52 ]. While the diagnostic scope of MRI regarding structural information just reaches CT because of slightly lower spatial resolution and motion artifacts (resulting from longer acquisition times), its main advantage over CT is the availability of additional functional information, e.g., from perfusion imaging and real-time imaging of respiratory motion [ 22 ]. Perfusion imaging is mainly used to detect and follow perfusion deficits related to slowed or missing pulmonary ventilation in areas of bronchial obstruction (hypoxic vasoconstriction).…”

“…The use of gadolinium-based contrast material remains a concern, so alternative approaches based on dynamic proton MRI with Fourier decomposition of cyclic signal changes of lung parenchyma in ventilated and perfused regions [15], T1mapping [19], oxygen-enhanced MR [22] and hyperpolarized 3 He [24] and 129 Xe [24] MRI are under investigation. However, because of the lack of robustness, the need for expensive hardware or limited availability of the necessary gases, none of these approaches has been adopted for clinical imaging routine.…”

Defining the Clinical Utility of the Lung Clearance Index. Are We There Yet?

“…As a result, an array of functional and imaging testing modalities have been and continue to be actively investigated in CF for their ability to provide an accurate assessment of airway disease [10][11][12][13][14] . Thanks to technological advances, parameters obtained from the multiple breath washout (MBW) technique have emerged as providing an alternative sensitive assessment of airway function.…”

Editorial for “Echo Time‐Dependence of Observed Lung T1 in Patients With Cystic Fibrosis and Correlation With Clinical Metrics”

“…They hypothesized that such a dependence might allow differentiating the influence of tissue composition from blood volume fraction on T 1 , thus providing additional information beyond perfusion. Recently (Triphan et al, this issue), this approach was applied at 1.5T to 75 CF patients across the pediatric age range (infant to adult), and T 1 as a function of TE (T 1 (TE)) was compared to a CF‐MRI score, clinical data, and LCI 10 . The data suggest that the T 1 dependence on TE contains information that may help to discern tissue structural changes at the tissue level and abnormal perfusion in CF patients.…”