Purpose
To apply a navigator‐based slice‐tracking method to prospectively compensate respiratory motion for kidney pseudo‐continuous arterial spin labeling (pCASL), using spin‐echo (SE) EPI ...acquisition.
Methods
A single gradient‐echo slice selection and projection readout at the location of the diaphragm along the inferior–superior direction was applied as a navigator. Navigator acquisition and fat suppression were inserted before each transverse imaging slice of the readouts of a 2D‐SE‐EPI‐based pCASL sequence. Motion information was calculated after exclusion of the signal saturation in the navigator signal caused by EPI excitations. The motion information was then used to directly adjust the slice positioning in real time.
Results
The respiratory motion from the navigator signal was calculated, and slice positioning was changed in real time based on the motion information. We could show that motion compensation reduces kidney movement, and that the coefficients of variation across renal perfusion values were significantly reduced when motion correction was applied. The average reduction of coefficients of variation was approximately 20%, resulting in a more accurate and detailed structure of the respective perfusion maps.
Conclusions
This study demonstrates the feasibility of a navigator‐based slice‐tracking technique in kidney imaging with a SE‐EPI readout pCASL sequence to reduce kidney motion.
Abstract In this work, the time evolution of the free induction decay caused by the local dipole field of a spherical magnetic perturber is analyzed. The complicated treatment of the diffusion ...process is replaced by the strong-collision-approximation that allows a determination of the free induction decay in dependence of the underlying microscopic tissue parameters such as diffusion coefficient, sphere radius and susceptibility difference. The interplay between susceptibility- and diffusion-mediated effects yields several dephasing regimes of which, so far, only the classical regimes of motional narrowing and static dephasing for dominant and negligible diffusion, respectively, were extensively examined. Due to the asymmetric form of the dipole field for spherical objects, the free induction decay exhibits a complex component in contradiction to the cylindrical case, where the symmetric local dipole field only causes a purely real induction decay. Knowledge of the shape of the corresponding frequency distribution is necessary for the evaluation of more sophisticated pulse sequences and a detailed understanding of the off-resonance distribution allows improved quantification of transverse relaxation.
To apply a navigator-based slice tracking method to prospectively compensate the respiratory motion for kidney vessel architecture imaging (VAI).
A dual gradient echo spin echo 2D EPI sequence was ...developed for kidney VAI. A single gradient-echo slice selection and projection readout at the location of the diaphragm along the inferior-superior direction was applied as a navigator. Navigator acquisition and fat suppression were inserted before each transverse imaging slice. Motion information was calculated after exclusion of the signal saturation in the navigator signal caused by imaging slices. The motion information was then directly sent back to the sequence and slice positioning was adjusted in real-time. The whole sequence was applied during a contrast agent pass-through.
VAI parametric maps show the structural heterogeneity of the renal vasculature. The respiratory motion from the navigator signal was precisely calculated and slice positioning was changed in real-time based on the motion information. The vibration amplitude of the signal intensity of the liver tissue at the liver-lung interface in the case of prospective motion correction (PMC) on is about 28% of the PMC off case. Compared to the case of PMC off, the coefficient of variation was reduced 30% of the case of PMC on.
This study demonstrates the feasibility of the motion-compensating technique in kidney VAI. The sequence may improve the evaluation of microvasculature in kidney diseases.
The purpose of this work is to apply multi-echo spin- and gradient-echo (SAGE) echo-planar imaging (EPI) combined with a navigator-based (NAV) prospective motion compensation method for a ...quantitative liver blood oxygen level dependent (BOLD) measurement with a breath-hold (BH) task.
A five-echo SAGE sequence was developed to quantitatively measure T
and T
* to depict function with sufficient signal-to-noise ratio, spatial resolution and sensitivity to BOLD changes induced by the BH task. To account for respiratory motion, a navigator was employed in the form of a single gradient-echo projection readout, located at the diaphragm along the inferior-superior direction. Prior to each transverse imaging slice of the spin-echo EPI-based readouts, navigator acquisition and fat suppression were incorporated. Motion data was obtained from the navigator and transmitted back to the sequence, allowing real-time adjustments to slice positioning. Six healthy volunteers and three patients with liver carcinoma were included in this study. Quantitative T
and T
* were calculated at each time point of the BH task. Parameters of t value from first-level analysis using a general linear model and hepatovascular reactivity (HVR) of Echo1, T
and T
* were calculated.
The motion caused by respiratory activity was successfully compensated using the navigator signal. The average changes of T
and T
* during breath-hold were about 1% and 0.7%, respectively. With the help of NAV prospective motion compensation whole liver t values could be obtained without motion artifacts. The quantified liver T
(34.7 ± 0.7 ms) and T
* (29 ± 1.2 ms) values agreed with values from literature. In healthy volunteers, the distribution of statistical t value and HVR was homogeneous throughout the whole liver. In patients with liver carcinoma, the distribution of t value and HVR was inhomogeneous due to metastases or therapy.
This study demonstrates the feasibility of using a NAV prospective motion compensation technique in conjunction with five-echo SAGE EPI for the quantitative measurement of liver BOLD with a BH task.
Background
Noninvasive monitoring of early abnormalities and therapeutic intervention in cystic fibrosis (CF) lung disease using MRI is important. Lung T1 mapping has shown potential for local ...functional imaging without contrast material. Recently, it was discovered that observed lung T1 depends on the measurement echo time (TE).
Purpose
To examine TE‐dependence of observed T1 in patients with CF and its correlation with clinical metrics.
Study Type
Prospective.
Population
In all, 75 pediatric patients with CF (8.6 ± 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 T1(TE) mapping at five TEs including TE1 = 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. T1(TE) was quantified automatically. Clinical data including spirometry (FEV1pred%) and lung clearance index (LCI) were collected.
Statistical Tests
T1(TE) was correlated with the CF‐MRI score, clinical data, and LCI.
Results
T1(TE) showed a different curvature in CF than in healthy adults: T1 at TE1 was shorter in CF (1157 ms ± 73 ms vs. 1047 ms ± 70 ms, P < 0.001), but longer at TE3 (1214 ms ± 72 ms vs. 1314 ms ± 68 ms, P < 0.001) and later TEs. The correlations of T1(TE) with patient age (ρTE1‐TE5 = −0.55, −0.44, −0.24, −0.30, −0.22), and LCI (ρTE1‐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 (ρTE1‐TE5 = −0.43, −0.51, −0.47, −0.46, −0.44) and FEV1pred% (ρTE1‐TE5 = +0.44, +0.44, +0.43, +0.40, +0.39) (P < 0.05).
Data Conclusion
TE should be considered when measuring lung T1, 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 J. MAGN. RESON. IMAGING 2020;52:1645–1654.
Background
This work is intended to demonstrate that T1 measured in the lungs depends on the echo time (TE) used. Measuring lung T1 can be used to gain quantitative morphological and functional ...information. It is also shown that this dependence is particularly visible when using an ultra‐short TE (UTE) sequence with TE well below 1 ms for T1 quantification in lung tissue, rather than techniques with TE on the order of 1–2 ms.
Methods
The lungs of 12 healthy volunteers (aged 22 to 33 years) were examined at 1.5 Tesla. A segmented inversion recovery Look‐Locker multi‐echo sequence based on two‐dimensional UTE was used for independent T1 quantification at five TEs between TE1 = 70 μs and TE5 = 2.3 ms.
Results
The measured T1 was found to increase gradually with TE from 1060 ± 40 ms at TE1 to 1389 ± 53 ms at TE5 (P < 0.001).
Conclusion
Measuring T1 at ultra‐short echo times reveals a significant dependence of observed T1 on the echo time. Thus, any comparison of T1 values should also consider the TEs used. However, this dependence on TE could also be exploited to gain additional diagnostic information on the tissue compartments in the lung. J. Magn. Reson. Imaging 2015;42:610–616.
T1 maps have been shown to yield useful diagnostic information on lung function in patients with chronic obstructive pulmonary disease (COPD) and asthma, both for native T1 and ΔT1, the relative ...reduction while breathing pure oxygen. As parameter quantification is particularly interesting for longitudinal studies, the purpose of this work was both to examine the reproducibility of lung T1 mapping and to compare T1 found in COPD and asthma patients using IRSnapShotFLASH embedded in a full MRI protocol. 12 asthma and 12 COPD patients (site 1) and further 15 COPD patients (site 2) were examined on two consecutive days. In each patient, T1 maps were acquired in 8 single breath-hold slices, breathing first room air, then pure oxygen. Maps were partitioned into 12 regions each to calculate average values. In asthma patients, the average T1,RA = 1206ms (room air) was reduced to T1,O2 = 1141ms under oxygen conditions (ΔT1 = 5.3%, p < 5⋅10-4), while in COPD patients both native T1,RA = 1125ms was significantly shorter (p < 10-3) and the relative reduction to T1,O2 = 1081ms on average ΔT1 = 4.2%(p < 10-5). On the second day, with T1,RA = 1186ms in asthma and T1,RA = 1097ms in COPD, observed values were slightly shorter on average in all patient groups. ΔT1 reduction was the least repeatable parameter and varied from day to day by up to 23% in individual asthma and 30% in COPD patients. While for both patient groups T1 was below the values reported for healthy subjects, the T1 and ΔT1 found in asthmatics lies between that of the COPD group and reported values for healthy subjects, suggesting a higher blood volume fraction and better ventilation. However, it could be demonstrated that lung T1 quantification is subject to notable inter-examination variability, which here can be attributed both to remaining contrast agent from the previous day and the increased dependency of lung T1 on perfusion and thus current lung state.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Background
There is a clinical need for imaging‐derived biomarkers for the management of chronic obstructive pulmonary disease (COPD). Observed pulmonary T1 (T1(TE)) depends on the echo‐time (TE) and ...reflects regional pulmonary function.
Purpose
To investigate the potential diagnostic value of T1(TE) for the assessment of lung disease in COPD patients by determining correlations with clinical parameters and quantitative CT.
Study Type
Prospective non‐randomized diagnostic study.
Population
Thirty COPD patients (67.7 ± 6.6 years). Data from a previous study (15 healthy volunteers 26.2 ± 3.9 years) were used as reference.
Field Strength/Sequence
Study participants were examined at 1.5 T using dynamic contrast‐enhanced three‐dimensional gradient echo keyhole perfusion sequence and a multi‐echo inversion recovery two‐dimensional UTE (ultra‐short TE) sequence for T1(TE) mapping at TE1‐5 = 70 μsec, 500 μsec, 1200 μsec, 1650 μsec, and 2300 μsec.
Assessment
Perfusion images were scored by three radiologists. T1(TE) was automatically quantified. Computed tomography (CT) images were quantified in software (qCT). Clinical parameters including pulmonary function testing were also acquired.
Statistical Tests
Spearman rank correlation coefficients (ρ) were calculated between T1(TE) and perfusion scores, clinical parameters and qCT. A P‐value <0.05 was considered statistically significant.
Results
Median values were T1(TE1‐5) = 644 ± 78 msec, 835 ± 92 msec, 835 ± 87 msec, 831 ± 131 msec, 893 ± 220 msec, all significantly shorter than previously reported in healthy subjects. A significant increase of T1 was observed from TE1 to TE2, with no changes from TE2 to TE3 (P = 0.48), TE3 to TE4 (P = 0.94) or TE4 to TE5 (P = 0.02) which demonstrates an increase at shorter TEs than in healthy subjects. Moderate to strong Spearman's correlations between T1 and parameters including the predicted diffusing capacity for carbon monoxide (DLCO, ρ < 0.70), mean lung density (MLD, ρ < 0.72) and the perfusion score (ρ > −0.69) were found. Overall, correlations were strongest at TE2, weaker at TE1 and rarely significant at TE4‐TE5.
Data Conclusion
In COPD patients, the increase of T1(TE) with TE occurred at shorter TEs than previously found in healthy subjects. Together with the lack of correlation between T1 and clinical parameters of disease at longer TEs, this suggests that T1(TE) quantification in COPD patients requires shorter TEs. The TE‐dependence of correlations implies that T1(TE) mapping might be developed further to provide diagnostic information beyond T1 at a single TE.
Level of Evidence
2
Technical Efficacy
Stage 1
Background
Recent studies support magnetic resonance angiography (MRA) as a diagnostic tool for pulmonary arterial disease.
Purpose
To determine MRA image quality and reproducibility, and the ...dependence of MRA image quality and reproducibility on disease severity in patients with chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF).
Material and Methods
Twenty patients with COPD (mean age 66.5 ± 8.9 years; FEV1% = 42.0 ± 13.3%) and 15 with CF (mean age 29.3 ± 9.3 years; FEV1% = 66.6 ± 15.8%) underwent morpho-functional chest magnetic resonance imaging (MRI) including time-resolved MRA twice one month apart (MRI1, MRI2), and COPD patients underwent non-contrast computed tomography (CT). Image quality was assessed visually using standardized subjective 5-point scales. Contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were measured by regions of interest. Disease severity was determined by spirometry, a well-evaluated chest MRI score, and by computational CT emphysema index (EI) for COPD.
Results
Subjective image quality was diagnostic for all MRA at MRI1 and MRI2 (mean score = 4.7 ± 0.6). CNR and SNR were 4 43.8 ± 8.7 and 50.5 ± 8.7, respectively. Neither image quality score nor CNR or SNR correlated with FEV1% or chest MRI score for COPD and CF (r = 0.239–0.248). CNR and SNR did not change from MRI1 to MRI2 (P = 0.434–0.995). Further, insignificant differences in CNR and SNR between MRA at MRI1 and MRI2 did not correlate with FEV1% nor chest MRI score in COPD and CF (r = −0.238–0.183), nor with EI in COPD (r = 0.100–0.111).
Conclusion
MRA achieved diagnostic quality in COPD and CF patients and was highly reproducible irrespective of disease severity. This supports MRA as a robust alternative to CT in patients with underlying muco-obstructive lung disease.
To determine if morphological non-contrast enhanced magnetic resonance imaging (MRI) of the lung is sensitive to detect mosaic signal intensity in infants and preschool children with cystic fibrosis ...(CF).
50 infant and preschool CF patients (mean age 3.5 ± 1.4y, range 0–6y) routinely underwent morphological (T2-weighted turbo-spin echo sequence with half-Fourier acquisition, HASTE) and contrast-enhanced 4D perfusion MRI (gradient echo sequence with parallel imaging and echo sharing, TWIST). MRI studies were independently scored by two readers blinded for patient age and clinical data (experienced Reader 1 = R1, inexperienced Reader 2 = R2). The extent of lung parenchyma signal abnormalities on HASTE was rated for each lobe from 0 (normal), 1 (<50% of lobe affected) to 2 (≥50% of lobe affected). Perfusion MRI was rated according to the previously established MRI score, and served as the standard of reference.
Inter-method agreement between MRI mosaic score and perfusion score was moderate with κ = 0.58 (confidence interval 0.45–0.71) for R1, and with κ = 0.59 (0.46–0.72) for R2. Bland-Altman analysis revealed a slight tendency of the mosaic score to underestimate perfusion abnormalities with a score bias of 0.48 for R1 and 0.46 for R2. Inter-reader agreement for mosaic score was substantial with κ = 0.71 (0.62–0.79), and a low bias of 0.02.
This study demonstrates that non-contrast enhanced MRI reliably detects mosaic signal intensity in infants and preschool children with CF, reflecting pulmonary blood volume distribution. It may thus be used as a surrogate for perfusion MRI if contrast material is contra-indicated or alternative techniques are not available.
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