Vikas Gulani

MR Fingerprinting of Adult Brain Tumors: Initial Experience.

MR fingerprinting is a technique in which pseudorandomized acquisition parameters are used to simultaneously quantify multiple tissue properties, including T1 and T2 relaxation times. The authors evaluated the ability of MR fingerprinting–derived T1 and T2 relaxometry to differentiate the 3 common types of intra-axial brain tumors (17 glioblastomas, 6 lower grade gliomas, and 8 metastases). Using these parameters, they explored the T1 and T2 properties of peritumoral white matter in various tumor types. Mean T2 values could differentiate solid tumor regions of lowergrade gliomas from metastases and the mean T1 of peritumoral white matter surrounding lowergrade gliomas differed from peritumoral white matter around glioblastomas. BACKGROUND AND PURPOSE: MR fingerprinting allows rapid simultaneous quantification of T1 and T2 relaxation times. This study assessed the utility of MR fingerprinting in differentiating common types of adult intra-axial brain tumors. MATERIALS AND METHODS: MR fingerprinting acquisition was performed in 31 patients with untreated intra-axial brain tumors: 17 glioblastomas, 6 World Health Organization grade II lower grade gliomas, and 8 metastases. T1, T2 of the solid tumor, immediate peritumoral white matter, and contralateral white matter were summarized within each ROI. Statistical comparisons on mean, SD, skewness, and kurtosis were performed by using the univariate Wilcoxon rank sum test across various tumor types. Bonferroni correction was used to correct for multiple-comparison testing. Multivariable logistic regression analysis was performed for discrimination between glioblastomas and metastases, and area under the receiver operator curve was calculated. RESULTS: Mean T2 values could differentiate solid tumor regions of lower grade gliomas from metastases (mean, 172 ± 53 ms, and 105 ± 27 ms, respectively; P = .004, significant after Bonferroni correction). The mean T1 of peritumoral white matter surrounding lower grade gliomas differed from peritumoral white matter around glioblastomas (mean, 1066 ± 218 ms, and 1578 ± 331 ms, respectively; P = .004, significant after Bonferroni correction). Logistic regression analysis revealed that the mean T2 of solid tumor offered the best separation between glioblastomas and metastases with an area under the curve of 0.86 (95% CI, 0.69–1.00; P < .0001). CONCLUSIONS: MR fingerprinting allows rapid simultaneous T1 and T2 measurement in brain tumors and surrounding tissues. MR fingerprinting–based relaxometry can identify quantitative differences between solid tumor regions of lower grade gliomas and metastases and between peritumoral regions of glioblastomas and lower grade gliomas.

Magnetic resonance fingerprinting – An overview

Magnetic Resonance Fingerprinting (MRF) is a new approach to quantitative magnetic resonance imaging that allows simultaneous measurement of multiple tissue properties in a single, time-efficient acquisition. The ability to reproducibly and quantitatively measure tissue properties could enable more objective tissue diagnosis, comparisons of scans acquired at different locations and time points, longitudinal follow-up of individual patients and development of imaging biomarkers. This review provides a general overview of MRF technology, current preclinical and clinical applications and potential future directions. MRF has been initially evaluated in brain, prostate, liver, cardiac, musculoskeletal imaging, and measurement of perfusion and microvascular properties through MR vascular fingerprinting.

Single breath-hold 3D cardiac T 1 mapping using through-time spiral GRAPPA

The quantification of cardiac T1 relaxation time holds great potential for the detection of various cardiac diseases. However, as a result of both cardiac and respiratory motion, only one two‐dimensional T1 map can be acquired in one breath‐hold with most current techniques, which limits its application for whole heart evaluation in routine clinical practice. In this study, an electrocardiogram (ECG)‐triggered three‐dimensional Look–Locker method was developed for cardiac T1 measurement. Fast three‐dimensional data acquisition was achieved with a spoiled gradient‐echo sequence in combination with a stack‐of‐spirals trajectory and through‐time non‐Cartesian generalized autocalibrating partially parallel acquisition (GRAPPA) acceleration. The effects of different magnetic resonance parameters on T1 quantification with the proposed technique were first examined by simulating data acquisition and T1 map reconstruction using Bloch equation simulations. Accuracy was evaluated in studies with both phantoms and healthy subjects. These results showed that there was close agreement between the proposed technique and the reference method for a large range of T1 values in phantom experiments. In vivo studies further demonstrated that rapid cardiac T1 mapping for 12 three‐dimensional partitions (spatial resolution, 2 × 2 × 8 mm3) could be achieved in a single breath‐hold of ~12 s. The mean T1 values of myocardial tissue and blood obtained from normal volunteers at 3 T were 1311 ± 66 and 1890 ± 159 ms, respectively. In conclusion, a three‐dimensional T1 mapping technique was developed using a non‐Cartesian parallel imaging method, which enables fast and accurate T1 mapping of cardiac tissues in a single short breath‐hold.

Investigating and reducing the effects of confounding factors for robust T1 and T2 mapping with cardiac MR fingerprinting

This study aims to improve the accuracy and consistency of T1 and T2 measurements using cardiac MR Fingerprinting (cMRF) by investigating and accounting for the effects of confounding factors including slice profile, inversion and T2 preparation pulse efficiency, and B1+. The goal is to understand how measurements with different pulse sequences are affected by these factors. This can be used to determine which factors must be taken into account for accurate measurements, and which may be mitigated by the selection of an appropriate pulse sequence. Simulations were performed using a numerical cardiac phantom to assess the accuracy of over 600 cMRF sequences with different flip angles, TRs, and preparation pulses. A subset of sequences, including one with the lowest errors in T1 and T2 maps, was used in subsequent analyses. Errors due to non-ideal slice profile, preparation pulse efficiency, and B1+ were quantified in Bloch simulations. Corrections for these effects were included in the dictionary generation and demonstrated in phantom and in vivo cardiac imaging at 3u202fT. Neglecting to model slice profile and preparation pulse efficiency led to underestimated T1 and overestimated T2 for most cMRF sequences. Sequences with smaller maximum flip angles were less affected by slice profile and B1+. Simulating all corrections in the dictionary improved the accuracy of T1 and T2 phantom measurements, regardless of acquisition pattern. More consistent myocardial T1 and T2 values were measured using different sequences after corrections. Based on these results, a pulse sequence which is minimally affected by confounding factors can be selected, and the appropriate residual corrections included for robust T1 and T2 mapping.

Estimation of perfusion properties with MR Fingerprinting Arterial Spin Labeling

In this study, the acquisition of ASL data and quantification of multiple hemodynamic parameters was explored using a Magnetic Resonance Fingerprinting (MRF) approach. A pseudo-continuous ASL labeling scheme was used with pseudo-randomized timings to acquire the MRF ASL data in a 2.5u202fmin acquisition. A large dictionary of MRF ASL signals was generated by combining a wide range of physical and hemodynamic properties with the pseudo-random MRF ASL sequence and a two-compartment model. The acquired signals were matched to the dictionary to provide simultaneous quantification of cerebral blood flow, tissue time-to-peak, cerebral blood volume, arterial time-to-peak, B1, and T1. A study in seven healthy volunteers resulted in the following values across the population in grey matter (meanu202f±u202fstandard deviation): cerebral blood flow of 69.1u202f±u202f6.1u202fml/min/100u202fg, arterial time-to-peak of 1.5u202f±u202f0.1u202fs, tissue time-to-peak of 1.5u202f±u202f0.1u202fs, T1 of 1634u202fms, cerebral blood volume of 0.0048u202f±u202f0.0005. The CBF measurements were compared to standard pCASL CBF estimates using a one-compartment model, and a Bland-Altman analysis showed good agreement with a minor bias. Repeatability was tested in five volunteers in the same exam session, and no statistical difference was seen. In addition to this validation, the MRF ASL acquisitions sensitivity to the physical and physiological parameters of interest was studied numerically.

Advantages of time-resolved contrast-enhanced 4D MR angiography in splenic arterial steal syndrome

Splenic artery steal syndrome (SASS) is a severe complication affecting up to 10% of orthotopic liver transplant (OLT) patients. In this case report, we present a 35-year-old male with OLT secondary to liver failure due to hemochromatosis, who developed SASS. We describe potential application of different imaging techniques for diagnosis of SASS with focus on the value of time-resolved contrast enhanced 4D magnetic resonance angiography (MRA).