Quantitative MRI using STrategically Acquired Gradient Echo (STAGE): optimization for 1.5 T scanners and T1 relaxation map validation

Rationale and Objectives. Accurate signal to tracer concentration maps are critical to quantitative MRI. The purpose of this study was to evaluate and optimize spoiled gradient echo (SPGR) MR sequences for the use of gadolinium (Gd-DTPA) as a kinetic tracer.Methods. Water-gadolinium phantoms were constructed for a physiologic range of gadolinium concentrations. Observed and calculated SPGR signal to concentration curves were generated. Using a percentage error determination, optimal pulse parameters for signal to concentration mapping were obtained.Results. The accuracy of the SPGR equation is a function of the chosen MR pulse parameters, particularly the time to repetition (TR) and the flip angle (FA). At all experimental values of TR, increasing FA decreases the ratio between observed and calculated signals. Conversely, for a constant FA, increasing TR increases this ratio. Using optimized pulse parameter sets, it is possible to achieve excellent accuracy (approximately 5%) over a physiologic range of concentration tracer concentrations.Conclusion. Optimal pulse parameter sets exist and their use is essential for deriving accurate signal to concentration curves in quantitative MRI.

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Matching Quantitative MRI Parameters with Histological Features of Treatment-Naïve IDH Wild-Type Glioma

Cancers ◽

10.3390/cancers13164060 ◽

2021 ◽

Vol 13 (16) ◽

pp. 4060

Author(s):

Gabriele D. Maurer ◽

Julia Tichy ◽

Patrick N. Harter ◽

Ulrike Nöth ◽

Lutz Weise ◽

...

Keyword(s):

Relaxation Time ◽

Tumor Cells ◽

Relaxation Times ◽

Relative Difference ◽

Quantitative Mri ◽

Wild Type ◽

Tissue Properties ◽

Histological Features ◽

T1 Relaxation ◽

Treatment Naïve

Quantitative MRI allows to probe tissue properties by measuring relaxation times and may thus detect subtle changes in tissue composition. In this work we analyzed different relaxation times (T1, T2, T2* and T2′) and histological features in 321 samples that were acquired from 25 patients with newly diagnosed IDH wild-type glioma. Quantitative relaxation times before intravenous application of gadolinium-based contrast agent (GBCA), T1 relaxation time after GBCA as well as the relative difference between T1 relaxation times pre-to-post GBCA (T1rel) were compared with histopathologic features such as the presence of tumor cells, cell and vessel density, endogenous markers for hypoxia and cell proliferation. Image-guided stereotactic biopsy allowed for the attribution of each tissue specimen to its corresponding position in the respective relaxation time map. Compared to normal tissue, T1 and T2 relaxation times and T1rel were prolonged in samples containing tumor cells. The presence of vascular proliferates was associated with higher T1rel values. Immunopositivity for lactate dehydrogenase A (LDHA) involved slightly longer T1 relaxation times. However, low T2′ values, suggesting high amounts of deoxyhemoglobin, were found in samples with elevated vessel densities, but not in samples with increased immunopositivity for LDHA. Taken together, some of our observations were consistent with previous findings but the correlation of quantitative MRI and histologic parameters did not confirm all our pathophysiology-based assumptions.

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Evaluation of MRI sequences for quantitative T1 brain mapping

10.1101/195859 ◽

2017 ◽

Author(s):

P Tsialios ◽

M Thrippleton ◽

C Pernet

Keyword(s):

T1 Mapping ◽

Blood Perfusion ◽

Quantitative Mri ◽

T1 Relaxation Time ◽

T1 Relaxation ◽

Wide Range ◽

Fitting Procedures ◽

Speed Up ◽

Mri Sequences ◽

Lower Image Quality

AbstractT1 mapping constitutes a quantitative MRI technique finding significant application in brain imaging. It allows improved evaluation of contrast uptake, blood perfusion, volume, and provides more specific biomarkers of disease progression compared to conventional T1-weighted images. While there are many techniques for T1-mapping, there is also a wide range of reported T1-values in tissues, raising the issue of protocols’ reproducibility and standardization. The gold standard for obtaining T1-maps is based on acquiring IR-SE sequence. Widely used alternative sequences are IR-SE-EPI, VFA (DESPOT), DESPOT-HIFI and MP2RAGE that speed up scanning and fitting procedures. A custom MRI phantom was used to assess the reproducibility and accuracy of the different methods. All scans were performed using a 3T Siemens Prisma scanner. The acquired data were processed using two different codes. The main difference was observed for VFA (DESPOT) which grossly overestimated T1 relaxation time by 214 ms [CI: 126 270 ms] compared to the IR-SE sequence. MP2RAGE and DESPOT-HIFI sequences gave slightly shorter T1 than IR-SE (∼20 to 30ms) and can be considered as alternative and time-efficient methods for acquiring accurate T1 maps of the human brain, while IR-SE-EPI gave identical results, at a cost of a lower image quality.

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Assessment of Myocardial Viability in Persistent Defects on Thallium-201 SPECT after Reinjection Using Gradient-Echo MRI

Nuklearmedizin ◽

10.1055/s-0038-1629799 ◽

1996 ◽

Vol 35 (05) ◽

pp. 146-152 ◽

Cited By ~ 3

Author(s):

A. Kögler ◽

H.-A. Schmitt ◽

D. Emrich ◽

H. Kreuzer ◽

D. L. Munz ◽

...

Keyword(s):

Wall Thickness ◽

Myocardial Viability ◽

Cardiac Cycle ◽

Single Photon ◽

Contractile Function ◽

Left Ventricular ◽

Wall Thickening ◽

Gradient Echo ◽

Systolic Wall Thickening

SummaryThis prospective study assessed myocardial viability in 30 patients with coronary heart disease and persistent defects despite reinjection on TI-201 single-photon computed tomography (SPECT). In each patient, three observers graded TI-201 uptake in 7 left ventricular wall segments. Gradient-echo magnetic resonance imaging in the region of the persistent defect generated 12 to 16 short axis views representing a cardiac cycle. A total of 120 segments were analyzed. Mean end-diastolic wall thickness and systolic wall thickening (± SD) was 11.5 ± 2.7 mm and 5.8 ± 3.9 mm in 48 segments with normal TI-201 uptake, 10.1 ± 3.4 mm and 3.7 ± 3.1 mm in 31 with reversible lesions, 11.3 ± 2.8 mm and 3.3 ± 1.9 mm in 10 with mild persistent defects, 9.2 ± 2.9 mm and 3.2 ±2.2 mm in 15 with moderate persistent defects, 5.8 ± 1.7 mm and 1.3 ± 1.4 mm in 16 with severe persistent defects, respectively. Significant differences in mean end-diastolic wall thickness (p <0.0005) and systolic wall thickening (p <0.005) were found only between segments with severe persistent defects and all other groups, but not among the other groups. On follow-up in 11 patients after revascularization, 6 segments with mild-to-moderate persistent defects showed improvement in mean systolic wall thickening that was not seen in 6 other segments with severe persistent defects. These data indicate that most myocardial segments with mild and moderate persistent TI-201 defects after reinjection still contain viable tissue. Segments with severe persistent defects, however, represent predominantly nonviable myocardium without contractile function.

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