scholarly journals Performance evaluation of a PET insert for preclinical MRI in stand-alone PET and simultaneous PET–MRI modes

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Gaelle Emvalomenos ◽  
Sofie Trajanovska ◽  
Binh T. T. Pham ◽  
Peter Doughty ◽  
Jerome Burnet ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Spin Echo ◽  
Relaxation Times ◽  
Temperature Stability ◽  
Effect Of Temperature ◽  
Fast Spin Echo ◽  
T2 Relaxation ◽  
Absolute Sensitivity ◽  
Field Homogeneity ◽  
T1 And T2

Abstract Background This study aimed to evaluate the performance of a preclinical PET insert in three configurations: as a stand-alone unit outside the MRI bore, inside the bore of a cryogen-free 3T MRI and, finally, while performing simultaneous PET/MRI studies. Methods The PET insert consists of two rings of six detectors, each detector comprising 8 × 12 SiPMs reading out dual offset layers of pixelated LYSO crystals with a 1.4-mm pitch. The inner diameter is 60 mm, transaxial field of view (FoV) 40 mm and axial FoV 98 mm. Evaluation was based on NEMA NU 4-2008 guidelines with appropriate modifications. Spatial resolution and sensitivity were measured inside and outside the MR bore. Image quality, count rate and quantitative performance were measured in all three configurations. The effect of temperature stability on PET sensitivity during fast spin echo sequences was also evaluated. B0 field homogeneity and T1 and T2 relaxation times were measured using a water-filled phantom, with and without simultaneous PET operation. Finally, PET and MRI scans of a mouse injected with 10 MBq [18F]NaF and a mouse injected with 16 MBq [18F]FDG were performed in sequential and simultaneous modes. Results Peak absolute sensitivity was 10.15% with an energy window of 250–750 keV. Absolute sensitivity values outside and inside the MR bore with MR idle agreed to within 0.1%. Outside the MR bore, spatial resolution was 1.21/1.59 mm FWHM (radial/tangential) 5 mm from the centre of the FoV which compared well with 1.19/1.26 mm FWHM inside the MR bore. There were no substantial differences between all three scan configurations in terms of peak NEC rate (175 kcps at 17 MBq), scatter or random fractions. Uniformity and recovery coefficients were also consistent between scanning modes. B0 field homogeneity and T1 and T2 relaxation times were unaltered by the presence of the PET insert. No significant differences were observed between sequential and simultaneous scans of the animals. Conclusions We conclude that the performance of the PET insert and MRI system is not significantly affected by the scanning mode.

Performance Evaluation of a PET Insert for Preclinical MRI in Standalone PET and Simultaneous PET-MRI Modes

2021 ◽  
Author(s):  
Gaelle Emvalomenos ◽  
Sofie Trajanovska ◽  
Binh T.T. Pham ◽  
Peter Doughty ◽  
Jerome Burnet ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Spin Echo ◽  
Relaxation Times ◽  
Temperature Stability ◽  
Effect Of Temperature ◽  
Fast Spin Echo ◽  
T2 Relaxation ◽  
Absolute Sensitivity ◽  
Field Homogeneity ◽  
T1 And T2

Abstract Background: This study aimed to evaluate the performance of a preclinical PET insert in three configurations: as a standalone unit outside the MRI bore, inside the bore of a cryogen-free 3T MRI and, finally, while performing simultaneous PET/MRI studies.Methods: The PET insert consists of 2 rings of 6 detectors, each detector comprising 8x12 SiPMs reading out dual offset layers of pixelated LYSO crystals with a 1.4mm pitch. The inner diameter is 60mm, transaxial Field of View (FoV) 40mm and axial FoV 98mm. Evaluation was based on NEMA NU 4-2008 guidelines with appropriate modifications. Spatial resolution and sensitivity were measured inside and outside the MR bore. Image quality, count rate and quantitative performance were measured in all three configurations. The effect of temperature stability on PET sensitivity during fast spin echo sequences was also evaluated. B0 field homogeneity, T1 and T2 relaxation times were measured using a water-filled phantom, with and without simultaneous PET operation. Finally, PET and MRI scans of a mouse injected with 10 MBq [18F]NaF and a mouse injected with 16 MBq [18F]FDG were performed in sequential and simultaneous modes. Results: Peak absolute sensitivity was 10.15% with an energy window of 250-750 keV. Absolute sensitivity values outside and inside the MR bore with MR idle agreed to within 0.1%. Outside the MR bore spatial resolution was 1.21/1.59 mm FWHM (radial/tangential) 5mm from the centre of the FoV which compared well with 1.19/1.26mm FWHM inside the MR bore. There were no substantial differences between all three scan configurations in terms of peak NEC rate (175 kcps at 17MBq), scatter or random fractions. Uniformity and recovery coefficients were also consistent between scanning modes. B0 field homogeneity and T1 and T2 relaxation times were unaltered by the presence of the PET insert. No significant differences were observed between sequential and simultaneous scans of the animals.Conclusion: We conclude that performance of the PET insert and MRI system are not significantly affected by scanning mode.

Determining the effect of water temperature on the T1 and T2 relaxation times of the lung tissue at 9.4 T MRI: A drowning mouse model

2021 ◽  
pp. 101836
Author(s):  
Kodama Saki ◽  
Hata Junichi ◽  
Kanawaku Yoshimasa ◽  
Nakagawa Hiroshi ◽  
Oshiro Hinako ◽  
...  
Keyword(s):  
Mouse Model ◽  
Water Temperature ◽  
Lung Tissue ◽  
Relaxation Times ◽  
T2 Relaxation ◽  
Effect Of Water ◽  
T1 And T2

Evaluation of Relaxation Time Measurements by Magnetic Resonance Imaging

1987 ◽  
Vol 28 (3) ◽  
pp. 345-351 ◽  
Author(s):  
L. Kjær ◽  
C. Thomsen ◽  
O. Henriksen ◽  
P. Ring ◽  
M. Stubgaard ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Relaxation Time ◽  
Magnetic Resonance ◽  
Diffusion Processes ◽  
Relaxation Times ◽  
Gradient Field ◽  
Maximum Deviation ◽  
Resonance Imaging ◽  
T2 Relaxation ◽  
T1 And T2

Several circumstances may explain the great variation in reported proton T1 and T2 relaxation times usually seen. This study was designed to evaluate the accuracy of relaxation time measurements by magnetic resonance imaging (MRI) operating at 1.5 tesla. Using a phantom of nine boxes with different concentrations of CuSO4 and correlating the calculated T1 and T2 values with reference values obtained by two spectrometers (corrected to MRI-proton frequency=64 MHz) we found a maximum deviation of about 10 per cent. Measurements performed on a large water phantom in order to evaluate the homogeneity in the imaging plane showed a variation of less than 10 per cent within 10 cm from the centre of the magnet in all three imaging planes. Changing the gradient field strength apparently had no influence on the T2 values recorded. Consequently diffusion processes seem without significance. It is concluded that proton T1 and T2 relaxation times covering the majority of the biologic range can be measured by MRI with an overall accuracy of 5 to 10 per cent. Quality control studies along the lines indicated in this study are recommended.

Disease Detection By MR Imaging: T1 And T2 Relaxation Times

1988 ◽  
pp. 415-420
Author(s):  
Luis E. Todd ◽  
Guillermo Elizondo ◽  
Ralph Weissleder
Keyword(s):  
Mr Imaging ◽  
Relaxation Times ◽  
Disease Detection ◽  
T2 Relaxation ◽  
T1 And T2

scholarly journals Myocardial Tissue Characterization By T2 Mapping in Thalassemia Major

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 27-28
Author(s):  
Alessia Pepe ◽  
Nicola Martini ◽  
Rita Borrello ◽  
Vincenzo Positano ◽  
Laura Pistoia ◽  
...  
Keyword(s):  
Tissue Characterization ◽  
Spin Echo ◽  
T2 Mapping ◽  
Relaxation Times ◽  
Thalassemia Major ◽  
Fast Spin Echo ◽  
Myocardial Inflammation ◽  
Healthy Population ◽  
Myocardial Iron ◽  
Magnetic Resonance Imaging Mri

Introduction.The presence of iron deposits results in a significant reduction in all magnetic resonance imaging (MRI) relaxation times (T1, T2 and T2*). In the clinical setting the T2* technique is the method of choice for cardiac iron quantification and it has revolutionized the management of patients with hemoglopinopathies. Purpose.To compare myocardial T2 against T2* in patients with thalassemia major (TM) for myocardial iron characterization. Methods.133 TM patients (79 females, 38.4±11.3 years) enrolled in the Extension Myocardial Iron Overload in Thalassemia (eMIOT) Network were considered. T2 and T2* images were acquired, respectively, with multi-echo fast-spin-echo and gradient-echo sequences. Global heart T2 and T2* values were obtained by averaging the values in all 16 myocardial segments. The normal T2 range was established as mean±2 standard deviations on data acquired on 80 healthy volunteers (males: 48-56 ms and females: 50-57 ms). The lower limit of normal for global heart T2*, established on the same healthy population, was 32 ms. Results.A significant correlation was detected between global heart T2 and T2* values (R=0.577; P<0.0001) (Figure). Out of the 113 (84.9%) patients with a normal global heart T2* value, none had a decreased global heart T2 value, while 58 (51.3%) had an increased T2 value. Out of the 20 patents with a decreased global heart T2* value, only 10 (50%) had also a reduced T2 value. Conversely, 9 (45.0%) had a normal global heart T2 value and one (4.5) showed an increased T2 value. The 59 patients with increased global heart T2 value were significantly older than the remaining patients (40.8±10.5 vs 36.4±11.6 years; P=0.019) Conclusion.All patients with decreased T2 value had also a decreased T2* value and in half of the patients iron load was undetected by T2, suggesting that T2 mapping does not offer any advantage in terms of sensitivity for MIO assessment. However, more than half of TM patients had an increased T2 value, thus may be caused by the presence of myocardial inflammation and/or edema. So, T2 mapping could reveal subclinical myocardial involvement in TM patients. Figure Disclosures Pistoia: Chiesi Farmaceutici S.p.A.:Other: speakers' honoraria.Meloni:Chiesi Farmaceutici S.p.A.:Other: speakers' honoraria.

scholarly journals The Effect of Intraventricular Hemorrhage on Brain Development in Premature Infants: A Synthetic MRI Study

2021 ◽  
Vol 12 ◽  
Author(s):  
Chunxiang Zhang ◽  
Xin Zhao ◽  
Meiying Cheng ◽  
Kaiyu Wang ◽  
Xiaoan Zhang
Keyword(s):  
Relaxation Time ◽  
Premature Infants ◽  
Intraventricular Hemorrhage ◽  
Brain Volume ◽  
Relaxation Times ◽  
T2 Relaxation Time ◽  
T2 Relaxation ◽  
T1 And T2 ◽  
The Brain ◽  
Synthetic Mri

Objectives: Synthetic MRI can obtain multiple parameters in one scan, including T1 and T2 relaxation time, proton density (PD), brain volume, etc. This study aimed to investigate the parameter values T1 and T2 relaxation time, PD, and volume characteristics of intraventricular hemorrhage (IVH) newborn brain, and the ability of synthetic MRI parameters T1 and T2 relaxation time and PD to diagnose IVH.Materials and methods: The study included 50 premature babies scanned with conventional and synthetic MRI. Premature infants were allocated to the case group (n = 15) and NON IVH (n = 35). The T1, T2, PD values, and brain volume were obtained by synthetic MRI. Then we assessed the impact of IVH on these parameters.Results: In the posterior limbs of the internal capsule (PLIC), genu of the corpus callosum (GCC), central white matter (CWM), frontal white matter (FWM), and cerebellum (each p < 0.05), the T1 and T2 relaxation times of the IVH group were significantly prolonged. There were significant differences also in PD. The brain volume in many parts were also significantly reduced, which was best illustrated in gray matter (GM), cerebrospinal fluid and intracranial volume, and brain parenchymal fraction (BPF) (each p < 0.001, t = −5.232 to 4.596). The differential diagnosis ability of these quantitative values was found to be excellent in PLIC, CWM, and cerebellum (AUC 0.700–0.837, p < 0.05).Conclusion: The quantitative parameters of synthetic MRI show well the brain tissue characteristic values and brain volume changes of IVH premature infants. T1 and T2 relaxation times and PD contribute to the diagnosis and evaluation of IVH.

Patellar Malalignment Is Associated With Patellofemoral Lesions and Cartilage Relaxation Times After Hamstring Autograft Anterior Cruciate Ligament Reconstruction

2020 ◽  
Vol 48 (9) ◽  
pp. 2242-2251
Author(s):  
Tzu-Chieh Liao ◽  
Alejandro G. Morales Martinez ◽  
Valentina Pedoia ◽  
Benjamin C. Ma ◽  
Xiaojuan Li ◽  
...  
Keyword(s):  
Lateral Displacement ◽  
Spin Echo ◽  
Cruciate Ligament ◽  
Relaxation Times ◽  
Fast Spin Echo ◽  
Healthy Controls ◽  
Resonance Imaging ◽  
Anterior Cruciate ◽  
Fast Spin ◽  
And Cartilage

Background: There is growing evidence suggesting a link between patellofemoral joint (PFJ) osteoarthritis in anterior cruciate ligament (ACL)–reconstructed knees and altered joint alignment. Purpose: To determine whether patellar alignment differs between participants with and without ACL reconstruction (ACLR) and to identify possible associations between patellar alignment and PFJ osteoarthritis features over 3 years. Study Design: Cohort study; Level of evidence, 2. Methods: A total of 37 participants with ACLR (sex, 23 male; mean ± SD age, 28.1 ± 7.4 years) and 20 healthy controls (13 male; 30.4 ± 4.8 years) participated. Patients underwent magnetic resonance imaging: (1) sagittal T2-weighted fat-saturated fast spin echo images to calculate patellar alignment, (2) sagittal 3-dimensional intermediate-weighted fast spin echo Cube sequence for clinical morphological grading (modified Whole-Organ Magnetic Resonance Imaging Score [WORMS]), and (3) sagittal combined T1ρ/T2 mapping sequence for performing voxel-based relaxometry. Patellar alignment of the ACLR knees were assessed at 6 months (baseline). One-way analysis of variance was used to compare patellar alignment among the ACLR (at 6 months), contralateral, and control knees. Within the ACLR group, a logistic regression model was used to identify if patellar alignment measures at baseline were risk factors for worsening of PFJ structural changes over 3 years. Statistical parametric mapping was used to evaluate the longitudinal associations between patellar alignment and cartilage relaxation times at 3 years. Results: When compared with control knees, ACLR knees exhibited a laterally and anteriorly displaced patella ( P = .045 and P = .041), less flexion ( P = .031), and less lateral spin ( P = .012). Furthermore, excessive lateral displacement was a significant predictor of worsening of WORMS ( P = .050). Lateral displacement was positively correlated with increased T1ρ and T2 in the patellar and trochlear cartilage at 3 years. Patellar lateral spin revealed similar negative findings. Conclusion: Participants with ACLR exhibited a laterally and anteriorly displaced patella, less flexion, and less lateral spin when compared with healthy controls. Excessive patellar lateral displacement was the strongest predictor to the development of PFJ osteoarthritis features longitudinally.

scholarly journals Reliability of Synthetic Brain MRI for Assessment of Ischemic Stroke with Phantom Validation of a Relaxation Time Determination Method

2020 ◽  
Vol 9 (6) ◽  
pp. 1857
Author(s):  
Chia-Wei Li ◽  
Ai-Ling Hsu ◽  
Chi-Wen C. Huang ◽  
Shih-Hung Yang ◽  
Chien-Yuan Lin ◽  
...  
Keyword(s):  
Ischemic Stroke ◽  
Relaxation Time ◽  
Brain Mri ◽  
Relaxation Times ◽  
Onset Time ◽  
Magnetic Resonance Images ◽  
Diagnostic Tools ◽  
Cupric Sulfate ◽  
T2 Relaxation ◽  
T1 And T2

The reliability of relaxation time measures in synthetic magnetic resonance images (MRIs) of homemade phantoms were validated, and the diagnostic suitability of synthetic imaging was compared to that of conventional MRIs for detecting ischemic lesions. Phantoms filled with aqueous cupric-sulfate (CuSO4) were designed to mimic spin-lattice (T1) and spin-spin (T2) relaxation properties and were used to compare their accuracies and stabilities between synthetic and conventional scans of various brain tissues. To validate the accuracy of synthetic imaging in ischemic stroke diagnoses, the synthetic and clinical scans of 18 patients with ischemic stroke were compared, and the quantitative contrast-to-noise ratios (CNRs) were measured, using the Friedman test to determine significance in differences. Results using the phantoms showed no significant differences in the interday and intersession synthetic quantitative T1 and T2 values. However, between synthetic and referenced T1 and T2 values, differences were larger for longer relaxation times, showing that image intensities in synthetic scans are relatively inaccurate in the cerebrospinal fluid (CSF). Similarly, CNRs in CSF regions of stroke patients were significantly different on synthetic T2-weighted and T2-fluid-attenuated inversion recovery images. In contrast, differences in stroke lesions were insignificant between the two. Therefore, interday and intersession synthetic T1 and T2 values are highly reliable, and discrepancies in synthetic T1 and T2 relaxation times and image contrasts in CSF regions do not affect stroke lesion diagnoses. Additionally, quantitative relaxation times from synthetic images allow better estimations of ischemic stroke onset time, consequently increasing confidence in synthetic MRIs as diagnostic tools for ischemic stroke.

scholarly journals Myocardial Mapping in Systemic Sarcoidosis: A Comparison of Two Measurement Approaches

2020 ◽  
Vol 193 (01) ◽  
pp. 68-76
Author(s):  
Darius Dabir ◽  
Julian Luetkens ◽  
Daniel Kuetting ◽  
Jennifer Nadal ◽  
Hans Heinz Schild ◽  
...  
Keyword(s):  
T1 Mapping ◽  
Tissue Characterization ◽  
Cardiac Involvement ◽  
T2 Mapping ◽  
Relaxation Times ◽  
Short Axis Slice ◽  
T2 Relaxation ◽  
Standard Mapping ◽  
Systemic Sarcoidosis ◽  
T1 And T2

Purpose To investigate if T1 and T2 mapping is able to differentiate between diseased and healthy myocardium in patients with systemic sarcoidosis, and to compare the standard mapping measurement (measurement within the whole myocardium of the midventricular short axis slice, SAX) to a more standardized method measuring relaxation times within the midventricular septum (ConSept). Materials and Methods 24 patients with biopsy-proven extracardiac sarcoidosis and 17 healthy control subjects were prospectively enrolled in this study and underwent CMR imaging at 1.5 T including native T1 and T2 mapping. Patients were divided into patients with (LGE+) and without (LGE–) cardiac sarcoidosis. T1 and T2 relaxation times were compared between patients and controls. Furthermore, the SAX and the ConSept approach were compared regarding differentiation between healthy and diseased myocardium. Results T1 and T2 relaxation times were significantly longer in all patients compared with controls using both the SAX and the ConSept approach (p < 0.05). However, LGE+ and LGE– patients showed no significant differences in T1 and T2 relaxation times regardless of the measurement approach used (ConSept/SAX) (p > 0.05). Direct comparison of ConSept and SAX T1 mapping showed high conformity in the discrimination between healthy and diseased myocardium (Kappa = 0.844). Conclusion T1 and T2 mapping may not only enable noninvasive recognition of cardiac involvement in patients with systemic sarcoidosis but may also serve as a marker for early cardiac involvement of the disease allowing for timely treatment. ConSept T1 mapping represents an equivalent method for tissue characterization in this population compared to the SAX approach. Further studies including follow-up examinations are necessary to confirm these preliminary results. Key Points:  Citation Format

Increased accuracy in MR diagnosis of uveal melanoma by carbohydrate loading

1998 ◽  
Vol 39 (3) ◽  
pp. 239-242
Author(s):  
K.-Å. Thuomas ◽  
P. Naeser ◽  
A. Wrigstad
Keyword(s):  
Uveal Melanoma ◽  
Spindle Cell ◽  
Spin Echo ◽  
Tumour Size ◽  
Relaxation Times ◽  
Fast Spin Echo ◽  
Subtraction Technique ◽  
Mixed Cell ◽  
Carbohydrate Loading ◽  
Fast Spin

Purpose: To evaluate patients with clinically diagnosed uveal melanoma Material and Methods: Forty-eight consecutive patients were examined with spin-echo (SE) and fast spin-echo (FSE) MR sequences that utilized glucosefructose enhancement together with a subtraction technique on a 1.5 T unit Results: Twenty-seven patients were enucleated and the eyes histologically examined for tumours (spindle cell, mixed cell, and epitheloid cell). The remaining patients were referred for other treatment. There were no significant differences in T2 although T2 was longer in the amelanotic lesions. Carbohydrate loading in combination with a subtraction technique gave: an increased signal intensity; a prolongation of T2; and an increased tumour size. The FSE sequences were as good as the SE sequences in the visualization of uveal malignant melanoma Conclusion: MR imaging performed with carbohydrate loading registers metabolic changes induced in the tumour. This gives the method great validity in the diagnosis of uveal melanoma. The method is especially useful in amelanotic tumours that have longer relaxation times than melanotic tumours. The SE technique can be replaced with the FSE technique

Sign in / Sign up

Export Citation Format

Share Document