Turbo Factor Research Articles

Assessment of the Impact of Turbo Factor on Image Quality and Tissue Volumetrics in Brain Magnetic Resonance Imaging Using the Three-Dimensional T1-Weighted (3D T1W) Sequence.

The 3D T1W turbo field echo sequence is a standard imaging method for acquiring high-contrast images of the brain. However, the contrast-to-noise ratio (CNR) can be affected by the turbo factor, which could affect the delineation and segmentation of various structures in the brain and may consequently lead to misdiagnosis. This study is aimed at evaluating the effect of the turbo factor on image quality and volumetric measurement reproducibility in brain magnetic resonance imaging (MRI). Brain images of five healthy volunteers with no history of neurological diseases were acquired on a 1.5 T MRI scanner with varying turbo factors of 50, 100, 150, 200, and 225. The images were processed and analyzed with FreeSurfer. The influence of the TFE factor on image quality and reproducibility of brain volume measurements was investigated. Image quality metrics assessed included the signal-to-noise ratio (SNR) of white matter (WM), CNR between gray matter/white matter (GM/WM) and gray matter/cerebrospinal fluid (GM/CSF), and Euler number (EN). Moreover, structural brain volume measurements of WM, GM, and CSF were conducted. Turbo factor 200 produced the best SNR (median = 17.01) and GM/WM CNR (median = 2.29), but turbo factor 100 offered the most reproducible SNR (IQR = 2.72) and GM/WM CNR (IQR = 0.14). Turbo factor 50 had the worst and the least reproducible SNR, whereas turbo factor 225 had the worst and the least reproducible GM/WM CNR. Turbo factor 200 again had the best GM/CSF CNR but offered the least reproducible GM/CSF CNR. Turbo factor 225 had the best performance on EN (-21), while turbo factor 200 was next to the most reproducible turbo factor on EN (11). The results showed that turbo factor 200 had the least data acquisition time, in addition to superior performance on SNR, GM/WM CNR, GM/CSF CNR, and good reproducibility characteristics on EN. Both image quality metrics and volumetric measurements did not vary significantly (p > 0.05) with the range of turbo factors used in the study by one-way ANOVA analysis. Since no significant differences were observed in the performance of the turbo factors in terms of image quality and volume of brain structure, turbo factor 200 with a 74% acquisition time reduction was found to be optimal for brain MR imaging at 1.5 T.

Iterative Denoising Accelerated 3D FLAIR Sequence for Hydrops MR Imaging at 3T.

3D FLAIR sequences have become the criterion standard for identifying endolymphatic hydrops, but scan time remains an important limitation to their widespread use. Our purpose was to evaluate the diagnostic performance and image quality of an accelerated 3D FLAIR sequence combined with an iterative denoising algorithm. This was a retrospective study performed on 30 patients with clinical suspicion of endolymphatic hydrops who underwent 3T MR imaging 4 hours after gadolinium injection using two 3D FLAIR sequences. The first (conventional FLAIR) was accelerated with a conventional turbo factor of 187. The second was accelerated with an increased turbo factor of 263, resulting in a 33% scan time reduction (5 minutes 36 seconds versus 8 minutes 15 seconds, respectively). A sequence was reconstructed in-line immediately after the accelerated 3D FLAIR acquisition from the same raw data with iterative denoising (accelerated-FLAIR iterative denoising). The signal intensity ratio image quality score and endolymphatic hydrops diagnosis were evaluated. The mean signal intensity ratio for symptomatic and asymptomatic ears of accelerated-FLAIR iterative denoising was significantly higher than the mean SNR of conventional FLAIR (29.5 versus 19 and 25.9 versus 16.3, P < .001). Compared with the conventional FLAIR sequence, the image-quality score was higher with accelerated-FLAIR iterative denoising (mean image-quality score, 3.8 [SD, 0.4] versus 3.3 [SD, 0.6] for accelerated-FLAIR iterative denoising and conventional FLAIR, respectively, P = .003). There was no significant difference in the diagnosis of endolymphatic hydrops between the 2 sequences. Interreader agreement was good-to-excellent. The iterative denoising algorithm applied to an accelerated 3D FLAIR sequence for exploration of endolymphatic hydrops enabled significantly reducing the scan time without compromising image quality and diagnostic performance.

Optimization of acquisition parameters for cortical inhomogeneous magnetization transfer (ihMT) imaging using a rapid gradient echo readout.

Imaging biomarkers with increased myelin specificity are needed to better understand the complex progression of neurological disorders. Inhomogeneous magnetization transfer (ihMT) imaging is an emergent technique that has a high degree of specificity for myelin content but suffers from low signal to-noise ratio (SNR). This study used simulations to determine optimal sequence parameters for ihMT imaging for use in high-resolution cortical mapping. MT-weighted cortical image intensity and ihMT SNR were simulated using modified Bloch equations for a range of sequence parameters. The acquisition time was limited to 4.5 min/volume. A custom MT-weighted RAGE sequence with center-out k-space encoding was used to enhance SNR at 3 T. Pulsed MT imaging was studied over a range of saturation parameters, and the impact of the turbo factor on the effective ihMT resolution was investigated. 1 mm isotropic ihMTsat maps were generated in 25 healthy adults. Greater SNR was observed for larger number of bursts consisting of 6-8 saturation pulses each, combined with a high readout turbo factor. However, that protocol suffered from a point spread function that was more than twice the nominal resolution. For high-resolution cortical imaging, we selected a protocol with a higher effective resolution at the cost of a lower SNR. We present the first group-average ihMTsat whole-brain map at 1 mm isotropic resolution. This study presents the impact of saturation and excitation parameters on ihMTsat SNR and resolution. We demonstrate the feasibility of high-resolution cortical myelin imaging using ihMTsat in less than 20 min.

Dose sensitivity of MAGIC-f polymer gel using different MRI sequences

This study aims to evaluate the dose sensitivity of MAGIC-f gel irradiated by high-energy photon beams, comparing quantification using different MRI sequences. Irradiation was performed using 6 MV photons with 600 cGy/min dose rate, field size of 20x20 cm², and 94 cm source-to-surface distance. Two gel batches were produced on different days and placed in vials. In the first batch, doses of 0, 2, 4, 6, 8, 10, 20, and 40 Gy were planned. The second batch was irradiated with doses of 0, 2, 4, 6, 10, 12, 14, and 16 Gy. MR images were acquired with Spin Echo (SE, TR=3 s) and Multi Spin Echo (MSE, TR = 3s or 10s, turbo factor 24) sequences. The dose is assessed via changes in the transverse relaxation time in the irradiated gel. In MSE, dose sensitivity in the first batch was 0.27 (TR=3 s) and 0.28 Gy-1s-1 (TR=10 s) and in the second batch, 0.31 and 0.31 Gy-1s-1 (TR = 3 s and TR = 10 s, respectively). In the SE sequence, dose sensitivity was 0.42 for the first batch and 0.43 Gy-1s-1 for the second batch. Linearity of dose-response was only obtained for doses below 10 Gy. Comparing the dose sensitivity extracted from MSE and SE sequences using TR= 3s, differences around 30% were found. Thus, although MSE-MRI offers a faster protocol of imaging acquisition it is less precise for quantification of relaxation times, as TE is not a well-defined quantity. The performance of the gel as a dosimeter is consequently sequence dependent.

Effects of MR imaging time reduction on substitute CT generation for prostate MRI-only treatment planning.

The introduction of MRI linear accelerators (MR-linacs) and the increased use of MR imaging in radiotherapy, requires improved approaches to MRI-only radiotherapy. MRI provides excellent soft tissue visualisation but does not provide any electron density information required for radiotherapy dose calculation, instead MRI is registered to CT images to enable dose calculations. MRI-only radiotherapy eliminates registration errors and reduces patient discomfort, workload and cost. Electron density requirements may be addressed in different ways, from manually applying bulk density corrections, to more computationally intensive methods to produce substitute CT datasets (sCT), requiring additional sequences, increasing overall imaging time. Reducing MR imaging time would reduce potential artefacts from intrafraction motion and patient discomfort. The aim of this study was to assess the impact of reducing MR imaging time on a hybrid atlas-voxel sCT conversion for prostate MRI-only treatment planning, considering both anatomical and dosimetric parameters. 10 volunteers were scanned on a Siemens Skyra 3T MRI. Sequences included the 3D T2-weighted (T2-w) SPACE sequence used for sCT conversion as previously validated against CT, along with variations to this sequence in repetition time (TR), turbo factor, and combinations of these to reduce the imaging time. All scans were converted to sCT and were compared to the sCT from the original SPACE sequence, evaluating for anatomical changes and dosimetric differences for a standard prostate VMAT plan. Compared to the previously validated T2-w SPACE sequence, scan times were reduced by up to 80%. The external volume and bony anatomy were compared, with all but one sequence meeting a DICE coefficient of 0.9 or better, with the largest variations occurring at the edges of the external body volume. The generated sCT agreed with the gold standard sCT within an isocentre dose of 1% and a gamma pass rate of 99% for a 1%/1mm gamma tolerance for all but one sequence. This study demonstrates that the MR imaging sequence time was able to be reduced by approximately 80% with similar dosimetric results.

ANALISA PENGARUH VARIASI ECHO TRAIN LENGTH (ETL) PADA SEKUEN T2 WEIGHTED IMAGE (T2WI) AXIAL PROPELLER TERHADAP KUALITAS CITRA PEMERIKSAAN BRAIN MAGNETIK RESONANCE IMAGING (MRI)

Backgroud: Echo Train Length (ETL) or turbo factor refers to the echo number of radiofrequency pulse refocusing 1800 after excitation RF pulse which used in Fast Spin Echo (FSE). ETL was is the single most important parameter on the image quality. Longer ETLs result in more T2-weighting because more late echoes with longer TE’s contribute to the overall signal. Longer ETL’s also associated with a decrease in the overall signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) because the later echoes are weaker and the image having blurring. The ETL was influence with scanning time. PROPELLER sequences can be reducing the artefact motion. The aim of this research is to known how the effect of the ETLs variation on sequences T2WI axial PROPELLER to the best image quality and the ETLs value which have best quality.&#x0D; &#x0D; Methods: This type of study is a quantitative study conducted with an experimental approach in Radiology Installation of Santo Borromeo’s Bandung. Data is collected by the examination brain MRI in 6 (six) patients, after a brain MRI scanning with axial slice T2WI PROPELLER sequences, with variation of Echo Train Length (ETL). The variation of ETL we used are 12, 18, 24 and 30. And the estimation using Region of Interest (ROI) at the ventricle lateral, nucleus caudate, putamen, thalamus and internal capsule. The assessment results are summarized and then in a statistical test using SPSS version 23.0 with the method of Pearson correlate and linier regression.&#x0D; &#x0D; Results: The result showed that there is having effect of Echo Train Length (ETL) on sequences T2WI axial PROPELLER to the image quality. There is a strong correlation which the result of significant value 0,000 &lt; p value 0.05. The relation effect variation of ETL with SNR very strong is nucleus caudate and CNR very strong between nucleus caudate and ventricle lateral. The mean rank value of SNR and CNR have been showed is ETL 12 with a mean rank up to 152,57 and 121,18&#x0D; &#x0D; Conclusion:There was the influence of the echo train length toward image quality of brain MRI on sequences T2WI axial PROPELLER.&#x0D; The best echo train length value of brain MRI on sequence T2WI axial PROPELLER is 12.

Inner SPACE: 400-Micron Isotropic Resolution MRI of the Human Brain.

ObjectivesClinically relevant neuroanatomy is challenging to teach, learn and remember since many functionally important structures are visualized best using histology stains from serial 2D planar sections of the brain. In clinical patients, the locations of specific structures then must be inferred from spatial position and surface anatomy. A 3D MRI dataset of neuroanatomy has several advantages including simultaneous multi-planar visualization in the same brain, direct end-user manipulation of the data and image contrast identical to clinical MRI. We created 3D MRI datasets of the postmortem brain with high spatial and contrast resolution for simultaneous multi-planar visualization of complex neuroanatomy.Materials and MethodsWhole human brains (N = 6) were immersion-fixed in 4% formaldehyde for 4 weeks, then washed continuously in water for 48 h. The brains were imaged on a clinical 3-T MRI scanner with a 64-channel head and neck coil using a 3D T2-weighted sequence with 400-micron isotropic resolution (voxel = 0.064 mm3; time = 7 h). Besides resolution, this sequence has multiple adjustments to improve contrast compared to a clinical protocol, including 93% reduced turbo factor and 77% reduced effective echo time.ResultsThis MRI microscopy protocol provided excellent contrast resolution of small nuclei and internal myelinated pathways within the basal ganglia, thalamus, brainstem, and cerebellum. Contrast was sufficient to visualize the presence and variation of horizontal layers in the cerebral cortex. 3D isotropic resolution datasets facilitated simultaneous multi-planar visualization and efficient production of specific tailored oblique image orientations to improve understanding of complex neuroanatomy.ConclusionWe created an unlabeled high-resolution digital 3D MRI dataset of neuroanatomy as an online resource for readers to download, manipulate, annotate and use for clinical practice, research, and teaching that is complementary to traditional histology-based atlases. Digital MRI contrast is quantifiable, reproducible across brains and could help validate novel MRI strategies for in vivo structure visualization.

Improved Neural Imaging Sequence and Comparison with Conventional Methods

The purpose of this study was to improve the contrast between the nerves and blood by reconsidering the imaging parameters of the sampling perfection with application-optimized contrasts using different flip angle evolutions (SPACE) method, and to compare it with conventional methods, including the constructive interference in steady state (CISS) and T2-weighted SPACE (T2-SPACE) methods. In the phantom study, the repetition time (TR), echo time (TE), flip angle (FA), and turbo factor (TF) of SPACE were varied using the restore pulse. The parameters for which the nerve-blood contrast (C1) and cerebrospinal fluid-nerve contrast (C2) were equal were selected. Though multiple conditions resulted in C1 and C2 equivalence, we determined/set the TR=500 ms, TE=21 ms, FA=120°, and TF=30, considering the acquisition time, specific absorption rate (SAR), and artifacts. This sequence was called "short TR and short TE SPACE with restore pulse (SSSR)". In the phantom and healthy volunteer studies, the contrast between the nerves and blood in the SSSR method was statistically superior in both the physical and visual assessments compared with conventional methods. In the healthy volunteer study, C1 improved from 0.08 for CISS and 0.18 for T2-SPACE to 0.43 for SSSR. This is because the nerve signals in conventional methods were low due to the heavy T2-weighted, while those in the SSSR method were high due to the short TE and effect of the restore pulse. In conclusion, the contrast between the nerves and blood was significantly higher in the SSSR method compared with conventional methods.

Diagnosis of deep vein thrombosis using 3D black-blood thrombus imaging (BTI): preliminary clinical experience

Background Deep vein thrombosis (DVT) is a common but elusive illness that can lead to fatal pulmonary embolism and sudden death. Effective treatment of DVT requires accurate evaluation of thrombus distribution and stage. MRI is one of diagnostic imaging modalities for DVT, and two conventional methods are MPRAGE[1] and CE-MRV[2]. Recently, 3D T1-weighted variable-flipangle turbo spin-echo (SPACE) was proposed as a black-blood technique that permits more direct visualization of DVT[3]. However, signal suppression of tremendously slow venous blood flow remains a challenge for SPACE. The unsuppressed blood signal could be a confounder in thrombus detection[3]. We hypothesized that the 3D black-blood thrombus imaging (BTI) technique[4] that combines SPACE with DANTE black-blood preparation[5] (DANTE-SPACE) might address the above issue. Methods Experiment The IRB-approved study was performed on a 3T scanner (Siemens TimTrio, Germany). DANTE-SPACE was first optimized on 8 healthy subjects (4 F 4 M, age 25 ± 4) and then tested on 12 patients (6 F 6 M, age 52 ± 13) with DVT. The optimized parameters for DANTE included: FA 15°, pulse trains 175, RF gap 1 ms, gradient 20 mT/m. The parameters for SPACE included: 3D coronal imaging with a resolution of 1.1 × 1.1 × (1.1-1.3) mm (interpolated to 0.55 × 0.55 × [0.55-0.65] mm),TR/ TE 650/9.8 ms, turbo factor 40, GRAPPA 2, scan time ~4 min. The scan was targeted to the thrombus region that was pre-determined by ultrasound within 3 days. Conventional SPACE, MPRAGE, and CE-MRV were conducted for comparison.

Analisis Informasi Anatomi Dengan dan Tanpa Parallel Acquisition Technique Menggunakan Sekuen 2D Thick Slab Single Shot Fast Spin Echo pada Pemeriksaan Magnetic Resonance Cholangiopancreatography (MRCP)

Backgroud: 2D thick slab single shot fast spin echo (SSFSE) sequence in MRCP examination is a sequence of fast spin echo (FSE) which has a long turbo factor so that the time of acquisition in this sequence is longer than usual that will potentially cause image blurring. Parallel acquisition or SENSE technique is a technique used to reduce acquisition time and improve spatial resolution. The purpose of this study was to determine differences in anatomical information with and without parallel acquisition technique in 2D thick slab SSFSE sequences on MRCP examination.Methods: This research was an experimental study. This research was conducted by Philips 1.5 T MRI unit in dr. S Hardjolukito Yogyakarta Hospital. Data were 20 MRCP images from 10 normal volunteers with and without parallel acquisition technique on sequences of 2D thick slab SSFSE. Assessment of the images was conducted qualitatively in the form of respondents's assessment of the clearance of anatomical information includes the gallbladder, right hepatic duct, left hepatic duct, common bile duct, common hepatic duct, cystic duct, and the main pancreatic duct. Quantitative data analyzed by Cohen's Kappa test, cross tabulation, and Wilcoxon tests.Results: The result showed that there was a difference between the clearance of the overall anatomical information between 2D thick slab SSFSE sequences with and without parallel acquisition technique in MRCP with p = 0.000 (p-value 0.05), based on the mean rank obtained sequences of 2D thick slab SSFSE SENSE (14.50) better than the 2D thick slab SSFSE (0.00). Analysis of each anatomy showed significant differences in all organs except the gallbladder p = 0.059, p = left hepatic duct and the common bile duct 0.059 with p = 0.08.Conclusion: Parallel acquisition technique (SENSE) was well used because it has a faster acquisition time without decreasing image resolution.

Accelerated 4D flow imaging using randomly undersampled echo planer imaging with compressed-sensing reconstruction

Background 4D flow imaging using phase contrast CMR (PC CMR) allows visualization and quantification of blood flow. One of the major limitations of 4D flow imaging is its long scan time (in the order of 10-20 min). In this study, we sought to investigate an accelerate 4D flow imaging sequence that combines an efficient data sampling strategy using echo planar imaging (EPI) with randomly undersampled 3D k-space sampling pattern. The randomly undersampled k-space data are then reconstructed using compressed sensing (CS). Methods Figure 1 shows the k-space acquisition strategy. Similar to regular EPI acquisition, the k-space data are divided into multiple segments. For each segment, the profiles are undersampled with the CS rate such that all EPI segments have the same undersampling pattern. The proposed EPI random sampling strategy was implemented. Seven subjects were recruited (26 ± 12 years; 3 males) for 4D flow CMR on a 1.5T Philips Achieva magnet. Images were acquired axially using a GRE sequence (FOV =3 40 ×2 80 ×6 0 mm 3 ,r esolution =2× 2×3m m 3 ,T R/TE/a = 7.4/3.8 ms/20°, EPI factor = 3, Turbo Factor =2 , CS rate =3 ) in av olume covering the ascending and descending aorta, and the aortic bifurcation. Only foot-head flow encoding was used to provide an adequate temporal resolution of 30 ms for the measurements. A single beam navigator placed on the right hemi-diaphragm was used to gate the acquisition with the respiratory cycle. The nominal scan time for this scan was 3:30 minutes at 70 bpm assuming 100% gating efficiency (vs. 8:40 minutes if standard parallel imaging with rate 4 was used). For each subject, the 4D-PC scan was followed by a standard breath-hold 2D-PC scan with the same flow encoding direction (FOV = 340 × 280 mm2, resolution = 2 × 2 mm 2 , slice thickness = 5 mm 3 , SENSE rate = 2.5). The acquired 2D slice is selected from the previously obtained 4D scan and approximately at the aortic bifurcation. Data are then transferred to a separate station where the CS reconstruction was performed using a total variation minimization algorithm. Next, flow quantifications were performed on both the ascending and the descending aorta for all acquisitions and then compared between the 2D scans and the corresponding slices in the 4D scans.

Safety of EEG–fMRI recordings in newborn infants at 3T: A study using a baby-size phantom

ObjectiveWe aimed to study EEG electrode temperatures during MRI recordings using a neonatal-size phantom to establish the safety of neonatal EEG–MRI. MethodsWe constructed a phantom set-up for co-registration of EEG and MRI measurements with newborn size configurations. The set-up consisted of a spherical glass phantom fitted with a customised MRI-compatible 64-channel EEG cap and EEG amplifier. Temperatures were recorded during and after five different scanning sequences (two T2∗ sensitised BOLD fMRI, one T1-weighted and two T2-weighted spin echo) in five electrode locations using a thermistor that was integrated into the electrode housing. A temperature increase >4°C was defined a priori as the safety limit. ResultsDuring fMRI and T1 sequences, none of the electrodes showed meaningful temperature changes. Only one MRI sequence (T2 with Max turbo factor 25; SAR 89%) caused temperature increase in one electrode (Fpz; +4.1°C) that slightly exceeded our predefined safety limit, while the conventional T2 sequence was within safety limits (up to +1.7°C). ConclusionsCo-registration of EEG and fMRI can be considered safe in babies with respect to electrode heating, which is the primary safety concern. SignificanceThe present findings open up a possibility to commence studies where EEG and MRI/fMRI are co-registered in human babies. Such studies hold significant promise of a better understanding of the early development of brain function and neurovascular coupling.

Turboprop+: Enhanced turboprop diffusion‐weighted imaging with a new phase correction

Faster periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) diffusion-weighted imaging acquisitions, such as Turboprop and X-prop, remain subject to phase errors inherent to a gradient echo readout, which ultimately limits the applied turbo factor (number of gradient echoes between each pair of radiofrequency refocusing pulses) and, thus, scan time reductions. This study introduces a new phase correction to Turboprop, called Turboprop+. This technique employs calibration blades, which generate 2-D phase error maps and are rotated in accordance with the data blades, to correct phase errors arising from off-resonance and system imperfections. The results demonstrate that with a small increase in scan time for collecting calibration blades, Turboprop+ had a superior immunity to the off-resonance-related artifacts when compared to standard Turboprop and recently proposed X-prop with the high turbo factor (turbo factor = 7). Thus, low specific absorption rate and short scan time can be achieved in Turboprop+ using a high turbo factor, whereas off-resonance related artifacts are minimized.

Fast‐spin‐echo imaging of inner fields‐of‐view with 2D‐selective RF excitations

To demonstrate the feasibility of two-dimensional selective radio frequency (2DRF) excitations for fast-spin-echo imaging of inner fields-of-view (FOVs) in order to shorten acquisitions times, decrease RF energy deposition, and reduce image blurring. Fast-spin-echo images (in-plane resolution 1.0 x 1.0 mm(2) or 0.5 x 1.0 mm(2)) of inner FOVs (40 mm, 16 mm oversampling) were obtained in phantoms and healthy volunteers on a 3 T whole-body MR system using blipped-planar 2DRF excitations. Positioning the unwanted side excitations in the blind spot between the image section and the slice stack to measure yields minimum 2DRF pulse durations (about 6 msec) that are compatible with typical echo spacings of fast-spin-echo acquisitions. For the inner FOVs, the number of echoes and refocusing RF pulses is considerably reduced which compared to a full FOV (182 mm) reduces the RF energy deposition by about a factor of three and shortens the acquisition time, e.g., from 39 seconds to 12 seconds for a turbo factor of 15 or from 900 msec to 280 msec for a single-shot acquisition, respectively. Furthermore, image blurring occurring for high turbo factors as in single-shot acquisitions is considerably reduced yielding effectively higher in-plane resolutions. Inner-FOV acquisitions using 2DRF excitations may help to shorten acquisitions times, ameliorate image blurring, and reduce specific absorption rate (SAR) limitations of fast-spin-echo (FSE) imaging, in particular at higher static magnetic fields.

Effects of caffeine abstinence on adenosine induced coronary flow reserve quantified on phase contrast velocity encoded MRI of the coronary sinus

Introduction: Adenosine is a common pharmacological vasodilator agent used in first pass perfusion MRI as well as nuclear cardiology and echocardiography. Coronary flow reserve (CFR) by adenosine is inhibited by caffeine and therefore caffeine abstinence is routinely proscribed in patients. However, the guidelines differ regarding how long abstinence is needed from 12 to 24 hours. Purpose: This study was performed to investigate if 12 h caffeine abstinence is enough to provide maximal coronary flow reserve (CFR). Methods: 12 healthy individuals (5 females, 39 ± 14 years) were imaged using a 1.5 T Philips Intera CV at rest and during adenosine infusion (140 μg/kg/min) at two occasions, after 12 and 24 h caffeine abstinence respectively. Coronary sinus flow was measured during breath hold with a phase contrast velocity encoded (PC) TFE sequence with 20 phases per cardiac cycle. Typical imaging parameters were: SENSE factor 2, TE/TR/flip: 3.1/4.8 ms/15°, turbo factor 5, spatial resolution 1.2 × 1.2 × 7 mm and VENC 80 cm/s. CFR was calculated as the ratio between coronary sinus flow/min at adenosine and rest. Cardiac output was measured using PC-MRI of the ascending aorta. Results: CFR was higher (5.4 ± 1.0) at 24 h caffeine abstinence compared to 12 h (4.6 ± 0.8, p = 0.03). In most patients the difference was minimal but in three patients (25%) the increase in CFR at 12 h was less than 30% of that at 24 h caffeine abstinence. The increase in HR did not differ at 24 h (40 ± 7%) and 12 h abstinence (39 ± 5%, p = 0.62) nor did the increase in cardiac output (55 ± 8% vs. 48 ± 8%, p = 0.68). Reported symptoms and the blood pressure reaction did not differ between 24 h and 12 h abstinence, Figure 1. Conclusion: Twelve hours caffeine abstinence results in a lower coronary flow reserve compared to 24 hours and there is a large inter-individual difference to caffeine abstinence. This needs to be taken into consideration when performing adenosine perfusion imaging studies. (Figure Presented). (Less)

Myocardial T2 quantitation in patients with iron overload at 3 Tesla

To investigate the feasibility of measuring myocardial T2 at 3 Tesla for assessment of tissue iron in thalassemia major and other iron overloaded patients. A single-breathhold electrocardiogram-triggered black-blood multi-echo spin-echo (MESE) sequence with a turbo factor of 2 was implemented at 3 Tesla (T). Myocardial and liver T2 values were measured with three repeated breathholds in 8 normal subjects and 24 patients. Their values, together with the T2 values measured using a breathhold multi-echo gradient-echo sequence, were compared with those at 1.5T in the same patients. At 3T, myocardial T2 was found to be 39.6 +/- 7.4 ms in normal subjects. In patients, it ranged from 12.9 to 50.1 ms. "T2 and T2(*) [corrected] were observed to correlate in heart (rho = 0.93, P [corrected] < 0.0001) and liver (rho = 0.95, P < 0.0001). Myocardial T2 and T2 at 3T were also highly correlated with the 1.5T measurements. Preliminary results indicated that myocardial T2 quantitation was relatively insensitive to B1 variation, and reproducible with 3.2% intra-exam and 3.8% inter-exam variations. Myocardial T2 quantitation is feasible at 3T. Given the substantially decreased T2 and increased B0 inhomogeneity, the rapid myocardial T2 measurement protocol demonstrated here may present a robust alternative to study cardiac iron overload at 3T.

TU‐D‐332‐02: Abdominal Fat Quantification Accuracy Using Water Saturated B‐SSFP MRI Sequences: A Verification Study

Purpose: To verify the fat quantification accuracy of abdominal fat quantification results on images acquired with a Water Saturated b‐SSFP (WS b‐SSFP) MRI Sequence. Method and Materials: 10 healthy (5 female and 5 male) volunteers underwent both WS T1W TSE and WS b‐SSFP scans with breath hold on a 1.5 T clinical MR scanner. For the WS T1W TSE sequence, the parameters were as follows: TR/TE/flip angle = 500 ms/5 ms/90°, turbo factor = 7 and readout bandwidth = 128 KHz. For the WS 3D b‐SSFP sequences, the imaging parameters were as follows: TR/TE/flip angle = 2.9 ms/1.2 ms/55°, ETL = 128 with 12 dummy echoes, and readout bandwidth = 200 KHz. For WS T1W TSE sequence, 6 axial slices centered at L2‐L3 level were acquired in two consecutive expired breath‐holds, with 14 seconds each. Since WS b‐SSFP is a much faster scan, 8 slices (with slice 2–7 imaged at the same positions of the 6 TSE slices) were obtained in 11 seconds in one breath‐hold. For each subject, fat volumes from six common slices of WS TSE and WS b‐SSFP were measured and summed. Total abdominal fat (TAF), intra‐abdominal fat (IAF), and subcutaneous abdominal fat (SAF) volumes from images of both scans were measured and compared. Results: The TAF, IAF, and SAF mean differences of the fat volume measured from images of the two scans are only 0.34%, −0.25%, and 0.91%, respectively. The Bland‐Altman plots show that all the measurement differences between WS b‐SSFP and WS TSE are within the 95% of difference. Conclusion: The two methods are the same in terms of the measurement accuracy for human abdominal imaging. Therefore, WS b‐SSFP MRI can be used for abdominal fat quantification to reduce imaging and post‐processing difficulties and ultimately reduce research cost in abdominal fat distribution studies.

Fast, three-dimensional, MR Imaging for polymer gel dosimetric applications involving high dose and steep dose gradients

Polymer gels constitute water equivalent integrating detectors, which, combined with magnetic resonance imaging (MRI), can provide accurate three dimensional (3D) dose distributions in contemporary radiotherapy applications where the small field dimensions and steep dose gradients induce limitations to conventional dosimeters. One of the main obstacles for adapting the method for routine use in the clinical setting is the cost effectiveness of the MRI readout method. Currently, optimized Carr-Purcell-Meiboom-Gill (CPMG) multiple spin echo imaging pulse sequences are commonly used which however result in long imaging times. This work evaluates the efficiency of 3D, dual-echo, k-space segmented turbo spin echo (TSE) scanning sequences for accurate dosimetry with sub-millimetre spatial resolution in strenuous radiation therapy applications. PABIG polymer gel dosimeters were irradiated with an 192Ir High Dose Rate brachytherapy source, the 4 mm and 8 mm collimator helmets of a gamma knife unit and a custom made x-knife collimator of 1 cm diameter. Profile and dose distribution measurements using TSE are benchmarked against corresponding findings obtained by the commonly used, but time consuming, CPMG sequence as well as treatment planning calculations, Monte Carlo (MC) simulations and film measurements. The implementation of a high Turbo factor was found to provide comparable accuracy, allowing a 64-fold MRI scan acceleration compared to conventional multi-echo sequences. The availability of TSE sequences in typical MRI installations greatly facilitates the introduction of polymer gel dosimetry in the clinical environment as a practicable tool for the determination of full 3D dose distributions in contemporary radiotherapy applications.

An evaluation of the TSE MR sequence for time efficient data acquisition in polymer gel dosimetry of applications involving high doses and steep dose gradients

The use of magnetic resonance imaging as a readout method for polymer gel dosimetry commonly involves long imaging sessions, particularly when high spatial resolution is required in all three dimensions, for the investigation of dose distributions with steep dose gradients and stringent dose delivery specifications. In this work, a volume selective turbo spin echo (TSE) pulse sequence is compared to the established Carr-Purcell-Meiboom-Gill (CPMG) multiecho acquisition with regard to providing accurate dosimetric results in significantly reduced imaging times. Polyethylene glycol diacrylate based (PABIG) gels were irradiated and subsequently scanned to obtain R2 relaxation rate measurements, using a CPMG multiecho sequence and a dual echo TSE utilizing an acceleration (turbo) factor of 64. R2 values, plotted against corresponding Monte Carlo dose calculations, provided calibration data of PABIG gels dose response over a wide dose range. A linear R2 versus dose relationship was demonstrated for both sequences with TSE results presenting reduced dose sensitivity. Although TSE data were found to deviate from linearity at lower doses compared to CPMG data, a relatively wide dynamic dose range of response extending up to approximately 100 Gy was observed for both sequences. The TSE and CPMG sequences were evaluated with a brachytherapy irradiation using a high dose rate 192Ir source and a gamma knife stereotactic radiosurgery irradiation with a single 4 mm collimator helmet shot. Dosimetric results obtained with the TSE and CPMG are shown to compare equally well with the expected dose distributions for these irradiations. The 60-fold scan time reduction achieved with TSE implies that this sequence could prove to be a useful tool for the introduction of polymer gel dosimetry in clinical radiation therapy applications involving high doses and steep dose gradients.

A comparison of fast MRI of hips with and without parallel imaging using SENSE

This study was undertaken to qualitatively and quantitatively compare fast MRI of hips with and without parallel imaging using SENSE (sensitivity encoding). 27 patients underwent MRI of the hips with coronal T1 turbo spin echo (TSE) (repetition time (TR) 500 ms, effective echo time (TEeff) 15 ms, Turbo Factor 4), coronal IR-TSE (TR 2000 ms, TEeff 30 ms, inversion time (TI) 160 ms, Turbo Factor 20) and axial T2 TSE (TR 3000 ms, TEeff 80 ms, Turbo Factor 20) weighted images acquired with and without SENSE with a reduction factor of 2. Conventional imaging was performed in 8 min and 36 s. Images acquired with SENSE were acquired in 5 min and 31 s without a discernible reduction in image quality or a significant quantitative reduction in image signal to noise ratio, contrast to noise ratio or edge enhancement.