Inflow‐based vascular‐space‐occupancy (iVASO) MRI

Vascular‐space‐occupancy (VASO) MRI, a blood nulling approach for assessing changes in cerebral blood volume (CBV), is hampered by low signal‐to‐noise ratio (SNR) because only 10–20% of tissue signal is recovered when using nonselective inversion for blood nulling. A new approach, called inflow‐VASO (iVASO), is introduced in which only blood flowing into the slice has experienced inversion, thereby keeping tissue and cerebrospinal fluid (CSF) signal in the slice maximal and reducing CSF partial volume effects. SNR increases of 198% ± 12% and 334% ± 9% (mean ± SD, n = 7) with respect to VASO were found at TR values of 5s and 2s, respectively. When using inflow approaches, data interpretation is complicated by the fact that signal changes are affected by vascular transit times. An optimal TR‐range (1.5–2.5s) was derived in which the iVASO response during activation predominantly reflects arterial/arteriolar CBV (CBV_a) changes. In this TR‐range, perfusion contributions to the signal change are negligible because arterial label has not yet undergone capillary exchange, and arterial and precapillary blood signals are nulled. For TR = 2s, the iVASO signal change upon visual stimulation corresponded to a CBV_a increase of 58% ± 7%, in agreement with arteriolar CBV changes previously reported. The onset of the hemodynamic response for iVASO occurred 1.2 ± 0.5s (n = 7) faster than for conventional VASO. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Effect of inflow of fresh blood on vascular‐space‐occupancy (VASO) contrast

In vascular‐space‐occupancy (VASO)‐MRI, cerebral blood volume (CBV)‐weighted contrast is generated by applying a nonselective inversion pulse followed by imaging when blood water magnetization is zero. An uncertainty in VASO relates to the completeness of blood water nulling. Specifically, radio frequency (RF) coils produce a finite inversion volume, rendering the possibility of fresh, non‐nulled blood. Here, VASO‐functional MRI (fMRI) was performed for varying inversion volume and TR using body coil RF transmission. For thin inversion volume thickness (δ_tot < 10 mm), VASO signal changes were positive (ΔS/S = 2.1–2.6%). Signal changes were negative and varied in magnitude for intermediate inversion volumes (δ_tot = 100–300 mm), yet did not differ significantly (P > 0.05) for δ_tot > 300 mm. These data suggest that blood water is in steady state for δ_tot > 300 mm. In this appropriate range, long‐TR VASO data converged to a less negative value (ΔS/S = –1.4% ± 0.2%) than short‐TR data (ΔS/S = –2.2% ± 0.2%), implying that cerebral blood flow or transit‐state effects may influence VASO contrast at short TR. Magn Reson Med 61:473–480, 2009. © 2009 Wiley‐Liss, Inc.     

Implementation of vascular‐space‐occupancy MRI at 7T

Vascular‐space‐occupancy (VASO) MRI exploits the difference between blood and tissue T₁ to null blood signal and measure cerebral blood volume changes using the residual tissue signal. VASO imaging is more difficult at higher field because of sensitivity loss due to the convergence of tissue and blood T₁ values and increased contamination from blood‐oxygenation‐level‐dependent (BOLD) effects. In addition, compared to 3T, 7T MRI suffers from increased geometrical distortions, e.g., when using echo‐planar‐imaging, and from increased power deposition, the latter especially problematic for the spin‐echo‐train sequences commonly used for VASO MRI. Third, non‐steady‐state blood spin effects become substantial at 7T when only a head coil is available for radiofrequency transmit. In this study, the magnetization‐transfer‐enhanced‐VASO approach was applied to maximize tissue‐blood signal difference, which boosted signal‐to‐noise ratio by 149% ± 13% (n = 7) compared to VASO. Second, a 3D fast gradient‐echo sequence with low flip‐angle (7°) and short echo‐time (1.8 ms) was used to minimize the BOLD effect and to reduce image distortion and power deposition. Finally, a magnetization‐reset technique was combined with a motion‐sensitized‐driven‐equilibrium approach to suppress three types of non‐steady‐state spins. Our initial functional MRI results in normal human brains at 7T with this optimized VASO sequence showed better signal‐to‐noise ratio than at 3T. Magn Reson Med 69:1003–1013, 2013. © 2012 Wiley Periodicals, Inc.     

On the measurement of absolute cerebral blood volume (CBV) using vascular‐space‐occupancy (VASO) MRI

Recently, a vascular‐space‐occupancy (VASO) MRI technique was developed for quantitative assessment of cerebral blood volume (CBV). This method uses the T₁‐shortening effect of gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) with imaging parameters chosen that null the precontrast blood magnetization but allow the postcontrast blood magnetization to recover to equilibrium. A key advantage of VASO CBV estimation is that it provides a straightforward procedure for converting MR signals to absolute physiologic values. However, as with other T₁‐based steady‐state approaches, several important factors need to be considered that influence the accuracy of CBV values obtained with VASO MRI. Here, the transverse relaxation (T₂/T) effect in VASO MRI was investigated using multiecho spin‐echo and gradient‐echo experiments, resulting in underestimation of CBV by 14.9% ± 1.1% and 16.0% ± 2.5% for spin echo (TE = 10 ms) and gradient echo (TE = 6 ms), respectively. In addition, the influence of contrast agent clearance was studied by acquiring multiple postcontrast VASO images at 2.2‐min intervals, which showed that the concentration of Gd‐DTPA in the first 14 min (single dose) was sufficient for the blood magnetization to fully recover to equilibrium. Finally, the effect of vascular Gd‐DTPA leakage was assessed for scalp tissue, and signal extrapolation as a function of postinjection time was demonstrated to be useful in minimizing the associated errors. Specific recommendations for VASO MRI acquisition and processing strategies are provided. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.     

Three‐dimensional flow‐independent balanced steady‐state free precession vessel wall MRI of the popliteal artery: Preliminary experience and comparison with flow‐dependent black‐blood techniques

Purpose:

To examine the feasibility of flow‐independent T2‐prepared inversion recovery (T2IR) black‐blood (BB) magnetization preparation for three‐dimensional (3D) balanced steady‐state free precession (SSFP) vessel wall MRI of the popliteal artery, and to evaluate its performance relative to flow‐dependent double inversion recovery (DIR), spatial presaturation (SPSAT), and motion‐sensitizing magnetization preparation (MSPREP) BB techniques in healthy volunteers.

Materials and Methods:

Eleven subjects underwent 3D MRI at 1.5 Tesla with four techniques performed in a randomized order. Wall and lumen signal‐to‐noise ratio (SNR), wall‐to‐lumen contrast‐to‐noise ratio (CNR), vessel wall area, and lumen area were measured at proximal, middle, and distal locations of the imaged popliteal artery. Image quality scores based on wall visualization and degree of intraluminal artifacts were also obtained.

Results:

In the proximal region, DIR and SPSAT had higher wall SNR and wall‐to‐lumen CNR than both MSPREP and T2IR. In the middle and distal regions, DIR and SPSAT failed to provide effective blood suppression, whereas MSPREP and T2IR provided adequate black blood contrast with comparable wall‐to‐lumen CNR and image quality.

Conclusion:

The feasibility of 3D SSFP imaging of the popliteal vessel wall using flow‐independent T2IR was demonstrated with effective blood suppression and good vessel wall visualization. Although DIR and SPSAT are effective for thin slab imaging, MSPREP and T2IR are better suited for 3D thick slab imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Enhanced image quality in black‐blood MRI using the improved motion‐sensitized driven‐equilibrium (iMSDE) sequence

Purpose

To propose an improved motion‐sensitized driven‐equilibrium (iMSDE) pulse sequence to enhance the tissue signal‐to‐noise ratio (SNR) while maintaining the same flow suppression capability in black‐blood carotid artery magnetic resonance imaging (MRI).

Materials and Methods

Compared to the traditional MSDE sequence, the iMSDE sequence uses an extra refocusing pulse and two extra gradients to achieve SNR improvement. Computer simulation and phantom studies were used to evaluate both eddy currents and local B₁ inhomogeneity effects on SNR behaviors on both MSDE and iMSDE images. To further assess the SNR improvements brought by iMSDE in vivo, five healthy volunteers were also scanned with both sequences. The paired t‐test was used for statistical comparison.

Results

Both simulations and phantom studies demonstrated that eddy currents and local B₁ inhomogeneity will cause image SNR reduction in the MSDE sequence, and that these factors can be partially compensated for with the iMSDE sequence. In vivo comparison showed that the iMSDE sequence significantly improved the tissue‐lumen contrast‐to‐noise ratio (CNR) and static tissue SNR (P < 0.001 for both), while maintaining low lumen SNR in carotid MRI.

Conclusion

Compared to the traditional MSDE sequence, the iMSDE sequence can achieve improved soft‐tissue SNR and CNR in carotid artery MRI without sacrificing flow suppression capability and time efficiency. J. Magn. Reson. Imaging 2010;31:1256–1263. © 2010 Wiley‐Liss, Inc.     

Cine cardiac imaging using black‐blood steady‐state free precession (BB‐SSFP) at 3T

Purpose

To propose a new black‐blood (BB) pulse sequence that provides BB cine cardiac images with high blood‐myocardium contrast. The proposed technique is based on the conventional steady‐state free precession (SSFP) sequence.

Materials and Methods

Numerical simulations of the Bloch equation were conducted to compare the resulting signal‐to‐noise ratio (SNR) to that of conventional BB imaging, including the effects of changing the imaging flip angle and heart rates. Simulation results were verified using a gel phantom experiment and five normal volunteers were scanned using the proposed technique.

Results

The new sequence showed higher SNR and contrast‐to‐noise ratio (CNR) (≈100%) compared to the conventional BB imaging. Also, the borders of the left ventricle (LV) and right ventricle (RV) appear more distinguishable than the conventional SSFP. We were also able to cover about 80% of the cardiac cycle with short breath‐hold time (≈10 cardiac cycles) and with reasonable SNR and CNR.

Conclusion

Based on an SSFP conventional sequence, the new sequence provides BB cines that cover most of the cardiac cycle and with higher SNR and CNR than the conventional BB sequences. J. Magn. Reson. Imaging 2009;30:94–103. © 2009 Wiley‐Liss, Inc.     

Non‐contrast‐enhanced MR angiography for selective visualization of the hepatic vein and inferior vena cava with true steady‐state free‐precession sequence and time‐spatial labeling inversion pulses: Preliminary results

Purpose

To selectively visualize the hepatic vein and inferior vena cava (IVC) using three‐dimensional (3D) true steady‐state free‐precession (SSFP) MR angiography with time‐spatial labeling inversion pulse (T‐SLIP), and to optimize the acquisition protocol.

Materials and Methods

Respiratory‐gated 3D true SSFP scans were conducted in 23 subjects in combination with two different T‐SLIPs (one placed in the thorax to suppress the arterial signal and the other in the abdomen to suppress the portal venous signal). One of the most important factors was the inversion time (TI) of abdominal T‐SLIP, and the image quality was evaluated at four different TIs of 800, 1200, 1600, and 2000 msec in terms of relative signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), and mean visualization scores.

Results

No significant difference was observed in SNR and CNR between each TI. However, IVC visualization scores were better at TIs of 1600 and 2000 msec, and overall image quality was better at TIs of 1200 and 1600 msec. Therefore, the TI of 1600 msec was considered to provide the optimal balance between IVC visualization and signal suppression of the portal vein in our protocol.

Conclusion

True SSFP scan with T‐SLIPs enabled selective visualization of the hepatic vein and IVC without an exogenous contrast agent. J. Magn. Reson. Imaging 2009;29:474–479. © 2009 Wiley‐Liss, Inc.     

Vascular space occupancy-dependent functional MRI by tissue suppression

PURPOSE: To measure the cerebral blood volume (CBV) dynamics during neural activation, a novel technique named vascular space occupancy (VASO)-based functional MRI (fMRI) was recently introduced for noninvasive CBV detection. However, its application is limited because of its low contrast-to-noise ratio (CNR) due to small signal change from the inverted blood. MATERIALS AND METHODS: In this study a new approach-VASO with tissue suppression (VAST)-is proposed to enhance CNR. This technique is compared with VASO and blood oxygenation level-dependent (BOLD) fMRI in block-design and event-related visual experiments. RESULTS: Based on acquired T(1) maps, 75.3% of the activated pixels detected by VAST are located in the cortical gray matter. Temporal characteristics of functional responses obtained by VAST were consistent with that of VASO. Although the baseline signal was decreased by the tissue suppression, the CNR of VAST was about 43% higher than VASO. CONCLUSION: With the improved sensitivity, VAST fMRI provides a useful alternative for mapping the spatial/temporal features of regional CBV changes during brain activation. However, the technical imperfectness of VAST, such as the nonideal inversion efficiency and physiological contaminations, limits its application to precise CBV quantification.     

Phase‐sensitive black‐blood coronary vessel wall imaging

Black‐blood MR coronary vessel wall imaging may become a powerful tool for the quantitative and noninvasive assessment of atherosclerosis and positive arterial remodeling. Although dual‐inversion recovery is currently the gold standard, optimal lumen‐to‐vessel wall contrast is sometimes difficult to obtain, and the time window available for imaging is limited due to competing requirements between blood signal nulling time and period of minimal myocardial motion. Further, atherosclerosis is a spatially heterogeneous disease, and imaging at multiple anatomic levels of the coronary circulation is mandatory. However, this requirement of enhanced volumetric coverage comes at the expense of scanning time. Phase‐sensitive inversion recovery has shown to be very valuable for enhancing tissue‐tissue contrast and for making inversion recovery imaging less sensitive to tissue signal nulling time. This work enables multislice black‐blood coronary vessel wall imaging in a single breath hold by extending phase‐sensitive inversion recovery to phase‐sensitive dual‐inversion recovery, by combining it with spiral imaging and yet relaxing constraints related to blood signal nulling time and period of minimal myocardial motion. Magn Reson Med 63:1021–1030, 2010. © 2010 Wiley‐Liss, Inc.     

Estimating cerebral blood volume with expanded vascular space occupancy slice coverage

A model for quantifying cerebral blood volume (CBV) based on the vascular space occupancy (VASO) technique and varying the extent of blood nulling yielding task‐related signal changes with various amounts of blood oxygenation level‐dependent (BOLD) and VASO weightings was previously described. Challenges associated with VASO include limited slice coverage and the confounding inflow of fresh blood. In this work, an approach that extends the previous model to multiple slices and accounts for the inflow effect is described and applied to data from a multiecho sequence simultaneously acquiring VASO, cerebral blood flow (CBF), and BOLD images. This method led to CBV values (7.9 ± 0.3 and 5.6 ± 0.3 ml blood/100 ml brain during activation [CBV_ACT] and rest [CBV_REST], respectively) consistent with previous studies using similar visual stimuli. Furthermore, an increase in effective blood relaxation (0.65 ± 0.01) compared to the published value (0.62) was detected, likely reflecting inflow of fresh blood. Finally, cerebral metabolic rate of oxygen (CMRO₂) estimates using a multiple compartment model without assumption of CBV_REST led to estimates (18.7 ± 17.0%) that were within published ranges. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Improvements in carotid plaque imaging using a new eight‐element phased array coil at 3T

Purpose

To design and compare an eight‐channel phased array (PA) coil for carotid imaging to an established four‐channel PA design at 3T.

Materials and Methods

An eight‐channel PA (8PA) coil was designed specifically for imaging the carotid bifurcation and compared with the existing four‐channel (4PA) design using a phantom and by in vivo black‐blood magnetic resonance imaging (MRI). The 8PA and 4PA were compared in terms of coverage, signal‐to‐noise ratio (SNR), and contrast‐to‐noise ratio (CNR).

Results

The 8PA showed up to 1.7‐fold improvement in SNR at a depth of 3.5 cm and greater longitudinal coverage at a given SNR on a phantom. The 8PA showed improved vessel wall SNR for high spatial resolution (0.63 mm²) PD, T1, and T2 (1.7, 1.7, 1.6 times, respectively; P ≤ 0.002) and improved CNR (1.7, 1.6, 1.5 times, respectively; P ≤ 0.002). Ultrahigh‐resolution (0.27 mm²) T1‐weighted images showed better SNR and CNR (1.4 times, P ≤ 0.0001) on 8PA compared to 4PA.

Conclusion

Carotid imaging studies may benefit from the improved SNR and larger coverage provided by use of the 8PA. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.     

Spin‐locked balanced steady‐state free‐precession (slSSFP)

A spin‐locked balanced steady‐state free‐precession (slSSFP) pulse sequence is described that combines a balanced gradient‐echo acquisition with an off‐resonance spin‐lock pulse for fast MRI. The transient and steady‐state magnetization trajectory was solved numerically using the Bloch equations and was shown to be similar to balanced steady‐state free‐precession (bSSFP) for a range of T₂/T₁ and flip angles, although the slSSFP steady‐state could be maintained with considerably lower radio frequency (RF) power. In both simulations and brain scans performed at 7T, slSSFP was shown to exhibit similar contrast and signal‐to‐noise ratio (SNR) efficiency to bSSFP, but with significantly lower power. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

MR angiography of the cerebral perforating arteries with magnetization prepared anatomical reference at 7T: Comparison with time‐of‐flight

Purpose

To develop a magnetic resonance imaging (MRI) protocol that visualizes both the perforating arteries and the related anatomy in a single acquisition at 7T.

Material and Methods

T₁‐weighted magnetization prepared imaging (MPRAGE) was empirically modified for use as angiography method at 7T. The resulting sequence depicts the vasculature simultaneously with the surrounding anatomical structures, and is referred to as “magnetization prepared anatomical reference MRA” (MPARE‐MRA). The method was compared to time‐of‐flight (TOF) MRA in seven healthy subjects. The conspicuity of the perforating arteries and the contrast between gray and white matter were evaluated both quantitatively by contrast‐to‐noise (CNR) measurements, and qualitatively by two radiologists who scored the images.

Results

The contrast‐to‐noise ratio (CNR) between blood and background was 28 ± 9 for MPARE‐MRA and 35 ± 16 for TOF‐MRA, indicating good conspicuity of the vessels. CNR values were: internal capsule (IC) vs. caudate head (CH): 4.2 ± 0.7; IC vs. putamen: 3.5 ± 0.6; white matter vs. gray matter: 9.7 ± 2.5.

Conclusion

The benefits of ultra‐high‐field MRI can transform MPRAGE into a new angiography method to image small vessels and associated parenchyma at the same time. This technique can be used to study the correlation between tissue damage and vascular pathology. J. Magn. Reson. Imaging 2008;28:1519–1526. © 2008 Wiley‐Liss, Inc.     

Shorter difference between myocardium and blood optimal inversion time suggests diffuse fibrosis in dilated cardiomyopathy

Purpose:

To find evidence of diffuse fibrosis in dilated cardiomyopathy (DCM) patients by comparing measurements on clinical late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) studies between DCM and healthy subjects.

Materials and Methods:

LGE‐CMR and the Look–Locker images from 20 DCM patients and 17 healthy controls were analyzed. Blood signal‐to‐noise ratio (SNR), myocardium SNR, and blood‐to‐myocardium contrast‐to‐noise ratio (CNR) were measured on the LGE‐CMR images. The optimal inversion time (TI) to null blood and myocardium was determined on the Look–Locker images. The postcontrast T₁ was estimated using a phantom study that correlated optimal TI and heart rate to T₁.

Results:

The blood SNR was lower, myocardium SNR was higher, and the blood‐to‐myocardium CNR was lower (6.6 ± 0.7 vs. 10.3 ± 0.9, P = 0.004) on DCM LGE‐CMR images as compared to controls. The blood‐myocardium optimal TI difference (ΔTI) was lower (38 ± 2 msec vs. 55 ± 3 msec, P < 0.001) in DCM, and the estimated blood‐myocardium T₁ difference (ΔT₁) (116 ± 6 msec vs. 152 ± 8 msec, P = 0.001) was also lower.

Conclusion:

DCM patients have reduced blood‐myocardium ΔTI and ΔT₁, and lower CNR as compared to controls, suggesting the presence of diffuse fibrosis. This may impact the interpretation of LGE data. J. Magn. Reson. Imaging 2009;30:967–972. © 2009 Wiley‐Liss, Inc.     

Efficiency of inversion pulses for background suppressed arterial spin labeling.

Background suppression strategies for arterial spin labeling (ASL) MRI offer reduced noise from motion and other system instabilities. However, the inversion pulses used for suppression can also attenuate the ASL signal, which may offset the advantages of background suppression. Numerical simulations were used to optimize the inversion efficiency of four candidate pulses over a range of radiofrequency (RF) and static magnetic field variations typical of in vivo imaging. Optimized pulses were then used within a pulsed ASL sequence to assess the pulses' in vivo inversion efficiencies for ASL. The measured in vivo inversion efficiency was significantly lower than theoretical predictions (e.g., 93% experimental compared to 99% theoretical) for the tangent hyperbolic pulse applied in a background suppression scheme. This inefficiency was supported by an in vitro study of human blood. These results suggest that slow magnetization transfer (MT) in blood, either with bound water or macromolecular protons, dominates the inversion inefficiency in blood. Despite the attenuated signal relative to unsuppressed ASL, the signal-to-noise ratio (SNR) with suppression was improved by 23-110% depending on the size of the region measured. Knowledge of efficiency will aid optimization of the number of suppression pulses and provide more accurate quantification of blood flow.     

Vascular space occupancy (VASO) cerebral blood volume‐weighted MRI identifies hemodynamic impairment in patients with carotid artery disease

Purpose

To assess the role of vascular space occupancy (VASO) magnetic resonance imaging (MRI), a noninvasive cerebral blood volume (CBV)‐weighted technique, for evaluating CBV reactivity in patients with internal carotid artery (ICA) stenosis.

Materials and Methods

VASO reactivity, defined as a signal change in response to hypercapnic stimulus (4‐second exhale, 14‐second breath‐hold), was measured in the left and right ICA flow territories in patients (n = 10) with varying degrees of unilateral and bilateral ICA stenosis and in healthy volunteers (n = 10).

Results

Percent VASO reactivity was more negative (P < 0.01) bilaterally in patients (ipsilateral: ?3.6 ± 1.5%; contralateral: ?3.4 ± 1.2%) compared with age‐matched controls (left: ?1.9 ± 0.6%; right: ?1.9 ± 0.8%). Owing to the nature of the VASO contrast mechanism, this more negative VASO reactivity was attributed to autoregulatory CBV effects in patients. A postbreath‐hold overshoot, which was absent in healthy volunteers, was observed unilaterally in a subset of patients.

Conclusion

More negative VASO reactivity was observed in patients with ICA stenosis and may be a marker of autoregulatory effects. Furthermore, the postbreath‐hold overshoot observed in patients is consistent with compensatory microvascular vasoconstriction and may be a marker of hemodynamic impairment. Based on the results of this feasibility study, VASO should be useful for identifying CBV adjustments in patients with steno‐occlusive disease of the ICA. J. Magn. Reson. Imaging 2009;29:718–724. © 2009 Wiley‐Liss, Inc.

     

3D single‐shot VASO using a maxwell gradient compensated GRASE sequence

The vascular space occupancy (VASO) method was recently proposed as a functional MRI (fMRI) method that is capable of detecting activation‐related changes in blood volume (CBV), without the need for a blood‐pool contrast agent. In the present work we introduce a new whole‐brain VASO technique that is based on a parallel‐accelerated single‐shot 3D GRASE (gradient and spin echo) readout. The GRASE VASO sequence employs a flow‐compensated correction scheme for concomitant Maxwell gradients which is necessary to avoid smearing artifacts that may occur due to violation of the Carr–Purcell–Meiboom–Gill (CPMG) condition for off‐resonance excitation. Experiments with 6 min of visual‐motor stimulation were performed on eight subjects. At P < 0.01, average percent signal change and t‐score for visual stimulation were ?3.11% and ?8.42, respectively; activation in left and right motor cortices and supplementary motor area was detected with ?2.75% and ?6.70, respectively. Sensitivity and signal changes are comparable to those of echo‐planar imaging (EPI)‐based single‐slice VASO, as indicated by additional visual‐task experiments (?3.39% and ?6.93). The method makes it possible to perform whole‐brain cognitive activation studies based on CBV contrast. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Flow‐independent T2‐prepared inversion recovery black‐blood MR imaging

Purpose:

To develop a magnetization preparation method to achieve robust, flow‐independent blood suppression for cardiac and vascular magnetic resonance imaging (MRI).

Materials and Methods:

T₂Prep‐IR sequence consists of a T₂ preparation followed by a nonselective adiabatic inversion pulse. T₂Prep separates the initial longitudinal magnetization of arterial wall from lumen blood. After the inversion recovery pulse the imaging acquisition is then delayed for a period that allows the blood signal to approach the zero‐crossing point. Compared to the conventional double inversion recovery (DIR) preparation, T₂Prep‐IR prepares all the spins regardless of their velocity and direction. T₂Prep‐IR was incorporated into the fast spin echo and fast gradient echo acquisition sequences and images in various planes were acquired in the carotid arteries, thoracic aorta, and heart of normal volunteers. Blood suppression and image quality were compared qualitatively between two different preparations.

Results:

For in‐plane flow carotid images, persistent flow‐related artifacts on the DIR images were removed with T₂Prep‐IR. For cardiac applications, T₂Prep‐IR provided robust blood suppression regardless of the flow direction and velocity, including the cardiac long‐axis views and the aorta that are often problematic with DIR.

Conclusion:

T₂Prep‐IR may overcome the flow dependence of DIR by providing robust flow‐independent black‐blood images. J. Magn. Reson. Imaging 2010;31:248–254. © 2009 Wiley‐Liss, Inc     

Left ventricular infarct size,peri‐infarct zone,and papillary scar measurements: A comparison of high‐resolution 3D and conventional 2D late gadolinium enhancement cardiac MR

Purpose

To compare higher spatial resolution 3D late gadolinium enhancement (LGE) cardiovascular magnetic resonance (Cardiac MR) with 2D LGE in patients with prior myocardial infarction.

Materials and Methods

Fourteen patients were studied using high spatial resolution 3D LGE (1.3 × 1.3 × 5.0 mm³) and conventional 2D LGE (2 × 2 × 8 mm³) scans. The signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) were measured. Total infarct volume, peri‐infarct volume measured in a limited slab, and papillary muscle scar volume were compared using Bland–Altman analysis. Image quality was graded.

Results

3D LGE had higher scar SNR (P < 0.001), higher myocardial SNR (P = 0.001), higher papillary scar‐blood CNR (P = 0.01), and greater sharpness (P = 0.01). The scar volumes agreed (14.5 ± 8.2 for 2D, vs. 13.2 ± 8.8 for 3D), with bias ± 2 standard deviations (SDs) of 0.5 ± 6.8 mL, P = 0.59 R = 0.91. The peri‐infarct volumes correlated but less strongly than scar (P = 0.40, R = 0.77). For patients with more heterogeneous scar, larger peri‐infarct volumes were measured by 3D (1.9 ± 1.1 mL for 2D vs. 2.4 ± 1.6 mL for 3D, P = 0.15, in the matched region). Papillary scar, present in 6/14 (42%) patients, was more confidently identified on 3D LGE.

Conclusion

Higher spatial resolution 3D LGE provides sharper images and higher SNR, but less myocardial nulling. Scar volumes agree well, with peri‐infarct volumes correlating less well. 3D LGE may be superior in visualization of papillary muscle scar. J. Magn. Reson. Imaging 2009;30:794–800. © 2009 Wiley‐Liss, Inc.