Phase-sensitive inversion recovery (PSIR) single-shot TrueFISP for assessment of myocardial infarction at 3 tesla

PURPOSE: The aim of the current study was to show if contrast-to-noise ratio (CNR) could be improved without loss of diagnostic accuracy if a phase-sensitive inversion recovery (PSIR) single-shot TrueFISP sequence is used at 3.0 T instead of 1.5 T. MATERIAL AND METHODS: Ten patients with myocardial infarction were examined on a 1.5 T magnetic resonance (MR) system (Avanto, Siemens Medical Systems) and at a 3.0 T MR system. Imaging delayed contrast enhancement was started 10 minutes after application of contrast material. A phase-sensitive inversion recovery (PSIR) single-shot TrueFISP sequence was used at 1.5 and 3.0 T and compared with a segmented IR turboFLASH sequence at 1.5 T, which served as the reference method. Infarct volumes and CNR of infarction and normal myocardium were compared with the reference method. RESULTS: The PSIR Single-Shot TrueFISP technique allows for imaging nine slices during a single breathhold without adaptation of the inversion time. The mean value of CNR between infarction and normal myocardium was 5.9 at 1.5 T and 12.2 at 3.0 T (magnitude images). The CNR mean value of the reference method was 8.4. The CNR mean value at 3.0 T was significantly (P = 0.03) higher than the mean value of the reference method. The correlation coefficients of the infarct volumes, determined with the PSIR single-shot TrueFISP technique at 1.5 T and at 3.0 T and compared with the reference method, were r = 0.96 (P = 0.001) and r = 0.99 (P = 0.0001). CONCLUSION: The use of PSIR single-shot TrueFISP at 3.0 T allows for accurate detection and assessment of myocardial infarction. CNR is significantly higher at 3.0 T compared with 1.5 T. The PSIR single-shot technique at 3.0 T provides a higher CNR than the segmented reference technique at 1.5 T.     

Quantitative breath-hold monitoring of myocardial gadolinium enhancement using inversion recovery TrueFISP.

The purpose of this work was to develop and evaluate the accuracy of a breath-hold IR-TrueFISP acquisition capable of monitoring gadolinium (Gd) concentrations through T1 measurements in the left ventricular blood pool and segments of the myocardium over an extended duration. Measurements using a phantom were performed to assess the accuracy of the technique. Accurate T1 measurements in the expected range after contrast agent administration were obtained with several theoretical formulations. Accurate T1 values before the administration of the contrast agent were obtained only when the incomplete recovery of magnetization during the delay time (TD) between imaging segments was incorporated into the observed signal intensity calculations. T1 measurements over a 1-hr time period were performed in four subjects with known myocardial infarctions. In this small study, Gd differences between recent and old myocardial infarctions were observed.     

Phase-sensitive inversion recovery for detecting myocardial infarction using gadolinium-delayed hyperenhancement.

After administration of gadolinium, infarcted myocardium exhibits delayed hyperenhancement and can be imaged using an inversion recovery (IR) sequence. The performance of such a method when using magnitude-reconstructed images is highly sensitive to the inversion recovery time (TI) selected. Using phase-sensitive reconstruction, it is possible to use a nominal value of TI, eliminate several breath-holds otherwise needed to find the precise null time for normal myocardium, and achieve a consistent contrast. Phase-sensitive detection is used to remove the background phase while preserving the sign of the desired magnetization during IR. Experimental results are presented which demonstrate the benefits of both phase-sensitive IR image reconstruction and surface coil intensity normalization for detecting myocardial infarction (MI). The phase-sensitive reconstruction method reduces the variation in apparent infarct size that is observed in the magnitude images as TI is changed. Phase-sensitive detection also has the advantage of decreasing the sensitivity to changes in tissue T(1) with increasing delay from contrast agent injection.     

T(1) quantification with inversion recovery TrueFISP.

A snapshot FLASH sequence can be used to acquire the time course of longitudinal magnetization during its recovery after a single inversion pulse. However, excitation pulses disturb the exponential recovery of longitudinal magnetization and may produce systematic errors in T(1) estimations. In this context the possibility of using the TrueFISP sequence to detect the recovery of longitudinal magnetization for quantitative T(1) measurements was examined. Experiments were performed on different Gd-doped water phantoms and on humans. T(1) values derived from inversion recovery TrueFISP were in excellent agreement with the single-point method even for flip angles up to 50 degrees. In terms of T(1) accuracy and SNR, the proposed method seems to be superior to the conventional inversion recovery snapshot FLASH technique. Magn Reson Med 45:720-723, 2001.     

Inversion recovery single-shot TurboFLASH for assessment of myocardial infarction at 3 Tesla

PURPOSE: The aim of the study was to assess the diagnostic accuracy of imaging myocardial infarction with a single-shot inversion recovery turbofast low-angle shot (SS IR turboFLASH) sequence at 3.0 Tesla in comparison with an established segmented inversion recovery turboFLASH sequence at 1.5 Tesla. MATERIALS AND METHODS: Fifteen patients with myocardial infarction were examined at a 1.5 Tesla magnetic resonance (MR) System (Avanto, Siemens, Medical Solutions) and at a 3.0 Tesla MR system (TIM Trio, Siemens, Medical Solutions). Imaging delayed enhancement was started 15 minutes after application of contrast material. A SS IR turboFLASH was performed at 3.0 Tesla and compared with a segmented IR turboFLASH sequence at 1.5 and at 3.0 Tesla. The IR turboFLASH sequence at 1.5 Tesla served as reference method. Infarct volumes, contrast/noise ratio (CNR) of infarcted and normal myocardium were compared with the reference method. RESULTS: The Single-Shot IR turboFLASH technique allows imaging 9 slices during a single breath-hold. The CNR between infarction and normal myocardium of the reference method was 6.4 at 1.5 Tesla. The mean value of CNR of the IR turboFLASH sequence was 7.3 at 3.0 Tesla for the single-shot technique and 14.1 at 3.0 Tesla for the segmented technique. No significant difference was found for the CNR values of the reference technique at 1.5 Tesla and the single-shot technique at 3.0 Tesla, however for the comparison of the segmented technique at 1.5 and at 3 Tesla (P = 0.0001). The correlation coefficients of the infarct volumes, determined with the Single-Shot IR turboFLASH and the segmented IR turboFLASH technique at 3.0 compared with the reference method, were r = 0.95 (P < 0.0001) and r = 0.95 (P < 0.0001). CONCLUSION: The loss of CNR, which is caused by replacement of the segmented technique by the single-shot technique, is completely compensated by the approximately 2-fold CNR increase at the higher field strength. The IR turboFLASH technique at 3.0 Tesla IR can be used as a single-shot technique with acquisition of 9 slices during a single breath-hold without loss of diagnostic accuracy compared with the segmented technique at 1.5 Tesla.     

心脏MR反转恢复序列在心肌梗死中的临床应用

目的分析磁共振反转时间(TI)的反转恢复技术的原理及特性,探讨其在心肌梗死中判断心肌存活的临床应用价值及相关注意事项。方法回顾性分析经反转时间的反转恢复技术获得的磁共振心肌梗死图像30例并总结其图像特点。结果在反转时间的反转恢复技术比较其图像质量及心肌与血池对比程度,显示对于坏死心肌判断TI时间的选择,TI=280～320 ms时图像质量最佳。结论在磁共振心肌活性成像的临床应用中,应恰当、合理地选择反转时间的反转恢复技术才能获得最佳的心肌与血池对比的图像,才更利于心肌梗死的诊断与鉴别诊断。     

Single-shot fluid attenuated inversion recovery (FLAIR) magnetic resonance imaging of the bladder

The purpose of this study was to reduce artifacts and increase imaging speed in fluid-attenuated inversion recovery (FLAIR) imaging of the urinary bladder. An existing half-Fourier, single-shot fast spin-echo imaging sequence was modified to allow presaturation with a non-slice-selective inversion recovery pulse (NSI SSFLAIR). Four independent, blinded readers rated severity of bladder artifacts and image quality in six normal male volunteers. NSI SSFLAIR effectively suppressed bladder urine signal in all six cases using a TI of 2900-3100 msec. Although NSI SSFLAIR images were noisier than standard fast spin-echo images, imaging time was only 10 seconds per slice location. Furthermore, perceived image sharpness was only minimally reduced, and conspicuity of the seminal vesicles and peripheral zone of the prostate were nearly equivalent. NSI SSFLAIR provides rapid T2-weighted imaging of the bladder wall and perivesicular tissues with nearly complete negation of signal from urine in the bladder.     

Phase-sensitive inversion recovery single-shot balanced steady-state free precession for detection of myocardial infarction during a single breathhold

RATIONALE AND OBJECTIVES: We sought to show that phase-sensitive detection and a single-shot technique allow imaging of the heart for detection of myocardial infarction during a single breathhold without adaptation of the inversion time. MATERIALS AND METHODS: Thirty-five patients at 2 weeks to 3 months after Q-wave myocardial infarction were examined on a 1.5-T MR system 10 minutes after the administration of a double-dose extravascular contrast agent. In order to determine the optimal inversion recovery time (TI), a TI scout sequence was performed. An IR-turboFlash sequence with optimized TI was used as standard of reference. A phase-sensitive inversion recovery (PSIR) single-shot TrueFISP sequence, which allows imaging of nine slices during one breathhold (TR/TE/FA/BW: 2.2 ms/1.1 ms/60 degrees , 8 degrees /1220 Hz/Px) was used with a nominal TI of 200 ms. Spatial resolution was identical for both techniques: 1.3 mm x 1.8 mm x 8 mm. Infarct volumes, area of infarction on a selected slice, and scan time for imaging delayed contrast enhancement (DCE) were compared. RESULTS: The mean values for the time of imaging DCE were 10 minutes 43 seconds for the IR turboFLASH and 17 seconds (P<.001) for the PSIR single-shot TrueFISP sequence. No significant difference was found for the mean values of the infarct volumes with 18.7 ml (IR turboFLASH) and 17.3 ml (PSIR single-shot TrueFISP). The values for the correlation coefficients of the infarct volumes and infarct areas of the two different techniques were r=0.95 (P<.004) and r=0.97 (P<.002). The regression equations were y=0.76+0.92*x and y=0.07+0.93*x, respectively. CONCLUSIONS: PSIR single-shot TrueFISP allows for accurate identification of myocardial infarction during a single breathhold with reduction of scan time by a factor of 38.     

Salvage assessment with cardiac MRI following acute myocardial infarction underestimates potential for recovery of systolic strain

Objectives

Our aim was to evaluate the relationship between the degree of salvage following acute ST elevation myocardial infarction (STEMI) and subsequent reversible contractile dysfunction using cardiac magnetic resonance (CMR) imaging.

Methods

Thirty-four patients underwent CMR examination 1–7 days after primary percutaneous coronary intervention (PPCI) for acute STEMI with follow-up at 1 year. The ischaemic area-at-risk (AAR) was assessed with T2-weighted imaging and myocardial necrosis with late gadolinium enhancement. Myocardial strain was quantified with complementary spatial modulation of magnetisation (CSPAMM) tagging.

Results

Ischaemic segments with poor (<25 %) or intermediate (26–50 %) salvage index were associated with worse Eulerian circumferential (Ecc) strain immediately post-PPCI (?9.1 %?±?0.6, P?=?0.033 and ?11.8 %?±?1.3, P?=?0.003, respectively) than those with a high (51–100 %) salvage index (?14.4 %?±?1.3). Mean strain in ischaemic myocardium improved between baseline and follow-up (?10.1 %?±?0.5 vs. ?16.2 %?±?0.5 %, P?<?0.0001). Segments with poor salvage also showed an improvement in strain by 1 year (?9.1 %?±?0.6 vs. ?15.3 %?±?0.6, P?=?0.033) although they remained the most functionally impaired.

Conclusions

Partial recovery of peak systolic strain following PPCI is observed even when apparent salvage is less than 25 %. Late gadolinium enhancement (LGE) may not equate to irreversibly injured myocardium and salvage assessment performed within the first week of revascularisation may underestimate the potential for functional recovery.

Key Points

? MRI can measure how much myocardium is damaged after a heart attack. ? Heart muscle that appears initially non-viable may sometimes partially recover. ? Enhancement around the edges of infarcts may resolve over time. ? Evaluating new cardio-protective treatments with MRI requires appreciation of its limitations.     

Artifact suppression in imaging of myocardial infarction using B1-weighted phased-array combined phase-sensitive inversion recovery.

Regions of the body with long T1, such as cerebrospinal fluid (CSF), may create ghost artifacts on gadolinium-hyperenhanced images of myocardial infarction when inversion recovery (IR) sequences are used with a segmented acquisition. Oscillations in the transient approach to steady state for regions with long T1 may cause ghosts, with the number of ghosts being equal to the number of segments. B1-weighted phased-array combining provides an inherent degree of ghost artifact suppression because the ghost artifact is weighted less than the desired signal intensity by the coil sensitivity profiles. Example images are shown that illustrate the suppression of CSF ghost artifacts by the use of B1-weighted phased-array combining of multiple receiver coils.     

Late gadolinium enhancement of acute myocardial infarction in mice at 7T: cine-FLASH versus inversion recovery

Purpose

To investigate myocardial infarction (MI), late gadolinium (Gd) enhancement (LGE), cardiovascular magnetic resonance imaging (CMRI) is used as the current gold standard for the in vivo diagnosis in patients and preclinical studies. While inversion recovery (IR) fast gradient echo LGE imaging is the preferred technique at clinical field strengths it remains to be investigated which is the best sequence at higher field strength. We therefore compared the IR technique against cine fast low shot angle (cine‐FLASH) for the quantification of MI size in mice at 7T in vivo.

Materials and Methods

Five mice were used to optimize cine‐FLASH and IR parameters. Nine mice were subsequently imaged with optimized parameters using both techniques 2–3 days after MI and ≈30 minutes post Gd injection.

Results

The difference in infarct size values was within 3.3% between the two CMRI techniques and within 7.5% of histological values by Bland–Altman analysis. Contrast‐to‐noise‐ratio between infarcted and normal tissue as well as blood was higher for cine‐FLASH with the additional benefit of a 2‐time‐fold shorter scan time than with the IR method. Furthermore, left ventricular function/volumes could be calculated from cine‐FLASH images before as well as after Gd injection.

Conclusion

In conclusion, cine‐FLASH LGE MRI represents an attractive alternative to IR LGE MRI for infarct size assessment in mice at high field strengths because it provides similar accuracy while being more robust, faster, and less user dependent. J. Magn. Reson. Imaging 2010;32:878–886. © 2010 Wiley‐Liss, Inc.     

Dynamic contrast-enhanced myocardial perfusion imaging using saturation-prepared TrueFISP

PURPOSE: To develop and test a saturation-recovery TrueFISP (SR-TrueFISP) pulse sequence for first-pass myocardial perfusion imaging. MATERIALS AND METHODS: First-pass magnetic resonance imaging (MRI) of Gd-DTPA (2 mL) kinetics in the heart was performed using an SR-TrueFISP pulse sequence (TR/TE/alpha = 2.6 msec/1.4 msec/55 degrees ) with saturation preparation TD = 30 msec before the TrueFISP readout. Measurements were also performed with a conventional saturation-recovery TurboFLASH (SRTF) pulse sequence for comparison. RESULTS: SR-TrueFISP images were of excellent quality and demonstrated contrast agent wash-in more clearly than SRTF images. The signal increase in myocardium was higher in SR-TrueFISP than in SRTF data. Precontrast SNR and peak CNR were not significantly different between both sequences despite 57% improved spatial resolution for SR-TrueFISP. CONCLUSION: SR-TrueFISP first-pass MRI of myocardial perfusion leads to a substantial improvement of image quality and spatial resolution. It is well suited for first-pass myocardial perfusion studies at cardiovascular MR systems with improved gradient hardware.     

心脏MR反转恢复序列在判定心肌活性中的临床应用

目的探讨磁共振反转恢复序列以不同反转时间成像在判定心肌活性中的临床应用。方法 32例临床证实无心肌梗死患者均经胸部反转恢复序列磁共振成像。所有患者按不同的反转时间(TI)分为两组,即A组:TI介于280～320ms;B组:TI<280ms和TI>320 ms。获自两组不同TI心肌活性的磁共振成像资料是由两名经验丰富的影像医师综合评价和回顾性分析的。结果两组间图像质量及心肌与血池对比程度比较有显著性差异,A组明显优于B组(P<0.05)。结论在采用反转恢复序列进行心脏磁共振成像中,选择合适的TI(280～320 ms)可获得最佳的心肌与血池对比图像,为临床尽早明确诊断心脏病提供可靠依据。     

Quantitative dynamic contrast-enhanced MRI in tumor-bearing rats and mice with inversion recovery TrueFISP and two contrast agents at 4.7 T

PURPOSE: To characterize tumor vascularization by dynamic-contrast enhanced (DCE) MRI using low and medium molecular weight paramagnetic contrast agents (CA) and inversion recovery (IR) true fast imaging with steady state precession (TrueFISP) in tumor-bearing rats and mice. MATERIALS AND METHODS: T(1) mapping was performed using IR True FISP in phantoms and in vivo at 4.7 T and validated with a segmented IR gradient-echo (IR GE) method. CA concentration in DCE-MRI studies in vivo was calculated from time-series T(1) maps using the CAs GdDOTA and P792 (low and medium molecular weight, respectively). Standard vascular input functions (VIFs) were measured in the jugular veins and were used for modeling of the CA kinetics with a two-compartment model. In rat breast tumors, vascular permeability (transfer constant K(trans)), fractional plasma volume v(p), and fractional leakage space v(e) were quantified and parametric maps were generated. RESULTS: The IR TrueFISP T(1) was slightly underestimated in phantoms and overestimated in vivo (10%) with respect to IR GE. VIFs showed only small interindividual variation. Mean K(trans) values were 0.062 +/- 0.017 min(-1) for GdDOTA and 0.015 +/- 0.005 min(-1) for P792 (N = 12). Mean v(e) and v(p) values were 0.15 +/- 0.04 (0.09 +/- 0.03) and 0.04 +/- 0.01 (0.03 +/- 0.01) for GdDOTA (P792). CONCLUSION: DCE-MRI with IR TrueFISP provided absolute values for K(trans), v(p), and v(e). Direct comparison between GdDOTA and P792 revealed significant differences in the VIF, model-fit-quality, permeability, leakage space, and plasma volume. The larger molecular weight CA P792 appears to be better for measuring tumor vascular parameters.     

Role of first pass and delayed enhancement in assessment of segmental functional recovery after acute myocardial infarction

Purpose

Assessing myocardial viability is crucial in decision making and prognostic restratification after acute myocardial infarction (MI). A number of noninvasive imaging modalities have been employed in viability identification, but contrast-enhanced magnetic resonance (MR) imaging has been shown to be extremely accurate because of its transmural resolution and precise definition of microvascular obstruction. Our purpose was to assess functional recovery after acute MI, with special focus on the role of infarct transmurality and microvascular obstruction.

Materials and methods

Forty-six consecutive patients with first acute MI, reperfused by primary percutaneous transluminal coronary angioplasty (PTCA) (n=40) or fibrinolysis (n=6), underwent MR imaging within the first week to assess oedema, microvascular obstruction, function and viability and then again after 4?C6 months to assess functional recovery and scar.

Results

At first MR examination, postcontrast images were analysed according to three patterns, based on a combination of first-pass and delayed-enhancement data: pattern 1 (normal first pass and late hyperenhancement <50% thickness) identified viable myocardium, whereas pattern 2 (late hyperenhancement >50% thickness, with or without first-pass perfusion defect) and pattern 3 (perfusion defect at first pass and late hypoenhancement) recognised nonviable myocardium, with 93% sensitivity, 75% specificity, 92% positive predictive value and 78% negative predictive value for identifying viable tissue. Furthermore, by dividing pattern 2 into two subpatterns, 2A and 2B, based on absence or presence of microvascular obstruction in >50% transmural infarcts, we were able to better identify the segments without recovery or that were nonviable with a 1.39 relative risk of failed recovery.

Conclusions

After acute MI, not all infarcts with transmurality >50% can be considered nonviable; microvascular obstruction detected at first pass can help to better stratify these cases.     

Single-shot spiral image acquisition with embedded z-shimming for susceptibility signal recovery

PURPOSE: To efficiently and effectively recover the susceptibility-induced signal losses for functional MRI (fMRI) experiments. MATERIALS AND METHODS: The signal losses near air/tissue interfaces at the ventral brain regions introduce difficulties in the neuroimaging studies concerned with brain functions such as memory, emotion, and olfaction processes. The z-shimming technique has been introduced in fMRI image acquisition to recover such losses. One significant drawback of such an approach is its time consuming nature. In this report, a single-shot spiral imaging method, which combines spiral-in and spiral-out acquisitions along with embedded z-shimming gradient, was proposed and implemented to achieve signal recovery without sacrificing temporal resolution. RESULTS: Using the proposed method, final images were shown in the ventral brain regions. The images were acquired with a throughput of 16 slices/second and demonstrated effectiveness and efficiency in signal recovery near air/tissue interfaces. CONCLUSION: Uniform recovery can be achieved efficiently near air/tissue interfaces where susceptibility-induced spatial gradients are pronounced. We anticipate that our method would be well suited for fMRI studies involving the ventral brain areas.     

磁共振FAIR灌注成像技术在急性脑梗死中的临床研究进展

急性脑梗死是一类发病率、致残率和致死率均较高的疾病,急性脑梗死前期脑血流灌注即会发生变化,反映在影像学上即是缺血半暗带的演变.其相当于潜在可挽救的缺血组织,因此了解急性脑梗死血流灌注的变化是研究治疗的关键.多种影像学技术可用于脑血流灌注的检测,但其都具有电离辐射,操作复杂,加之对比剂副作用,广泛应用受到一定限制.近年,MRI血流敏感性交替反转恢复(flowsensitive alternating inversion recovery,FAIR)技术得到了快速发展,它无创,不需对比剂,可重复操作并能敏感地反映梗死前期脑血流灌注的变化.因此,本文就最近几年有关急性脑梗死血流灌注变化的FAIR研究概况加以综述,为本病的临床诊治及进一步研究提供参考.     

Gated magnetic resonance imaging for assessment of cardiac function and myocardial infarction

Gated magnetic resonance imaging (MRI) is a promising noninvasive imaging modality capable of evaluating cardiac function and blood flow in the great vessels. MRI detects acute and chronic myocardial infarctions in experimental animals and in man.     

Measurement of human myocardial perfusion by double-gated flow alternating inversion recovery EPI.

This paper presents a flow-sensitive alternating inversion recovery (FAIR) method for measuring human myocardial perfusion at 1.5 T. Slice-selective/non-selective IR images were collected using a double-gated IR echoplanar imaging sequence. Myocardial perfusion was calculated after T1 fitting and extrapolation of the mean signal difference SI(Sel - SI(NSel). The accuracy of the method was tested in a porcine model using graded intravenous adenosine dose challenge. Comparison with radiolabeled microsphere measurements showed a good correlation (r = 0.84; mean error = 20%, n = 6) over the range of flows tested (0.9-7 ml/g/min). Applied in humans, this method allowed for the measurement of resting myocardial flow (1.04+/-0.37 ml/g/min, n = 11). The noise in our human measurements (SE(flow) = 0.2 ml/g/min) appears to come primarily from residual respiratory motion. Although the current signal-to-noise ratio limits our ability to measure small fluctuations in resting flow accurately, the results indicate that this noninvasive method has great promise for the quantitative assessment of myocardial flow reserve in humans.