Myocardial tagging with 3D-CSPAMM

PURPOSE: To introduce a true three-dimensional (3D) tagging technique for the assessment of myocardial tissue motion. MATERIALS AND METHODS: To generate a 3D tagging grid, a complementary spatial modulation of magnetization (CSPAMM) was applied in three spatial directions. Imaging was performed using a conventional fast 3D gradient-echo sequence. For automatic analysis of the 3D-CSPAMM data set, evaluation software, based on a 3D extension of the HARP technique, was used. RESULTS: Successful application of the 3D-CSPAMM technique in healthy subjects allowed the accurate determination of quantitative 3D motion patterns in the human heart. CONCLUSION: 3D-CSPAMM may contribute to the quantification of the local 3D myocardial motion pattern throughout the cardiac cycle.     

Myocardial tagging with SSFP.

This work presents the first implementation of myocardial tagging with refocused steady-state free precession (SSFP) and magnetization preparation. The combination of myocardial tagging (a noninvasive method for quantitative measurement of regional and global cardiac function) with the high tissue signal-to-noise ratio (SNR) obtained with SSFP is shown to yield improvements in terms of the myocardium-tag contrast-to-noise ratio (CNR) and tag persistence when compared to the current standard fast gradient-echo (FGRE) tagging protocol. Myocardium-tag CNR and tag persistence were studied using numerical simulations as well as phantom and human experiments. Both quantities were found to decrease with increasing imaging flip angle (alpha) due to an increased tag decay rate and a decrease in myocardial steady-state signal. However, higher alpha yielded better blood-myocardium contrast, indicating that optimal alpha is dependent on the application: higher alpha for better blood-myocardium boundary visualization, and lower alpha for better tag persistence. SSFP tagging provided the same myocardium-tag CNR as FGRE tagging when acquired at four times the bandwidth and better tag- and blood-myocardium CNRs than FGRE tagging when acquired at equal or twice the receiver bandwidth (RBW). The increased acquisition efficiency of SSFP allowed decreases in breath-hold duration, or increases in temporal resolution, as compared to FGRE.     

Myocardial wall tagging with undersampled projection reconstruction.

Azimuthally undersampled projection reconstruction (PR) acquisition is investigated for use in myocardial wall tagging with MR using grid tags to provide increased temporal and spatial resolution. PR can provide the high-resolution images required for tagging with very few projections, at the expense of artifact. Insight is provided into the PR undersampling artifact, in the context of measuring myocardial motion with tags. For Fourier transform imaging, at least 112 phase-encodings must be collected to image tagging grids spaced 7 pixels apart. PR requires about 80 projections, a 1.4-fold reduction in scan time. Magn Reson Med 45:562-567, 2001. Published 2001 Wiley-Liss, Inc.     

Myocardial tagging with B1 insensitive adiabatic DANTE inversion sequences

A new technique, based on adiabatic delays alternating with nutations for tailored excitation (DANTE) inversion sequences, is presented for generating uniform contrast tags across the myocardial wall even in the presence of B₁ inhomogeneities. The utility of this pulse was demonstrated using a surface coil for both transmission and signal reception in phantom and animal heart tagging studies. The experimental data demonstrated uniform grid contrast over a sixfold variation of B₁ magnitude, sharp tagging profiles, and the ability to follow the cardiac wall motion through the deformation of the fine rectangular tagging grid at different phases throughout the cardiac cycle.     

Myocardial delineation via registration in a polar coordinate system

Rationale and Objectives. Cardiovascular disease is the number one cause of premature death in the western world. Analysis of cardiac function provides clinically useful diagnostic and prognostic information; however, manual analysis of function via delineation is prohibitively time consuming. This article describes a technique for analysis of dynamic magnetic resonance images of the left ventricle using a non-rigid registration algorithm. A manually delineated contour of a single phase was propagated through the dynamic sequence.

Materials and Methods. Short-axis cine magnetic resonance images were resampled into polar coordinates before all the time frames were aligned using a non-rigid registration algorithm. The technique was tested on 10 patient data sets, a total of 1,052 images were analyzed.

Results. Results of this approach were investigated and compared with manual delineation at all phases in the cardiac cycle, and with registration performed in a Cartesian coordinate system. The results correlated very well with manually delineated contours.

Conclusion. A novel approach to the registration and subsequent delineation of cardiac magnetic resonance images has been introduced. For the endocardium, the polar resampling technique correlated well with manual delineation, and better than for images registered without radial resampling in a Cartesian coordinate system. For the epicardium, the difference was not as apparent with both techniques correlating well.     

Myocardial tagging and strain analysis at 3 Tesla: comparison with 1.5 Tesla imaging

PURPOSE: To determine whether imaging at 3 T could improve and prolong the tag contrast compared to images acquired at 1.5 T in normal volunteers, and whether such improvement would translate into the ability to perform strain measurements in diastole. MATERIALS AND METHODS: Normal volunteers (N = 13) were scanned at 1.5 T (GE Signa CV/i) and 3.0 T (GE VH/i). An ECG-triggered, segmented k-space, spoiled-gradient-echo grid-tagged sequence was used during cine acquisition. Tag contrast was determined by the difference of the mean signal intensity (SI) of the tagline to the mean SI of the myocardium divided by the standard deviation (SD) of the noise (CNR(tag)). Matched short-axis (SA) slices were analyzed. Strain measurements were performed on images using a 2D strain analysis software program (harmonic phase (HARP)). RESULTS: The average CNR(tag) over the cardiac cycle was superior at 3 T compared to 1.5 T for all slices (3 T: 23.4 +/- 12.1, 1.5 T: 9.8 +/- 8.4; P < 0.0001). This difference remained significant at cycle initiation, end-systole, and the end R-R interval (at cycle termination: 3 T = 14.0 +/- 11.0 vs. 1.5 T = 4.4 +/- 3.5; P < 0.01). Strain measures were obtainable only in early systole for 1.5 T images, but were robust throughout the entire R-R interval for 3 T images. CONCLUSION: Imaging at 3 T had a significant benefit for myocardial tag persistence through the cardiac cycle. The improvement allowed strain analysis to be performed into diastole.     

A modified quadrupole gradient set for use in high resolution MRI tagging

A special purpose gradient set with a Cos(20) current distribution has been constructed for high resolution MR imaging of small samples in a clinical Signa 1.5 T scanner using the existing gradient amplifiers. The X, Y, and Z gradient coils can attain gradient field strengths of 11.3, 4.7, and 15.2 G/cm at 100 amps current, respectively, with a slew rate of 20 G/cm/ms and usable ramp time of 150 μs. Field distortions are less than 2% over the central 8 cm of the bore, suitable for high resolution tagging of isolated canine hearts.     

The combined use of Gated Cardiac Blood Pool Scanning and Myocardial Imaging with Postassium-43 in the Evaluation of Patients with Myocardial infarction.

Fourteen patients with transmural myocardial infarction were studied by gated cardiac blood pool scanning (to determine regional ventricular function) and 43-K myocardial imaging (to determine the regional distribution of myocardial perfusion). An akinetic area on the gated scan and an area of decreased tracer concentration on the 43-K image were detected. The area of reduced 43-K concentration averaged 33.5% of the left ventricular circumference which correlated (r = 0.74, p less than 0.01) with the area of infarction determined by the zone of akinesis, 34.2% of left ventricular circumference. The extent of akinesis and left ventricular ejection fraction were significantly different in those patients with left ventricular failure than in those without failure.     

Myocardial function in infarcted and remote regions early after infarction in man: Assessment by magnetic resonance tagging and strain analysis

Early after infarction in the perfusion bed of the left anterior descending coronary artery, cine MRI with spatial modulation of magnetization (SPAMM) tagging (7-mm grid) was used for short- and long-axis cardiac imaging. Two-dimensional strain analysis of triangular finite elements was performed between end-diastole and end-systole. Patients (n = 10) were compared with age-matched healthy subjects (n = 8). The anteroseptal region at midventricular level was considered representative for “infarcted” and the posterolateral region at basal level was considered “remote”. The left ventricular end-diastolic volume index was larger in the patients (69 ± 15 ml/m² versus 56 ± 4 ml/m², P < 0.05). Short-axis images showed in the infarcted region a decrease of first principal strain (greatest systolic lengthening: 1.10 ±. 06 versus 1.27 ± 0.04, P < 0.0001), and in the remote region an increase (1.48 ± 0.11 versus 1.36 ± 0.07, P < 0.025). The lateral and inferior ventricular regions at mid- and basal levels were found to function normally. Long-axis images yielded similar results. Early after infarction, regions with dysfunction, normal function, and hyperfunction can be delineated with MR tagging. The compensatory increased contraction in the remote region is possibly triggered by the Frank-Starling mechanism.     

Improved sampling of myocardial motion with variable separation tagging

A novel tagging method is introduced that increases the spatial resolution of estimates of myocardial radial thickening. The separation of adjacent parallel tag planes is customized to match the expected motion of specific regions of the heart wall. In regions in which the tags increase their separation over systole (radial thickening), the tag planes are placed close together at end diastole. In regions in which the tags decrease their separation over systole (circumferential shortening), the tags are placed farther apart so they remain detectable at end systole. With variable separation tagging (VTAG), parallel plane tagging can be used to obtain higher-resolution estimates of radial thickening and circumferential shortening simultaneously.     

Delayed enhancement in hypertrophic cardiomyopathy: comparison with myocardial tagging MRI

PURPOSE: To evaluate the relationship between delayed enhancement (DE) and regional left ventricular function in hypertrophic cardiomyopathy (HCM) using gadolinium enhancement MRI and myocardial tagging MRI. MATERIALS AND METHODS: Cine imaging, delayed enhancement imaging, and tagging MRI were performed in 25 patients with HCM. The location, pattern, and extent of DE were evaluated. Circumferential shortening (Ecc) was obtained by analyzing MR tagging images with HARP software. RESULTS: DE occurred in 21 (84%) patients with a high frequency of localization in the septum and the right ventricular attachment sites. Circumferential shortening was significantly decreased in the enhanced segments compared with nonenhanced segments (P < 0.0001). The myocardial wall was thicker in the enhanced segments than in the nonenhanced segments (P < 0.0001). However, circumferential shortening was significantly decreased in the enhanced segments of the same thickness (P < 0.0001). Circumferential shortening was more substantially impaired in the segments with focal nodular enhancement than those in the segments with ill-defined patchy enhancement (P = 0.0002). CONCLUSION: In HCM, DE is commonly found and circumferential shortening is significantly impaired in the regions with DE, regardless of the degree of myocardial hypertrophy. Focal nodular enhancement is particularly related with regional dysfunction in patients with HCM.     

DISA SPECT对心梗后骨髓干细胞移植心肌灌注和代谢的评价

目的:探讨DISASPECT在评价心肌梗死患者骨髓干细胞移植后心肌血流灌注和细胞代谢改变的价值。材料和方法:18例心肌梗死行骨髓干细胞移植治疗的患者在术前2周、术后3个月行DISA显像(18F-FDG心肌代谢显像和99Tcm-MIBI心肌灌注显像),其中4例在术后9个月再次进行复查。用目测法和半定量法分析图像。结果:①干细胞移植治疗前后99Tcm-MIBI显像和18F-FDG显像的F值分别为5.27±0.55、5.05±0.41与6.50±1.71、6.24±0.93,两者比较差异有统计学意义(P<0.05)。②18例中3例代谢靶心图面积治疗前后无明显变化,15例治疗后靶心图面积出现不同程度的恢复(83%),治疗后代谢恢复的面积占治疗前缺损面积的25.2%±4.8%。结论:心肌梗死行骨髓干细胞移植治疗后,心肌血流灌注与细胞代谢均有显著性差异;灌注结合代谢能较好地观察和评价心肌梗死行骨髓干细胞移植治疗后改善程度。     

Steady-state free precession with myocardial tagging: CSPAMM in a single breathhold.

A method is presented that combines steady-state free precession (SSFP) cine imaging with myocardial tagging. Before the tagging preparation at each ECG-R wave, the steady-state magnetization is stored as longitudinal magnetization by an alpha/2 flip-back pulse. Imaging is continued immediately after tagging preparation, using linearly increasing startup angles (LISA) with a rampup over 10 pulses. Interleaved segmented k-space ordering is used to prevent artifacts from the increasing signal during the LISA rampup. First, this LISA-SSFP method was evaluated regarding ghost artifacts from the steady-state interruption by comparing LISA with an alpha/2 startup method. Next, LISA-SSFP was compared with spoiled gradient echo (SGRE) imaging, regarding tag contrast-to-noise ratio and tag persistence. The measurements were performed in phantoms and in six subjects applying breathhold cine imaging with tagging (temporal resolution 51 ms). The results show that ghost artifacts are negligible for the LISA method. Compared to the SGRE reference, LISA-SSFP was two times faster, with a slightly better tag contrast-to-noise. Additionally, the tags persisted 126 ms longer with LISA-SSFP than with SGRE imaging. The high efficiency of LISA-SSFP enables the acquisition of complementary tagged (CSPAMM) images in a single breathhold.     

Differentiation of tumor from viable myocardium using cardiac tagging with MR imaging

We report the application of myocardial tagging by MR to define tissue planes and differentiate contractile from noncontractile tissue in a neonate with congenital cardiac rhabdomyoma. Using custom-written pulse programming software, six 2 mm thick radiofrequency (RF) slice-selective presaturation pulses (tags) were used to label the chest wall and myocardium in a star pattern in diastole, approximately 60 ms before the R-wave gating trigger. This method successfully delineated the myocardium from noncontractile tumor, providing information that influenced clinical management. This RF tagging technique allowed us to confirm the exact intramyocardial location of a congenital cardiac tumor.     

Patient acceptance of MR colonography with improved fecal tagging versus conventional colonoscopy

Objective

Conventional colonoscopy (CC) is the gold standard for colonic examinations. However, patient acceptance is not high. Patient acceptance is influenced by several factors, notably anticipation and experience. This has led to the assumption that patient acceptance would be higher in non-invasive examinations such as MR/CT colonography (MRC/CTC) and perhaps even higher without bowel preparation. The purpose of this study was to evaluate patient acceptance of MRC with fecal tagging versus CC.

Materials and methods

In a 14-month period, all patients first-time referred to our department for CC were asked to participate in the study. Two days prior to MRC, patients ingested an oral contrast mixture (barium/ferumoxsil) together with four meals each day. Standard bowel purgation was performed before CC. Before and after MRC and CC a number of questions were addressed.

Results

Sixty-four (34 men, 30 women) patients referred for CC participated in the study. 27% had some discomfort ingesting the contrast mixture, and 49% had some discomfort with the bowel purgation. As a future colonic examination preference, 71% preferred MRC, 13% preferred CC and 15% had no preference. If MRC was to be performed with bowel purgation, 75% would prefer MRC, 12% would prefer CC and 12% had no preference.

Conclusion

This study shows that there is a potential gain in patient acceptance by using MRC for colonic examination, since MRC is considered less painful and less unpleasant than CC. In addition, the results indicate that patients in this study prefer fecal tagging instead of bowel purgation.     

MR多技术扫描检测活性心肌及其和心肌声学造影对比的临床研究

目的 评价MR多技术扫描和心肌声学造影（MCE）在检测心肌灌注、判断心肌存活中的作用。资料与方法 应用MR多技术扫描对36例冠心病患者进行检查,并将结果与冠状动脉造影、MCE结果对照。结果 共有81支冠状动脉狭窄≥70％,狭窄的冠状动脉供血区域为334个（57．99％）节段。MR心肌灌注扫描见268个（46．53％）节段呈缺血改变,MR心肌活性扫描见83个（14．4l％）节段心肌梗死。以冠状动脉造影结果为标准,MR心肌灌注扫描的敏感性为80．2％,特异性为100％,总符合率为88．5％,Kappa值为0．773。定性MCE检查共有202个（35．07％）节段呈缺血改变。以冠状动脉造影结果为标准,定性MCE的敏感性为60．5％,特异性为100％,总符合率为77．1％,Kappa值为0．563。MR心肌灌注扫描所发现的缺血节段比狭窄冠状动脉的供血节段少但无统计学意义（P=0．468）,MCE所发现的缺血节段比狭窄冠状动脉的供血节段少（P=0．000）;MR心肌灌注扫描检出缺血节段比MCE检出的多（P=0．000）。结论 MR多技术扫描可清晰显示心肌缺血或梗死的位置、程度,可重复性好,与冠状动脉造影结果的一致性较高。MCE为临床提供了元创、可重复地准确测定心肌缺血的新方法,但其评价方法具有一定主观性且低估心肌缺血的范围,检查者的经验和检查方法在一定程度上影响其准确性。