Steady-state free precession sequences in myocardial first-pass perfusion MR imaging: comparison with TurboFLASH imaging

The aim of this study was to compare the image quality of a saturation-recovery gradient-recalled echo (GRE; TurboFLASH) and a saturation-recovery SSFP (SR-TrueFISP) sequence for myocardial first-pass perfusion MRI. Eight patients with chronic myocardial infarction and 8 volunteers were examined with a TurboFLASH (TR 2.1 ms, TE 1 ms, FA 8°) and a SR-TrueFISP sequence (TR 2.1 ms, TE 0.9 ms, FA, 50°) on a 1.5 T scanner. During injection of 0.05 mmol/kg BW Gd-DTPA at 4 ml/s, three short axis slices (8 mm) of the left ventricle (LV) were simultaneously scanned during breath-hold. Maximum signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) between infarcted and normal myocardium, and percentage signal intensity change (PSIC) were measured within the LV lumen and in four regions of the LV myocardium for the three slices separately. For the LV lumen, SR-TrueFISP was superior in SNR and PSIC (factor 3.2 and 1.6, respectively). Mean maximum SNR, PSIC, and CNR during peak enhancement in the LV myocardium were higher for SR-TrueFISP compared with TurboFLASH (factor 2.4, 1.25, and 1.24, respectively). The SNR was higher in the septal portion of the ventricle than in anterior/posterior and lateral regions. The SR-TrueFISP provides higher SNR and improves image quality compared with TurboFLASH in first-pass myocardial perfusion MRI.     

Assessment of myocardial viability using delayed enhancement magnetic resonance imaging at 3.0 Tesla

OBJECTIVE: Cardiac magnetic resonance imaging (MRI) at 3.0 T has recently become available and potentially provides a significant improvement of tissue contrast in T1-weighted imaging techniques relying on Gd-based contrast enhancement. Imaging at high-field strength may be especially advantageous for methods relying on strong T1-weighting and imaging after contrast material administration. The aim of this study was to compare cardiac delayed enhancement (DE) MRI at 3.0 T and 1.5 T with respect to image quality, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) between infarcted and normal myocardium. MATERIALS AND METHODS: Forty consecutive patients with history of myocardial infarction were examined at 3.0 T (n = 20) or at 1.5 T (n = 20). Myocardial function was assessed using cine steady-state-free-precession (SSFP) sequences (TR 3.1 milliseconds, TE 1.6 milliseconds, flip angle 70 degrees , and a matrix of 168 x 256 at 1.5 T and TR 3.4 milliseconds, TE 1.7 milliseconds, flip angle 50 degrees and a matrix of 168 x 256 at 3.0 T), acquired in long- and short-axes views. DE images were obtained 15 minutes after the administration of 0.15 mmol of Gd-DTPA/kg body weight using a segmented inversion recovery prepared gradient echo sequence at 1.5 T (TR 9.6 milliseconds, TE 4.4 milliseconds, flip angle 25 degrees , matrix 160 x 256, bandwidth 140 Hertz/pixel) and at 3.0 T (TR 9.8 milliseconds, TE 4.3 milliseconds, flip angle 30 degrees , matrix 150 x 256, bandwidth 140 Hertz/pixel). For image analysis, standardized SNR and CNR measurements were performed in infarcted and remote myocardial regions. Two independent observers rated image quality on a 4-point scale (0 = poor image quality, 1 = sufficient image quality, 2 = good image quality, 3 = excellent image quality). RESULTS: High diagnostic image quality was obtained in all patients. Rating of mean image quality was 2.2 +/- 0.8 at 1.5 T and 2.5 +/- 0.6 at 3.0 T (P = 0.012) for observer 1 and 2.2 +/- 0.7 at 1.5 T and 2.6 +/- 0.6 at 3.0 T (P = 0.003) for observer 2, respectively. Interobserver agreement was good (kappa = 0.68 at 1.5 T and 0.78 at 3.0 T). SNR measurements yielded a mean SNR of 37.8 +/- 13.9/22.9 +/- 6.0 in infarcted myocardium (P < 0.001) and 5.6 +/- 2.2/5.9 +/- 2.4 in normal myocardium (P = 0.45) at 3.0 T/1.5 T, respectively. CNR measurements revealed mean values of 32.4 +/- 13.0/16.7 +/- 5.4 (P< 0.001) at 3.0 T/1.5 T, respectively. CONCLUSIONS: Delayed enhancement MRI at 3.0 T is feasible and provides superior image quality compared with 1.5 T. Furthermore, using identical contrast doses, increased SNR and CNR values were recorded at 3.0 T.     

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.     

3-Tesla MRI for the evaluation of myocardial viability: a comparative study with 1.5-Tesla MRI

PURPOSE: We compared 3-Tesla (3-T) and 1.5-Tesla (1.5-T) cardiac magnetic resonance imaging (MRI) for the assessment of myocardial viability in nearly identical experimental conditions. MATERIALS AND METHODS: Thirty-five patients (mean age 63+/-11; 94.2% men) submitted to primary coronary angioplasty underwent both 3-T and 1.5-T cardiac MRI, which was considered the gold standard. Comparison was performed on the basis of the same viability imaging protocol, which included resting cine-MR [balanced fast-field echo (B-FFE) sequence] followed by contrast-enhanced MR to evaluate perfusion and delayed enhancement (DE). We then performed functional index measurements and visual estimation of kinesis, perfusion and DE referring to a 5-point scale. Image quality was assessed on the basis of signal to noise ratio (SNR) and contrast to noise ratio (CNR). RESULTS: We found nonsignificant differences between the two scanners (P=NS) in measuring the functional and viability parameters. Myocardial SNR was significantly higher with 3-T MRI compared with 1.5-T MRI (61.3% gain). Even though a loss of CNR was recorded in B-FFE and in first-pass perfusion sequences (12.4% and 23.7%, respectively), on DE images, we quantified the increase of SNR and CNR of infarction of 387.8% and 330%, respectively. CONCLUSIONS: We found that 3-T MRI showed high concordance with 1.5-T MRI in the evaluation of functional and viability parameters and provided better evidence of damaged myocardium.     

ACUT2E TSE-SSFP: a hybrid method for T2-weighted imaging of edema in the heart.

ACUT(2)E TSE-SSFP is a hybrid between steady state free precession (SSFP) and turbo spin echo (TSE) for bright-blood T2-weighted imaging with signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) similar to dark-blood TSE. TSE-SSFP uses a segmented SSFP readout during diastole with 180 degrees pulses following a 90 degrees preparation. The 180 degrees refocusing pulses make TSE-SSFP similar to TSE but TSE-SSFP uses gradient moment nulling, whereas TSE uses gradient crushing. TSE-SSFP produced T2-weighted images with minimal T1 weighting. TSE-SSFP and TSE had similar SNR (155.9 +/- 6.0 vs 160.9 +/- 7.0; P = NS) for acute myocardial infarction (MI) and twice the SNR of T2-prepared SSFP (73.1 +/- 3.4, P < 0.001). TSE-SSFP and TSE had approximately double the CNR of T2-prepared SSFP for differentiating acute MI from normal myocardium. Imperfect blood suppression, present in all animals on some TSE images, was a problem eliminated by TSE-SSFP and T2-prepared SSFP.     

Value of subtraction technique in Gd-DTPA-enhanced magnetic resonance angiography of the thoracic aorta.

AIM: To assess routine image subtraction in 3D gadopentate dimeglumine (Gd-DTPA)-enhanced magnetic resonance (MR) angiography of the thoracic aorta. MATERIALS AND METHODS: This was a prospective study of 22 consecutive patients referred for magnetic resonance imaging (MRI) of the thoracic aorta. All patients had 3D MR aortography (TR/TE/FA; 5/2 ms/25 degrees ) performed before and after bolus intravenous injection of Gd-DTPA. The Gd-DTPA enhanced and unenhanced data sets were subtracted and maximum intensity projections (MIP) projections of the thoracic aorta were performed. The standard unsubtracted MIP images were initially evaluated. These were then reviewed together with the subtracted images to assess for additional diagnostic information. Signal to noise ratios (SNR) and contrast to noise ratios (CNR) were measured. RESULTS: In four cases there was mild image degradation due to patient movement. In no case did subtraction alter the diagnosis. The mean SNR in the unsubtracted MIP images was 10.8 +/- 4.0 (median 11.1) and on the subtracted images was 21.2 +/- 9.9 (median 20.7;P < 0.0001). The mean aorta-to-mediastinal fat CNR was 3.9 +/- 2.8 (median 3.9) on the unsubtracted images and 15.0 +/- 10.6 (median 13) on the subtracted images (P < 0.0001). The mean aorta-to-vertebral body CNR was 5.2 +/- 3.1 (median 4.4) on the unsubtracted images and 15.1 +/- 9.3 on the subtracted images (P < 0.0001). CONCLUSION: Image subtraction significantly improved both the SNR and CNR, but did not alter the final diagnosis, and does not appear warranted in routine practice.     

Blood pool agent strongly improves 3D magnetic resonance coronary angiography using an inversion pre-pulse.

The ability of a blood pool contrast agent to enhance MR coronary angiography was defined. The proximal coronary vessels of pigs were imaged before and after administration of Gd-DTPA bound covalently to bovine serum albumin (0.2 mmol/ kg). The contrast agent resulted in a reduction of the blood T1 value to 33+/-5 msec, as determined in vivo with a Look-Locker technique. Both 2D and 3D imaging techniques were performed. An inversion pulse suppressed the signal of nonblood tissue postcontrast. After contrast agent administration, in the 3D data set the signal-to-noise ratio (SNR) of blood and contrast-to-noise ratio (CNR) of blood to myocardium were improved by factors of 2.0+/-0.2 and 15+/-8, respectively (P < 0.05). Postcontrast, the 3D acquisition was superior to the 2D technique in terms of spatial resolution, SNR of blood, and CNR of blood to myocardium. The high contrast of the 3D data set allowed for direct and rapid display of coronary arteries using a "closest vessel projection."     

Quantification of myocardial perfusion with FAST sequence and Gd bolus in patients with normal cardiac function

The present study reports on a new calibration of the magnetic resonance imaging (MRI) signal intensity of a fast gradient-echo sequence used for in vivo myocardial perfusion quantification in patients. The signal from a FAST sequence preceded by a arrhythmia-insensitive magnetization preparation was calibrated in vitro using tubes filled with various gadolinium (Gd) solutions. Single short-axis views of the heart were obtained in patients (n = 10) with normal cardiac function. Myocardial and blood signal intensity were converted to concentration of Gd according to the in vitro calibration curve and fitted by a one-compartment model. K1 [first-order transfer constant from the blood to the myocardium for the gadolinium-diethylenetriamine-pentaacetic acid (Gd-DTPA)] and Vd (distribution volume of Gd-DTPA in myocardium) obtained from the fit of the MRI-derived perfusion curves were 0.72+/-0.22 (mL/min/g) and 15.3+/-5.22%. These results were in agreement with previous observations on animals and demonstrated that a reliable measurement of myocardial perfusion can be obtained by MRI in patients with an in vitro calibration procedure.     

Delayed gadolinium-enhanced magnetic resonance imaging (dGEMRIC) of hip joint cartilage: better cartilage delineation after intra-articular than intravenous gadolinium injection

PURPOSE: To investigate and compare delayed gadolinium (Gd-DTPA)-enhanced magnetic resonance imaging (MRI) of cartilage (dGEMRIC) in the hip joint using intravenous (i.v.) or ultrasound-guided intra-articular (i.a.) Gd-DTPA injection. MATERIAL AND METHODS: In 10 patients (50% males, mean age 58 years) with clinical and radiographic hip osteoarthritis (OA; Kellgren score II-III), MRI of the hip was performed twice on a clinical 1.5T MR scanner: On day 1, before and 90-180 min after 0.3 mmol/kg body weight i.v. Gd-DTPA and, on day 8, 90-180 min after ultrasound-guided i.a. injection of a 4 mmol/l Gd-DTPA solution. Coronal STIR, coronal T1 fat-saturated spin-echo, and a cartilage-sensitive gradient-echo sequence (3D T1 SPGR) in the sagittal plane were applied. RESULTS Both the post-i.v. and post-i.a. Gd-DTPA images showed significantly higher signal-to-noise (SNR) and contrast-to-noise (CNR) in the joint cartilage compared to the non-enhanced images (P < 0.002). I.a. Gd-DTPA provided significantly higher SNR and CNR compared to i.v. Gd-DTPA (P < 0.01). Furthermore, a better delineation of the cartilage in the synovial/cartilage zone and of the chondral/subchondral border was observed. CONCLUSION: The dGEMRIC MRI method markedly improved delineation of hip joint cartilage compared to non-enhanced MRI. The i.a. Gd-DTPA provided the best cartilage delineation. dGEMRIC is a clinically applicable MRI method that may improve identification of early subtle cartilage damage and the accuracy of volume measurements of hip joint cartilage.     

Magnetic resonance imaging of myocardial infarction using albumin-(Gd-DTPA), a macromolecular blood-volume contrast agent in a rat model

Magnetic resonance (MR) contrast enhancement of acute myocardial infarction was studied in rats using albumin-(Gd-DTPA), a paramagnetic macromolecule with prolonged intravascular retention after intravenous injection. Histologic examination and distribution measurements of radiolabeled microspheres confirmed induction of regional myocardial infarction after ligation of the left coronary artery. ECG-gated spin-echo images at 2.0 Tesla, employing short, T1-weighted pulse sequence settings, demonstrated time-persistent and significant (P less than .05) enhancement of normal myocardium (66%) and an even greater enhancement of the infarcted area (100%), for as long as 60 minutes after injection of 160 mg/kg albumin-(Gd-DTPA). The contrast difference between normal and infarcted myocardium was increased significantly (P less than .05) after administration of albumin-(Gd-DTPA). The prolonged enhancing effects of albumin-(Gd-DTPA) on MR images are useful for evaluating regional differences in blood volume and capillary integrity between normal and infarcted myocardium.     

Diagnostic value of late gadolinium-enhanced MRI and first-pass dynamic MRI for predicting functional recovery in patients after acute myocardial infarction

Purpose The aim of this study was to determine the comparative diagnostic values of late gadolinium-enhanced magnetic resonance imaging (MRI) and first-pass dynamic MRI for predicting functional recovery of regional myocardial contraction in patients early after acute myocardial infarction. Materials and methods First-pass and late-enhanced MRI were performed in 18 patients 5.5 ± 2.5 days after the onset of myocardial infarction. Images analysis was performed using a 12-segment model. Regional systolic wall thickening (SWT) was measured on cine-MRI obtained 273 ± 130 days later. Results Late-enhanced MRI revealed hyperenhancement in all patients, whereas hypoenhancement on first-pass MRI was observed in 67% (12/18) of the patients. The area under the receiver operating characteristics curve was 0.86 for late-enhanced MRI and 0.74 for first-pass MRI (P = 0.27). First-pass MRI was useful for predicting functional recovery of the segments that showed hyperenhancement of >50% of tissue on late-enhanced MRI. In these segments, preserved SWT was observed in 15 of 33 segments (45%) with first-pass hypoenhancement of ≤50% of tissue, but in only 2 of 22 segments (9%) with first-pass hypoenhancement of >50% of tissue. Conclusion Whereas the diagnostic capability of first-pass MRI alone is limited, complementary use of first-pass MRI can enhance the diagnostic performance of late-enhanced MRI because hypoenhancement during first-pass imaging is more specific to nonviable myocardium. An abstract of this article was presented at the Japan Radiological Society spring meeting in 2002     

Quantitation of reperfused myocardial infarction by Gd-DOTA-enhanced magnetic resonance imaging. An experimental study.

Because there is evidence that myocardial infarct size is modified by coronary artery reperfusion, an ex vivo experimental model of myocardial infarction was developed to determine the influence of the timing of gadolinium-tetraazacyclododecane tetraacetic acid (Gd-DOTA)-enhanced magnetic resonance imaging (MRI) on the accuracy of infarct size quantitation. Eighteen dogs underwent a 2-hour coronary occlusion followed by 1 (n = 6), 6 (n = 6), or 48 (n = 6) hours of reperfusion. Gd-DOTA was injected 10 minutes before the dogs were killed. T1 (SE 250/26) and T2 (SE 1500/78) weighted images were performed on excised hearts. Gd-DOTA concentration was measured in myocardium by atomic emission spectrometry, and correlated with myocardial blood flow evaluated by radioactive microspheres. All dogs presented with myocardial infarction (mean size 20.4% +/- 3.1% of the left ventricle), and a corresponding area of increased signal intensity on T1-weighted MR images. In none of the three groups did the area of high signal intensity correlate with the ischemic area. By contrast, after 6 and 48 hours of reperfusion, the high signal intensity area (17.9% +/- 2.4%) closely matched the area of nonreversible jeopardized tissue (16.4% +/- 2.5%), as determined on tetrazolium-stained heart slices. Although a noreflow phenomenon was observed in the jeopardized tissue, Gd-DOTA concentration was higher in the subendocardial central ischemic zone than in normally perfused myocardium. Gd-DOTA imaging enhancement seems to be the consequence of a delayed clearance of the agent from the injured tissue. Gd-DOTA-enhanced MRI accurately quantitates the size of reperfused myocardial infarction on the ex vivo heart for more than 6 hours after the beginning of reperfusion. It remains to be determined whether the in vitro results obtained here can be applied to assess the myocardial infarct size in vivo.     

A fast navigator-gated 3D sequence for delayed enhancement MRI of the myocardium: comparison with breathhold 2D imaging

PURPOSE: To develop a rapid navigator-gated three-dimensional (3DNAV) delayed-enhancement MRI (DE-MRI) sequence for myocardial viability assessment, and to evaluate its performance with breathhold two-dimensional (2DBH) DE-MRI sequence as the reference standard. MATERIALS AND METHODS: 2DBH DE-MRI was initiated 10 minutes after contrast administration and followed by 3DNAV DE-MRI in 23 patients at 1.5 T. Comparison was performed using three qualitative criteria (image quality score, diagnostic outcome, relative diagnostic confidence score) in all patients, and three quantitative criteria (infarct volume, infarct signal-to-noise ratio [SNR(inf)], and infarct-viable myocardium contrast-to-noise ratio [CNR(inf-myo)]) in patients with hyperenhanced myocardium. RESULTS: Compared to 2DBH DE-MRI, 3DNAV DE-MRI provided slightly better image quality, the same final diagnostic outcomes, and better relative diagnostic confidence score with 79% SNR(inf) improvement (P = 0.002) and 90% CNR(inf-myo) improvement (P = 0.004) in 39% less scan time (414 +/- 118 seconds for 2DBH and 251 +/- 93 seconds for 3DNAV). The measured infarct volumes demonstrated excellent correlation (18.9 +/- 19.0 mL for 2DBH DE-MRI vs. 17.6 +/- 19.0 mL for 3DNAV DE-MRI, r(2) = 0.998, P < 0.001, N = 7) and narrow limits of agreement (-1.3 +/- 1.8 mL). CONCLUSION: 3DNAV DE-MRI provides improved image quality and similar infarct detection in less scan time compared to the standard 2DBH DE-MRI.     

Blood pool contrast agent CMD-A2-Gd-DOTA-enhanced MR imaging of infarcted myocardium in pigs.

The purpose of this study was to assess the ability of the new blood pool contrast agent meglumine-carboxymethyldextran-ethylenediamino-gadoterate (CMD-A2-Gd-DOTA) to depict acute occlusive myocardial infarction (AMI). First-pass gradient-echo and delayed spin-echo magnetic resonance imaging (MRI) was performed 5 days after induction of AMI in a pig model. MRI was correlated with pathology. First-pass imaging with CMD-A2-Gd-DOTA allowed detection of infarcted myocardium in all pigs (n = 7). The infarction was recognized as a black spot on MRI as well as on a parametric image. The signal intensity (SI) amplitudes of normal versus infarcted myocardium were 80.55 +/- 18.61 versus 8.48 +/- 15.50 on MRI and 81.62 +/- 18.50 versus 1.61 +/- 3.73 on the parametric image (both P values < 0.001. The contrast ratio between normal and infarcted myocardium was not significantly improved on spin-echo MRI, suggesting largely intact vascular integrity outside the occluded area. CMD-A2-Gd-DOTA is useful for depicting occlusive myocardial infarction by first-pass MRI. Spin-echo imaging is promising in assessing vascular integrity. J. Magn. Reson. Imaging 1999;10:170-177.     

In vitro release of vascular endothelial growth factor from gadolinium-doped biodegradable microspheres.

A drug delivery vehicle was constructed that could be visualized noninvasively with MRI. The biodegradable polymer poly(DL-lactic-co-glycolic acid) (PLGA) was used to fabricate microspheres containing vascular endothelial growth factor (VEGF) and the MRI contrast agent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). The microspheres were characterized in terms of size, drug and contrast agent encapsulation, and degradation rate. The PLGA microspheres had a mean diameter of 48 +/- 18 microm. The gadolinium loading was 17 +/- 3 microg/mg polymer and the VEGF loading was 163 +/- 22 ng/mg polymer. Electron microscopy revealed that the Gd was dispersed throughout the microspheres and it was confirmed that the Gd loading was sufficient to visualize the microspheres under MRI. VEGF and Gd-DTPA were released from the microspheres in vitro over a period of approximately 6 weeks in three phases: a burst, followed by a slow steady-state, then a rapid steady-state. Biodegradable Gd-doped microspheres can be effectively used to deliver drugs in a sustained manner, while being monitored noninvasively with MRI.     

1 M Gd-chelate (gadobutrol) for multislice first-pass magnetic resonance myocardial perfusion imaging

The aim of the study was to evaluate a 1 M gadolinium-chelate (gadobutrol) for first-pass MR myocardial perfusion examinations in patients with suspected coronary artery disease (CAD). In phantom studies, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) values of gadobutrol were compared with gadopentetate (Gd-DTPA). 25 consecutive patients with clinically suspected CAD were examined with dynamic rest/stress MR perfusion examinations using 0.05 mmol kg(-1) gadobutrol. Semi-quantitative evaluation of the myocardial perfusion was performed by calculating the myocardial perfusion reserve index (MPRI). Hypoperfused regions were correlated with data from X-ray coronary angiography. In phantom studies, SNR/CNR of gadobutrol-doped blood samples were consistently higher for all applied flip angles at concentrations < or =1.0 mmol L(-1) compared with Gd-DTPA. Assessment of 81 stress perfusion series with gadobutrol in 25 patients yielded a sensitivity of 82% and specificity of 91% for significant CAD. Combining the information from all perfusion series of one patient yielded a sensitivity of 89% and specificity of 94% on a per-vessel basis. Gadobutrol exhibited favourable signal properties in phantom studies. Rest/stress myocardial perfusion examinations using 1 M gadobutrol yielded high sensitivity and specificity in detection of malperfused areas (82% and 91%, respectively). This is comparable with recently published perfusion data using 0.5 M Gd-DTPA.     

Left ventricular postmyocardial infarction remodeling studied by combining MR-tagging with delayed MR contrast enhancement

OBJECTIVES: We sought to monitor the evolution of noninfarcted and infarcted myocardium function in the process of left ventricular (LV) remodeling after a reperfused myocardial infarction. MATERIAL AND METHODS: Pigs (n = 8) were subjected to reperfused infarction. Magnetic resonance imaging (MRI) was performed at 3 days and 8 weeks after infarction. Regional circumferential shortening (Ecc) and principal strain L1 in the infarcted, peri-infarcted, and remote myocardium were evaluated by tagged cine MRI combined with matched late enhancement data (Gadolinium-DOTA-enhanced IR-GRE) Global LV function was evaluated by cine MRI. Animals were euthanized after the second imaging session and tissue samples from the different myocardial regions were obtained for histopathologic study. RESULTS: There was a significant deterioration in Ecc between the 3-day and 8-week studies in the peri-infarcted myocardium at apex (-9.9% +/- 4.5% to -6.5 +/- 3.9; P = 0.046) whereas it remained stable for all other regions at all levels. A trend toward improvement in Ecc existed in the infarcted myocardium when infarction transmurality was less than 50% of the LV wall (-7.5% +/- 0.8% to -12.2% +/- 2.9% P = 0.06). Ecc in infarcted myocardium was significantly inferior (P < 0.002) to that in remote and peri-infarcted myocardium at the apical level (2.7% +/- 2.6% vs. -14.4% +/- 3.3% and -9.9% +/- 4.5%, respectively). Global LV function substantially deteriorated after infarction and was associated with a significant LV dilation. CONCLUSION: These results confirm the hypothesis that scarred myocardium imposes additional functional burden to the peri-infarcted myocardium.     

Time-resolved contrast-enhanced three-dimensional pulmonary MR-angiography: 1.0 M gadobutrol vs. 0.5 M gadopentetate dimeglumine

PURPOSE: To compare contrast characteristics and image quality of 1.0 M gadobutrol with 0.5 M Gd-DTPA for time-resolved three-dimensional pulmonary magnetic resonance angiography (MRA). MATERIALS AND METHODS: Thirty-one patients and five healthy volunteers were examined with a contrast-enhanced time-resolved pulmonary MRA protocol (fast low-angle shot [FLASH] three-dimensional, TR/TE = 2.2/1.0 msec, flip angle: 25 degrees, scan time per three-dimensional data set = 5.6 seconds). Patients were randomized to receive either 0.1 mmol/kg body weight (bw) or 0.2 mmol/kg bw gadobutrol, or 0.2 mmol/kg bw Gd-DTPA. Volunteers were examined three times, twice with 0.2 mmol/kg bw gadobutrol using two different flip angles and once with 0.2 mmol/kg bw Gd-DTPA. All contrast injections were performed at a rate of 5 mL/second. Image analysis included signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements in lung arteries and veins, as well as a subjective analysis of image quality. RESULTS: In patients, significantly higher SNR and CNR were observed with Gd-DTPA compared to both doses of gadobutrol (SNR: 35-42 vs.17-25; CNR 33-39 vs. 16-23; P < or = 0.05). No relevant differences were observed between 0.1 mmol/kg bw and 0.2 mmol/kg bw gadobutrol. In volunteers, gadobutrol and Gd-DTPA achieved similar SNR and CNR. A significantly higher SNR and CNR was observed for gadobutrol-enhanced MRA with an increased flip angle of 40 degrees. Image quality was rated equal for both contrast agents. CONCLUSION: No relevant advantages of 1.0 M gadobutrol over 0.5 M Gd-DTPA were observed for time-resolved pulmonary MRA in this study. Potential explanations are T2/T2*-effects caused by the high intravascular concentration when using high injection rates.     

Low tube voltage improves computed tomography imaging of delayed myocardial contrast enhancement in an experimental acute myocardial infarction model

OBJECTIVE: We sought to evaluate the influence of tube voltage on the visualization of acute myocardial infarction (MI) in cardiac multislice spiral computed tomography (MSCT). MATERIALS AND METHODS: Acute MI was induced in 12 domestic pigs by a 45-minute balloon occlusion of the left anterior descending artery. Delayed enhancement magnetic resonance imaging was performed 15 minutes after the injection of 0.2 mmol/kg Gd-DTPA. On the same day, retrospectively ECG-gated MSCT was performed at 120, 100, and 80 kV (16x0.75mm, 550mAseff.) 15 minutes after the injection of 140 mL of iopromide (1 g/iodine/kg). The pigs were killed and the hearts were excised and stained with 2,3,5-triphenyltetrazolium chloride. The area of acute MI, contrast-to-noise ratio (CNR), and percent signal difference were compared among the different imaging techniques by applying Bland-Altman plots and 2-way analysis of variance. RESULTS: On MSCT at 120, 100, and 80 kV, the respective mean acute MI sizes were 18.4+/-11.4%, 19.3+/-11.5%, and 20.5+/-11.6%. The mean MI sizes were 20.8+/-12.2% and 20.1+/-12.4% on magnetic resonance imaging and 2,3,5-triphenyltetrazolium chloride staining. Analysis of variance did not show any statistically significant differences between the different techniques with respect to the size of acute MI (P=0.9880). Comparing the different kV settings on MSCT, the highest percent signal difference (74.7+/-12.1%) and the highest CNR (6.7+/-1.8) between infarcted and healthy remote myocardium were achieved at 80 kV. CONCLUSIONS: When compared with routine scan protocols, low tube voltage MSCT allows for the assessment of the MI size with an improved CNR and contrast resolution. This technique appears to be advantageous for assessing myocardial viability from contrast enhanced late-phase MSCT.     

Gd-DTPA bolus tracking in the myocardium using T1 fast acquisition relaxation mapping (T1 FARM).

MRI methods currently used for bolus tracking in the myocardium, such as saturation recovery turbo-fast low-angle shot (FLASH) (srTFL), are limited by signal intensity (SI) saturation at high contrast agent (CA) concentrations. By using T1 fast acquisition relaxation mapping (T1 FARM), a Gd-DTPA bolus (0.075 vs. 0.025 mmol/kg) may be injected without causing saturation. This study tested the feasibility of in vivo T1 FARM bolus tracking under rest/stress conditions in seven beagles with multiple permanently occluded branches of the left anterior descending (LAD) coronary artery. Although it underestimated the myocardial perfusion reserve (MPR) measured ex vivo using radioactive microspheres (mean +/- SEM; 3.60 +/- 0.26), the MPR determined upon application of the modified Kety model (1.86 +/- 0.10) enabled distinction between normal and infarcted tissue. The partition coefficient (lambda) estimated at rest and stress using the modified Kety model underestimated ex vivo radioactive measurements in infarcted tissue (0.25 +/- 0.01 vs. 0.26 +/- 0.01 vs. 0.79 +/- 0.08 ml/g, P < 0.0001) yet was accurate in normal tissue (0.28 +/- 0.01 vs. 0.30 +/- 0.01 vs. 0.33 +/- 0.01 ml/g, P = NS). Thus, although unsuitable for myocardial viability assessment, T1 FARM bolus tracking shows potential for assessment of myocardial perfusion.