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.     

Volume‐targeted and whole‐heart coronary magnetic resonance angiography using an intravascular contrast agent

Purpose

To compare volume‐targeted and whole‐heart coronary magnetic resonance angiography (MRA) after the administration of an intravascular contrast agent.

Materials and Methods

Six healthy adult subjects underwent a navigator‐gated and ‐corrected (NAV) free breathing volume‐targeted cardiac‐triggered inversion recovery (IR) 3D steady‐state free precession (SSFP) coronary MRA sequence (t‐CMRA) (spatial resolution = 1 × 1 × 3 mm³) and high spatial resolution IR 3D SSFP whole‐heart coronary MRA (WH‐CMRA) (spatial resolution = 1 × 1 × 2 mm³) after the administration of an intravascular contrast agent B‐22956. Subjective and objective image quality parameters including maximal visible vessel length, vessel sharpness, and visibility of coronary side branches were evaluated for both t‐CMRA and WH‐CMRA.

Results

No significant differences (P = NS) in image quality were observed between contrast‐enhanced t‐CMRA and WH‐CMRA. However, using an intravascular contrast agent, significantly longer vessel segments were measured on WH‐CMRA vs. t‐CMRA (right coronary artery [RCA] 13.5 ± 0.7 cm vs. 12.5 ± 0.2 cm; P < 0.05; and left circumflex coronary artery [LCX] 11.9 ± 2.2 cm vs. 6.9 ± 2.4 cm; P < 0.05). Significantly more side branches (13.3 ± 1.2 vs. 8.7 ± 1.2; P < 0.05) were visible for the left anterior descending coronary artery (LAD) on WH‐CMRA vs. t‐CMRA. Scanning time and navigator efficiency were similar for both techniques (t‐CMRA: 6.05 min; 49% vs. WH‐CMRA: 5.51 min; 54%, both P = NS).

Conclusion

Both WH‐CMRA and t‐CMRA using SSFP are useful techniques for coronary MRA after the injection of an intravascular blood‐pool agent. However, the vessel conspicuity for high spatial resolution WH‐CMRA is not inferior to t‐CMRA, while visible vessel length and the number of visible smaller‐diameter vessels and side‐branches are improved. J. Magn. Reson. Imaging 2009;30:1191–1196. © 2009 Wiley‐Liss, Inc.     

Four‐dimensional velocity‐encoded magnetic resonance imaging improves blood flow quantification in patients with complex accelerated flow

Purpose:

To evaluate the use of four‐dimensional (4D) velocity‐encoded magnetic resonance imaging (VEC MRI) for blood flow quantification in patients with semilunar valve stenosis and complex accelerated flow.

Materials and Methods:

Peak velocities (Vmax) and stroke volumes (SV) were quantified by 2D and 4D VEC MRI in volunteers (n = 7) and patients with semilunar valve stenosis (n = 18). Measurements were performed above the aortic and pulmonary valve with both techniques and, additionally, at multiple predefined planes in the ascending aorta and in the pulmonary trunk within the 4D dataset. In patients, 4D VEC MRI streamline analysis identified flow patterns and regions of highest flow velocity (4D_{max‐targeted}) for further measurements and Vmax was also measured by Doppler‐echocardiography.

Results:

In patients, 4D VEC MRI showed higher Vmax than 2D VEC MRI (2.7 ± 0.6 m/s vs. 2.4 ± 0.5 m/s, P < 0.03) and was more comparable to Doppler‐echocardiography (2.8 ± 0.7 m/s). 4D_{max‐targeted} revealed highest Vmax values (3.1 ± 0.6 m/s). SV measurements showed significant differences between different anatomical levels in the ascending aorta in patients with complex accelerated flow, whereas differences in volunteers with laminar flow patterns were negligible (P = 0.004).

Conclusion:

4D VEC MRI improves MRI‐derived blood flow quantification in patients with semilunar valve stenosis and complex accelerated flow. J. Magn. Reson. Imaging 2013;37:208–216. © 2012 Wiley Periodicals, Inc.     

Head‐to‐head comparison between delayed enhancement and percent infarct mapping for assessment of myocardial infarct size in a canine model

Purpose

To compare a novel method, percent‐infarct‐mapping (PIM), with conventional delayed enhancement (DE) of contrast for accurate myocardial viability assessment. Contrary to signal intensity (SI), the longitudinal relaxation‐rate enhancement (ΔR1) is an intrinsic parameter linearly proportional to the concentration of contrast agent (CA). Determining ΔR1 voxel‐by‐voxel, after administering an infarct‐avid CA, allows determination of per‐voxel percentage of infarcted tissue. The feasibility of generating PIM is demonstrated in canine reperfused infarction using an infarct‐avid, persistent‐CA (PCA), (Gd)(ABE‐DTTA). PIM is compared to the DE method using Gd(DTPA), and both to triphenyltetrazolium chloride (TTC) staining histochemistry.

Materials and Methods

In six dogs, 48 hours following closed‐chest, 180‐minute coronary occlusion, DE imaging was carried out. PCA was administered immediately thereafter. Pixel‐by‐pixel R1 maps of the entire left ventricle (LV) were generated 48 hours after PCA using inversion‐recovery with multiple inversion times. R1, ΔR1, and percent‐infarct values were calculated voxel‐by‐voxel.

Results

Significant correlations (P < 0.01, R ≥ 0.8) were obtained for percent‐infarct‐per‐slice (PIS) determined by DE or PIM vs. those from corresponding TTC‐stained slices. Compared to TTC, DE overestimated PIS by 32 ± 18%. PIM underestimated PIS by 2.5 ± 4.9%. Infarction fraction overestimation was 29 ± 6% of LV by DE, but only 1.0 ± 2.3% by PIM. Errors with PIM were significantly smaller than those with DE. Infarct area determined by signal intensity was similarly overestimated whether using Gd(DTPA) or Gd(ABE‐DTTA).

Conclusion

The ΔR1‐based PIM method is highly reproducible and more accurate than DE for quantifying myocardial viability in vivo. J. Magn. Reson. Imaging 2008;28:1386–1392. © 2008 Wiley‐Liss, Inc.     

Flow‐sensitive 4D MRI of the thoracic aorta: Comparison of image quality,quantitative flow,and wall parameters at 1.5 T and 3 T

Purpose:

To evaluate the effect of field strength on flow‐sensitive 4D magnetic resonance imaging (MRI) of the thoracic aorta. A volunteer study at 1.5 T and 3 T was conducted to compare phase‐contrast MR angiography (MRA) and 3D flow visualization quality as well as quantification of aortic hemodynamics.

Materials and Methods:

Ten healthy volunteers were examined by flow‐sensitive 4D MRI at both 1.5 T and 3 T MRI with identical imaging parameters (TE/TR = 6/5.1 msec, spatial/temporal resolution ≈2 mm/40.8 msec). Analysis included assessment of image quality of derived aortic 3D phase contrast (PC) angiography and 3D flow visualization (semiquantitative grading on a 0–2 scale, two blinded observers) and quantification of blood flow velocities, net flow per cardiac cycle, wall shear stress (WSS), and velocity noise.

Results:

Quality of 3D blood flow visualization (average grading = 1.8 ± 0.4 at 3 T vs. 1.1 ± 0.7 at 1.5 T) and the depiction of aortic lumen geometry by 3D PC‐MRA (1.7 ± 0.5 vs. 1.2 ± 0.6) were significantly (P < 0.01) improved at 3 T while velocity noise was significantly higher (P < 0.01) at 1.5 T. Velocity quantification resulted in minimally altered (0.05 m/s, 3 mL/cycle and 0.01 N/m²) but not statistically different (P = 0.40, P = 0.39, and P = 0.82) systolic peak velocities, net flow, and WSS for 1.5 T compared to 3 T.

Conclusion:

Flow‐sensitive 4D MRI at 3 T provided improved image quality without additional artifacts related to higher fields. Imaging at 1.5 T MRI, which is more widely available, was also feasible and provided information on aortic 3D hemodynamics of moderate quality with identical performance regarding quantitative analysis. J. Magn. Reson. Imaging 2012;36:1097–1103. © 2012 Wiley Periodicals, Inc.     

Auto‐Threshold quantification of late gadolinium enhancement in patients with acute heart disease

Purpose:

To assess the Otsu‐Auto‐Threshold (OAT) for accuracy and reproducibility for sizing irreversible injury in late gadolinium enhancement (LGE) images of patients with acute heart disease. The OAT method automatically identifies high signal intensity areas using a cutoff derived from the signal intensity histogram and therefore is user‐independent.

Materials and Methods:

LGE was performed in 28 patients with acute myocardial infarction (MI) and 30 patients with acute myocarditis. LGE mass was compared between OAT and thresholds using 2 standard deviations (SD), 3SD, and 5SD above remote myocardium, and full‐width‐at‐half‐maximum (FWHM). A separate, blinded visual assessment served as the standard of truth.

Results:

In patients with acute MI, OAT and 5SD did not differ (26.1 ± 11.4 g vs. 25.4 ± 11.1 g, P = 0.088), but thresholds of 2SD and 3SD overestimated LGE mass by 37% and 20%, respectively, and FWHM underestimated by 15%. In acute myocarditis, OAT was not different from a visual quantification, but thresholds of 2SD and 3SD overestimated LGE mass by 46% and 19%, respectively, and thresholds of 5SD and FWHM underestimated LGE mass by 17% and 26%, respectively. OAT and FWHM showed the best intraobserver and interobserver reproducibility.

Conclusion:

Automatic thresholding using OAT may serve as an accurate and reproducible method to quantify irreversible myocardial injury in acute heart disease. J. Magn. Reson. Imaging 2013;37:382–390. © 2012 Wiley Periodicals, Inc.     

Pancreatic diffusion‐weighted imaging (DWI): Comparison between mass‐forming focal pancreatitis (FP), pancreatic cancer (PC), and normal pancreas

Purpose

To compare diffusion‐weighted imaging (DWI) findings and the apparent diffusion coefficient (ADC) values of pancreatic cancer (PC), mass‐forming focal pancreatitis (FP), and the normal pancreas.

Materials and Methods

DWI (b = 0 and 600 seconds/mm²) findings of 14 patients with mass‐forming FP proven by histopathology and or clinical follow‐up, 10 patients with histopathologically‐proven PC, and 14 subjects with normal pancreatic exocrine function and normal imaging findings were retrospectively evaluated. ADC values of the masses, the remaining pancreas, and the normal pancreas were measured.

Results

On b = 600 seconds/mm² DWI, mass‐forming FP was visually indistinguishable from the remaining pancreas whereas PC was hyperintense relative to the remaining pancreas. The mean ADC value of PC (1.46 ± 0.18 mm²/second) was significantly lower than the remaining pancreas (2.11 ± 0.32 × 10^–3 mm²/second; P < 0.0001), mass‐forming FP (2.09 ± 0.18 × 10^–3 mm²/second; P < 0.0001), and pancreatic gland in the control group (1.78 ± 0.07 × 10^–3 mm²/second; P < 0.0005). There was no significant difference of ADC values between the mass‐forming focal pancreatitis and the remaining pancreas (2.03 ± 0.2 × 10^–3 mm²/second; P > 0.05).

Conclusion

Differences on DWI may help to differentiate PC, mass‐forming FP, and normal pancreas from each other. J. Magn. Reson. Imaging 2009;29:350–356. © 2009 Wiley‐Liss, Inc.     

Contrast-enhanced MRI index of diffuse myocardial fibrosis is increased in primary aldosteronism

Purpose:

To assess the degree of myocardial fibrosis in patients with primary aldosteronism (PA).

Materials and Methods:

Twenty‐five patients with PA and 12 age‐matched healthy volunteers underwent cine and late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) on a 1.5 T MR system. From volume–time curves of cine MRI, the time for deceleration (Tdec) was determined to assess the left ventricle (LV) chamber stiffness. Based on phase‐sensitive reconstructed LGE images, a fibrosis index called enhancement value (EV) was computed as the signal intensity change in the myocardium over blood before and after contrast. Both Tdec and EV were compared between patients and controls. The association between Tdec and EV was investigated.

Results:

Patients showed a significantly higher EV (0.43 ± 0.05 vs. 0.36 ± 0.07; P = 0.002) and a significantly shorter Tdec (11.5 ± 3.5 %RR vs. 15.3 ± 2.4 %RR; P = 0.004) than controls. Significant correlations between EV and Tdec were observed in patients (r = ?0.46, P = 0.018), in controls (r = ?0.68, P = 0.015) and in all subjects (r = ?0.63, P < 0.001).

Conclusion:

The fibrosis index is increased in patients with PA and the increase imposes an adverse effect on LV diastolic function. J. Magn. Reson. Imaging 2012;35:1349–1355. © 2012 Wiley Periodicals, Inc.

     

Prediction of hemorrhagic transformation in acute ischemic stroke using texture analysis of postcontrast T1‐weighted MR images

Purpose:

To test the hypothesis that texture analysis of postcontrast T1‐weighted MR images will predict hemorrhagic transformation (HT) in patients with acute ischemic stroke (AIS) with better accuracy than visual evidence of contrast‐enhancement (VE).

Materials and Methods:

Thirty‐four AIS patients were examined within 3.5 ± 1.5 h after stroke. T1‐weighted MR images were acquired 19 ± 7 min postcontrast injection. HT was determined by follow‐up imaging at 24–72 h. Postcontrast images were evaluated for VE. Four second‐order textural features were extracted (f1, f2, f3, and f9) for each patient. Receiver operating characteristic (ROC) curves were constructed for VE and for textural features, with HT as the outcome measure.

Results:

The f2 for HT patients (n = 12) was significantly lower than in non‐HT patients (1058 ± 356 versus 1568 ± 527; P = 0.005); the converse was true for f3 (0.67 ± 0.12 versus 0.54 ± 0.13; P = 0.007). ROC analysis indicated that the f2 and f3 textural features were the only two significant predictors of HT (P = 0.0018 and P = 0.0042). The addition of VE to either f2 or f3 did not result in a significant improvement in accuracy.

Conclusion:

Texture analysis of postcontrast T1‐weighted images may be superior to visual evidence of enhancement for the prediction of HT. J. Magn. Reson. Imaging 2009;30:933–941. © 2009 Wiley‐Liss, Inc.     

Measuring aortic diameter with different MR techniques: Comparison of three‐dimensional (3D) navigated steady‐state free‐precession (SSFP), 3D contrast‐enhanced magnetic resonance angiography (CE‐MRA), 2D T2 black blood,and 2D cine SSFP

Purpose:

To compare nongated three‐dimensional (3D) contrast‐enhanced magnetic resonance angiography (CE‐MRA) with 3D‐navigated cardiac‐gated steady‐state free‐precession bright blood (3D‐nav SSFP) and noncontrast 2D techniques for ascending aorta dimension measurements.

Materials and Methods:

Twenty‐five clinical exams were reviewed to evaluate the ascending aorta at 1.5T using: breathhold cine bright blood (SSFP), cardiac‐triggered T2 black blood (T2 BB), axial 3D‐nav SSFP, and nongated 3D CE‐MRA. Three radiologists independently measured aortic size at three specified locations for each sequence. Means, SDs, interobserver correlation, and vessel edge sharpness were statistically evaluated.

Results:

Measurements were greatest for 3D‐nav SSFP and 3D CE‐MRA and smallest for T2 BB. There was no significant difference between 3D‐nav SSFP and 3D CE‐MRA (P = 0.43–0.86), but significance was observed comparing T2 BB to all sequences. Interobserver agreement was uniformly >0.9, with T2 BB best, followed closely by 3D‐nav SSFP and 2D cine SSFP, and 3D CE‐MRA being the worst. Edge sharpness was significantly poorer for 3D CE‐MRA compared to the other sequences (P < 0.001).

Conclusion:

If diameter measurements are the main clinical concern, 3D‐nav SSFP appears to be the best choice, as it has a sharp edge profile, is easy to acquire and postprocess, and shows very good interobserver correlation. J. Magn. Reson. Imaging 2010;31:177–184. © 2009 Wiley‐Liss, Inc.     

3D flow‐independent peripheral vessel wall imaging using T2‐prepared phase‐sensitive inversion‐recovery steady‐state free precession

Purpose:

To develop a 3D flow‐independent peripheral vessel wall imaging method using T₂‐prepared phase‐sensitive inversion‐recovery (T₂PSIR) steady‐state free precession (SSFP).

Materials and Methods:

A 3D T₂‐prepared and nonselective inversion‐recovery SSFP sequence was designed to achieve flow‐independent blood suppression for vessel wall imaging based on T₁ and T₂ properties of the vessel wall and blood. To maximize image contrast and reduce its dependence on the inversion time (TI), phase‐sensitive reconstruction was used to restore the true signal difference between vessel wall and blood. The feasibility of this technique for peripheral artery wall imaging was tested in 13 healthy subjects. Image signal‐to‐noise ratio (SNR), wall/lumen contrast‐to‐noise ratio (CNR), and scan efficiency were compared between this technique and conventional 2D double inversion recovery – turbo spin echo (DIR‐TSE) in eight subjects.

Results:

3D T₂PSIR SSFP provided more efficient data acquisition (32 slices and 64 mm in 4 minutes, 7.5 seconds per slice) than 2D DIR‐TSE (2–3 minutes per slice). SNR of the vessel wall and CNR between vessel wall and lumen were significantly increased as compared to those of DIR‐TSE (P < 0.001). Vessel wall and lumen areas of the two techniques are strongly correlated (intraclass correlation coefficients: 0.975 and 0.937, respectively; P < 0.001 for both). The lumen area of T₂PSIR SSFP is slightly larger than that of DIR‐TSE (P = 0.008). The difference in vessel wall area between the two techniques is not statistically significant.

Conclusion:

T₂PSIR SSFP is a promising technique for peripheral vessel wall imaging. It provides excellent blood signal suppression and vessel wall/lumen contrast. It can cover a 3D volume efficiently and is flow‐ and TI‐independent. J. Magn. Reson. Imaging 2010;32:399–408. © 2010 Wiley‐Liss, Inc.     

Image analysis in time-resolved large field of view 3D MR-angiography at 3T

Purpose

To qualitatively and quantitatively evaluate the image quality in accelerated time‐resolved 3D contrast‐enhanced MR angiography (tr‐CE‐MRA) at 3T.

Materials and Methods

In all, 113 MRA were performed in 107 patients on a 3T MR system after written informed consent and approval by the ethics committee. Twenty consecutive thoracic (n = 87) or craniocervical (n = 26) 3D data volumes were acquired. The timeframes with maximum arterial and venous contrast were determined and a total of 663 arterial and venous segments were analyzed by two blinded observers. Diagnostic image quality was graded by applying a 0 (low) to 3 (excellent) scale. Additionally, local signal‐to‐noise (SNR) and contrast‐to‐noise ratios (relative CNR) were evaluated.

Results

Tr‐CE‐MRA was successfully performed in all patients. Good to excellent image quality (2.42 ± 0.31) was observed in all individuals with preserved discrimination of arteries (2.43 ± 0.48) and veins (2.20 ± 0.56). Minor image degradation due to artifacts (2.62 ± 0.25) and constantly high vascular signal and contrast were detected. There was a significant superiority of coronal orientation during thoracic MRA (P < 0.05). In 18 cases tr‐CE‐MRA provided additional information on vascular pathologies.

Conclusion

Large field of view tr‐CE‐MRA enables constantly high‐quality thoracic and craniocervical angiographies. In addition, the dynamics of tr‐CE‐MRA can offer additional information on vascular pathologies. J. Magn. Reson. Imaging 2008;28:1116–1124. © 2008 Wiley‐Liss, Inc.     

Navigator respiratory‐triggered diffusion‐weighted imaging in the follow‐up after hepatic radiofrequency ablation—initial results

Purpose

To evaluate diffusion alterations after hepatic radiofrequency (RF) ablation using a navigator respiratory‐triggered diffusion‐weighted imaging (NRT‐DWI) sequence with regard to potential diagnostic information for detection of local tumor progression (LTP).

Materials and Methods

One hundred forty‐eight consecutive follow‐up magnetic resonance (MR) examinations of 54 patients after hepatic RF ablation were reviewed. Apparent diffusion coefficient (ADC) values of ablation zones and liver parenchyma were assessed using a single‐shot echoplanar imaging sequence with the NRT technique. ADC values of ablation zones and adjacent signal alterations identified in NRT‐DWI were analyzed with regard to LTP.

Results

Mean ADC values of ablation zones (119.9 ± 30.5 × 10^?5 mm²/sec) and liver (106.3 ± 21.2 × 10^?5 mm²/sec) differed significantly (P = 0.0003). No evident changes in ablations' ADC values over time could be identified. ADC values obtained from the entire ablation zone did not significantly differ regarding the presence of LTP. In 58 examinations, hyperintense areas in the periphery of the ablation zone were detected on the NRT‐DWI. Corresponding ADC values were significantly lower in patients with LTP (102.1 ± 22.4 versus 130.8 ± 47.6 × 10^?5 mm²/sec; P = 0.0124).

Conclusion

NRT‐DWI is useful in the follow‐up imaging after RF ablation. ADC‐based evaluation of signal alterations adjacent to the ablation zone may contribute to the identification of LTP and nontumoral posttreatment tissue changes. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.

     

Free‐breathing high‐spatial‐resolution delayed contrast‐enhanced three‐dimensional viability MR imaging of the myocardium at 3.0T: A feasibility study

Purpose

To assess the feasibility of free‐breathing high‐spatial‐resolution delayed contrast‐enhanced three‐dimensional (3D) viability magnetic resonance imaging (MRI) at 3.0T for the detection of myocardial damages.

Materials and Methods

Twenty‐five patients with myocardial diseases, including myocardial infarction and cardiomyopathies, were enrolled after informed consent was given. Free‐breathing 3D viability MRI with high spatial resolution (1.5 × 1.25 × 2.5 mm) at 3.0T, for which cardiac and navigator gating techniques were employed, was compared with breath‐hold two‐dimensional (2D) viability imaging (1.77 × 1.18 × 10 mm) for assessment of contrast‐to‐noise ratio (CNR) and myocardial damage.

Results

Free‐breathing 3D viability imaging was achieved successfully in 21 of the 25 patients. This imaging technique depicted 84.6% of hyperenhancing myocardium with a higher CNR between hyperenhancing myocardium and blood and with excellent agreement for the transmural extension of myocardial damage (k = 0.91). In particular, the 3D viability images delineated the myocardial infarction and linear hyperenhancing myocardium, comparable to the 2D viability images.

Conclusion

Free‐breathing high‐spatial‐resolution delayed contrast‐enhanced 3D viability MRI using 3.0T was feasible for the evaluation of hyperenhancing myocardium, as seen with myocardial infarction and cardiomyopathies. J. Magn. Reson. Imaging 2008;28:1361–1367. © 2008 Wiley‐Liss, Inc.     

Impact of blood flow on diffusion coefficients of the human kidney: A time‐resolved ECG‐triggered diffusion‐tensor imaging (DTI) study at 3T

Purpose:

To evaluate the impact of renal blood flow on apparent diffusion coefficients (ADC) and fractional anisotropy (FA) using time‐resolved electrocardiogram (ECG)‐triggered diffusion‐tensor imaging (DTI) of the human kidneys.

Materials and Methods:

DTI was performed in eight healthy volunteers (mean age 29.1 ± 3.2) using a single slice coronal echoplanar imaging (EPI) sequence (3 b‐values: 0, 50, and 300 s/mm²) at the timepoint of minimum (20 msec after R wave) and maximum renal blood flow (200 msec after R wave) at 3T. Following 2D motion correction, region of interest (ROI)‐based analysis of cortical and medullary ADC‐ and FA‐values was performed.

Results:

ADC‐values of the renal cortex at maximum blood flow (2.6 ± 0.19 × 10^?3 mm²/s) were significantly higher than at minimum blood flow (2.2 ± 0.11 × 10^?3 mm²/s) (P < 0.001), while medullary ADC‐values did not differ significantly (maximum blood flow: 2.2 ± 0.18 × 10^?3 mm²/s; minimum blood flow: 2.15 ± 0.14 × 10^?3 mm²/s). FA‐values of the renal medulla were significantly greater at maximal blood (0.53 ± 0.05) than at minimal blood flow (0.47 ± 0.05) (P < 0.01). In contrast, cortical FA‐values were comparable at different timepoints of the cardiac cycle.

Conclusion:

ADC‐values in the renal cortex as well as FA‐values in the renal medulla are influenced by renal blood flow. This impact has to be considered when interpreting renal ADC‐ and FA‐values. J. Magn. Reson. Imaging 2013;37:233–236. © 2012 Wiley Periodicals, Inc.

     

Comparison of 2D and multislab 3D magnetic resonance techniques for measuring carotid wall volumes

Purpose

To compare a multislab three‐dimensional volume‐selective fast spin‐echo (FSE) magnetic resonance (MR) sequence with a routine two‐dimensional FSE sequence for quantification of carotid wall volume.

Materials and Methods

One hundred normal subjects (50 men, mean age 44.6 years) underwent carotid vessel wall MR using 2D and 3D techniques. Carotid artery total vessel volume, lumen volume, wall volume, and wall/outer wall (W/OW) ratio were measured over 20 contiguous slices. Two‐ (2D) and three‐dimensional (3D) results were compared.

Results

The mean difference between 2D and 3D datasets (as a percentage of the mean absolute value) was 1.7% for vessel volume, 4.9% for lumen volume, 4.7% for wall volume, and 5.8% for W/OW ratio. There was good correlation between 2D and 3D models for total vessel volume (R² = 0.93, P < 0.001), lumen area (R² = 0.92, P < 0.001), and wall volume (R² = 0.77, P < 0.001). The correlation for the W/OW ratio was weaker (R² = 0.30; P < 0.001). The signal‐to‐noise ratio (SNR) for the 3D technique was 2.1‐fold greater than for the 2D technique (P < 0.001). When using the 3D sequence, scan time was reduced by 63%.

Conclusion

Multislab volume selective 3D FSE carotid arterial wall imaging performs similarly to a conventional 2D technique, but with over twice the SNR and substantially reduced scan time. J. Magn. Reson. Imaging 2008;28:1476–1482. © 2008 Wiley‐Liss, Inc.     

Proton,diffusion‐weighted imaging,and sodium (23Na) MRI of uterine leiomyomata after MR‐guided high‐intensity focused ultrasound: A preliminary study

Purpose

To determine the feasibility of using combined proton (¹H), diffusion‐weighted imaging (DWI), and sodium (²³Na) magnetic resonance imaging (MRI) to monitor the treatment of uterine leiomyomata (fibroids).

Materials and Methods

Eight patients with uterine leiomyomata were enrolled and treated using MRI‐guided high‐intensity frequency ultrasound surgery (MRg‐HIFUS). MRI scans collected at baseline and posttreatment consisted of T2‐, T1‐, and ¹H DWI, as well as posttreatment ²³Na MRI. The ²³Na and ¹H MRi were coregistered using a replacement phantom method. Regions of interest in treated and untreated uterine leiomyoma tissue were drawn on ¹H MRI and DWI, wherein the tissue apparent diffusion coefficient of water (ADC) and absolute sodium concentrations were measured.

Results

Regions of treated uterine tissue were clearly identified on both DWI and ²³Na images. The sodium concentrations in normal myometrium tissue were 35.8 ± 2.1 mmol (mM), in the fundus; 43.4 ± 3.8 mM, and in the bladder; 65.3 ± 0.8 mM with ADC in normal myometrium of 2.2 ± 0.3 × 10^?3mm²/sec. Sodium concentration in untreated leiomyomata were 28 ± 5 mM, and were significantly elevated (41.6 ± 7.6 mM, P < 0.05) after treatment. Apparent diffusion coefficient values in the treated leiomyomata (1.30 ± 0.38 × 10^?3 mm²/sec) were decreased compared to areas of untreated leiomyomata (1.75 ± ‐4048μ‐4050μ36 × 10?³ mm²/sec; P = 0.04).

Conclusion

Multiparametric imaging permits identification of uterine leiomyomata, revealing altered ²³Na MRI and DWI levels following noninvasive treatment that provides a mechanism to explore the molecular and metabolic pathways after treatment. J. Magn. Reson. Imaging 2009;29:649–656. © 2009 Wiley‐Liss, Inc.

     

Black-blood steady-state free precession (SSFP) coronary wall MRI for cardiac allografts: a feasibility study

Purpose:

To assess the hypothesis that steady‐state free procession (SSFP) allows for imaging of the coronary wall under the conditions of fast heart rate in heart transplantation (HTx) patients.

Materials and Methods:

With the approval of our Institutional Review Board, 28 HTx patients were scanned with a 1.5T scanner. Cross‐sectional black‐blood images of the proximal portions of the left main artery, left anterior descending artery, and right coronary artery were acquired with both a 2D, double inversion recovery (DIR) prepared turbo (fast) spin echo (TSE) sequence and a 2D DIR SSFP sequence. Image quality (scored 0–3), vessel wall area, thickness, signal‐to‐noise ratio (SNR, vessel wall), and contrast‐to‐noise ratio (CNR, wall‐lumen) were compared between TSE and SSFP.

Results:

The overall image quality of SSFP was higher than TSE (1.23 ± 0.95 vs. 0.88 ± 0.69, P < 0.001). SSFP had a higher coronary wall SNR (20.1 ± 8.5 vs. 14.9 ± 4.8, P < 0.001) and wall‐lumen CNR (8.2 ± 4.6 vs. 6.8 ± 3.7, P = 0.005) than TSE.

Conclusion:

Black‐blood SSFP coronary wall MRI provides higher image quality, SNR, and CNR than traditional TSE does in HTx recipients. It has the potential to become an alternative means to noninvasive imaging of cardiac allografts. J. Magn. Reson. Imaging 2012;35:1210‐1215. © 2012 Wiley Periodicals, Inc.     

Coronary MR angiography using citrate‐coated very small superparamagnetic iron oxide particles as blood‐pool contrast agent: Initial experience in humans

Purpose:

To evaluate very small superparamagnetic iron oxide particles (VSOP‐C184) as blood‐pool contrast agent for coronary MR angiography (CMRA) in humans.

Materials and Methods:

Six healthy volunteers and 14 patients with suspected coronary artery disease underwent CMRA after administration of VSOP‐C184 at the following doses: 20 μmol Fe/kg (4 patients), 40 μmol Fe/kg (5 patients), 45 μmol Fe/kg (6 healthy volunteers), and 60 μmol Fe/kg (5 patients). In healthy volunteers, contrast‐to‐noise ratio (CNR), signal‐to‐noise ratio (SNR), and vessel edge definition (VED) of contrast‐enhanced CMRA were compared with non–contrast‐enhanced CMRA. In patients, a per‐segment intention‐to‐diagnose evaluation of contrast‐enhanced CMRA for detection of significant coronary stenosis (≥50%) was performed.

Results:

Three healthy volunteers (45 μmol Fe/kg VSOP‐C184) and two patients (60 μmol Fe/kg VSOP‐C184) had adverse events of mild or moderate intensity. VSOP‐C184 significantly increased CNR (15.1 ± 4.6 versus 6.9 ± 1.9; P = 0.010), SNR (21.7 ± 5.3 versus 15.4 ± 1.6; P = 0.048), and VED (2.3 ± 0.6 versus 1.2 ± 0.2; P < 0.001) compared with non–contrast‐enhanced CMRA. In patients, contrast‐enhanced CMRA yielded sensitivity, specificity, and diagnostic accuracy for detection of significant coronary stenosis of 86.7%, 71.0%, 73.1%, respectively.

Conclusion:

CMRA using VSOP‐C184 was feasible and yielded moderate diagnostic accuracy for detection of significant coronary stenosis within this proof‐of‐concept setting. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

In vivo sodium imaging of human patellar cartilage with a 3D cones sequence at 3 T and 7 T

Purpose:

To compare signal‐to‐noise ratios (SNRs) and T*₂ maps at 3 T and 7 T using 3D cones from in vivo sodium images of the human knee.

Materials and Methods:

Sodium concentration has been shown to correlate with glycosaminoglycan content of cartilage and is a possible biomarker of osteoarthritis. Using a 3D cones trajectory, 17 subjects were scanned at 3 T and 12 at 7 T using custom‐made sodium‐only and dual‐tuned sodium/proton surface coils, at a standard resolution (1.3 × 1.3 × 4.0 mm³) and a high resolution (1.0 × 1.0 × 2.0 mm³). We measured the SNR of the images and the T*₂ of cartilage at both 3 T and 7 T.

Results:

The average normalized SNR values of standard‐resolution images were 27.1 and 11.3 at 7 T and 3 T. At high resolution, these average SNR values were 16.5 and 7.3. Image quality was sufficient to show spatial variations of sodium content. The average T*₂ of cartilage was measured as 13.2 ± 1.5 msec at 7 T and 15.5 ± 1.3 msec at 3 T.

Conclusion:

We acquired sodium images of patellar cartilage at 3 T and 7 T in under 26 minutes using 3D cones with high resolution and acceptable SNR. The SNR improvement at 7 T over 3 T was within the expected range based on the increase in field strength. The measured T*₂ values were also consistent with previously published values. J. Magn. Reson. Imaging 2010;32:446–451. © 2010 Wiley‐Liss, Inc.