Feasibility study of exploring a T₁-weighted dynamic contrast-enhanced MR approach for brain perfusion imaging

Purpose:

To investigate the feasibility of T₁‐weighted dynamic contrast‐enhanced (DCE) MRI for the measurement of brain perfusion.

Materials and Methods:

Dynamic imaging was performed on a 3.0 Tesla (T) MR scanner by using a rapid spoiled‐GRE protocol. T₁ measurement with driven equilibrium single pulse observation of T₁ (DESPOT1) was used to convert the MR signal to tracer concentration. Cerebral perfusion maps were obtained by using an improved gamma‐variate model in 10 subjects and compared with those with arterial spin label (ASL) approach.

Results:

The cerebral blood volume (CBV) values were calculated as 4.74 ± 1.09 and 2.29 ± 0.58 mL/100 g in gray matter (GM) and whiter matter (WM), respectively. Mean transit time (MTT) values were 6.15 ± 0.59 s in GM and 6.96 ± 0.79 s in WM. The DCE values for GM/WM cerebral blood flow (CBF) were measured as 53.41 ± 9.23 / 25.78 ± 8.91 mL/100 g/min, versus ASL values of 49.05 ± 10.81 / 23.00 ± 5.89 mL/100 g/min for GW/WM. Bland‐Altman plot revealed a small difference of CBF between two approaches (mean bias = 3.83 mL/100 g/min, SD = 11.29). There were 6 pairs of samples (5%, 6/120) beyond the 95% limits of agreement. The correlation plots showed that the slop of Y (CBF__DCE) versus X intercept (CBF__ASL) is 0.95 with the intercept of 4.53 mL/100 g/min (r = 0.74; P < 0.05).

Conclusion:

It is feasible to evaluate the cerebral perfusion by using T₁‐weighted DCE‐MRI with the improved kinetic model. J. Magn. Reson. Imaging 2012;35:1322–1331. © 2012 Wiley Periodicals, Inc.     

Estimation of intersubject variability of cerebral blood flow measurements using MRI and positron emission tomography

Purpose:

To investigate the within and between subject variability of quantitative cerebral blood flow (CBF) measurements in normal subjects using various MRI techniques and positron emission tomography (PET).

Materials and Methods:

Repeated CBF measurements were performed in 17 healthy, young subjects using three different MRI techniques: arterial spin labeling (ASL), dynamic contrast enhanced T1 weighted perfusion MRI (DCE) and phase contrast mapping (PCM). All MRI measurements were performed within the same session. In 10 of the subjects repeated CBF measurements by ¹⁵O labeled water PET had recently been performed. A mixed linear model was used to estimate between subject (CV_betw) and within subject (CV_with) coefficients of variation.

Results:

Mean global CBF, CV_betw and CV_with using each of the four methods were for PCM 65.2 mL/100 g/min, 17.4% and 7.4%, for ASL 37.1 mL/100 g/min, 16.2% and 4.8%, for DCE 43.0 mL/100 g/min, 20.0%, 15.1% and for PET 41.9 mL/100 g/min, 16.5% and 11.9%, respectively. Only for DCE and PCM a significant positive correlation between measurements was demonstrated.

Conclusion:

These findings confirm large between subject variability in CBF measurements, but suggest also that in healthy subjects a subject‐method interaction is a possible source of between subject variability and of method differences. J. Magn. Reson. Imaging 2012;35:1290–1299. © 2012 Wiley Periodicals, Inc.     

Timing bolus dynamic contrast‐enhanced (DCE) MRI assessment of hepatic perfusion: Initial experience

Purpose

To assess whether dynamic contrast‐enhanced (DCE) MRI timing bolus data from routine clinical examinations can be postprocessed to obtain hepatic perfusion parameters for diagnosing cirrhosis.

Materials and Methods

We retrospectively identified 57 patients (22 with cirrhosis and 35 without cirrhosis) who underwent abdominal MRI, which included a low‐dose (2 mL gadodiamide) timing bolus using a volumetric spoiled gradient echo T1‐weighted sequence through the abdomen. Using a dual‐input single‐compartment model, the following perfusion parameters were measured: arterial, portal, and total blood flow; arterial fraction; mean transit time; and distribution volume. Those parameters were compared between patients with and without cirrhosis using t‐tests. Receiver operating characteristic (ROC) curve analysis was used to identify the perfusion parameters that can best predict the presence of cirrhosis.

Results

The hepatic arterial fraction, arterial flow, and distribution volume in patients with cirrhosis (27.7 ± 8.3%, 44.8 ± 14.1 mL/minute/100 g, and 16.3 ± 4.5%, respectively) were significantly higher than those without cirrhosis (18.7 ± 4.4%, 28.5 ± 11.7 mL/minute/100 g, and 14.0 ± 4.2%, respectively; P < 0.05 for all). ROC analysis showed arterial fraction as the best predictor of cirrhosis, with sensitivity of 73% and specificity of 86%.

Conclusion

Timing bolus DCE MR images from routine examinations can be postprocessed to yield potentially useful hepatic perfusion parameters. J. Magn. Reson. Imaging 2009;29:1317–1322. © 2009 Wiley‐Liss, Inc.     

Perfusion imaging of the pancreas using an arterial spin labeling technique

Purpose

To investigate the feasibility of perfusion imaging of the pancreas using an arterial spin labeling (ASL) technique.

Materials and Methods

An adapted flow‐sensitive alternating inversion recovery (FAIR)‐TrueFISP ASL technique was implemented on a 1.5T scanner. Anatomical and perfusion imaging in three different parts of the pancreas were performed in 10 healthy volunteers. Quantitative perfusion values were calculated using the extended Bloch equations.

Results

Perfusion images of all subjects showed diagnostic image quality in the pancreatic tail and the head. Assessment of pancreatic tissue perfusion was possible in all organ parts. Mean perfusion values were 271 ± 79 mL/100g/min in the head, 351 ± 112 mL/100g/min in the body, and 243 ± 55 mL/100g/min in the tail of the pancreas. Total examination time for perfusion imaging of the entire organ was 15.4 minutes.

Conclusion

FAIR‐TrueFISP permits analysis of pancreatic tissue perfusion with good image quality in a clinically applicable measuring time. Assessment of perfusion disorders may be useful in the diagnosis of inflammatory pancreatic pathologies, endocrine and exocrine pancreatic disorders, and in monitoring of pancreatic transplants. J. Magn. Reson. Imaging 2008;28:1459–1465. © 2008 Wiley‐Liss, Inc.     

Comparison of ASL and DCE MRI for the non-invasive measurement of renal blood flow: quantification and reproducibility

Objectives

To investigate the reproducibility of arterial spin labelling (ASL) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) and quantitatively compare these techniques for the measurement of renal blood flow (RBF).

Methods

Sixteen healthy volunteers were examined on two different occasions. ASL was performed using a multi-TI FAIR labelling scheme with a segmented 3D-GRASE imaging module. DCE MRI was performed using a 3D-FLASH pulse sequence. A Bland-Altman analysis was used to assess repeatability of each technique, and determine the degree of correspondence between the two methods.

Results

The overall mean cortical renal blood flow (RBF) of the ASL group was 263?±?41 ml min^?1 [100 ml tissue]^?1, and using DCE MRI was 287?±?70 ml min^?1 [100 ml tissue]^?1. The group coefficient of variation (CV_g) was 18 % for ASL and 28 % for DCE-MRI. Repeatability studies showed that ASL was more reproducible than DCE with CV_gs of 16 % and 25 % for ASL and DCE respectively. Bland-Altman analysis comparing the two techniques showed a good agreement.

Conclusions

The repeated measures analysis shows that the ASL technique has better reproducibility than DCE-MRI. Difference analysis shows no significant difference between the RBF values of the two techniques.

Key Points

? Reliable non-invasive monitoring of renal blood flow is currently clinically unavailable. ? Renal arterial spin labelling MRI is robust and repeatable. ? Renal dynamic contrast-enhanced MRI is robust and repeatable. ? ASL blood flow values are similar to those obtained using DCE-MRI.     

Effects of respiratory cycle and body position on quantitative pulmonary perfusion by MRI

Purpose:

To evaluate the performance of lung perfusion imaging using two‐dimensional (2D) first pass perfusion MRI and a quantitation program based on model‐independent deconvolution algorithm.

Materials and Methods:

In eight healthy volunteers 2D first pass lung perfusion was imaged in coronal planes using a partial Fourier saturation recovery stead state free precession (SSFP) technique with a temporal resolution of 160 ms per slice acquisition. The dynamic signal in the lung was measured over time and absolute perfusion calculated based on a model‐independent deconvolution program.

Results:

In the supine position mean pulmonary perfusion was 287 ± 106 mL/min/100 mL during held expiration. It was significantly reduced to 129 ± 68 mL/min/100 mL during held inspiration. Similar differences due to respiration were observed in prone position with lung perfusion much greater during expiration than during inspiration (271 ± 101 versus 99 ± 38 mL/min/100 mL (P < 0.01)). There was a linear increase in pulmonary perfusion from anterior to posterior lung fields in supine position. The perfusion gradient reversed in the prone position with the highest perfusion in anterior lung and the lowest in posterior lung fields.

Conclusion:

Lung perfusion imaging using a 2D saturation recovery SSFP perfusion MRI coupled with a model‐independent deconvolution algorithm demonstrated physiologically consistent dynamic heterogeneity of lung perfusion distribution. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Comprehensive MR evaluation of renal disease: Added clinical value of quantified renal perfusion values over single MR angiography

Purpose:

To evaluate the diagnostic accuracy of quantified renal perfusion parameters in identifying and differentiating renovascular from renal parenchymal disease.

Materials and Methods:

In all, 27 patients underwent renal perfusion measurements on a 3.0 T magnetic resonance imaging (MRI) system. Imaging was performed with a saturation recovery TurboFLASH sequence (TR/TE 177/0.93 msec, flip angle 12°, 5 slices/sec). All patients also underwent high‐resolution MR angiography (MRA) (TR/TE 3.1/1.09, flip angle 23°, spatial resolution 0.9 × 0.8 × 0.9 mm³). MR perfusion measurements were analyzed with a two‐compartment model, quantifying the plasma flow (F_P)—a characteristic renal first‐pass perfusion parameter. A receiver‐operator characteristic analysis was used to determine the optimal threshold value for distinguishing normal and abnormal plasma flow values. Utilizing this cutoff, sensitivity and specificity of solitary MR perfusion measurements, MRA, and a diagnostic strategy combining the two were evaluated.

Results:

Quantified MR perfusion values yielded a sensitivity of 100% and a specificity of 85% utilizing the optimal plasma flow threshold value of 150 mL/100 mL/min, whereas single MRA achieved a sensitivity of 51.9% and a specificity of 90%. Combining both methods enabled improved detection of renovascular and renoparenchymal disease with a sensitivity of 96.3% and specificity of 90%.

Conclusion:

In distinction to MRA, quantified MR perfusion measurements allow for the detection of pure renal parenchymal disorders. The combination of MRA with these perfusion measurements suggests an algorithm by which parenchymal and renovascular diseases may be reliably distinguished and the hemodynamic significance of the latter reliably determined. J. Magn. Reson. Imaging 2010;31:125–133. © 2009 Wiley‐Liss, Inc.     

Impact of nonrigid motion correction technique on pixel-wise pharmacokinetic analysis of free-breathing pulmonary dynamic contrast-enhanced MR imaging

Purpose:

To investigates the impact of nonrigid motion correction on pixel‐wise pharmacokinetic analysis of free‐breathing DCE‐MRI in patients with solitary pulmonary nodules (SPNs). Misalignment of focal lesions due to respiratory motion in free‐breathing dynamic contrast‐enhanced MRI (DCE‐MRI) precludes obtaining reliable time–intensity curves, which are crucial for pharmacokinetic analysis for tissue characterization.

Materials and Methods:

Single‐slice 2D DCE‐MRI was obtained in 15 patients. Misalignments of SPNs were corrected using nonrigid B‐spline image registration. Pixel‐wise pharmacokinetic parameters K^trans, v_e, and k_ep were estimated from both original and motion‐corrected DCE‐MRI by fitting the two‐compartment pharmacokinetic model to the time–intensity curve obtained in each pixel. The “goodness‐of‐fit” was tested with χ²‐test in pixel‐by‐pixel basis to evaluate the reliability of the parameters. The percentages of reliable pixels within the SPNs were compared between the original and motion‐corrected DCE‐MRI. In addition, the parameters obtained from benign and malignant SPNs were compared.

Results:

The percentage of reliable pixels in the motion‐corrected DCE‐MRI was significantly larger than the original DCE‐MRI (P = 4 × 10^?7). Both K^trans and k_ep derived from the motion‐corrected DCE‐MRI showed significant differences between benign and malignant SPNs (P = 0.024, 0.015).

Conclusion:

The study demonstrated the impact of nonrigid motion correction technique on pixel‐wise pharmacokinetic analysis of free‐breathing DCE‐MRI in SPNs. J. Magn. Reson. Imaging 2011;33:968–973. © 2011 Wiley‐Liss, Inc.

     

Dynamic non-invasive ASL perfusion imaging of a normal pancreas with secretin augmented MR imaging

Objectives

To investigate prospectively the repeatability of pancreatic perfusion measurements using arterial spin labelling (ASL) and to determine the increase in perfusion due to secretin stimulation.

Material and methods

An (FAIR)-TrueFISP ASL sequence was applied to determine the perfusion of the pancreatic head in a 3T MRI scanner. Ten healthy volunteers (four men, six women: mean age 28.5 ± 4.6 years; age range 25–40 years) were investigated twice within 1 week. The inter-individual variability was calculated using the standard deviation. Intra-individual agreement between the first and second scan was estimated using the Pearson correlation coefficient. A paired Wilcoxon rank-sum test was used to compare perfusion at baseline (BL) and during secretin stimulation.

Results

The mean BL perfusion of the pancreatic head was 285 ± 96 mL/100 g/min with an intra-individual correlation coefficient of 0.67 (strong) for repeated measurements. Secretin stimulation led to a significant increase (by 81%) in perfusion of the pancreatic head to 486 ±156 mL/100 g/min (p=0.002) with an intra-individual correlation of 0.29 (weak). A return to BL values was observed after 239 ± 92 s with a moderate intra-individual correlation coefficient of 0.42 for repeat measurements.

Conclusion

Dynamic non-invasive ASL imaging of the pancreas permitted quantification of pancreatic perfusion in a clinically applicable setting.

Key Points

? ASL imaging of the pancreas permitted quantification of pancreatic perfusion? Secretin stimulation led to a significant increase in pancreatic perfusion? The intra-individual correlation coefficient for baseline perfusion was strong for repeated measurements

     

Dynamic contrast‐enhanced magnetic resonance imaging of abdominal solid organ and major vessel: Comparison of enhancement effect between Gd‐EOB‐DTPA and Gd‐DTPA

Purpose

To evaluate the differences in enhancement of the abdominal solid organ and the major vessel on dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) obtained with gadolinium ethoxybenzyldiethylenetriamine pentaacetic acid (Gd‐EOB‐DTPA: EOB) and gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) in the same patients.

Materials and Methods

A total of 13 healthy volunteers underwent repeat assessments of abdominal MR examinations with DCE‐MRI using either Gd‐DTPA at a dose of 0.1 mmol/kg body weight or EOB at a dose of 0.025 mmol/kg body weight. DCE images were obtained at precontrast injection and in the arterial phase (AP: 25 seconds), portal phase (PP: 70 seconds), and equilibrium phase (EP: 3 minutes). The signal intensities (SIs) of liver at AP, PP, and EP; the SIs of spleen, renal cortex, renal medulla, pancreas, adrenal gland, aorta at AP; and the SIs of portal vein and inferior vena cava (IVC) at PP were defined using region‐of‐interest measurements, and were used for calculation of signal intensity ratio (SIR).

Results

The mean SIRs of liver (0.195 ± 0.140), spleen (1.35 ± 0.353), renal cortex (1.58 ± 0.517), renal medulla (0.548 ± 0.259), pancreas (0.540 ± 0.183), adrenal gland (1.04 ± 0.405), and aorta (2.44 ± 0.648) at AP as well as the mean SIRs of portal vein (1.85 ± 0.477) and IVC (1.16 ± 0.187) at PP in the EOB images were significantly lower than those (0.337 ± 0.200, 1.99 ± 0.443, 2.01 ± 0.474, 0.742 ± 0.336, 0.771 ± 0.227, 1.26 ± 0.442, 3.22 ± 1.20, 2.73 ± 0.429, and 1.68 ± 0.366, respectively) in the Gd‐DTPA images (P < 0.05 each). There was no significant difference in mean SIR of liver at PP between EOB (0.529 ± 0.124) and Gd‐DTPA (0.564 ± 0.139). Conversely, the mean SIR of liver at EP was significantly higher with EOB (0.576 ± 0.167) than with Gd‐DTPA (0.396 ± 0.093) (P < 0.001).

Conclusion

Lower arterial vascular and parenchymal enhancement with Gd‐EOB, as compared with Gd‐DTPA, may require reassessment of its dose, despite the higher late venous phase liver parenchymal enhancement. J. Magn. Reson. Imaging 2009;29:636–640. © 2009 Wiley‐Liss, Inc.     

Measuring perfusion and permeability in renal cell carcinoma with dynamic contrast‐enhanced MRI: A pilot study

Purpose:

To retrospectively assess an improved quantitative methodology with separate assessment of perfusion and permeability for characterization of primary renal cell carcinoma (RCC) and monitoring antiangiogenic treatment.

Materials and Methods:

Fifteen RCC patients before surgery, 6 RCC patients before and after neoadjuvant antiangiogenic therapy, and 15 patients without renal disease underwent dynamic contrast‐enhanced (DCE)‐MRI of the kidney with integrated retrospective respiratory triggering and an individual arterial input function. Tracer kinetic analysis was performed with a two‐compartment‐filtration‐model for the kidney data and a two‐compartment‐exchange‐model for the tumor data, providing four independent parameters: the perfusion‐parameters plasma flow (F_P) and plasma volume (V_P), and the permeability‐parameters extraction flow (F_E) and extravascular‐extracellular volume (V_E).

Results:

In tumors F_P and F_E were significantly lower than in normal kidneys. Tracer kinetic analysis displayed hemodynamic alteration caused by vessel infiltration or necrosis. Papillary RCC could be differentiated from clear‐cell variants by a distinct perfusion pattern. In antiangiogenically treated RCC V_E was not significantly decreased, while the perfusion parameters V_P and F_P were significantly diminished.

Conclusion:

DCE‐MRI with integrated motion compensation enables evaluation of primary RCC and detects distinct perfusion patterns. Quantification with a two‐compartment‐exchange‐model produces a separate perfusion‐ and permeability characterization and may become a diagnostic tool to monitor antiangiogenic treatment. J. Magn. Reson. Imaging 2010; 31: 490–501. © 2010 Wiley‐Liss, Inc.     

Reproducibility of renal perfusion MR imaging in native and transplanted kidneys using non-contrast arterial spin labeling

Purpose:

To examine both inter‐visit and intra‐visit reproducibility of a MR arterial spin labeling (ASL) perfusion technique in native and transplanted kidneys over a broad range of renal function.

Materials and Methods:

Renal perfusion exams were performed at 1.5 T in a total of 24 subjects: 10 with native and 14 with transplanted kidneys. Using a flow‐sensitive alternating inversion recovery (FAIR) ASL scheme, 32 control/tag pairs were acquired and processed using a single‐compartment model. Two FAIR‐ASL MR exams were performed at least 24 h apart on all the subjects to assess inter‐visit reproducibility. ASL perfusion measurements were also repeated back‐to‐back within one scanning session in 8 native subjects and in 12 transplant subjects to assess intra‐visit reproducibility. Intra‐class correlations (ICCs) and coefficients of variation (CVs) were calculated as metrics of reproducibility.

Results:

Intra‐visit ICCs ranged from 0.96 to 0.98 while CVs ranged from 4.8 to 6.0%. Inter‐visit measurements demonstrated slightly more variation with ICCs from 0.89 to 0.94 and CVs from 7.6 to 13.1%. Medullary perfusion demonstrated greater variability compared with cortical blood flow: intra‐visit ICCs from 0.72 to 0.78 and CVs from 16.7 to 26.7%, inter‐visit ICCs from 0.13 to 0.63 and CVs from 19.8 to 37%.

Conclusion:

This study indicates that a FAIR‐ASL perfusion technique is reproducible in the cortex of native and transplanted kidneys over a broad range in renal function. In contrast, perfusion measurements in the medulla demonstrated moderate to poor reproducibility for intra‐visit and inter‐visit measures respectively. J. Magn. Reson. Imaging 2011;33:1414–1421. © 2011 Wiley‐Liss, Inc.     

Posterior hypoperfusion in Parkinson's disease with and without dementia measured with arterial spin labeling MRI

Purpose:

To determine whether quantitative arterial spin labeling (ASL) can be used to evaluate regional cerebral blood flow in Parkinson's disease with dementia (PDD) and without dementia (PD).

Materials and Methods:

Thirty‐five PD patients, 11 PDD patients, and 35 normal controls were scanned by using a quantitative ASL method with a 3 Tesla MRI unit. Regional cerebral blood flow was compared in the posterior cortex using region‐of‐interest analysis.

Results:

PD and PDD patients showed lower regional cerebral blood flow in the posterior cortex than normal controls (P = 0.002 and P = 0.001, respectively, analysis of variance with a Bonferroni post hoc test).

Conclusion:

This is the first study to detect hypoperfusion in the posterior cortex in PD and PDD patients using ASL perfusion MRI. Because ASL perfusion MRI is completely noninvasive and can, therefore, safely be used for repeated assessments, this method can be used to monitor treatment effects or disease progression in PD. J. Magn. Reson. Imaging 2011;33:803–807. © 2011 Wiley‐Liss, Inc.     

Quantitative contrast‐enhanced perfusion measurements of the human lung using the prebolus approach

Purpose

To investigate dynamic contrast‐enhanced MRI (DCE‐MRI) for quantification of pulmonary blood flow (PBF) and blood volume (PBV) using the prebolus approach and to compare the results to the global lung perfusion (GLP).

Materials and Methods

Eleven volunteers were examined by applying different contrast agent doses (0.5, 1.0, 2.0, and 3.0 mL gadolinium diethylene triamine pentaacetic acid [Gd‐DTPA]), using a saturation‐recovery (SR) true fast imaging with steady precession (TrueFISP) sequence. PBF and PBV were determined for single bolus and prebolus. Region of interest (ROI) evaluation was performed and parameter maps were calculated. Additionally, cardiac output (CO) and lung volume were determined and GLP was calculated as a contrast agent–independent reference value.

Results

The prebolus results showed good agreement with low‐dose single‐bolus and GLP: PBF (mean ± SD in units of mL/minute/100 mL) = single bolus 190 ± 73 (0.5‐mL dose) and 193 ± 63 (1.0‐mL dose); prebolus 192 ± 70 (1.0–2.0‐mL dose) and 165 ± 52 (1.0–3.0‐mL dose); GLP (mL/minute/100 mL) = 187 ± 34. Higher single‐bolus resulted in overestimated values due to arterial input function (AIF) saturation.

Conclusion

The prebolus approach enables independent determination of appropriate doses for AIF and tissue signal. Using this technique, the signal‐to‐noise ratio (SNR) from lung parenchyma can be increased, resulting in improved PBF and PBV quantification, which is especially useful for the generation of parameter maps. J. Magn. Reson. Imaging 2009;30:104–111. © 2009 Wiley‐Liss, Inc.     

Quantitative analysis of vertebral bone marrow perfusion using dynamic contrast-enhanced MRI: initial results in osteoporotic patients with acute vertebral fracture

Purpose:

To evaluate the potential of quantitative dynamic contrast‐enhanced MRI (DCE‐MRI) in vertebral bone marrow (vBM) of patients with acute osteoporotic vertebral compression fractures.

Materials and Methods:

Twenty‐six patients with acute osteoporotic fractures (16 female, 10 male, median age 72, range 48–89) and 10 subjects without known history of osteoporosis (6 female, 4 male, median 65, range 31–77) were examined 2D‐DCE‐MRI. Region of interest (ROI) data in fractured (n = 26) and normal‐appearing vertebrae (n = 271) were analyzed with a two‐compartment tracer‐kinetic‐model, providing estimates of at least three independent parameters: plasma flow (PF), plasma volume (PV), and extraction flow (EF). Parameters were correlated with dual x‐ray absorptiometry (DXA) (n = 15) and quantitative computed tomography (QCT) densitometry (n = 10).

Results:

Mean PF was significantly higher in fractures than in normal‐appearing vertebrae (69.37 vs. 11.72 mL/100 mL/min). Similarly, mean PV and EF differed significantly. Mean PF was significantly decreased in normal‐appearing vBM osteoporotic patients compared to the control group. Mean PF and PV were significantly decreased in lumbar compared to thoracic vertebrae. PV showed a significant correlation with QCT.

Conclusion:

Perfusion parameters were decreased significantly in normal‐appearing vBM of patients. Furthermore, significant perfusion alterations were observed in acute osteoporotic vertebral fractures compared to normal‐appearing vertebrae. J. Magn. Reson. Imaging 2011;33:676–683. © 2011 Wiley‐Liss, Inc.     

Measurement and comparison of T1 relaxation times in native and transplanted kidney cortex and medulla

Purpose:

To measure and compare cortical and medullary T1 values in native and transplanted kidneys with a wide range of function as measured by estimated glomerular filtration rate (eGFR).

Materials and Methods:

A total of 27 subjects (12 native and 15 transplants) were studied. Two magnetic resonance imaging (MRI) exams of T1 measurement were performed on separate days for reproducibility study. Group‐wise comparisons of renal T1 on day 1 were performed between subjects with native and transplanted kidneys and also between subjects based on an eGFR threshold of 60 mL/min/1.73m².

Results:

Transplanted kidneys had higher cortical renal T1 (1183 ± 136 msec) than native kidneys (1057 ± 94 msec) with similar results in the medulla. Subjects with an eGFR < 60 mL/min/1.73m² had higher renal T1 than subjects with an eGFR > 60 mL/min/1.73m² (cortical T1: P < 0.0001; medullary T1: P = 0.008). Renal T1 was highly reproducible for both native and transplant groups (with percent differences less than 10%).

Conclusion:

There are differences in cortical and medullary T1 between native and transplanted kidneys at different levels of function. J. Magn. Reson. Imaging 2011;33:1241–1247. © 2011 Wiley‐Liss, Inc.     

DCE-MRI of the human kidney using BLADE: a feasibility study in healthy volunteers

Purpose:

To evaluate the degree of motion compensation in the kidney using two different sampling methods, each in their optimized settings: A BLADE k‐space acquisition technique and a routinely used kidney perfusion acquisition scheme (TurboFLASH).

Materials and Methods:

Dynamic contrast enhanced magnetic resonance examinations were performed in 16 healthy volunteers on a 3 Tesla MR‐system with two parameterizations of the BLADE sequence and the standard reference acquisition scheme. Signal intensity enhanced time curves were analyzed with a mathematical model and a widely published separable compartment model on cortex regions to assess robustness versus motion artifacts.

Results:

BLADE‐measurements with a strip‐width of 32 lines constituted the smallest mean values for the sum of squared errors (6065 ± 4996) compared with the measurement with a strip‐width of 64 lines (13849 ± 14079) or the standard TurboFLASH (11884 ± 8076). Calculations concerning goodness of the fit of the applied compartment model yielded an overall average of the Akaike Fit Error of 732 ± 141 for BLADE (646 ± 149 for a strip‐width of 32 lines, 816 ± 53 for 64 lines) and 1626 ± 303 for the TurboFLASH (TFL) sequence.

Conclusion:

We demonstrated that renal dynamic contrast enhanced magnetic resonance imaging using BLADE k‐space sampling with a strip‐width of 32 is significantly less sensitive to motion than a widely published Turbo‐Flash sequence with nearly similar parameters. J. Magn. Reson. Imaging 2012;35:868–874. © 2011 Wiley Periodicals, Inc.     

Age dependence of T1 perfusion MRI‐based hemodynamic parameters in human kidneys

Purpose

To determine the association between renal cortical perfusion parameters from T1‐DCE magnetic resonance imaging (MRI) and age in human kidney.

Materials and Methods

Thirty‐five patients (mean age: 53 years, SD = 15 years) were imaged using inversion recovery (IR)‐prepared FLASH (pulse repitition time [TR] = 4.4 msec, echo time [TE] 2.2 msec, inversion time [TI] = 180 msec, FA 50°, matrix 128 × 256, 0.3 sec/slice) during the injection of Gadolinium‐DTPA. Tissue concentration–time courses were deconvolved. Renal blood flow (RBF), volume of distribution (RVD), and mean transit time (MTT) were derived from the resulting impulse response function.

Results

Mean RBF, RVD, and MTT were 127 mL/min/100 mL (SD = 81 mL/min/100 mL), 40 mL/100 mL (SD 23 mL/100 mL), and 22 sec (SD = 9 sec). A significant moderately negative correlation was found between RBF and age (R = ?0.447, P = 0.007), RVD and age (R = ?0.420, P = 0.012). MTT and age did not show a significant correlation (R = 0.017, P = 0.924). Repeating this analysis for each gender revealed a moderate age dependence of RBF (R = ?0.600 with P = 0.009) and RVD (R = ?0.540 with P = 0.021) in the male group only.

Conclusion

T1‐DCE quantitative perfusion MRI was sufficiently sensitive to demonstrate a significant negative correlation of RBF and RVD with patient age. This was due to a moderate age dependence of these quantities in males that seems to be absent in females. J. Magn. Reson. Imaging 2009;29:398–403. © 2009 Wiley‐Liss, Inc.

     

Limitations of dynamic contrast-enhanced MRI in monitoring radiation-induced changes in the fraction of radiobiologically hypoxic cells in human melanoma xenografts

Purpose

To investigate the potential of gadopentetate dimeglumine (Gd‐DTPA)‐based dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) in detecting radiation‐induced changes in the fraction of radiobiologically hypoxic cells in A‐07 human melanoma xenografts.

Materials and Methods

A‐07 tumors were randomly assigned to an unirradiated control group or a group given a single radiation dose of 20 Gy. DCE‐MRI and measurement of fraction of hypoxic cells were performed immediately before and 24 h after the radiation exposure. Tumor images of E · F (E is the initial extraction fraction of Gd‐DTPA and F is blood perfusion) and λ (λ is proportional to extracellular volume fraction) were produced by subjecting DCE‐MRI series to Kety analysis. Fraction of hypoxic cells was measured by using a radiobiological assay based on the paired survival curve method.

Results

Fraction of radiobiologically hypoxic cells was higher in irradiated tumors (26.2 ± 5.8%) than in unirradiated tumors (7.5 ± 2.7%) by a factor of 3.5 ± 1.5 (P = 0.0093), whereas only minor radiation‐induced changes in E · F and λ could be detected.

Conclusion

DCE‐MRI does not seem to offer insight into the changes in fraction of radiobiologically hypoxic cells occurring in A‐07 tumors within 24 h after irradiation with 20 Gy. J. Magn. Reson. Imaging 2008;28:1209–1218. © 2008 Wiley‐Liss, Inc.     

Measurement of deep gray matter perfusion using a segmented true–fast imaging with steady‐state precession (True‐FISP) arterial spin‐labeling (ASL) method at 3T

Purpose

To study the feasibility of using the MRI technique of segmented true–fast imaging with steady‐state precession arterial spin‐labeling (True‐FISP ASL) for the noninvasive measurement and quantification of local perfusion in cerebral deep gray matter at 3T.

Materials and Methods

A flow‐sensitive alternating inversion‐recovery (FAIR) ASL perfusion preparation was used in which the echo‐planar imaging (EPI) readout was replaced with a segmented True‐FISP data acquisition strategy. The absolute perfusion for six selected regions of deep gray matter (left and right thalamus, putamen, and caudate) were calculated in 11 healthy human subjects (six male, five female; mean age = 35.5 years ± 9.9).

Results

Preliminary measurements of the average absolute perfusion values at the six selected regions of deep gray matter are in agreement with published values for mean absolute cerebral blood flow (CBF) baselines acquired from healthy volunteers using positron emission tomography (PET).

Conclusion

Segmented True‐FISP ASL is a practical and quantitative technique suitable to measure local tissue perfusion in cerebral deep gray matter at a high spatial resolution without the susceptibility artifacts commonly associated with EPI‐based methods of ASL. J. Magn. Reson. Imaging 2009;29:1425–1431. © 2009 Wiley‐Liss, Inc.