Quantitative determination of Gd-DTPA concentration in T1-weighted MR renography studies

Bioinspired BSA@polydopamine@Fe Nanoprobe with Self-Purification Capacity for Targeted Magnetic Resonance Imaging of Acute Kidney Injury

Contrast-enhanced magnetic resonance imaging (CE-MRI) of acute kidney injury (AKI) is severely hindered by the poor targeting capacity and potential toxicity of current contrast agents. Herein, we propose one-step fabrication of a bovine serum albumin@polydopamine@Fe (BSA@PDA@Fe, BPFe) nanoprobe with self-purification capacity for targeted CE-MRI of AKI. BSA endows the BPFe nanoprobe with renal tubule-targeting ability, and PDA is capable of completely inhibiting the intrinsic metal-induced reactive oxygen species (ROS), which are always involved in Fe/Mn-based agents. The as-prepared nanoprobe owns a tiny size of 2.7 nm, excellent solubility, good T1 MRI ability, superior biocompatibility, and powerful antioxidant capacity. In vivo CE-MRI shows that the BPFe nanoprobe can accumulate in the renal cortex due to the reabsorption effect toward the serum albumin. In the AKI model, impaired renal reabsorption function can be effortlessly detected via the diminishment of renal cortical signal enhancement. More importantly, the administration of the BPFe nanoprobe would not aggravate renal damage of AKI due to the outstanding self-purification capacity. Besides, the BPFe nanoprobe is employed for CE-MR angiography to visualize fine vessel structures. This work provides an MRI contrast agent with good biosafety and targeting ability for CE-MRI of kidney diseases.

Abdominal Imaging in ADPKD: Beyond Total Kidney Volume

In the context of autosomal dominant polycystic kidney disease (ADPKD), measurement of the total kidney volume (TKV) is crucial. It acts as a marker for tracking disease progression, and evaluating the effectiveness of treatment strategies. The TKV has also been recognized as an enrichment biomarker and a possible surrogate endpoint in clinical trials. Several imaging modalities and methods are available to calculate the TKV, and the choice depends on the purpose of use. Technological advancements have made it possible to accurately assess the cyst burden, which can be crucial to assessing the disease state and helping to identify rapid progressors. Moreover, the development of automated algorithms has increased the efficiency of total kidney and cyst volume measurements. Beyond these measurements, the quantification and characterization of non-cystic kidney tissue shows potential for stratifying ADPKD patients early on, monitoring disease progression, and possibly predicting renal function loss. A broad spectrum of radiological imaging techniques are available to characterize the kidney tissue, showing promise when it comes to non-invasively picking up the early signs of ADPKD progression. Radiomics have been used to extract textural features from ADPKD images, providing valuable information about the heterogeneity of the cystic and non-cystic components. This review provides an overview of ADPKD imaging biomarkers, focusing on the quantification methods, potential, and necessary steps toward a successful translation to clinical practice.

Disposable point-of-care portable perfusion phantom for quantitative DCE-MRI

PURPOSE

To develop a disposable point-of-care portable perfusion phantom (DP4) and validate its clinical utility in a multi-institutional setting for quantitative dynamic contrast-enhanced magnetic resonance imaging (qDCE-MRI).

METHODS

The DP4 phantom was designed for single-use and imaged concurrently with a human subject so that the phantom data can be utilized as the reference to detect errors in qDCE-MRI measurement of human tissues. The change of contrast-agent concentration in the phantom was measured using liquid chromatography-mass spectrometry. The repeatability of the contrast enhancement curve (CEC) was assessed with five phantoms in a single MRI scanner. Five healthy human subjects were recruited to evaluate the reproducibility of qDCE-MRI measurements. Each subject was imaged concurrently with the DP4 phantom at two institutes using three 3T MRI scanners from three different vendors. Pharmacokinetic (PK) parameters in the regions of liver, spleen, pancreas, and paravertebral muscle were calculated based on the Tofts model (TM), extended Tofts model (ETM), and shutter speed model (SSM). The reproducibility of each PK parameter over three measurements was evaluated with the intraclass correlation coefficient (ICC) and compared before and after DP4-based error correction.

RESULTS

The contrast-agent concentration in the DP4 phantom was linearly increased over 10 min (0.17 mM/min, measurement accuracy: 96%) after injecting gadoteridol (100 mM) at a constant rate (0.24 ml/s, 4 ml). The repeatability of the CEC within the phantom was 0.997 when assessed by the ICC. The reproducibility of the volume transfer constant, K^trans , was the highest of the PK parameters regardless of the PK models. The ICCs of K^trans in the TM, ETM, and SSM before DP4-based error correction were 0.34, 0.39, and 0.72, respectively, while those increased to 0.93, 0.98, and 0.86, respectively, after correction.

CONCLUSIONS

The DP4 phantom is reliable, portable, and capable of significantly improving the reproducibility of qDCE-MRI measurements.

Single-nanometer iron oxide nanoparticles as tissue-permeable MRI contrast agents

Magnetic nanoparticles are robust contrast agents for MRI and often produce particularly strong signal changes per particle. Leveraging these effects to probe cellular- and molecular-level phenomena in tissue can, however, be hindered by the large sizes of typical nanoparticle contrast agents. To address this limitation, we introduce single-nanometer iron oxide (SNIO) particles that exhibit superparamagnetic properties in conjunction with hydrodynamic diameters comparable to small, highly diffusible imaging agents. These particles efficiently brighten the signal in T ₁-weighted MRI, producing per-molecule longitudinal relaxation enhancements over 10 times greater than conventional gadolinium-based contrast agents. We show that SNIOs permeate biological tissue effectively following injection into brain parenchyma or cerebrospinal fluid. We also demonstrate that SNIOs readily enter the brain following ultrasound-induced blood-brain barrier disruption, emulating the performance of a gadolinium agent and providing a basis for future biomedical applications. These results thus demonstrate a platform for MRI probe development that combines advantages of small-molecule imaging agents with the potency of nanoscale materials.

Portable Perfusion Phantom Offers Quantitative Dynamic Contrast-Enhanced Magnetic Resonance Imaging for Accurate Prostate Cancer Grade Stratification: A Pilot Study

RATIONALE AND OBJECTIVES

The study goal was to test whether the improved accuracy in quantitative dynamic contrast-enhanced magnetic resonance imaging measurement using a point-of-care portable perfusion phantom (P4) leads to better stratification of prostate cancer grade.

MATERIALS AND METHODS

A prospective clinical study was conducted recruiting 44 patients scheduled for multi-parameter MRI prostate exams. All participants were imaged with the P4 placed under their pelvic regions. Tissue sampling was carried out for 25 patients at 22 ± 18 (mean ± SD) days after multi-parameter MRI. On histologic examination, a total of 31 lesions were confirmed as prostate cancer. Tumors were classified into low grade (n = 14), intermediate grade (n = 10), and high grade (n = 7). Tumor perfusion was assessed by volume transfer constant, K^trans, before and after P4-based error correction, and the K^trans of low, intermediate and high-grade tumors were statistically compared.

RESULTS

After P4-based error correction, the K^trans of low, intermediate, and high-grade tumors were 0.109 ± 0.026 min^-1 (95% CI: 0.0094 to 0.124 min^-1), 0.163 ± 0.049 min^-1 (95% CI: 0.129 to 0.198 min^-1) and 0.356 ± 0.156 min^-1 (95% CI: 0.215 to 0.495 min^-1), respectively, with statistically significant difference among the groups (low vs intermediate: p = 0.002; intermediate vs high: p = 0.002; low vs high: p < 0.001). The sensitivity and specificity of K^trans value, 0.14 min^-1, to detect the clinically significant prostate cancer were 88% and 93%, respectively, after P4 based error correction, but those before error correction were 88% and 86%, respectively.

CONCLUSION

The P4 allows to reduce errors in quantitative dynamic contrast-enhanced magnetic resonance imaging measurement, enhancing accuracy in stratification of prostate cancer grade.

Effect of Gadoxetic Acid Injection Duration on Tumor Enhancement in Arterial Phase Liver MRI

RATIONALE AND OBJECTIVES

Rapid injection of gadoxetic acid has been shown not to increase tumor enhancement in arterial phase liver MRI for unknown reasons. This study aimed to investigate the effect of injection durations on peak contrast concentration in tumors and to correlate it with signal enhancement in gadoxetic acid-enhanced arterial phase MRI.

MATERIALS AND METHODS

Gadoxetic acid-enhanced arterial phase MRI was obtained using a bolus-tracking technique with injection durations of 1, 3, and 6s in six rabbits with VX2 liver tumors. The peak concentration of gadoxetic acid in the aorta and tumor was estimated by iopromide-enhanced time-resolved CT using the same injection volume and durations with those for MRI. Signal enhancement on MRI and peak enhancement on CT were compared and correlated.

RESULTS

There was no significant difference in MR signal enhancement of tumors among the 3 injection durations (p = 0.87). In CT, shorter injection durations significantly increased peak contrast concentration in the aorta (p < 0.01) but produced equivalent peak contrast concentration in tumors (p = 0.24). The longer injections resulted in the stronger correlation between peak contrast concentration in CT and MR signal enhancement in tumors (r = 0.31, 0.43, and 0.86 with 1s-, 3s-, and 6s-injection, respectively) with a statistical significance only found with 6s-injection (p = 0.03).

CONCLUSION

Estimation of contrast concentration by CT demonstrated that shorter injections did not increase peak contrast concentration in tumors despite increased peak concentration in the aorta. Furthermore, tumor signal enhancement in gadoxetic acid-enhanced arterial phase MRI was less correlated with the peak contrast concentration with shorter injections.

A modified two-compartment model for measurement of renal function using dynamic contrast-enhanced computed tomography

Objectives

To validate and adapt a modified two-compartment model, originally developed for magnetic resonance imaging, for measuring human single-kidney glomerular filtration rate (GFR) and perfusion using dynamic contrast-enhanced computed tomography (DCE-CT).

Methods

This prospective study was approved by the institutional review board, and written informed consent was obtained from all patients. Thirty-eight patients with essential hypertension (EH, n = 13) or atherosclerotic renal artery stenosis (ARAS, n = 25) underwent renal DCE-CT for GFR and perfusion measurement using a modified two-compartment model. Iothalamate clearance was used to measure reference total GFR, which was apportioned into single-kidney GFR by renal blood flow. Renal perfusion was also calculated using a conventional deconvolution algorithm. Validation of GFR and perfusion and inter-observer reproducibility, were conducted by using the Pearson correlation and Bland-Altman analysis.

Results

Both the two-compartment model and iothalamate clearance detected in ARAS patients lower GFR in the stenotic compared to the contralateral and EH kidneys. GFRs measured by DCE-CT and iothalamate clearance showed a close match (r = 0.94, P<0.001, and mean difference 2.5±12.2mL/min). Inter-observer bias and variation in model-derived GFR (r = 0.97, P<0.001; mean difference, 0.3±7.7mL/min) were minimal. Renal perfusion by deconvolution agreed well with that by the compartment model when the blood transit delay from abdominal aorta to kidney was negligible.

Conclusion

The proposed two-compartment model faithfully depicts contrast dynamics using DCE-CT and may provide a reliable tool for measuring human single-kidney GFR and perfusion.

Why Have Detection, Understanding and Management of Kidney Hypoxic Injury Lagged Behind those for the Heart?

The outcome of patients with acute myocardial infarction (AMI) has dramatically improved over recent decades, thanks to early detection and prompt interventions to restore coronary blood flow. In contrast, the prognosis of patients with hypoxic acute kidney injury (AKI) remained unchanged over the years. Delayed diagnosis of AKI is a major reason for this discrepancy, reflecting the lack of symptoms and diagnostic tools indicating at real time altered renal microcirculation, oxygenation, functional derangement and tissue injury. New tools addressing these deficiencies, such as biomarkers of tissue damage are yet far less distinctive than myocardial biomarkers and advanced functional renal imaging technologies are non-available in the clinical practice. Moreover, our understanding of pathogenic mechanisms likely suffers from conceptual errors, generated by the extensive use of the wrong animal model, namely warm ischemia and reperfusion. This model parallels mechanistically type I AMI, which properly represents the rare conditions leading to renal infarcts, whereas common scenarios leading to hypoxic AKI parallel physiologically type II AMI, with tissue hypoxic damage generated by altered oxygen supply/demand equilibrium. Better understanding the pathogenesis of hypoxic AKI and its management requires a more extensive use of models of type II-rather than type I hypoxic AKI.

Accurate Therapeutic Response Assessment of Pancreatic Ductal Adenocarcinoma Using Quantitative Dynamic Contrast-Enhanced Magnetic Resonance Imaging With a Point-of-Care Perfusion Phantom: A Pilot Study

OBJECTIVES

The aim of this study was to test the feasibility of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with concurrent perfusion phantom for monitoring therapeutic response in patients with pancreatic ductal adenocarcinoma (PDAC).

MATERIALS AND METHODS

A prospective pilot study was conducted with 8 patients (7 men and 1 woman) aged 46 to 78 years (mean age, 66 years). Participants had either locally advanced (n = 7) or metastatic (n = 1) PDAC, and had 2 DCE-MRI examinations: one before and one 8 ± 1 weeks after starting first-line chemotherapy. A small triplicate perfusion phantom was imaged with each patient, serving as an internal reference for accurate quantitative image analysis. Tumor perfusion was measured with K using extended Tofts model before and after phantom-based data correction. Results are presented as mean ± SD and 95% confidence intervals (CIs). Statistical difference was evaluated with 1-way analysis of variance.

RESULTS

Tumor-size change of responding group (n = 4) was -12% ± 4% at 8 weeks of therapy, while that of nonresponding group (n = 4) was 18% ± 15% (P = 0.0100). Before phantom-based data correction, the K change of responding tumors was 69% ± 23% (95% CI, 32% to 106%) at 8 weeks, whereas that of nonresponding tumors was -1% ± 41% (95% CI, -65% to 64%) (P = 0.0247). After correction, the data variation in each group was significantly reduced; the K change of responding tumors was 73% ± 6% (95% CI, 64% to 82%) compared with nonresponding tumors of -0% ± 5% (95% CI, -7% to 8%) (P < 0.0001).

CONCLUSIONS

Quantitative DCE-MRI measured the significant perfusion increase of PDAC tumors responding favorably to chemotherapy, with decreased variability after correction using a perfusion phantom.

Recent advances in renal imaging

Kidney diseases can be caused by a wide range of genetic, hemodynamic, toxic, infectious, and autoimmune factors. The diagnosis of kidney disease usually involves the biochemical analysis of serum and blood, but these tests are often insufficiently sensitive or specific to make a definitive diagnosis. Although radiologic imaging currently has a limited role in the evaluation of most kidney diseases, several new imaging methods hold great promise for improving our ability to non-invasively detect structural, functional, and molecular changes within the kidney. New methods, such as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and blood oxygen level-dependent (BOLD) MRI, allow functional imaging of the kidney. The use of novel contrast agents, such as microbubbles and nanoparticles, allows the detection of specific molecules in the kidney. These methods could greatly advance our ability to diagnose disease and also to safely monitor patients over time. This could improve the care of individual patients, and it could also facilitate the evaluation of new treatment strategies.

Exercise-induced calf muscle hyperemia: quantitative mapping with low-dose dynamic contrast enhanced magnetic resonance imaging

Peripheral artery disease (PAD) in the lower extremities often leads to intermittent claudication. In the present study, we proposed a low-dose DCE MRI protocol for quantifying calf muscle perfusion stimulated with plantar flexion and multiple new metrics for interpreting perfusion maps, including the ratio of gastrocnemius over soleus perfusion (G/S; for assessing the vascular redistribution between the two muscles) and muscle perfusion normalized by whole body perfusion (for quantifying the muscle's active hyperemia). Twenty-eight human subjects participated in this Institutional Review Board-approved study, with 10 healthy subjects ( group A) for assessing interday reproducibility and 8 healthy subjects ( group B) for exploring the relationship between plantar-flexion load and induced muscle perfusion. In a pilot group of five elderly healthy subjects and five patients with PAD ( group C), we proposed a protocol that measured perfusion for a low-intensity exercise and for an exhaustion exercise in a single MRI session. In group A, perfusion estimates for calf muscles were highly reproducible, with correlation coefficients of 0.90-0.93. In group B, gastrocnemius perfusion increased linearly with the exercise workload ( P < 0.05). With the low-intensity exercise, patients with PAD in group C showed substantially lower gastrocnemius perfusion compared with elderly healthy subjects [43.4 (SD 23.5) vs. 106.7 (SD 73.2) ml·min^-1·100 g^-1]. With exhaustion exercise, G/S [1.0 (SD 0.4)] for patients with PAD was lower than both its low-intensity level [1.9 (SD 1.3)] and the level in elderly healthy subjects [2.7 (SD 2.1)]. In conclusion, the proposed MRI protocol and the new metrics are feasible for quantifying exercise-induced muscle hyperemia, a promising functional test of PAD. NEW & NOTEWORTHY To quantitatively map exercise-induced hyperemia in calf muscles, we proposed a high-resolution MRI method shown to be highly reproducible and sensitive to exercise load. With the use of low contrast, it is feasible to measure calf muscle hyperemia for both low-intensity and exhaustion exercises in a single MRI session. The newly proposed metrics for interpreting perfusion maps are promising for quantifying intermuscle vascular redistribution or a muscle's active hyperemia.

Measurement of Murine Single-Kidney Glomerular Filtration Rate Using Dynamic Contrast-Enhanced MRI

PURPOSE

To develop and validate a method for measuring murine single-kidney glomerular filtration rate (GFR) using dynamic contrast-enhanced MRI (DCE-MRI).

METHODS

This prospective study was approved by the Institutional Animal Care and Use Committee. A fast longitudinal relaxation time (T1 ) measurement method was implemented to capture gadolinium dynamics (1 s/scan), and a modified two-compartment model was developed to quantify GFR as well as renal perfusion using 16.4T MRI in mice 2 weeks after unilateral renal artery stenosis (RAS, n = 6) or sham (n = 8) surgeries. This approach was validated by comparing model-derived GFR and perfusion to those obtained by fluorescein isothiocyanante (FITC)-inulin clearance and arterial spin labeling (ASL), respectively, using the Pearson's and Spearman's rank correlations and Bland-Altman analysis.

RESULTS

The compartmental model provided a good fitting to measured gadolinium dynamics in both normal and RAS kidneys. The proposed DCE-MRI method offered assessment of single-kidney GFR and perfusion, comparable to the FITC-inulin clearance (Pearson's correlation coefficient r = 0.95 and Spearman's correlation coefficient ρ = 0.94, P < 0.0001, and mean difference -7.0 ± 11.0 μL/min) and ASL (r = 0.92 and ρ = 0.84, P < 0.0001, and mean difference 4.4 ± 66.1 mL/100 g/min) methods.

CONCLUSION

The proposed DCE-MRI method may be useful for reliable noninvasive measurements of single-kidney GFR and perfusion in mice. Magn Reson Med 79:2935-2943, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Accuracy, repeatability, and interplatform reproducibility of T1 quantification methods used for DCE-MRI: Results from a multicenter phantom study

PURPOSE

To determine the in vitro accuracy, test-retest repeatability, and interplatform reproducibility of T₁ quantification protocols used for dynamic contrast-enhanced MRI at 1.5 and 3 T.

METHODS

A T₁ phantom with 14 samples was imaged at eight centers with a common inversion-recovery spin-echo (IR-SE) protocol and a variable flip angle (VFA) protocol using seven flip angles, as well as site-specific protocols (VFA with different flip angles, variable repetition time, proton density, and Look-Locker inversion recovery). Factors influencing the accuracy (deviation from reference NMR T₁ measurements) and repeatability were assessed using general linear mixed models. Interplatform reproducibility was assessed using coefficients of variation.

RESULTS

For the common IR-SE protocol, accuracy (median error across platforms = 1.4-5.5%) was influenced predominantly by T₁ sample (P < 10^-6 ), whereas test-retest repeatability (median error = 0.2-8.3%) was influenced by the scanner (P < 10^-6 ). For the common VFA protocol, accuracy (median error = 5.7-32.2%) was influenced by field strength (P = 0.006), whereas repeatability (median error = 0.7-25.8%) was influenced by the scanner (P < 0.0001). Interplatform reproducibility with the common VFA was lower at 3 T than 1.5 T (P = 0.004), and lower than that of the common IR-SE protocol (coefficient of variation 1.5T: VFA/IR-SE = 11.13%/8.21%, P = 0.028; 3 T: VFA/IR-SE = 22.87%/5.46%, P = 0.001). Among the site-specific protocols, Look-Locker inversion recovery and VFA (2-3 flip angles) protocols showed the best accuracy and repeatability (errors < 15%).

CONCLUSIONS

The VFA protocols with 2 to 3 flip angles optimized for different applications achieved acceptable balance of extensive spatial coverage, accuracy, and repeatability in T₁ quantification (errors < 15%). Further optimization in terms of flip-angle choice for each tissue application, and the use of B₁ correction, are needed to improve the robustness of VFA protocols for T₁ mapping. Magn Reson Med 79:2564-2575, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Modification of population based arterial input function to incorporate individual variation

This technical note describes how to modify a population-based arterial input function to incorporate variation among the individuals. In DCE-MRI, an arterial input function (AIF) is often distorted by pulsated inflow effect and noise. A population-based AIF (pAIF) has high signal-to-noise ratio (SNR), but cannot incorporate the individual variation. AIF variation is mainly induced by variation in cardiac output and blood volume of the individuals, which can be detected by the full width at half maximum (FWHM) during the first passage and the amplitude of AIF, respectively. Thus pAIF scaled in time and amplitude fitting to the individual AIF may serve as a high SNR AIF incorporating the individual variation. The proposed method was validated using DCE-MRI images of 18 prostate cancer patients. Root mean square error (RMSE) of pAIF from individual AIFs was 0.88±0.48mM (mean±SD), but it was reduced to 0.25±0.11mM after pAIF modification using the proposed method (p<0.0001).

Early perfusion changes within 1 week of systemic treatment measured by dynamic contrast-enhanced MRI may predict survival in patients with advanced hepatocellular carcinoma

OBJECTIVES

To correlate early changes in the parameters of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) within 1 week of systemic therapy with overall survival (OS) in patients with advanced hepatocellular carcinoma (HCC).

METHODS

Eighty-nine patients with advanced HCC underwent DCE-MRI before and within 1 week following systemic therapy. The relative changes of six DCE-MRI parameters (Peak, Slope, AUC, Ktrans, Kep and Ve) of the tumours were correlated with OS using the Kaplan-Meier model and the double-sided log-rank test.

RESULTS

All patients died and the median survival was 174 days. Among the six DCE-MRI parameters, reductions in Peak, AUC, and Ktrans, were significantly correlated with one another. In addition, patients with a high Peak reduction following treatment had longer OS (P = 0.023) compared with those with a low Peak reduction. In multivariate analysis, a high Peak reduction was an independent favourable prognostic factor in all patients [hazard ratio (HR), 0.622; P = 0.038] after controlling for age, sex, treatment methods, tumour size and stage, and Eastern Cooperative Oncology Group performance status.

CONCLUSIONS

Early perfusion changes within 1 week following systemic therapy measured by DCE-MRI may aid in the prediction of the clinical outcome in patients with advanced HCC.

KEY POINTS

• DCE-MRI is helpful to evaluate perfusion changes of HCC after systemic treatment. • Early perfusion changes within 1 week after treatment may predict overall survival. • High Peak reduction was an independent favourable prognostic factor after systemic treatment.

Optimization of saturation-recovery dynamic contrast-enhanced MRI acquisition protocol: monte carlo simulation approach demonstrated with gadolinium MR renography

Dynamic contrast-enhanced (DCE) MRI is widely used for the measurement of tissue perfusion and to assess organ function. MR renography, which is acquired using a DCE sequence, can measure renal perfusion, filtration and concentrating ability. Optimization of the DCE acquisition protocol is important for the minimization of the error propagation from the acquired signals to the estimated parameters, thus improving the precision of the parameters. Critical to the optimization of contrast-enhanced T1 -weighted protocols is the balance of the T1 -shortening effect across the range of gadolinium (Gd) contrast concentration in the tissue of interest. In this study, we demonstrate a Monte Carlo simulation approach for the optimization of DCE MRI, in which a saturation-recovery T1 -weighted gradient echo sequence is simulated and the impact of injected dose (D) and time delay (TD, for saturation recovery) is tested. The results show that high D and/or high TD cause saturation of the peak arterial signals and lead to an overestimation of renal plasma flow (RPF) and glomerular filtration rate (GFR). However, the use of low TD (e.g. 100 ms) and low D leads to similar errors in RPF and GFR, because of the Rician bias in the pre-contrast arterial signals. Our patient study including 22 human subjects compared TD values of 100 and 300 ms after the injection of 4 mL of Gd contrast for MR renography. At TD = 100 ms, we computed an RPF value of 157.2 ± 51.7 mL/min and a GFR of 33.3 ± 11.6 mL/min. These results were all significantly higher than the parameter estimates at TD = 300 ms: RPF = 143.4 ± 48.8 mL/min (p = 0.0006) and GFR = 30.2 ± 11.5 mL/min (p = 0.0015). In conclusion, appropriate optimization of the DCE MRI protocol using simulation can effectively improve the precision and, potentially, the accuracy of the measured parameters. Copyright © 2016 John Wiley & Sons, Ltd.

Dynamic Contrast-enhanced MR Imaging of Advanced Hepatocellular Carcinoma: Comparison with the Liver Parenchyma and Correlation with the Survival of Patients Receiving Systemic Therapy

Purpose To retrospectively compare the perfusion parameters of advanced hepatocellular carcinoma (HCC) measured with dynamic contrast material-enhanced (DCE) magnetic resonance (MR) imaging with surrounding liver parenchyma to determine the relationship between these parameters and uncensored overall survival (OS). Materials and Methods This retrospective study had institutional review board approval, and informed consent was waived. DCE MR imaging was performed in 92 patients with advanced HCC before systemic treatment was administered (19 patients received a placebo). Three semiquantitative (peak, slope, and area under the gadolinium concentration-time curve [AUC]) and six quantitative (arterial fraction, arterial flow, portal flow, total blood flow, distribution volume, and mean transit time) parameters were calculated by placing regions of interest in the largest area of the tumor and background liver parenchyma. The DCE MR imaging parameters between the tumor and normal liver were compared with paired Wilcoxon test. By using the Cox proportional hazards model for univariate and multivariate analyses, the association of DCE MR imaging parameters and OS was investigated. Results HCC demonstrated significantly higher peak, slope, AUC, arterial fraction, and arterial flow but lower portal flow, distribution volume, and mean transit time than did the background liver (all P < .05). Patients with high peak in the tumor had longer OS (P = .005) than did those with low peak. Cox multivariate analysis identified peak as an independent predictor of OS (P = .032) after adjusting for age, sex, treatment, tumor size, and portal vein thrombosis. Conclusion DCE MR imaging parameters can be used to differentiate advanced HCC from the background liver, and peak, a semiquantitative parameter, is associated with outcome in patients with advanced HCC before systemic therapy. ^© RSNA, 2016 An earlier incorrect version of this article appeared online. This article was corrected on July 22, 2016.

High-spatial and high-temporal resolution dynamic contrast-enhanced perfusion imaging of the liver with time-resolved three-dimensional radial MRI

PURPOSE

Detection, characterization, and monitoring the treatment of hepatocellular carcinomas (HCC) in patients with cirrhosis is challenging because of their variable and rapid arterial enhancement. Multiphase dynamic contrast-enhanced MRI is used clinically for HCC assessment; however, the method suffers from limited temporal resolution and difficulty in coordinating imaging and breath-hold timing within a narrow temporal window of interest. In this article, a volumetric, high-spatial resolution, and high-temporal resolution dynamic contrast-enhanced liver imaging method for improved detection and characterization of HCC is demonstrated.

METHODS

A time-resolved three-dimensional radial acquisition with iterative sensitivity-encoding reconstruction images the entire abdomen and thorax with high spatial and temporal resolution, using real-time three-dimensional fluoroscopy to match the breath hold to contrast arrival. The sequence was tested on 17 subjects, including eight patients with HCC or other hypervascular focal lesions.

RESULTS

This technique was successful in acquiring volumetric imaging of the entire liver with 2.1-mm isotropic spatial and true 4-s temporal resolution.

CONCLUSION

This technique may be suitable for detecting, characterizing, and monitoring the treatment of HCC. It also holds significant potential for perfusion modeling, which may provide a noninvasive means to rapidly determine the efficacy of chemotherapeutic agents in these tumors over the entire liver volume.

Measurement of single-kidney glomerular filtration function from magnetic resonance perfusion renography

Glomerular filtration rate (GFR) describes the flow rate of filtered fluid through the kidney, and is considered to be the reference standard in the evaluation of renal function. There are many ways to test the GFR clinically, such as serum creatinine concentration, blood urea nitrogen and SPECT renography, however, they're all not a good standard to evaluate the early damage of renal function. In recent years, the improvement of MRI hardware and software makes it possible to reveal physiological characteristics such as renal blood flow or GFR by dynamic contrast enhancement magnetic resonance perfusion renography (DEC MRPR). MRPR is a method used to monitor the transit of contrast material, typically a gadolinium chelate, through the renal cortex, the medulla, and the collecting system. This review outlines the basics of DCE MRPR included acquisition of dynamic MR perfusion imaging, calculation of the contrast concentration from signal intensity and compartment models, and some challenges of MRPR method faced in prospective clinical application.

Four-dimensional MRI of renal function in the developing mouse

The major roles of filtration, metabolism and high blood flow make the kidney highly vulnerable to drug-induced toxicity and other renal injuries. A method to follow kidney function is essential for the early screening of toxicity and malformations. In this study, we acquired high spatiotemporal resolution (four dimensional) datasets of normal mice to follow changes in kidney structure and function during development. The data were acquired with dynamic contrast-enhanced MRI (via keyhole imaging) and a cryogenic surface coil, allowing us to obtain a full three-dimensional image (isotropic resolution, 125 microns) every 7.7 s over a 50-min scan. This time course permitted the demonstration of both contrast enhancement and clearance. Functional changes were measured over a 17-week course (at 3, 5, 7, 9, 13 and 17 weeks). The time dimension of the MRI dataset was processed to produce unique image contrasts to segment the four regions of the kidney: cortex (CO), outer stripe (OS) of the outer medulla (OM), inner stripe (IS) of the OM and inner medulla (IM). Local volumes, time-to-peak (TTP) values and decay constants (DC) were measured in each renal region. These metrics increased significantly with age, with the exception of DC values in the IS and OS. These data will serve as a foundation for studies of normal renal physiology and future studies of renal diseases that require early detection and intervention.

Dynamic contrast-enhanced magnetic resonance imaging measurement of renal function in patients undergoing partial nephrectomy: preliminary experience

OBJECTIVES

To evaluate changes in single-kidney glomerular filtration rate (SK-GFR) using low-dose dynamic contrast-enhanced magnetic resonance (MR) renography (MRR) in patients undergoing partial nephrectomy for renal masses.

MATERIALS AND METHODS

In this Health Information Patient Protection Act-compliant prospective study, 18 patients with renal masses underwent preoperative MR imaging at 1.5 T for renal mass evaluation and low-dose gadolinium-enhanced MRR. Magnetic resonance renography was repeated approximately 48 to 72 hours and 6 months after partial nephrectomy. Single-kidney glomerular filtration rate was calculated from the MRR images, and the right and left kidney values were summed for total MR-GFR. Postoperative changes in SK-GFR and MR-GFR were compared with changes in estimated glomerular filtration rate calculated using modification of diet in renal disease formula, renal lesion characteristics, ischemia type (warm vs cold), and ischemia time.

RESULTS

A decrease in the operated kidney SK-GFR was seen in 15 of the 18 patients, with a mean (SD) loss of 31% (23%), whereas estimated glomerular filtration rate decreased in 13 of the 18 patients with mean (SD) decrease of 19% (14%). Decrease in SK-GFR was greatest in the patients with warm ischemia time greater than 40 minutes and least in the patients with cold ischemia. In the immediate postoperative period, 6 of 7 patients (86%) with preoperative MR-GFR less than 60 mL/min per 1.73 m failed to demonstrate compensatory increase in SK-GFR in the nonoperated kidney, whereas 5 of 11 patients with baseline MR-GFR more than 60 mL/min per 1.73 m showed compensatory increase in nonoperated kidney SK-GFR.

CONCLUSIONS

Magnetic resonance renography can demonstrate functional loss in the operated kidney and compensatory increase in the function of the contralateral kidney, thus enabling evaluation of various surgical techniques on kidney function.

New magnetic resonance imaging methods in nephrology

Established as a method to study anatomic changes, such as renal tumors or atherosclerotic vascular disease, magnetic resonance imaging (MRI) to interrogate renal function has only recently begun to come of age. In this review, we briefly introduce some of the most important MRI techniques for renal functional imaging, and then review current findings on their use for diagnosis and monitoring of major kidney diseases. Specific applications include renovascular disease, diabetic nephropathy, renal transplants, renal masses, acute kidney injury, and pediatric anomalies. With this review, we hope to encourage more collaboration between nephrologists and radiologists to accelerate the development and application of modern MRI tools in nephrology clinics.

Quantitative hepatic perfusion modeling using DCE-MRI with sequential breathholds

PURPOSE

To develop and demonstrate the feasibility of a new formulation for quantitative perfusion modeling in the liver using interrupted DCE-MRI data acquired during multiple sequential breathholds.

MATERIALS AND METHODS

A new mathematical formulation to estimate quantitative perfusion parameters using interrupted data was developed. Using this method, we investigated whether a second degree-of-freedom in the tissue residue function (TRF) improves quality-of-fit criteria when applied to a dual-input single-compartment perfusion model. We subsequently estimated hepatic perfusion parameters using DCE-MRI data from 12 healthy volunteers and 9 cirrhotic patients with a history of hepatocellular carcinoma (HCC); and examined the utility of these estimates in differentiating between healthy liver, cirrhotic liver, and HCC.

RESULTS

Quality-of-fit criteria in all groups were improved using a Weibull TRF (2 degrees-of-freedom) versus an exponential TRF (1 degree-of-freedom), indicating nearer concordance of source DCE-MRI data with the Weibull model. Using the Weibull TRF, arterial fraction was greater in cirrhotic versus normal liver (39 ± 23% versus 15 ± 14%, P = 0.07). Mean transit time (20.6 ± 4.1 s versus 9.8 ± 3.5 s, P = 0.01) and arterial fraction (39 ± 23% versus 73 ± 14%, P = 0.04) were both significantly different between cirrhotic liver and HCC, while differences in total perfusion approached significance.

CONCLUSION

This work demonstrates the feasibility of estimating hepatic perfusion parameters using interrupted data acquired during sequential breathholds.

Hepatocellular carcinoma: perfusion quantification with dynamic contrast-enhanced MRI

OBJECTIVE

The objective of our study was to report our initial experience with dynamic contrast-enhanced MRI (DCE-MRI) for perfusion quantification of hepatocellular carcinoma (HCC) and surrounding liver.

SUBJECTS AND METHODS

DCE-MRI of the liver was prospectively performed on 31 patients with HCC (male-female ratio, 26:5; mean age, 61 years; age range, 41-83 years). A dynamic coronal 3D FLASH sequence was performed at 1.5 T before and after injection of gadolinium-based contrast agent with an average temporal resolution of 3.8 seconds. Regions of interest were drawn on the abdominal aorta, portal vein, liver parenchyma, and HCC lesions by two observers in consensus. Time-activity curves were analyzed using a dual-input single-compartment model. The following perfusion parameters were obtained: arterial flow, portal venous flow, arterial fraction, distribution volume, and mean transit time (MTT).

RESULTS

Thirty-three HCCs (mean size, 3.9 cm; range, 1.1-12.6 cm) were evaluated in 26 patients. When compared with liver parenchyma, HCC showed significantly higher arterial hepatic blood flow and arterial fraction (p < 0.0001) and significantly lower distribution volume and portal venous hepatic blood flow (p < 0.0001-0.023), with no difference in MTT. Untreated HCCs (n = 16) had a higher arterial fraction and lower portal venous hepatic blood flow value than chemoembolized HCCs (n = 17, p < 0.04).

CONCLUSION

DCE-MRI can be used to quantify perfusion metrics of HCC and liver parenchyma and to assess perfusion changes after HCC chemoembolization.

Automatic detection of arterial input function in dynamic contrast enhanced MRI based on affinity propagation clustering

PURPOSE

To automatically and robustly detect the arterial input function (AIF) with high detection accuracy and low computational cost in dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

MATERIALS AND METHODS

In this study, we developed an automatic AIF detection method using an accelerated version (Fast-AP) of affinity propagation (AP) clustering. The validity of this Fast-AP-based method was proved on two DCE-MRI datasets, i.e., rat kidney and human head and neck. The detailed AIF detection performance of this proposed method was assessed in comparison with other clustering-based methods, namely original AP and K-means, as well as the manual AIF detection method.

RESULTS

Both the automatic AP- and Fast-AP-based methods achieved satisfactory AIF detection accuracy, but the computational cost of Fast-AP could be reduced by 64.37-92.10% on rat dataset and 73.18-90.18% on human dataset compared with the cost of AP. The K-means yielded the lowest computational cost, but resulted in the lowest AIF detection accuracy. The experimental results demonstrated that both the AP- and Fast-AP-based methods were insensitive to the initialization of cluster centers, and had superior robustness compared with K-means method.

CONCLUSION

The Fast-AP-based method enables automatic AIF detection with high accuracy and efficiency.

MR renographic measurement of renal function in patients undergoing partial nephrectomy

OBJECTIVE

The purpose of this review is to describe the role of functional renal MRI, or MR renography, in the care of patients with renal masses undergoing partial nephrectomy.

CONCLUSION

MR renography can be used to monitor renal functional outcome for patients undergoing partial nephrectomy and may help guide patient selection in this population with elevated risk of chronic kidney disease.

Diffusion-weighted intravoxel incoherent motion imaging of renal tumors with histopathologic correlation

PURPOSE

The aim of this study was to use intravoxel incoherent motion diffusion-weighted imaging to discriminate subtypes of renal neoplasms and to assess agreement between intravoxel incoherent motion (perfusion fraction, fp) and dynamic contrast-enhanced magnetic resonance imaging (MRI) metrics of tumor vascularity.

SUBJECTS AND METHODS

In this Health Insurance Portability and Accountability Act-compliant, institutional review board-approved prospective study, 26 patients were imaged at 1.5-T MRI using dynamic contrast-enhanced MRI with high temporal resolution and diffusion-weighted imaging using 8 b values (range, 0-800 s/mm). Perfusion fraction (fp), tissue diffusivity (Dt), and pseudodiffusivity (Dp) were calculated using biexponential fitting of the diffusion data. Apparent diffusion coefficient (ADC) was calculated with monoexponential fit using 3 b values of 0, 400, and 800 s/mm. Dynamic contrast-enhanced data were processed with a semiquantitative method to generate model-free parameter cumulative initial area under the curve of gadolinium concentration at 60 seconds (CIAUC60). Perfusion fraction, Dt, Dp, ADC, and CIAUC60 were compared between different subtypes of renal lesions. Perfusion fraction was correlated with CIAUC60.

RESULTS

We examined 14 clear cell, 4 papillary, 5 chromophobe, and 3 cystic renal cell carcinomas (RCCs). Although fp had higher accuracy (area under the curve, 0.74) for a diagnosis of clear cell RCC compared with Dt or ADC, the combination of fp and Dt had the highest accuracy (area under the curve, 0.78). The combination of fp and Dt diagnosed papillary RCC and cystic RCC with 100% accuracy, and clear cell RCC and chromophobe RCC, with 86.5% accuracy. There was significant strong correlation between fp and CIAUC60 (r = 0.82; P < 0.001).

CONCLUSION

Intravoxel incoherent motion parameters fp and Dt can discriminate renal tumor subtypes. Perfusion fraction demonstrates good correlation with CIAUC60 and can assess degree of tumor vascularity without the use of exogenous contrast agent.

Spatiotemporal quantification of local drug delivery using MRI

Controlled release formulations for local, in vivo drug delivery are of growing interest to device manufacturers, research scientists, and clinicians; however, most research characterizing controlled release formulations occurs in vitro because the spatial and temporal distribution of drug delivery is difficult to measure in vivo. In this work, in vivo magnetic resonance imaging (MRI) of local drug delivery was performed to visualize and quantify the time resolved distribution of MRI contrast agents. Three-dimensional T1 maps (generated from T1-weighted images with varied TR) were processed using noise-reducing filtering. A segmented region of contrast, from a thresholded image, was converted to concentration maps using the equation 1/T1=1/T1,0+R1C, where T1,0 and T1 are the precontrast and postcontrast T1 map values, respectively. In this technique, a uniform estimated value for T 1,0 was used. Error estimations were performed for each step. The practical usefulness of this method was assessed using comparisons between devices located in different locations both with and without contrast. The method using a uniform T1,0, requiring no registration of pre- and postcontrast image volumes, was compared to a method using either affine or deformation registrations.

Estimation of single-kidney glomerular filtration rate without exogenous contrast agent

PURPOSE

Measurement of single-kidney filtration fraction and glomerular filtration rate (GFR) without exogenous contrast is clinically important to assess renal function and pathophysiology, especially for patients with comprised renal function. The objective of this study is to develop a novel MR-based tool for noninvasive quantification of renal function using conventional MR arterial spin labeling water as endogenous tracer.

THEORY AND METHODS

The regional differentiation of the arterial spin labeling water between the glomerular capsular space and the renal parenchyma was characterized and measured according to their MR relaxation properties (T1ρ or T2 ), and applied to the estimation of filtration fraction and single-kidney GFR. The proposed approach was tested to quantify GFR in healthy volunteers at baseline and after a protein-loading challenge.

RESULTS

Biexponential decay of the cortical arterial spin labeling water MR signal was observed. The major component decays the same as parenchyma water; the minor component decays much slower as expected from glomerular ultra-filtrates. The mean single-kidney GFR was estimated to be 49 ± 9 mL/min at baseline and increased by 28% after a protein-loading challenge.

CONCLUSION

We developed an arterial spin labeling-based MR imaging method that allows us to estimate renal filtration fraction and singe-kidney GFR without use of exogenous contrast.

Functional MRI of the kidneys

Renal function is characterized by different physiologic aspects, including perfusion, glomerular filtration, interstitial diffusion, and tissue oxygenation. Magnetic resonance imaging (MRI) shows great promise in assessing these renal tissue characteristics noninvasively. The last decade has witnessed a dramatic progress in MRI techniques for renal function assessment. This article briefly describes relevant renal anatomy and physiology, reviews the applications of functional MRI techniques for the diagnosis of renal diseases, and lists unresolved issues that will require future work.

Solid pancreatic lesions: characterization by using timing bolus dynamic contrast-enhanced MR imaging assessment--a preliminary study

PURPOSE

To assess the feasibility of postprocessing dynamic contrast material-enhanced (DCE) magnetic resonance (MR) imaging timing bolus data by using a three-dimensional radial gradient-echo technique with k-space-weighted image contrast (KWIC) for the characterization of solid pancreatic diseases.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board, and informed consent was waived. A total of 45 patients suspected of having biliary or pancreatic disease underwent pancreatic MR examination with a 3.0-T imager with a low-dose (2 mL gadopentetate dimeglumine) timing bolus by using the radial KWIC technique. There were 24 patients with pancreatic cancers, eight with pancreatic neuroendocrine tumors (PNETs), three with chronic pancreatitis, and 10 with a normal pancreas. By using a dedicated postprocessing software program for DCE MR imaging, the following perfusion parameters were measured for tumor and nontumorous parenchyma: volume transfer coefficient (K(trans)) and extracellular extravascular volume fraction; the rate constant (k(ep)) and initial area under the concentration curve in 60 seconds (iAUC) were then generated. The perfusion parameters acquired on DCE MR images were compared among the groups by using the analysis of variance test.

RESULTS

K(trans), k(ep), and iAUC values in patients with pancreatic cancer (0.042 min(-1) ± 0.023 [standard deviation], 0.761 min(-1) ± 0.529, and 2.841 mmol/sec ± 1.811, respectively) were significantly lower than in patients with a normal pancreas (0.387 min(-1) ± 0.176, 6.376 min(-1) ± 2.529, and 7.156 mmol/sec ± 3.414, respectively) (P < .05 for all). In addition, k(ep) values of PNETs and normal pancreas also differed (P < .0001), and K(trans), k(ep), and iAUC values of pancreatic cancers and PNETs differed significantly (P < .0001, P = .038, and P < .0001, respectively).

CONCLUSION

Results of timing bolus DCE MR imaging with the radial KWIC sequence from routine examinations can be postprocessed to yield potentially useful perfusion parameters for the characterization of pancreatic diseases.

Contrast agents as a biological marker in magnetic resonance imaging of the liver: conventional and new approaches

Liver imaging is an important clinical area in everyday practice. The clinical meaning of different lesion types in the liver can be quite different. Therefore, the result of imaging studies of the liver can change therapeutic concepts fundamentally. Contrast agents are used in the majority of MR examinations of the liver parenchyma-despite the already good soft-tissue contrast in plain MRI. This can be explained by the advantages in lesion detection and characterization of contrast-enhanced MRI of the liver. Beyond the qualitative evaluation of contrast-enhanced liver MR examinations, quantification of parameters will be the demand of the future. This can be achieved by perfusion MRI, also called dynamic contrast-enhanced MRI (DCE-MRI) of the liver. Its basic principles and different clinical applications will be discussed in this article. Definite cut-off values to determine disease or therapeutic response will help to increase the objectivity and reliability of liver MRI in future. This is especially important in the oncological setting, where modern therapies cannot be assessed based on changes in size only.

Quantitative evaluation of acute renal transplant dysfunction with low-dose three-dimensional MR renography

PURPOSE

To assess prospectively the ability of quantitative low-dose three-dimensional magnetic resonance (MR) renography to help identify the cause of acute graft dysfunction.

MATERIALS AND METHODS

This HIPAA-compliant study was approved by the institutional review board, and written informed consent was obtained. Between December 2001 and May 2009, sixty patients with transplanted kidneys (41 men and 19 women; mean age, 49 years; age range, 22-71 years) were included. Thirty-one patients had normal function and 29 had acute dysfunction due to acute rejection (n = 12), acute tubular necrosis (ATN) (n = 8), chronic rejection (n = 6), or drug toxicity (n = 3). MR renography was performed at 1.5 T with three-dimensional gradient-echo imaging. With use of a multicompartment renal model, the glomerular filtration rate (GFR) and the mean transit time (MTT) of the tracer for the vascular compartment (MTT(A)), the tubular compartment (MTT(T)), and the collecting system compartment (MTT(C)) were calculated. Also derived was MTT for the whole kidney (MTT(K) = MTT(A) + MTT(T) + MTT(C)) and fractional MTT of each compartment (MTT(A/K) = MTT(A)/MTT(K), MTT(T/K) = MTT(T)/MTT(K), MTT(C/K) = MTT(C)/MTT(K)). These parameters were compared in patients in the different study groups. Statistical analysis was performed by using analysis of covariance.

RESULTS

There were significant differences in GFR and MTT(K) between the acute dysfunction group (36.4 mL/min ± 20.8 [standard deviation] and 177.1 seconds ± 46.8, respectively) and the normal function group (65.9 mL/min ± 27.6 and 140.5 seconds ± 51.8, respectively) (P < .001 and P = .004). The MTT(A/K) was significantly higher in the acute rejection group (mean, 12.7% ± 2.9) than in the normal function group (mean, 8.3% ± 2.2; P < .001) or in the ATN group (mean, 7.1% ± 1.4; P < .001). The MTT(T/K) was significantly higher in the ATN group (mean, 83.2% ± 9.2) than in the normal function group (mean, 72.4% ± 10.2; P = .031) or in the acute rejection group (mean, 69.2% ± 6.1; P = .003).

CONCLUSION

Low-dose MR renography analyzed by using a multicompartmental tracer kinetic renal model may help to differentiate noninvasively between acute rejection and ATN after kidney transplantation.

Hepatic perfusion imaging: concepts and application

Hepatic perfusion imaging with magnetic resonance (MR) imaging is an emerging technique for quantitative assessment of diffuse hepatic disease and hepatic lesion blood flow. The principal method that has been used is based on T1 dynamic contrast-enhanced MR imaging. Perfusion imaging shows promise in the assessment of tumor therapy response, staging of liver fibrosis, and evaluation of hepatocellular carcinoma. The future standardization of imaging protocols and MR imaging pulse sequences will allow for broader clinical applications.

Diagnosis of cirrhosis with intravoxel incoherent motion diffusion MRI and dynamic contrast-enhanced MRI alone and in combination: preliminary experience

PURPOSE

To report our preliminary experience with the use of intravoxel incoherent motion (IVIM) diffusion-weighted magnetic resonance imaging (DW-MRI) and dynamic contrast-enhanced (DCE)-MRI alone and in combination for the diagnosis of liver cirrhosis.

MATERIALS AND METHODS

Thirty subjects (16 with noncirrhotic liver, 14 with cirrhosis) were prospectively assessed with IVIM DW-MRI (n = 27) and DCE-MRI (n = 20). IVIM parameters included perfusion fraction (PF), pseudodiffusion coefficient (D*), true diffusion coefficient (D), and apparent diffusion coefficient (ADC). Model-free DCE-MR parameters included time to peak (TTP), upslope, and initial area under the curve at 60 seconds (IAUC60). A dual input single compartmental perfusion model yielded arterial flow (Fa), portal venous flow (Fp), arterial fraction (ART), mean transit time (MTT), and distribution volume (DV). The diagnostic performances for diagnosis of cirrhosis were evaluated for each modality alone and in combination using logistic regression and receiver operating characteristic analyses. IVIM and DCE-MR parameters were compared using a generalized estimating equations model.

RESULTS

PF, D*, D, and ADC values were significantly lower in cirrhosis (P = 0.0056-0.0377), whereas TTP, DV, and MTT were significantly increased in cirrhosis (P = 0.0006-0.0154). There was no correlation between IVIM- and DCE-MRI parameters. The highest Az (areas under the curves) values were observed for ADC (0.808) and TTP-DV (0.952 for each). The combination of ADC with DV and TTP provided 84.6% sensitivity and 100% specificity for diagnosis of cirrhosis.

CONCLUSION

The combination of DW-MRI and DCE-MRI provides an accurate diagnosis of cirrhosis.

MR urography in children. Part 2: how to use ImageJ MR urography processing software

MR urography (MRU) is an emerging technique particularly useful in paediatric uroradiology. The most common indication is the investigation of hydronephrosis. Combined static and dynamic contrast-enhanced MRU (DCE-MRU) provides both morphological and functional information in a single examination. However, specific post-processing must be performed and to our knowledge, dedicated software is not available in conventional workstations. Investigators involved in MRU classically use homemade software that is not freely accessible. For these reasons, we have developed a software program that is freely downloadable on the National Institute of Health (NIH) website. We report and describe in this study the features of this software program.

Technical aspects of MR perfusion

The most common methods for measuring perfusion with MRI are arterial spin labelling (ASL), dynamic susceptibility contrast (DSC-MRI), and T(1)-weighted dynamic contrast enhancement (DCE-MRI). This review focuses on the latter approach, which is by far the most common in the body and produces measures of capillary permeability as well. The aim is to present a concise but complete overview of the technical issues involved in DCE-MRI data acquisition and analysis. For details the reader is referred to the references. The presentation of the topic is essentially generic and focuses on technical aspects that are common to all DCE-MRI measurements. For organ-specific problems and illustrations, we refer to the other papers in this issue. In Section 1 "Theory" the basic quantities are defined, and the physical mechanisms are presented that provide a relation between the hemodynamic parameters and the DCE-MRI signal. Section 2 "Data acquisition" discusses the issues involved in the design of an optimal measurement protocol. Section 3 "Data analysis" summarizes the steps that need to be taken to determine the hemodynamic parameters from the measured data.

Use of cardiac output to improve measurement of input function in quantitative dynamic contrast-enhanced MRI

PURPOSE

To validate a new method for converting MR arterial signal intensity versus time curves to arterial input functions (AIFs).

MATERIALS AND METHODS

The method constrains AIF with patient's cardiac output (Q). Monte Carlo simulations of MR renography and tumor perfusion protocols were carried out for comparison with two alternative methods: direct measurement and population-averaged input function. MR renography was performed to assess the method's inter- and intraday reproducibility for renal parameters.

RESULTS

In simulations of tumor perfusion, the precision of the parameters (K(trans) and v(e)) computed using the proposed method was improved by at least a factor of three compared to direct measurement. Similar improvements were obtained in simulations of MR renography. Volunteer study for testing interday reproducibility confirmed the improvement of precision in renal parameters when using the proposed method compared to conventional methods. In another patient study (two injections within one session), the proposed method significantly increased the correlation coefficient (R) between GFR of the two exams (0.92 vs. 0.83) compared to direct measurement.

CONCLUSION

A new method significantly improves the precision of dynamic contrast-enhanced (DCE) parameters. The method may be especially useful for analyzing repeated DCE examinations, such as monitoring tumor therapy or angiotensin converting enzyme-inhibitor renography.

A clinically feasible method to estimate pharmacokinetic parameters in breast cancer

Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) is the MRI technique of choice for detecting breast cancer, which can be roughly classified as either quantitative or semiquantitative. The major advantage of quantitative DCE-MRI is its ability to provide pharmacokinetic parameters such as volume transfer constant (Ktrans) and extravascular extracellular volume fraction (ve). However, semiquantitative DCE-MRI is still the clinical MRI technique of choice for breast cancer diagnosis due to several major practical difficulties in the implementation of quantitative DCE-MRI in a clinical setting, including (1) long acquisition necessary to acquire 3D T1(0) map, (2) challenges in obtaining accurate artery input function (AIF), (3) long computation time required by conventional nonlinear least square (NLS) fitting, and (4) many illogical values often generated by conventional NLS method. The authors developed a new analysis method to estimate pharmacokinetic parameters Ktrans and ve from clinical DCE-MRI data, including fixed T1(0) to eliminate the long acquisition for T1(0) map and "reference region" model to remove the requirement of measuring AIF. Other techniques used in our analysis method are (1) an improved formula to calculate contrast agent (CA) concentration based on signal intensity of SPGR data, (2) FCM clustering-based techniques for automatic segmentation and generation of a clustered concentration data set (3) an empirical formula for CA time course to fit the clustered data sets, and (4) linear regression for the estimation of pharmacokinetic parameters. Preliminary results from computer simulation and clinical study of 39 patients have demonstrated (1) the feasibility of their analysis method for estimating Ktrans and ve from clinical DCE-MRI data, (2) significantly less illogical values compared to NLS method (typically less than 1% versus more than 7%), (3) relative insensitivity to the noise in DCE-MRI data; (4) reduction in computation time by a factor of more than 30 times compared to NLS method on average, (5) high statistic correlation between the method used and NLS method (correlation coefficients: 0.941 for Ktrans and 0.881 for ve), and (6) the potential clinical usefulness of the new method.

Dynamic contrast-enhanced MR imaging of the liver: current status and future directions

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MR imaging) is emerging as a tool that can quantify changes in liver perfusion that occur in both diffuse and focal liver diseases. Recent data show promise for DCE-MR imaging of the liver in diagnosing fibrosis and cirrhosis before morphologic changes can be detected. It may also be valuable in the assessment of hepatocellular carcinoma and liver metastases. Acquisition parameters, postprocessing methods, applications, and recent results of DCE-MR imaging of the liver are also described. Finally, it reviews the limitations and future directions of DCE-MR imaging for liver applications.

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.

Optimal k-space sampling for dynamic contrast-enhanced MRI with an application to MR renography

For time-resolved acquisitions with k-space undersampling, a simulation method was developed for selecting imaging parameters based on minimization of errors in signal intensity versus time and physiologic parameters derived from tracer kinetic analysis. Optimization was performed for time-resolved angiography with stochastic trajectories (TWIST) algorithm applied to contrast-enhanced MR renography. A realistic 4D phantom comprised of aorta and two kidneys, one healthy and one diseased, was created with ideal tissue time-enhancement pattern generated using a three-compartment model with fixed parameters, including glomerular filtration rate (GFR) and renal plasma flow (RPF). TWIST acquisitions with different combinations of sampled central and peripheral k-space portions were applied to this phantom. Acquisition performance was assessed by the difference between simulated signal intensity (SI) and calculated GFR and RPF and their ideal values. Sampling of the 20% of the center and 1/5 of the periphery of k-space in phase-encoding plane and data-sharing of the remaining 4/5 minimized the errors in SI (<5%), RPF, and GFR (both <10% for both healthy and diseased kidneys). High-quality dynamic human images were acquired with optimal TWIST parameters and 2.4 sec temporal resolution. The proposed method can be generalized to other dynamic contrast-enhanced MRI applications, e.g., MR angiography or cancer imaging.

Advanced MRI methods for assessment of chronic liver disease

OBJECTIVE

With recent advances in technology, advanced MRI methods such as diffusion-weighted and perfusion-weighted MRI, MR elastography, chemical shift-based fat-water separation, and MR spectroscopy can now be applied to liver imaging. We will review the respective roles of these techniques for assessment of chronic liver disease.

CONCLUSION

MRI plays an increasingly important role in assessment of patients with chronic liver disease because of the lack of ionizing radiation and the possibility of performing multiparametric imaging.

Estimates of glomerular filtration rate from MR renography and tracer kinetic models

PURPOSE

To compare six methods for calculating the single-kidney glomerular filtration rate (GFR) from T(1)-weighted magnetic resonance (MR) renography (MRR) against reference radionuclide measurements.

MATERIALS AND METHODS

In 10 patients, GFR was determined using six published methods: the Baumann-Rudin model (BR), the Patlak-Rutland method (PR), the two-compartment model without bolus dispersion (2C) and with dispersion (2CD), the three-compartment model (3CD), and the distributed parameter model (3C-IRF). Reference single-kidney GFRs were measured by radionuclide renography. The coefficient of variation of GFR (CV) was determined for each method by Monte Carlo analyses for one healthy and one dysfunctional kidney at a noise level (sigma(n)) of 2%, 5%, and 10%.

RESULTS

GFR estimates in patients varied from 6% overestimation (BR) to 50% underestimation (PR and 2CD applied to cortical data). Correlations with reference GFRs ranged from R = 0.74 (2CD, cortical data) to R = 0.85 (BR). In simulations, the lowest CV was produced by 3C-IRF in healthy kidney (1.7sigma(n)) and by PR in diseased kidney ((2.2-2.4)sigma(n)). In both kidneys the highest CV was obtained with 2CD ((5.9-8.2)sigma(n)) and with 3CD in diseased kidney (8.9sigma(n) at sigma(n) = 10%).

CONCLUSION

GFR estimates depend on the renal model and type of data used. Two- and three-compartment models produce comparable GFR correlations.