A compact solution for estimation of physiological parameters from ultrafast prostate dynamic contrast enhanced MRI

The Tofts pharmacokinetic model requires multiple calculations for analysis of dynamic contrast enhanced (DCE) MRI. In addition, the Tofts model may not be appropriate for the prostate. This can result in error propagation that reduces the accuracy of pharmacokinetic measurements. In this study, we present a compact solution allowing estimation of physiological parameters K ^trans and v _e from ultrafast DCE acquisitions, without fitting DCE-MRI data to the standard Tofts pharmacokinetic model. Since the standard Tofts model can be simplified to the Patlak model at early times when contrast efflux from the extravascular extracellular space back to plasma is negligible, K ^trans can be solved explicitly for a specific time. Further, v _e can be estimated directly from the late steady-state signal using the derivative form of Tofts model. Ultrafast DCE-MRI data were acquired from 18 prostate cancer patients on a Philips Achieva 3T-TX scanner. Regions-of-interest (ROIs) for prostate cancer, normal tissue, gluteal muscle, and iliac artery were manually traced. The contrast media concentration as function of time was calculated over each ROI using gradient echo signal equation with pre-contrast tissue T1 values, and using the 'reference tissue' model with a linear approximation. There was strong correlation (r  =  0.88-0.91, p   <  0.0001) between K ^trans extracted from the Tofts model and K ^trans estimated from the compact solution for prostate cancer and normal tissue. Additionally, there was moderate correlation (r  =  0.65-0.73, p   <  0.0001) between extracted versus estimated v _e. Bland-Altman analysis showed moderate to good agreement between physiological parameters extracted from the Tofts model and those estimated from the compact solution with absolute bias less than 0.20 min^-1 and 0.10 for K ^trans and v _e, respectively. The compact solution may decrease systematic errors and error propagation, and could increase the efficiency of clinical workflow. The compact solution requires high temporal resolution DCE-MRI due to the need to adequately sample the early phase of contrast media uptake.

Whole-lesion histogram and texture analyses of breast lesions on inline quantitative DCE mapping with CAIPIRINHA-Dixon-TWIST-VIBE

PURPOSE

To investigate the diagnostic capability of whole-lesion (WL) histogram and texture analysis of dynamic contrast-enhanced (DCE) MRI inline-generated quantitative parametric maps using CAIPIRINHA-Dixon-TWIST-VIBE (CDTV) to differentiate malignant from benign breast lesions and breast cancer subtypes.

MATERIALS AND METHODS

From February 2018 to November 2018, DCE MRI using CDTV was performed on 211 patients. The inline-generated parametric maps included K^trans, k_ep, V_e, and IAUGC₆₀. Histogram and texture features were extracted from the above parametric maps respectively based on a WL analysis. Student's t tests, one-way ANOVAs, Mann-Whitney U tests, Jonckheere-Terpstra tests, and ROC curves were used for statistical analysis.

RESULTS

Compared with benign breast lesions, malignant breast lesions showed significantly higher K^trans_{_median, 5th percentile, entropy, and diff-entropy}, IAUGC_{60_median, 5th percentile, entropy, and diff-entropy}, k_{ep_mean, median, 5th percentile, entropy, and diff-entropy}, and V_{e_95th percentile, diff-variance, and contrast}, and significantly lower k_{ep_skewness} and V_{e_SD, entropy, diff-entropy, and skewness} (all p ≤ 0.011). The combination of all the extracted parameters yielded an AUC of 0.85 (sensitivity 76%, specificity 86%). k_{ep_contrast} showed a significant difference among different subtypes of breast cancer (p = 0.006). k_{ep_skewness} showed a significant difference between lymph node-positive and lymph node-negative breast cancer (p = 0.007). The IAGC_{60_5th percentile} had an AUC of 0.71 (sensitivity 50%, specificity 91%) for differentiating between high- and low-proliferation groups of breast cancer.

CONCLUSIONS

The WL histogram and texture analyses of CDTV-DCE-derived parameters may give additional information for further evaluation of breast cancer.

KEY POINTS

• Inline DCE mapping with CDTV is effective and time-saving. • WL histogram and texture-extracted features could distinguish breast cancer from benign lesions accurately. • k_{ep_contrast}, k_{ep_skewness}, and IAUGC_{60_5th percentile} could predict breast cancer subtypes, lymph node metastasis, and proliferation abilities, respectively.

Use of Indicator Dilution Principle to Evaluate Accuracy of Arterial Input Function Measured With Low-Dose Ultrafast Prostate Dynamic Contrast-Enhanced MRI

Accurately measuring arterial input function (AIF) is essential for quantitative analysis of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI). We used the indicator dilution principle to evaluate the accuracy of AIF measured directly from an artery following a low-dose contrast media ultrafast DCE-MRI. In total, 15 patients with biopsy-confirmed localized prostate cancers were recruited. Cardiac MRI (CMRI) and ultrafast DCE-MRI were acquired on a Philips 3 T Ingenia scanner. The AIF was measured at iliac arties following injection of a low-dose (0.015 mmol/kg) gadolinium (Gd) contrast media. The cardiac output (CO) from CMRI (CO_CMRI) was calculated from the difference in ventricular volume at diastole and systole measured on the short axis of heart. The CO from DCE-MRI (CO_DCE) was also calculated from the AIF and dose of the contrast media used. A correlation test and Bland–Altman plot were used to compare CO_CMRI and CO_DCE. The average (±standard deviation [SD]) area under the curve measured directly from local AIF was 0.219 ± 0.07 mM·min. The average (±SD) CO_CMRI and CO_DCE were 6.52 ± 1.47 L/min and 6.88 ± 1.64 L/min, respectively. There was a strong positive correlation (r = 0.82, P < .01) and good agreement between CO_CMRI and CO_DCE. The CO_DCE is consistent with the reference standard CO_CMRI. This indicates that the AIF can be measured accurately from an artery with ultrafast DCE-MRI following injection of a low-dose contrast media.

Comparison of arterial input functions measured from ultra-fast dynamic contrast enhanced MRI and dynamic contrast enhanced computed tomography in prostate cancer patients

The purpose of this study was to evaluate the accuracy of arterial input functions (AIFs) measured from dynamic contrast enhanced (DCE) MRI following a low dose of contrast media injection. The AIFs measured from DCE computed tomography (CT) were used as 'gold standard'. A total of twenty patients received CT and MRI scans on the same day. Patients received 120 ml Iohexol in DCE-CT and a low dose of (0.015 mM kg^-1) of gadobenate dimeglumine in DCE-MRI. The AIFs were measured in the iliac artery and normalized to the CT and MRI contrast agent doses. To correct for different temporal resolution and sampling periods of CT and MRI, an empirical mathematical model (EMM) was used to fit the AIFs first. Then numerical AIFs (AIF_CT and AIF_MRI) were calculated based on fitting parameters. The AIF_MRI was convolved with a 'contrast agent injection' function ([Formula: see text]) to correct for the difference between MRI and CT contrast agent injection times (~1.5 s versus 30 s). The results show that the EMMs accurately fitted AIFs measured from CT and MRI. There was no significant difference (p  >  0.05) between the maximum peak amplitude of AIFs from CT (22.1  ±  4.1 mM/dose) and MRI after convolution (22.3  ±  5.2 mM/dose). The shapes of the AIF_CT and [Formula: see text] were very similar. Our results demonstrated that AIFs can be accurately measured by MRI following low dose contrast agent injection.

Retrospectively gated MRI for in vivo assessment of endothelium-dependent vasodilatation and endothelial permeability in murine models of endothelial dysfunction

Endothelial dysfunction is linked to impaired endothelial-dependent vasodilatation and permeability changes. Here, we quantify both of these phenomena associated with endothelial dysfunction by MRI in vivo in mice. Endothelial function was evaluated in the brachiocephalic artery (BCA) and left carotid artery (LCA) in ApoE/LDLR(-/-) and high-fat diet (HFD)-fed mice as compared with control mice (C57BL/6J). The 3D IntraGate® FLASH sequence was used for evaluation of changes in vessels' cross-sectional area (CSA) and volume following acetylcholine (Ach) administration. Evaluation of endothelial permeability after administration of contrast agent (Galbumin, BioPAL) was based on the variable flip angle method for the assessment of parameters based on the relaxation time (T1 ) value. In order to confirm the involvement of nitric oxide (NO) in response to Ach, L-NAME-treated mice were also analyzed. To confirm that endothelial permeability changes accompany the impairment of Ach-dependent vasodilatation, permeability changes were analyzed in isolated, perfused carotid artery. In C57BL/6J mice, Ach-induced vasodilatation led to an approximately 25% increase in CSA in both vessels, which was temporarily dissociated from the effect of Ach on heart rate. In ApoE/LDLR(-/-) or HFD-fed mice Ach induced a paradoxical vasoconstriction that amounted to approximately 30% and 50% decreases in CSA of BCA and LCA respectively. In ApoE/LDLR(-/-) and HFD-fed mice endothelial permeability in BCA was also increased (fall in T1 by about 25%). In L-NAME-treated mice Ach-induced vasodilatation in BCA was lost. In isolated, perfused artery from ApoE/LDLR(-/-) mice endothelial permeability was increased. MRI-based assessment of endothelium-dependent vasodilatation induced by Ach and endothelial permeability using a retrospectively self-gated 3D gradient-echo sequence (IntraGate® FLASH) enables the reliable detection of systemic endothelial dysfunction in mice and provides an important tool for the experimental pharmacology of the endothelium in murine models of diseases in vivo. Copyright © 2016 John Wiley & Sons, Ltd.

Analytical corrections of banding artifacts in driven equilibrium single pulse observation of T2 (DESPOT2)

PURPOSE

DESPOT2 is a single-component T₂ mapping technique based on bSSFP imaging. It has seen limited application because of banding artifacts and magnetization transfer (MT) effects. In this work, acquisitions are optimized to minimize MT effects, while exact and approximate analytical equations enable automatic correction of banding artifacts within the T₂ maps in mere seconds.

THEORY AND METHODS

The technique was verified on an agar phantom at 3 tesla. The T₂ resulting from four different data combination techniques was compared with the T₂ from CPMG. Two comparable DESPOT2 scan protocols (short vs. long TR/T_RF ) designed to minimize MT effects, were tested both in the phantom and in vivo. A third protocol was tested in the brain of 8 volunteers and analytical correction schemes were compared with DESPOT2-FM.

RESULTS

The T₂ measurements in agar agree with CPMG within ∼7% and in vivo results agree with values reported in the literature. The approximate analytical solutions provide increased robustness to hardware imperfections and higher T₂ -to-noise ratio than the exact solutions.

CONCLUSION

New analytical solutions enable fast and accurate whole-brain T₂ mapping from previously measured T₁ and B₁ maps, and bSSFP images with at least two phase offsets and two flip angles (=4 datasets, 8 min scan). Magn Reson Med 76:1790-1804, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Improved T1, contrast concentration, and pharmacokinetic parameter quantification in the presence of fat with two-point Dixon for dynamic contrast-enhanced magnetic resonance imaging

PURPOSE

To evaluate the impact of fat and fat-suppression on the quantification of T1, gadolinium concentration, and pharmacokinetic parameters in DCE-MRI.

METHODS

T1 values were measured in fat-free phantoms using variable flip angle with no fat suppression, quick or interleaved fat saturation (QFS), or two-point Dixon and were compared with reference values measured with inversion recovery-prepared turbo spin echo. Relaxivity of gadolinium-benzyloxypropionictetraacetate (Gd-BOPTA) was measured in emulsions of Gd-BOPTA solution and fat using Dixon in-phase and water-only images. Liver T1 and pharmacokinetic parameters of 15 patients were calculated from Dixon in-phase and water-only images and were correlated with liver fat signal fraction.

RESULTS

T1 values measured using Dixon water-only and non-fat-suppressed images matched the reference values; while T1 values measured using QFS showed large deviations. Relaxivities and Gd measured in the Dixon water-only images were less affected by the fat than those measured in the in-phase images. The correlation between liver fat fraction and the differences in measured pharmacokinetic parameters using Dixon in-phase and water-only images were significant (P < 0.05) for T1, K(trans), and incremental area under the curve, but not Ve (P = 0.1).

CONCLUSION

Dixon water-only images provided more reliable estimation of T1, Gd, and pharmacokinetic parameters when fat was present.