Dynamic Contrast-enhanced Perfusion Magnetic Resonance Research Articles

Diagnostic efficacy of dynamic contrast-enhanced magnetic resonance perfusion imaging in detecting local tumor recurrence in patients with head and neck malignancies after definitive treatment.

Accurate interpretation of post-treatment imaging in head and neck malignancies poses a challenge due to treatment sequelae. Magnetic resonance (MR) perfusion helps in this scenario by evaluating the hemodynamic characteristics of lesions. This study aimed to elucidate the diagnostic efficacy of dynamic contrast-enhanced (DCE)-MR perfusion imaging in detecting recurrence in patients after they underwent definitive treatment for head and neck tumors. Thirty patients who had received definitive curative-intent treatment for histopathology-proven malignant head and neck tumors and in whom recurrent tumor was detected on precontrast MR imaging (MRI) were accrued in the study. Patients underwent DCE-MR perfusion imaging. Time to peak (TTP), relative maximum enhancement (RME), and relative washout (RWO) ratio were calculated by using time-intensity curve (TIC). The diagnostic accuracy was compared with histopathology. A cut-off value of ≥125.3 for RME showed a sensitivity of 76.2% and specificity of 66.7% for differentiating post-radiation changes and recurrence. The optimal cut-off for RWO ratio was ≥-6.24 with a sensitivity of 76.2% and specificity of 55.6%. The optimal cut-off of TTP was ≤45.8 s with a sensitivity of 61.9% and specificity of 77.8%. Diagnostic accuracies of RME, RWO, and TTP were 73.3%, 70%, and 66.7%, respectively. DCE-MRI had significant diagnostic accuracy in detecting and differentiating recurrences. TIC analysis of high-temporal resolution DCE-MRI can provide information regarding microcirculation of tumors, and hence can be considered as an imaging modality of choice for assessment of early local tumor recurrence in head and neck tumors.

Diagnostic Utility of Integration of Dynamic Contrast-Enhanced and Dynamic Susceptibility Contrast MR Perfusion Employing Split Bolus Technique in Differentiating High-Grade Glioma.

Background : Despite documented correlation between glioma grades and dynamic contrast-enhanced (DCE) magnetic resonance (MR) perfusion-derived parameters, and its inherent advantages over dynamic susceptibility contrast (DSC) perfusion, the former remains underutilized in clinical practice. Given the inherent spatial heterogeneity in high-grade diffuse glioma (HGG) and assessment of different perfusion parameters by DCE (extravascular extracellular space volume [Ve] and volume transfer constant in unit time [k-trans]) and DSC (rCBV), integration of the two into a protocol could provide a holistic assessment. Considering therapeutic and prognostic implications of differentiating WHO grade 3 from 4, we analyzed the two grades based on a combined DCE and DSC perfusion. Methods : Perfusion sequences were performed on 3-T MR. Cumulative dose of 0.1 mmol/kg of gadodiamide, split into two equal boluses, was administered with an interval of 6 minutes between the DCE and DSC sequences. DCE data were analyzed utilizing commercially available GenIQ software. Results : Of the 41 cases of diffuse gliomas analyzed, 24 were WHO grade III and 17 grade IV gliomas (2016 WHO classification). To differentiate grade III and IV gliomas, Ve cut-off value of 0.178 provided the best combination of sensitivity (88.24%) and specificity (87.50%; AUC: 0.920; p < 0.001). A relative cerebral blood volume (rCBV) of value 3.64 yielded a sensitivity of 70.59% and specificity of 62.50% ( p = 0.018). The k-trans value, although higher in grade III than in grade IV gliomas, did not reach statistical significance ( p = 0.108). Conclusion : Uniqueness of employed combined perfusion technique, treatment naïve patients at imaging, user-friendly postprocessing software utilization, and ability of Ve and rCBV to differentiate between grade III and IV gliomas ( p < 0.05) are the strengths of the present study, contributing to the existing literature and moving a step closer to achieving accurate MR perfusion-based glioma grading.

Intraoperative Real-Time Near-Infrared Image-Guided Endoscopic Endonasal Surgery for Pituitary Tumors

For endoscopic endonasal surgery of pituitary tumors, tissue identification and intraoperative judgment depend largely on surgeon expertise. In the present study, we assess whether the delayed-window indocyanine green (ICG) technique can identify pituitary gland tumors in real-time during surgery and analyze the mechanism of ICG fluorescence in the pituitary gland and tumor. Twenty-five patients with a pituitary adenoma were administered 12.5 mg of ICG intravenously during surgery. Thereafter, near-infrared (NIR) visualization was performed from 0 to 180 minutes. Only 8 patients underwent dynamic contrast-enhanced perfusion magnetic resonance imaging (MRI) owing to predicaments with insurance coverage. Consequently, we analyzed these 8 patients extensively. The pituitary gland and pituitary adenoma were visualized in all 25 patients with NIR fluorescence. The relative ratio of the fluorescence emission of the normal gland to that of the tumor (signal/background ratio [SBR] of the normal gland vs. the tumor) had increased after 15 minutes, peaking (5.8) at 90 minutes, demonstrating that the pituitary gland was distinctly visualized during that period. The tumor/blood (SBR tumor) and normal gland/blood (SBR gland) NIR fluorescence was significantly and positively correlated with each transfer constant on dynamic contrast-enhanced MRI, indicating vascular permeability. The results from the present study exhibit the utility of the delayed-window ICG technique in distinguishing the normal pituitary gland from a tumor during endoscopic endonasal surgery from 15 to 90 minutes after ICG administration. Permeability can contribute to gadolinium enhancement on MRI, as well as ICG retention and NIR fluorescence in a normal pituitary gland and tumor.

Concurrent immunotherapy and re-irradiation utilizing stereotactic body radiotherapy for recurrent high-grade gliomas.

Clinical trials evaluating immune checkpoint inhibition (ICI) in recurrent high-grade gliomas (rHGG) report 7%-20% 6-month progression-free survival (PFS), while re-irradiation demonstrates 28%-39% 6-month PFS. We evaluate outcomes of patients treated with ICI and concurrent re-irradiation utilizing stereotactic body radiotherapy/fractionated stereotactic radiosurgery (SBRT) compared to ICI monotherapy. Patients ≥18-years-old with rHGG (WHO grade III and IV) receiving ICI + SBRT or ICI monotherapy between January 1, 2016 and January 1, 2019 were included. Adverse events, 6-month PFS and overall survival (OS) were assessed. Log-rank tests were used to evaluate PFS and OS. Histogram analyses of apparent diffusion coefficient maps and dynamic contrast-enhanced magnetic resonance perfusion metrics were performed. Twenty-one patients with rHGG (ICI + SBRT: 16; ICI: 5) were included. The ICI + SBRT and ICI groups received a mean 7.25 and 6.2 ICI cycles, respectively. There were five grade 1, one grade 2 and no grade 3-5 AEs in the ICI + SBRT group, and four grade 1 and no grade 2-5 AEs in the ICI group. Median PFS was 2.85 and 1month for the ICI + SBRT and ICI groups; median OS was 7 and 6months among ICI + SBRT and ICI groups, respectively. There were significant differences in pre and posttreatment tumor volume in the cohort (12.35 vs. 20.51; p= .03), but not between treatment groups. In this heavily pretreated cohort, ICI with re-irradiation utilizing SBRT was well tolerated. Prospective studies are warranted to evaluate potential therapeutic benefits to re-irradiation with ICI + SBRT in rHGG.

Diagnostic yield of simultaneous dynamic contrast-enhanced magnetic resonance perfusion measurements and [18F]FET PET in patients with suspected recurrent anaplastic astrocytoma and glioblastoma

PurposeBoth amino acid positron emission tomography (PET) and magnetic resonance imaging (MRI) blood volume (BV) measurements are used in suspected recurrent high-grade gliomas. We compared the separate and combined diagnostic yield of simultaneously acquired dynamic contrast-enhanced (DCE) perfusion MRI and O-(2-[18F]-fluoroethyl)-L-tyrosine ([18F]FET) PET in patients with anaplastic astrocytoma and glioblastoma following standard therapy.MethodsA total of 76 lesions in 60 hybrid [18F]FET PET/MRI scans with DCE MRI from patients with suspected recurrence of anaplastic astrocytoma and glioblastoma were included retrospectively. BV was measured from DCE MRI employing a 2-compartment exchange model (2CXM). Diagnostic performances of maximal tumour-to-background [18F]FET uptake (TBRmax), maximal BV (BVmax) and normalised BVmax (nBVmax) were determined by ROC analysis using 6-month histopathological (n = 28) or clinical/radiographical follow-up (n = 48) as reference. Sensitivity and specificity at optimal cut-offs were determined separately for enhancing and non-enhancing lesions.ResultsIn progressive lesions, all BV and [18F]FET metrics were higher than in non-progressive lesions. ROC analyses showed higher overall ROC AUCs for TBRmax than both BVmax and nBVmax in both lesion-wise (all lesions, p = 0.04) and in patient-wise analysis (p < 0.01). Combining TBRmax with BV metrics did not increase ROC AUC. Lesion-wise positive fraction/sensitivity/specificity at optimal cut-offs were 55%/91%/84% for TBRmax, 45%/77%/84% for BVmax and 59%/84%/72% for nBVmax. Combining TBRmax and best-performing BV cut-offs yielded lesion-wise sensitivity/specificity of 75/97%. The fraction of progressive lesions was 11% in concordant negative lesions, 33% in lesions only BV positive, 64% in lesions only [18F]FET positive and 97% in concordant positive lesions.ConclusionThe overall diagnostic accuracy of DCE BV imaging is good, but lower than that of [18F]FET PET. Adding DCE BV imaging did not improve the overall diagnostic accuracy of [18F]FET PET, but may improve specificity and allow better lesion-wise risk stratification than [18F]FET PET alone.

Dynamic contrast-enhanced magnetic resonance perfusion volumetrics can differentiate tuberculosis of the spine and vertebral malignancy

There is considerable overlap in radiologic features of tubercular and malignant spinal lesions on conventional magnetic resonance imaging (MRI). To evaluate the role of dynamic contrast-enhanced (DCE) MRI perfusion parameters in differentiating vertebral malignancy from spinal tuberculosis. This was a prospective study and we enrolled consecutive patients presenting with a clinical/radiologic evidence of vertebral lesions. DCE-MRI of the spine was performed using 3D volume interpolated breath-hold examination (VIBE) sequence after intravenously injecting 0.1 mmol/kg body weight of gadopentetate dimeglumine. We used Tofts model to calculate DCE parameters that included Ktrans (transfer constant), kep (rate constant), ve (fractional volume of extracellular extravascular space), and iAUC (initial area under the curve). We compared the mean value of each perfusion parameter by type of lesion (tubercular/malignant) at 0.05 significance level and performed receiver operating characteristic curve analysis. We could confirm histologic/cytologic diagnosis in 35 of the 45 patients recruited. Of these, 19 were tubercular and 16 were malignant lesions. The mean (± standard deviation) of kep (min-1) was significantly higher (2.89 ± 3.3) in malignant compared to tubercular lesions (0.81 ± 0.19), whereas ve was significantly lower in malignant (0.27 ± 0.13 mL/g) compared to benign lesions (0.47 ± 0.12 mL/g) at 0.05 significance level. kep cutoff of ≥1.17 min-1 had a sensitivity of 93.8% and specificity of 100% with a diagnostic accuracy of 94.4% in detecting malignant disease. High kep is the single best predictor of malignant vertebral lesions. We recommend kep cutoff value of ≥1.17 min-1 that has high diagnostic accuracy in identifying malignant lesions.

T2* dynamic contrast enhanced MR perfusion for cervical cord lesions; does it work?

BackgroundThe goal of this work was to assess the value of magnetic resonance (MR) perfusion in narrowing the differential diagnosis of cord lesions.Thirty eight patients with different cervical cord lesions were involved in this study. This includes 20 males and 18 females, ranging between 13 and 60 years old.Conventional MR with T2W (axial and sagittal) and pre and post contrast T1W (axial and sagittal) in addition to the T2* MR perfusion sequence were done. The final diagnosis of cervical cord tumors was achieved by biopsy and histopathological diagnosis, while inflammatory lesions were proved by clinical, laboratory data and follow-up for six months.ResultsNeoplastic lesions were found in 13 patients, while 25 patients had inflammatory lesions. Relative cord/cerebral blood volume (rCBV) was significantly higher in neoplastic lesions when compared to non-neoplastic ones (2 ± 1.13 vs 1.01 ± 0.62), respectively. A cutoff value of 1.38 or higher has high sensitivity of 78% and specificity of 83% in differentiating between these lesions.ConclusionT2* is a valuable technique in differentiating neoplastic from non-neoplastic cervical cord lesions.

MRI Features Associated with TERT Promoter Mutation Status in Glioblastoma.

Telomerase reverse transcriptase (TERT) promoter mutations are associated with worse prognosis in glioblastoma. The purpose of this study was to evaluate whether TERT mutation status was associated with specific morphologic and quantitative imaging features. Twenty-nine patients with isocitrate dehydrogenase 1/2-wildtype glioblastoma (13 TERT-wildtype, 16 TERT-mutated), who underwent preoperative magnetic resonance (MR) imaging were included in this retrospective study. Qualitative imaging phenotypes were evaluated using the Visually Accessible Rembrandt Images (VASARIs) feature set. Histogram analysis of apparent diffusion coefficient (ADC) and dynamic contrast-enhanced MR perfusion values were performed on enhancing tumor volumes-of-interest, and differences between TERT-wildtype and TERT-mutated tumors were assessed. VASARI analysis demonstrated that the majority of morphologic features were not significantly different between TERT-wildtype and TERT-mutated tumors, although a higher proportion of TERT-wildtype tumors featured nonenhancing tumor crossing midline (P = .014). TERT-mutated tumors demonstrated lower median rate constant kep (.38 vs. .76, P = .03) and lower median volume transfer coefficient Ktrans (.13 vs. .31, P = .02). There was no significant difference in median plasma volume vp (P = .92) or ADC values (P = .66) between the two groups. We further found a significant interaction between median kep and Ktrans and TERT status, respectively, suggesting greater risk of death with increasing blood-brain barrier dysfunction in TERT-mutated but not in TERT-wildtype tumors. Our study demonstrates evidence of altered permeability metrics associated with TERT mutation in glioblastoma, laying the foundation for future prospective studies assessing implications for therapeutic management and clinical outcomes.

Assessment of the Agreement between Cerebral Hemodynamic Indices Quantified Using Dynamic Susceptibility Contrast and Dynamic Contrast-enhanced Perfusion Magnetic Resonance Imagings.

Background:Brain tumor is one of the most common tumors. A successful treatment might be achieved with an early identification. Pathological investigation as the gold standard method for tumor identification has some limitations. Noninvasive assessment of tumor specifications may be possible using perfusion-weighted magnetic resonance imaging (MRI). Cerebral blood volume (CBV) and cerebral blood flow (CBF) could be calculated based on dynamic contrast-enhanced MRI (DCE-MRI) in addition to dynamic susceptibility contrast MRI (DSC-MRI) modality. Each category of the cerebral hemodynamic and permeability indices revealed the specific tumor characteristics and their collection could help for better identification of the tumor. Some mathematical methods were developed to determine both cerebral hemodynamic and permeability indices based on a single-dose DCE perfusion MRI. There are only a few studies available on the comparison of DSC- and DCE-derived cerebral hemodynamic indices such as CBF and CBV.Aim:The objective of the study was to validate first-pass perfusion parameters derived from T1-based DCE method in comparison to the routine T2*-based DSC protocol.Materials and Methods:Twenty-nine patients with brain tumor underwent DCE- and DSC-MRIs to evaluate the agreement between DSC- and DCE-derived cerebral hemodynamic parameters. Agreement between DSC- and DCE-derived cerebral hemodynamic indices was determined using the statistical method described by Bland and Altman. The reliability between DSC- and DCE-derived cerebral hemodynamic indices was measured using the intraclass correlation analysis.Results:The achieved magnitudes for DCE-derived CBV (gray matter [GM]: 5.01 ± 1.40 mL/100 g vs. white matter [WM]: 1.84 ± 0.74 mL/100 g) and DCE-derived CBF (GM: 60.53 ± 12.70 mL/100 g/min vs. WM: 32.00 ± 6.00 mL/100 g/min) were in good agreement with other studies. The intraclass correlation coefficients showed that the cerebral hemodynamic indices could accurately be estimated based on the DCE-MRI using a single-compartment model (>0.87), and DCE-derived cerebral hemodynamic indices are significantly similar to the magnitudes achieved based on the DSC-MRI (P < 0.001). Furthermore, an acceptable agreement was observed between DSC- and DCE-derived cerebral hemodynamic indices.Conclusion:Based on the measurement of the cerebral hemodynamic and blood–brain barrier permeability using DCE-MRI, a more comprehensive collection of the physiological parameters cloud be achieved for tumor evaluations.

Magnetic resonance perfusion for differentiating low-grade from high-grade gliomas at first presentation.

Magnetic resonance perfusion for differentiating low-grade from high-grade gliomas at first presentation.

Role of Dynamic Contrast-Enhanced Perfusion Magnetic Resonance Imaging in Grading of Pediatric Brain Tumors on 3T

Background/Aims: Perfusion magnetic resonance imaging (MRI) is useful for preoperative assessment of brain tumors. Dynamic susceptibility contrast perfusion MRI is commonly used for evaluation of brain tumors. Dynamic contrast-enhanced (DCE) MRI is an alternative method that has mainly been used in adult brain tumors. In this preliminary study, we report our initial experience with the DCE perfusion MRI in pediatric brain tumors. Methods: Sixty-four newly diagnosed pediatric brain tumor patients underwent DCE perfusion MRI on a 3-T scanner. Hemodynamic and kinetic parametric maps were generated and the regions with the highest values were measured on each map. Statistical differences were sought to differentiate between low-grade tumors, high-grade tumors, and medulloblastomas. The perfusion metrics of common posterior fossa tumors were also compared. Results: Relative corrected cerebral blood volume (rCBV) and fractional plasma volume measures differed significantly between high- and low-grade tumors (p < 0.05). High-grade tumors could be differentiated from low-grade tumors, with an rCBV cutoff value of 2.41 and 88.6% sensitivity and 65% specificity. There was no significant difference in K^trans, K_ep, V_e, or λ^tr between these 2 groups of tumors. rCBV, relative quantification of the cerebral blood flow, and permeability indices were found to be significantly different in various posterior fossa tumors, i.e., pilocytic astrocytoma, ependymoma, and medulloblastoma (p < 0.05). Conclusion: DCE-derived perfusion metrics are useful in differentiating high-grade tumors from low-grade ones and discriminating among various posterior fossa tumors in the pediatric age group.

Comparative Evaluation of 3-Dimensional Pseudocontinuous Arterial Spin Labeling With Dynamic Contrast-Enhanced Perfusion Magnetic Resonance Imaging in Grading of Human Glioma

The study was performed to compare dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) with 3-dimensional (3D) pseudocontinuous arterial spin labeling (PCASL) MRI in gliomas with an aim to see whether arterial spin labeling (ASL)-derived cerebral blood flow (CBF) values can be used as an alternative to DCE-MRI for its grading. Sixty-four patients with glioma (37 male; mean age, 43 years; 38 high grade and 26 low grade) underwent 3D-PCASL and DCE-MRI. The DCE indices (relative cerebral blood volume, rCBV; relative CBF, rCBF; permeability, k and kep; and leakage, ve) and ASL (absolute and rCBF) values were quantified from the tumors. Student independent t test was used to compare ASL and DCE-MRI indices. Pearson correlation was used to see correlation between DCE- and ASL-derived CBF values in tumor and normal parenchyma. On Student t test, neither ASL-derived absolute CBF (P = 0.78) nor rCBF (P = 0.12) values were found to be significantly different in 2 groups, whereas DCE indices except ve were significantly higher in high-grade gliomas. Arterial spin labeling-derived rCBF values weakly correlated with DCE-derived rCBF values, whereas these did not show correlation in normal grey (P = 0.12, r = 0.2) and white (P = 0.26, r = 0.14) matter regions. Three-dimensional pseudocontinuous arterial spin labeling does not appear to be a reliable technique in the current form and may not be a suitable replacement for DCE in grading of glioma.

The role of T1-weighted dynamic contrast-enhanced perfusion magnetic resonance imaging in gross target volume delineation of glioma patients

Objective To investigate whether the T1-weighted dynamic contrast-enhanced perfusion magnetic resonance imaging (DCEPMRI) technique can help to delineate the clinical target volume of brain glioma patients.Methods The DCE T1-weighted images from 28 glioma patients were collected after GdDTPA was injected.After the acquired images were processed and analyzed using modified Tofts-Kermode'two compartment analysis model and de-convolution method,the value and its pseudo mapping of quantitative parameter Ktrans related to microvascular permeability were obtained.The tumor size in the largest diameter slice measured both in routine enhanced MRI and Ktrans mapping of T1-weighted DCEPMRI were compared.Results The vascular permeability and tumor infiltration was lower in low grade glioma,the difference of the tumor size between T1-weighted DCEPMRI and routine enhanced MRI reached 0.2％ -0.3％ there was significant difference of tumor size between T1 -weighted DCEPMRI and routine enhanced MRI ( grade Ⅰ and Ⅱ grade with 2.93 cm2∶2.46 cm2(t=6.90,P=0.000) and 4.18 cm2∶3.21 cm2(t=10.22,P=0.000) ).While in high grade glioma,the vascular permeability and the tumor infiltration were higher,the difference of the tumor size between T1-weighted DCEPMRI and routine enhanced MRI reached 25％ - 26％( the size of grade Ⅲ and Ⅳ were 6.46 cm2 vs 5.48 cm2 ( t =10.83,P =0.000) and 8.26 cm2 vs 6.52 cm2(t =18.53,P =0.000) ).Conclusions The pseudo mapping of quantitative parameter Ktrans related to microvascular permeability acquired by T1-weighted DCEPMRI reflect the infiltrating circumscription in glioma,T1-weighted DCEPMRI can provide more information in delineation the clinical target volume,and it can be used as a new method for tumor volume evaluation. Key words: Dynamic contrast-enhanced perfusion magnetic resonance imaging,T1-weighted; Microvascular permeability; Brain neoplasms/radiotherapy; Delineation of target volume

Pilot study on evaluation of any correlation between MR perfusion (Ktrans) and diffusion (apparent diffusion coefficient) parameters in brain tumors at 3 Tesla

Purpose: To assess any correlation of volume transfer constant (Ktrans) with apparent diffusion coefficient (ADC) in different brain tumor types at 3 T magnetic resonance (MR) imaging. Materials and methods: Thirteen patients with brain tumors (8 men, 5 women; mean age 54.6 ± 17.7 years) were enrolled in this retrospective study. All patients underwent dynamic contrast-enhanced T1-weighted MR perfusion and diffusion-weighted imaging using a 3 T scanner. Ktrans was estimated by specially designed software. For each tumor, regions of interest (ROIs) were manually selected on corresponding Ktrans and ADC maps. Pearson correlation coefficients were obtained for maximum, mean and minimum values of Ktrans and ADC of all ROIs. Based on clinicopathologic results, the final diagnoses of patients were glioblastoma multiforme (3), low-grade to anaplastic gliomas (4), meningiomas (3) and metastatic tumors (3). Results: Ktrans(max) values were significantly inversely correlated with ADC(min) values (r = –0.536, P < 0.001) and ADC(mean) values (r = –0.465, P < 0.001). Ktrans(mean) and Ktrans(min) values were significantly inversely correlated with ADC(mean) (r = –0.228, P = 0.038) and ADC(max) values (r = –0.355, P = 0.001), respectively. Conclusion: We found that irrespective of brain tumor type, there is an inverse correlation between ADC and Ktrans. Our findings highlight an intricate relationship between vascular permeability and the tumor microenvironment, probably modulating and/or interacting with changes such as increased cellularity, ischemic insult and varying extracellular matrix composition.

ADMA Increases Arterial Stiffness and Decreases Cerebral Blood Flow in Humans

Preclinical studies have revealed that the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine (ADMA), increases vascular tone in cerebral blood vessels. Marked elevations of ADMA blood levels were found in patients with diseases characterized by decreased cerebral perfusion, such as ischemic stroke. Arterial stiffness is an independent predictor of stroke and other adverse cardiovascular events. The aim of this study was to investigate the influence of a systemic subpressor dose of ADMA on arterial stiffness and cerebral perfusion in humans. Using a double-blind, vehicle-controlled study design, we allocated 20 healthy men in random order to infusion of either ADMA (0.10 mg ADMA/kg per min) or vehicle over a period of 40 minutes. Arterial stiffness was assessed noninvasively by pulse wave analysis. All volunteers underwent measurement of cerebral perfusion by dynamic contrast-enhanced perfusion magnetic resonance imaging of the brain. Infusion of ADMA significantly decreased total cerebral perfusion by 15.1+/-4.5% (P=0.007), whereas blood flow in the vehicle group increased by 7.7+/-2.8% (P=0.02). ADMA also increased arterial stiffness as assessed by measurement of the augmentation index (-12.6+/-1.9 to -9.6+/-1.5, P=0.007). Our results document for the first time that subpressor doses of ADMA increase vascular stiffness and decrease cerebral perfusion in healthy subjects. Thus, ADMA is an important endogenous modulator of cerebral vascular tone and may be involved in the pathogenesis of cerebrovascular disease.

Cluster analysis of dynamic cerebral contrast-enhanced perfusion MRI time-series

We performed neural network clustering on dynamic contrast-enhanced perfusion magnetic resonance imaging time-series in patients with and without stroke. Minimal-free-energy vector quantization, self-organizing maps, and fuzzy c-means clustering enabled self-organized data-driven segmentation with respect to fine-grained differences of signal amplitude and dynamics, thus identifying asymmetries and local abnormalities of brain perfusion. We conclude that clustering is a useful extension to conventional perfusion parameter maps.

Decreased Pulmonary Perfusion in Pulmonary Vein Stenosis After Radiofrequency Ablation: Assessment With Dynamic Magnetic Resonance Perfusion Imaging

The functional impact of pulmonary vein (PV) stenosis on pulmonary perfusion after radiofrequency ablation (RFA) for atrial fibrillation (AF) has not been systematically evaluated previously. Therefore, we correlated magnetic resonance (MR) pulmonary perfusion imaging with single-photon emission CT (SPECT) perfusion and with the degree of PV stenosis (PVS) apparent on MR angiography (MRA) after RF ablation. Joint radiology-cardiology collaborative magnetic resonance unit at the Kerckhoff Heart Center. This was a cohort study of 110 patients who were routinely examined by MRA after RFA for AF, whereby 51 patients with a PV diameter reduction of > 25% or with clinical symptoms (ie, dyspnea and cough) were enrolled into the study. Patients were examined at follow-up by MR perfusion imaging and MRA, and the results were compared to those from patients who underwent SPECT scanning and from a control group of 26 untreated patients. Twelve patients underwent PVS dilatation as well as 22 sequential follow-up examinations. Pulmonary perfusion was evaluated using a dynamic contrast-enhanced three-dimensional MR perfusion sequence (1.5 T, 2.5-s temporal resolution, and 0.05 cm spatial resolution), and high-resolution, contrast-enhanced MRA was performed to measure PV diameter. PV dilatation was performed using an angioplasty catheter that was 8 to 10 mm in diameter. The localization and extent of perfusion defects measured by MRI or SPECT scanning were precisely matched. MR perfusion imaging detected 20 of 21 perfusion defects (sensitivity, 95.2%; specificity, 100%). PVSs and perfusion deficits correlated closely and showed the following threshold: perfusion decreased substantially in PVs <or= 6 mm in diameter (21 of 25 areas; 84.0%) compared to 2 of 180 areas (1.1%) with PVs > 6 mm in diameter. After PVS dilatation, perfusion was restored partially after weeks, and complete normalization was seen in 4 of 12 patients (33%). PVSs caused severe perfusion deficits, which were reliably demonstrated by MR perfusion imaging. Clinical symptoms correlated better with MR perfusion than they did with MRA. The combination with MRA to assess underlying PVS allowed a "one-stop-shopping" MRI procedure to be carried out. The results led to alterations of RFA techniques, and therefore MRA and MR perfusion imaging may be beneficial in patient follow-up and in evaluating new ablation techniques.

Scale‐invariant segmentation of dynamic contrast‐enhanced perfusion MR images with inherent scale selection

AbstractSelection of the best set of scales is problematic when developing signal‐driven approaches for pixel‐based image segmentation. Often, different possibly conflicting criteria need to be fulfilled in order to obtain the best trade‐off between uncertainty (variance) and location accuracy. The optimal set of scales depends on several factors: the noise level present in the image material, the prior distribution of the different types of segments, the class‐conditional distributions associated with each type of segment as well as the actual size of the (connected) segments. We analyse, theoretically and through experiments, the possibility of using the overall and class‐conditional error rates as criteria for selecting the optimal sampling of the linear and morphological scale spaces. It is shown that the overall error rate is optimized by taking the prior class distribution in the image material into account. However, a uniform (ignorant) prior distribution ensures constant class‐conditional error rates. Consequently, we advocate for a uniform prior class distribution when an uncommitted, scale‐invariant segmentation approach is desired. Experiments with a neural net classifier developed for segmentation of dynamic magnetic resonance (MR) images, acquired with a paramagnetic tracer, support the theoretical results. Furthermore, the experiments show that the addition of spatial features to the classifier, extracted from the linear or morphological scale spaces, improves the segmentation result compared to a signal‐driven approach based solely on the dynamic MR signal. The segmentation results obtained from the two types of features are compared using two novel quality measures that characterize spatial properties of labelled images. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Detection of areas with viable remnant tumor in postchemotherapy patients with Ewing’s sarcoma by dynamic contrast-enhanced MRI using pharmacokinetic modeling

An approach is presented for monitoring the effects of neoadjuvant chemotherapy in patients with Ewing’s sarcoma using dynamic contrast-enhanced perfusion magnetic resonance (MR) images. For that purpose, we modify the three-compartment pharmacokinetic permeability model introduced by Tofts et al. (Magn Reson Med 1991;17:357–67) to a two-compartment model. Perfusion MR images acquired using an intravenous injection with Gadolinium (Gd-DTPA) are analyzed with this two-compartment pharmacokinetic model as well as the with an extended pharmacokinetic model that includes the (local) arrival time t 0 of the tracer as an endogenous (estimated) parameter. For each MR section, a wash-in parameter associated with each voxel is estimated twice by fitting each of the two pharmacokinetic models to the dynamic MR signal. A comparison of the two wash-in parametric images (global versus local arrival time) with matched histologic macroslices demonstrates a good correspondence between areas with viable remnant tumor and a high wash-in rate. This can be explained by the high number and permeability of the (leaking) capillaries in viable tumor tissue. The novel pharmacokinetic model based on a local arrival time of tracer results in the best fit of the wash-in rate, the most important factor discerning viable from nonviable tumor components. However, parameter estimates obtained with this model are also more sensitive to noise in the MR signal. The novel pharmacokinetic model resulted in a sensitivity between 0.22 and 0.60 and a specificity between 0.61 and 1. The model based on a global arrival time gave sensitivities between 0.33 and 0.77 and specificities between 0.58 and 0.99. Both statistics are computed as the fraction of correctly labeled voxels (viable or nonviable tumor) within a specified ROI, which delineates the tumor. We conclude that the added value of estimating the local arrival time of tracer first manifests itself for moderate noise levels in the MR signal. The novel pharmacokinetic model should moreover be preferred when pharmacokinetic modeling is applied on the average signal intensity within a ROI, where noise has less effect on the fitted parameters.