Contrast-enhanced Magnetic Resonance Imaging Sequences Research Articles

The value of dynamic contrast-enhanced MRI and diffusion-weighted sequence in the evaluation of endometrial lesions

Background/Aim: Endometrial abnormalities represent a diagnostic challenge due to overlapping imaging features with normal endometrium. Aim of this study was to assess accuracy of dynamic contrast-enhanced and diffusion-weighted magnetic resonance imaging (MRI) in evaluation of endometrial lesions in comparison with T2 and to assess local staging validity and degree of myometrial invasion in malignancy. Methods: Forty patients with abnormal vaginal bleeding or sonographic thickened endometrial were recruited. MRI examination of pelvis was per-formed using 1.5 T scanner with a pelvic array coil. Conventional T1-and T2, dynamic contrast-enhanced (DCE) sequences and diffusion-weighted image (DWI) were performed. Results: Mean age of patients was 53.2 years and 60 % of patients COM-plained of post-menopausal bleeding. Irregular margin, type III enhancement curve, a high signal in T2WI and DWI and low signal of apparent diffusion coefficient (ADC) were significantly associated with malignancy. The optimum ADC threshold value for distinguishing benign from malignant endometrial lesions was 0.905 × 10 -3 mm 2 /S, with 95.5 % sensitivity and 92.9 % specificity. DWI was most sensitive to malignant endometrial lesions, followed by DCE (89.6 %, 98.4 %) and T2 (86.7 %, 91.4 %). DWI and DCE staging correlated with FIGO staging (p = 0.0001 and p = 0.019, respectively). DWI had the best sensitivity for myometrial invasion (95.6 %), followed by DCE (91.9 %) and T2WI (90.1 %). All three sequences had 89.7 % specificity. Conclusion: DWI and DCE MRI were superior to conventional MRI at distinguishing malignant from benign endometrial lesions and can improve myometrial invasion depth evaluation and therapy planning when COM-bined with morphological T2WI. ADC cutoff at a high b value improved MRI diagnostic sensitivity and specificity.

Synthesizing MR Image Contrast Enhancement Using 3D High-Resolution ConvNets.

Gadolinium-based contrast agents (GBCAs) have been widely used to better visualize disease in brain magnetic resonance imaging (MRI). However, gadolinium deposition within the brain and body has raised safety concerns about the use of GBCAs. Therefore, the development of novel approaches that can decrease or even eliminate GBCA exposure while providing similar contrast information would be of significant use clinically. In this work, we present a deep learning based approach for contrast-enhanced T1 synthesis on brain tumor patients. A 3D high-resolution fully convolutional network (FCN), which maintains high resolution information through processing and aggregates multi-scale information in parallel, is designed to map pre-contrast MRI sequences to contrast-enhanced MRI sequences. Specifically, three pre-contrast MRI sequences, T1, T2 and apparent diffusion coefficient map (ADC), are utilized as inputs and the post-contrast T1 sequences are utilized as target output. To alleviate the data imbalance problem between normal tissues and the tumor regions, we introduce a local loss to improve the contribution of the tumor regions, which leads to better enhancement results on tumors. Extensive quantitative and visual assessments are performed, with our proposed model achieving a PSNR of 28.24 dB in the brain and 21.2 dB in tumor regions. Our results suggest the potential of substituting GBCAs with synthetic contrast images generated via deep learning.

Subsampled brain MRI reconstruction by generative adversarial neural networks.

A main challenge in magnetic resonance imaging (MRI) is speeding up scan time. Beyond improving patient experience and reducing operational costs, faster scans are essential for time-sensitive imaging, such as fetal, cardiac, or functional MRI, where temporal resolution is important and target movement is unavoidable, yet must be reduced. Current MRI acquisition methods speed up scan time at the expense of lower spatial resolution and costlier hardware. We introduce a practical, software-only framework, based on deep learning, for accelerating MRI acquisition, while maintaining anatomically meaningful imaging. This is accomplished by MRI subsampling followed by estimating the missing k-space samples via generative adversarial neural networks. A generator-discriminator interplay enables the introduction of an adversarial cost in addition to fidelity and image-quality losses used for optimizing the reconstruction. Promising reconstruction results are obtained from feasible sampling patterns of up to a fivefold acceleration of diverse brain MRIs, from a large publicly available dataset of healthy adult scans as well as multimodal acquisitions of multiple sclerosis patients and dynamic contrast-enhanced MRI (DCE-MRI) sequences of stroke and tumor patients. Clinical usability of the reconstructed MRI scans is assessed by performing either lesion or healthy tissue segmentation and comparing the results to those obtained by using the original, fully sampled images. Reconstruction quality and usability of the DCE-MRI sequences is demonstrated by calculating the pharmacokinetic (PK) parameters. The proposed MRI reconstruction approach is shown to outperform state-of-the-art methods for all datasets tested in terms of the peak signal-to-noise ratio (PSNR), the structural similarity index (SSIM), as well as either the mean squared error (MSE) with respect to the PK parameters, calculated for the fully sampled DCE-MRI sequences, or the segmentation compatibility, measured in terms of Dice scores and Hausdorff distance. The code is available on GitHub.

Can diffusion weighted imaging be used as an alternative to contrast-enhanced imaging on magnetic resonance enterography for the assessment of active inflammation in Crohn disease?

The present study aimed to investigate the potential use of T2-weighted sequences with diffusion weighted imaging (DWI) in magnetic resonance (MR) enterography instead of conventional contrast-enhanced MR imaging (MRI) sequences for the evaluation of active inflammation in Crohn disease.Two-hundred thirteen intestinal segments of 43 patients, who underwent colonoscopy within 2 weeks before or after MR enterography were evaluated in this retrospective study. DWI sequences, T2-weighted sequences, and contrast-enhanced T1-weighted sequences were acquired in the MR enterography scan after cleaning of the bowel and using an oral contrast agent. First, the intestinal segments that had active inflammation in MR enterography were qualitatively evaluated in T2-weighted and contrast-enhanced T1-weighted sequences and then MR activity index (MRAI 1) and MRAI 2 were formed with and without contrast-enhanced sequences in 2 separate sessions.The correlation coefficient between contrast enhanced and DWI MR enterography scores (MRAI 1 and MRAI 2) of intestinal inflammation was 0.97 for all segments. In addition, separate correlation coefficients were calculated for terminal ileum, right colon, transverse colon, left colon, and rectum, and there was a strong correlation between the MRAI 1 and MRAI 2 scores of each segment (r = 0.86–0.97, P < .001). On the other hand, MR enterography had 88.7% sensitivity, 97.9% specificity, 95.5% positive predictive value, 94.6% negative predictive value, and 94.8% accuracy for detection of active inflammation in all intestinal segments in Crohn disease.DWI and T2-weighted sequences acquired with cleaning of the bowel can be used instead of contrast-enhanced MRI sequences for the evaluation of active inflammation in Crohn disease.

Post-treatment prostate MRI.

Accurate early detection of recurrent prostate cancer after surgical or nonsurgical treatment is increasingly relevant in the era of evolving options for salvage therapy. The importance of differentiating between local tumor recurrence, distant metastatic disease, and a combination of both in a patient with biochemical recurrence of prostate cancer is essential for appropriate treatment selection. Magnetic resonance imaging (MRI) is the best test for localization and characterization of locally residual or recurrent prostate cancer. It is essential for the radiologist involved in prostate MRI interpretation to be familiar with key imaging findings and advantages of different sequences to reach a confident diagnosis in the post-treatment setting. In this pictorial review, we present imaging findings of post-treatment prostate MRI including expected post-treatment anatomy and imaging characteristics, and the typical appearances of local tumor recurrence after radical prostatectomy, radiation therapy, and focal therapy for prostate cancer. While a multi-parametric MRI approach remains key just as in the treatment-naïve gland, this review emphasizes the much greater importance of the dynamic contrast-enhanced MRI sequence for evaluation in the post-treatment setting.

Magnetic resonance imaging (MRI) compared with computed tomography (CT) for interobserver agreement of gross tumor volume delineation in pancreatic cancer: a multi-institutional contouring study on behalf of the AIRO group for gastrointestinal cancers

Background: Due to the high soft tissue resolution, magnetic resonance imaging (MRI) could improve the accuracy of pancreatic tumor delineation in radiation treatment planning. A multi-institutional study was proposed to evaluate the impact of MRI on inter-observer agreement in gross tumor volume (GTV) and duodenum delineation for pancreatic cancer compared with computer tomography (CT).Material and Methods: Two clinical cases of borderline resectable (Case 1) and unresectable (Case 2) pancreatic cancer were selected. In two sequential steps, diagnostic contrast-enhanced CT scan and MRI sequences were sent to the participating centers. CT-GTVs were contoured while blinded to MRI data sets. DICE index was used to evaluate the spatial overlap accuracy.Results: Thirty-one radiation oncologists from different Institutions submitted the delineated volumes. CT- and MRI-GTV mean volumes were 21.6 ± 9.0 cm3 and 17.2 ± 6.0 cm3, respectively for Case 1, and 31.3 ± 15.6 cm3 and 33.2 ± 20.2 cm3, respectively for Case 2. Resulting MRI-GTV mean volume was significantly smaller than CT–GTV in the borderline resectable case (p < .05). A substantial agreement was shown by the median DICE index for CT– and MRI–GTV resulting as 0.74 (IQR: 0.67–0.75) and 0.61 (IQR: 0.57–0.67) for Case 1; a moderate agreement was instead reported for Case 2: 0.59 (IQR:0.52–0.66) and 0.53 (IQR:0.42–0.62) for CT– and MRI–GTV, respectively.Conclusion: Diagnostic MRI resulted in smaller GTV in borderline resectable case with a substantial agreement between observers, and was comparable to CT scan in interobserver variability, in both cases. The greater variability in the unresectable case underlines the critical issues related to the outlining when vascular structures are more involved. The integration of MRI with contrast-enhancement CT, thanks to its high definition of tumor relationship with neighboring vessels, could offer a greater accuracy of target delineation.

Can unenhanced MRI of the breast replace contrast-enhanced MRI in assessing response to neoadjuvant chemotherapy?

The goals of neoadjuvant chemotherapy (NAC) are to reduce tumor volume and to offer a prognostic indicator in assessing treatment response. Contrast-enhanced magnetic resonance imaging (CE-MRI) is an established method for evaluating response to NAC in patients with breast cancer. To validate the role of unenhanced MRI (ue-MRI) compared to CE-MRI for assessing response to NAC in women with breast cancer. Seventy-one patients with ongoing NAC for breast cancer underwent MRI before, during, and at the end of NAC. Ue-MRI was performed with T2-weighted sequences with iterative decomposition of water and fat and diffusion-weighted sequences. CE-MRI was performed using three-dimensional T1-weighted sequences before and after administration of gadobenate dimeglumine. Two blinded observers rated ue-MRI and CE-MRI for the evaluation of tumor response. Statistical analysis was performed to compare lesion size and ADC values changes during therapy, as well as inter-observer agreement. There were no statistically significant differences between ue-MRI and CE-MRI sequences for evaluation of lesion size at baseline and after every cycle of treatment ( P > 0.05). The mean tumor ADC values at baseline and across the cycles of NAC were significantly different for the responder group. Ue-MRI can achieve similar results to CE-MRI for the assessment of tumor response to NAC. ADC values can differentiate responders from non-responders.

Pitfalls of diffusion-weighted imaging of the female pelvis.

Diffusion-weighted imaging (DWI) is widely used in protocols for magnetic resonance imaging (MRI) of the female pelvis. It provides functional and structural information about biological tissues, without the use of ionizing radiation or intravenous administration of contrast medium. High signal intensity on DWI with simultaneous low signal intensity on apparent diffusion coefficient maps is usually associated with malignancy. However, that pattern can also be seen in many benign lesions, a fact that should be recognized by radiologists. Correlating DWI findings with those of conventional (T1- and T2-weighted) MRI sequences and those of contrast-enhanced MRI sequences is mandatory in order to avoid potential pitfalls. The aim of this review article is the description of the most relevant physiological and benign pathological conditions of the female pelvis that can show restricted diffusion on DWI.

The utility of CT and MRI in detecting male urethral recurrence after radical cystectomy.

To evaluate the utility of computed tomography (CT) and magnetic resonance imaging (MRI) in detecting male urethral recurrence (UR). Between December 2008 and March 2016, 12 men (age range 61-85years; median, 74years) with urethral bloody discharge or pain were histologically confirmed as UR after radical cystectomy due to urothelial carcinoma. Of these patients, eight underwent both CT and MRI. The remaining four patients underwent CT only. CT and MRI were compared regarding UR detection rate. CT and MRI were also evaluated to determine which modality was more accurate for depicting UR. UR detection rate of each MRI sequence were recorded. Standard reference was biopsy or urethrectomy in 11 patients and size change in one patient after treatment. UR detection rate with CT was 41.7% (5/12), while that with MRI was 100% (8/8) (p=0.0147). Of the eight patients who were diagnosed UR with MRI, six were detected with MRI alone and two with both MRI and CT (p=0.0313). UR detection rates of T2-weighted, T1-weighted, diffusion-weighted, and contrast-enhanced MRI were 87.5% (7/8), 62.5% (5/8), 100% (5/5), and 87.5% (7/8), respectively. MRI is superior to CT in detecting male URs in symptomatic patients after radical cystectomy. T2-weighted, diffusion-weighted, and contrast-enhanced MRI sequences are useful for detecting male UR.

Quantification of regional deformation of the lungs by non-rigid registration of three-dimensional contrast-enhanced magnetic resonance imaging.

Assessment of lung function is vital for the diagnosis of a variety of pathological conditions. Research has been proposed to study pulmonary mechanics and kinematics using two-dimensional (2D) magnetic resonance imaging (MRI). This allows estimation of regional lung tissue mechanics but is limited to 2D information. An approach based on three-dimensional (3D) contrast-enhanced MR angiogram of pulmonary blood vessels and a non-rigid image registration technique is proposed for quantification of lung regional deformations, which can potentially be used for assessment of pulmonary parenchymal mechanics and regional ventilation for disease diagnosis without ionizing radiation. On three volunteers, an end-expiration scan and end-inspiration scan was acquired successively for each volunteer using a 3D breath-hold contrast-enhanced MRI sequence several minutes after gadolinium injection. Subsequently, a rectangle box lung mask is manually selected for each end-expiration scan, applying non-rigid registration algorithms using cubic B-splines as transformations to align each pair of images. This incorporates the Normalized Correlation Coefficient similarity with the bending energy term as cost function with a multi-resolution multi-grid approach. Finally, the lung regional 3D deformations were obtained using the transformations obtained by registration. The alignment accuracy after non-rigid registration was estimated by using a set of branch points of pulmonary blood vessels as anatomical landmarks for each pair of images. With contrast enhancement, the pulmonary blood vessel signal was enhanced, which greatly facilitated the non-rigid registration in the lung parenchyma. The average landmarks distances in three pairs of datasets are reduced from 17.9, 20.3 and 16.3 mm, to 1.0, 1.6 and 1.2 mm, respectively, by non-rigid registration. After registration, the average distances error of each pair of datasets was less than 0.6 mm in the right-to-left (RL) direction, less than 0.9 mm in the inferior-to-superior (IS) direction, and less than 1.2 mm in the anterior-to-posterior (AP) direction. Results demonstrated that the proposed method can accurately register lungs with large deformations to evaluate lung regional deformation. It may be used for quantitative assessment of 3D lung regional ventilation avoiding ionizing radiation.

Magnetic resonance imaging for characterizing myocardial diseases.

The National Institute of Health defined cardiomyopathy as diseases of the heart muscle. These myocardial diseases have different etiology, structure and treatment. This review highlights the key imaging features of different myocardial diseases. It provides information on myocardial structure/orientation, perfusion, function and viability in diseases related to cardiomyopathy. The standard cardiac magnetic resonance imaging (MRI) sequences can reveal insight on left ventricular (LV) mass, volumes and regional contractile function in all types of cardiomyopathy diseases. Contrast enhanced MRI sequences allow visualization of different infarct patterns and sizes. Enhancement of myocardial inflammation and infarct (location, transmurality and pattern) on contrast enhanced MRI have been used to highlight the key differences in myocardial diseases, predict recovery of function and healing. The common feature in many forms of cardiomyopathy is the presence of diffuse-fibrosis. Currently, imaging sequences generating the most interest in cardiomyopathy include myocardial strain analysis, tissue mapping (T1, T2, T2*) and extracellular volume (ECV) estimation techniques. MRI sequences have the potential to decode the etiology by showing various patterns of infarct and diffuse fibrosis in myocarditis, amyloidosis, sarcoidosis, hypertrophic cardiomyopathy due to aortic stenosis, restrictive cardiomyopathy, arrythmogenic right ventricular dysplasia and hypertension. Integrated PET/MRI system may add in the future more information for the diagnosis and progression of cardiomyopathy diseases. With the promise of high spatial/temporal resolution and 3D coverage, MRI will be an indispensible tool in diagnosis and monitoring the benefits of new therapies designed to treat myocardial diseases.

Role of PI-RADSv2 with multiparametric MRI in determining who needs active surveillance or definitive treatment according to PRIAS.

To evaluate the role of Prostate Imaging Reporting and Data System v. 2 (PI-RADSv2) in triaging patients with prostate cancer according to Prostate Cancer Research International: Active Surveillance (PRIAS). Between January 2012 and December 2014, 456 patients with biopsy-proven cancer underwent multiparametric 3T magnetic resonance imaging (MRI) using T2 -weighted, diffusion-weighted, and dynamic contrast-enhanced MRI sequences, and then radical prostatectomy. Two radiologists independently reviewed MR images using PI-RADSv2. For AS, PRIAS required clinical stage <T3, prostate-specific antigen (PSA) ≤10 ng/mL, PSA density <0.2 ng/mL2 , Gleason score (GS) ≤6, and the number of positive cores ≤2. For AS, PI-RADSv2 required an index lesion scored <4. Standard reference was prostatectomy, in which insignificant cancer was defined as a small (<0.5 cm3 ) organ-confined lesion with GS ≤6. Sensitivity and specificity for insignificant cancer were obtained with PRIAS, PI-RADSv2, and both. The sensitivity and specificity with PRIAS were 82.9% (68/82) and 70.9% (265/374), respectively. PI-RADSv2 decreased the sensitivity to 61% (50/82) to 80.5% (66/82), but increased the specificity to 77.8% (291/374) to 90.8% (340/374). The combination of PRIAS and PI-RDASv2 increased significantly the specificity to 89.6% (335/374) to 92.8% (347/374) (P < 0.001). PRIAS using multiparametric MRI can identify a greater number of insignificant cancers than PI-RADSv2. However, PI-RADSv2 helps detect many significant cancers that are misdiagnosed as insignificant cancer with PRIAS. 3 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;45:1753-1759.

Pediatric tumours: pseudotumour or a tumour?

Differentiation between tumours and pseudo-tumours is essential for planning adequate treatment and for estimating outcome and future prognosis. Per definition, tumour and pseudo-tumours are lesions that look alike on ultrasound (US), computer tomography (CT) or magnetic resonance imaging (MRI) studies. Misinterpretation may lead to a significant delay of adequate treatment for malignant tumours or on the contrary may result in over-treatment of a tumour-like, benign lesion. The essential question is how does a radiologist reliably differentiate between both entities? Typically, he will use anatomical imaging studies like US, CT or MRI. A tumour is suspected when a focal density or signal alteration is seen displacing or infiltrating adjacent structures with or without a matching contrast enhancement and possibly surrounded by vasogenic edema. Unfortunately, many pseudo-tumours including abscesses, resolving hematomas, vascular malformations, benign cysts, and even metabolic disorders may have similar imaging features. In addition, a frequent, difficult question is the differentiation between postsurgical changes and residual tumour after recent tumour surgery or between radiation induced lesions and recurrent or residual tumour. The recent development of functional MRI sequences like diffusion tensor imaging (DTI), perfusion weighted imaging (PWI), 1H magnetic resonance spectroscopy (MRS), susceptibility weighted imaging (SWI) and dynamic contrast enhanced MRI sequences facilitates the differentiation between tumours and pseudo-tumours. It is impossible to present a complete list of pseudo-tumours, however the current presentation will discuss how a multidisciplinary, multi-imaging and multi-sequence approach may facilitate differentiation between tumors and pseudo-tumours.

Cardiac magnetic resonance imaging in the current practice

Radiol Bras. 2014 Jan/Fev;47(1):V Because of increasing scientific and technological advances, the use of cardiac magnetic resonance imaging (MRI) keeps exponentially increasing over at least 30 years, and for many years has been utilized as a routine in the clinical practice both on outpatient and emergency/inpatient bases, particularly in centers where the clinical staff could remain updated, following the advances in the technology applied to cardiac imaging. Even being the most recent diagnostic method in terms of cardiac imaging if compared with scintigraphy and echocardiography, cardiac MRI has its high value demonstrated as a one-stop-shop imaging method with innumerable advantages over other methods because of its high spatial resolution associated with capacity of tissue characterization by means of conventional and contrast-enhanced MRI sequences. With such characteristics, morphology, biventricular function, perfusion at rest or under pharmacological stress for investigation of ischemia, areas of injury and myocardial viability can be evaluated in a single procedure. Additionally, cardiac MRI is an increasingly promising method in the assessment of coronary arteries. New high-field 3T magnets have added even higher spatial resolution and tissue contrast, improving the imaging quality in procedures such as myocardial perfusion scan, so the definitive inclusion of this method in the algorithm of cardiac evaluation is inevitable. Cardiac MRI is currently considered a gold standard to quantify cardiac mass and volume, because of its low variability, high reproducibility and better accuracy when compared with other imaging methods utilized in cardiology. In Brazil, the first guideline on the utilization of such method was published in 2006 and the number of quali-

A dialyzer-based flow system for validating dynamic contrast enhanced MR image acquisition

Dynamic contrast enhanced magnetic resonance imaging (MRI) has proven to be quite sensitive for the characterization of masses and early response to therapy. However, it is fraught with a number of procedural challenges as well as a lack of standardization. In this article, we describe the use of a simple dialyzer-based flow system to evaluate reproducibility of dynamic contrast enhanced MRI under active flow conditions. The MR signal during a bolus injection of Gd-DTPA was analyzed to test the precision and variability of contrast agent kinetics during a typical dynamic contrast enhanced MRI sequence. A simple model allows an estimation of the washout rate constant of Gd-DTPA through the polysulfone tubules of the dialyzer. The simple flow phantom described here provided reproducible measurements of the washout rate constants. The washout rate increased from 0.20 ± 0.005 min(-1) to 0.25 ± 0.008 min(-1) over 32 weeks. Measurements were also made at week 24 using dynamic computed tomography and found to be 0.27 ± 0.006 min(-1) . Overall, the computed tomography derived rate constants results were found be ∼12% higher than the corresponding MRI values. In this study, we show that a simple dialyzer-based flow phantom can be used for testing dynamic contrast enhanced MRI pulse sequences and also allows for short-term reproducibility testing of rate constants.

Resonancia magnética dinámica en el diagnóstico de las lesiones tumorales y seudotumorales del sistema musculoesquelético

The greater temporal resolution provided in ultrafast dynamic contrast-enhanced magnetic resonance imaging sequences makes it possible to know the physiological phenomenon of the distribution of the contrast material through a time-signal intensity curve. Analyzing these curves enables us to deduce information relevant to the vascularization and perfusion of tissues, capillary permeability, and the interstitial space in the tumor. A steep curve with early washout in a space-occupying lesion greatly increases the possibility of histological malignancy, although this type of curve is not rare in benign lesions and relatively flat curves are not rare in malignant tumors. Nevertheless, dynamic studies of the uptake of contrast material provide important information for the characterization of neoplasms that, together with the usual signs, can help to differentiate between benign and malignant tumors of adipocyte, chondroid, or neural lineage, clearing up diagnostic uncertainty in certain benign lesions such as osteoid osteoma and ischemic musculoskeletal disease. Furthermore, it enables the accurate determination of the response to chemotherapy, detecting recurrence within the treated tumor early, delimiting more precisely the margins between the tumor and peritumoral edema, and helping in diagnostic planning by determining the most vascularized areas of the tumor, which are more likely to be malignant.

The effect of blood inflow and B1‐field inhomogeneity on measurement of the arterial input function in axial 3D spoiled gradient echo dynamic contrast‐enhanced MRI

A major potential confound in axial 3D dynamic contrast-enhanced magnetic resonance imaging studies is the blood inflow effect; therefore, the choice of slice location for arterial input function measurement within the imaging volume must be considered carefully. The objective of this study was to use computer simulations, flow phantom, and in vivo studies to describe and understand the effect of blood inflow on the measurement of the arterial input function. All experiments were done at 1.5 T using a typical 3D dynamic contrast-enhanced magnetic resonance imaging sequence, and arterial input functions were extracted for each slice in the imaging volume. We simulated a set of arterial input functions based on the same imaging parameters and accounted for blood inflow and radiofrequency field inhomogeneities. Measured arterial input functions along the vessel length from both in vivo and the flow phantom agreed with simulated arterial input functions and show large overestimations in the arterial input function in the first 30 mm of the vessel, whereas arterial input functions measured more centrally achieve accurate contrast agent concentrations. Use of inflow-affected arterial input functions in tracer kinetic modeling shows potential errors of up to 80% in tissue microvascular parameters. These errors emphasize the importance of careful placement of the arterial input function definition location to avoid the effects of blood inflow.

Pulse sequence and timing of contrast‐enhanced MRI for assessing blood–brain barrier disruption after transcranial focused ultrasound in the presence of hemorrhage

To optimize the timing of contrast-enhanced magnetic resonance imaging (MRI) that best indicates blood-brain barrier (BBB) disruption induced by focused ultrasound (FUS) along with an ultrasound contrast agent (UCA) and to verify that the contrast-enhanced spin-echo MRI sequence can indicate the degree and location of BBB disruption in the presence of hemorrhage better than a gradient-echo sequence. Sonication was applied to 12 rat brains with four different doses of UCA to cause variable degrees of hemorrhage. Two imaging sequences were performed to acquire T1-weighted (T1W) images at two time-points after the administration of a T1-shortening contrast agent. The contrast enhancement at the sonicated regions was quantified and correlated against Evans blue (EB) staining. The spin-echo T1W images at 10 minutes post-contrast enhancement showed the best correlation with EB staining in both quantity of EB extravasation (r = 0.812; P < 0.01) and spatial distribution (r = 0.528, P < 0.01). This capability was more robust than the gradient-echo sequence. Our results suggest that contrast-enhanced T1W spin-echo sequence acquired in the early phase post-contrast enhancement should be considered to monitor the degree and location of BBB disruption under the possibility of hemorrhage induced by FUS.

Evaluation of heart perfusion in patients with acute myocardial infarction using dynamic contrast-enhanced magnetic resonance imaging.

To investigate the diagnostic ability of quantitative magnetic resonance imaging (MRI) heart perfusion in acute heart patients, a fast, multislice dynamic contrast-enhanced MRI sequence was applied to patients with acute myocardial infarction. Seven patients with acute transmural myocardial infarction were studied using a Turbo-fast low angle shot (FLASH) MRI sequence to monitor the first pass of an extravascular contrast agent (CA), gadolinium diethylene triamine pentaacetic acid (Gd-DTPA). Quantitation of perfusion, expressed as Ki (mL/100 g/minute), in five slices, each having 60 sectors, provided an estimation of the severity and extent of the perfusion deficiency. Reperfusion was assessed both by noninvasive criteria and by coronary angiography (CAG). The Ki maps clearly delineated the infarction in all patients. Thrombolytic treatment was clearly beneficial in one case, but had no effect in the two other cases. Over the time-course of the study, normal perfusion values were not reestablished following thrombolytic treatment in all cases investigated. This study shows that quantitative MRI perfusion values can be obtained from acutely ill patients following acute myocardial infarction. The technique provides information on both the volume and severity of affected myocardial tissue, enabling the power of treatment regimes to be assessed objectively, and this approach should aid individual patient stratification and prognosis.

Prediction of the effects of gonadotropin-releasing hormone agonist therapy in uterine leiomyoma by T1 contrast-enhanced magnetic resonance imaging sequences

Uterine leiomyomas occur in 20% of women of reproductive age and often cause symptoms, including prolonged or heavy menstrual bleeding, pelvic pressure or pain, infertility, or spontaneous abortion (1). Gonadotropin-releasing hormone (GnRH) agonists are a popular treatment for uterine leiomyomas because they decrease uterine blood loss due to myomas and the volume of the myomas themselves. However, after cessation of GnRH agonist therapy, the myomas return to their original size. Thus, surgical resection remains the mainstay of treatment.