Magnetic resonance cardiac perfusion imaging–a clinical perspective

Coronary artery disease (CAD) with its clinical appearance of stable or unstable angina and acute myocardial infarction is the leading cause of death in developed countries. In view of increasing costs and the rising number of CAD patients, there has been a major interest in reliable non-invasive imaging techniques to identify CAD in an early (i.e. asymptomatic) stage. Since myocardial perfusion deficits appear very early in the “ischemic cascade”, a major breakthrough would be the non-invasive quantification of myocardial perfusion before functional impairment might be detected. Therefore, there is growing interest in other, target-organ-specific parameters, such as relative and absolute myocardial perfusion imaging. Magnetic resonance (MR) imaging has been proven to offer attractive concepts in this respect. However, some important difficulties have not been resolved so far, which still causes uncertainty and prevents the broad application of MR perfusion imaging in a clinical setting. This review explores recent technical developments in MR hardware, software and contrast agents, as well as their impact on the current and future clinical status of MR imaging of first-pass myocardial perfusion imaging.     

关于diffusion weighted imaging中文译名之管见

1965年Stejskal和Tanner完成diffusion weighted imaging (DWI)的序列设计,之后这一MR功能成像技术在临床的研究和应用不断深入.截止到2012年6月,在Pubmed数据库上检索到DWI相关研究文献近9000篇,涉及全身各系统的各种良恶性病变.DWI已成为目前研究和应用最为广泛的MR功能成像手段之一.然而,有关DWI的中文译名至今未得到规范和统一,目前并存"扩散加权成像"和"弥散加权成像"两种称谓.以"磁共振+扩散加权"在万方数据库和中国知网CNKI上检索,分别可检索到相关文献603和1031篇;以"磁共振+弥散加权"可分别检索到681和1166篇.一个技术并存两种译名,且两种名称的使用频度不分伯仲,在科学上是非常不严谨的现象,有必要引起重视.     

Is there any role for diffusion weighted magnetic resonance imaging before transthoracic CT guided biopsy?

Aim of the work

To evaluate the role of diffusion weighted imaging (DWI) in the planning for CT guided biopsy of lung and mediastinal lesions.

Magnetic resonance imaging of Alzheimer’s disease

A modern challenge for neuroimaging techniques is to contribute to the early diagnosis of neurodegenerative diseases, such as Alzheimer’s disease (AD). Early diagnosis includes recognition of pre-demented conditions, such as mild cognitive impairment (MCI) or having a high risk of developing AD. The role of neuroimaging therefore extends beyond its traditional role of excluding other conditions such as neurosurgical lesions. In addition, early diagnosis would allow early treatment using currently available therapies or new therapies in the future. Structural imaging can detect and follow the time course of subtle brain atrophy as a surrogate marker for pathological processes. New MR techniques and image analysis software can detect subtle brain microstructural, perfusion or metabolic changes that provide new tools to study the pathological processes and detect pre-demented conditions. This review focuses on markers of macro- and microstructural, perfusion, diffusion and metabolic MR imaging and spectroscopy in AD.     

Magnetic resonance imaging of pulmonary nodules: accuracy in a granulomatous disease–endemic region

Objective

To estimate the diagnostic accuracy of signal intensity of the lesion-to-spinal cord ratio (LSR) and apparent diffusion coefficient (ADC) in diffusion-weighted (DW) magnetic resonance imaging of pulmonary nodules suspicious for lung cancer in granulomatous lung disease-endemic regions.

Methods

Forty-nine patients with indeterminate solitary pulmonary nodules detected by chest computed tomography and histopathologically confirmed diagnoses were included in the study. DW images were analysed semiquantitatively by focusing regions of interest on the lesion and spinal cord at the same level (for LSR calculation). ADCs were estimated from ratios of the two image signal intensities. Ratios of T1 and T2 signal intensity between nodules and muscle were calculated for comparison.

Results

Mean ADCs?±?standard deviations for lung cancer and benign lesions were 0.9?±?0.2 and 1.3?±?0.2?×?10^-3 mm²/s, respectively. Mean LSRs were 1.4?±?0.3 for lung cancer and 1?±?0.1 for benign lesions. ADCs and LSRs differed significantly between malignant and benign lesions (P?<?0.001). Mean T2 signal intensity ratios also differed significantly between benign and malignant lesions (0.8?±?0.2 vs. 1.6?±?0.2; P?<?0.05).

Conclusions

DWI can help to differentiate malignant from benign lesions according to ADC and the LSR with good accuracy.

Key Points

? DW imaging can help differentiate malignant from benign pulmonary nodules. ? ADC and LSR signal intensities had only small overlap between malignant and benign pulmonary nodules. ? Mean T2 signal intensity ratios differed significantly between benign and malignant lesions.

     

Magnetic resonance imaging findings in Kimura’s disease

Although early diagnosis of Kimuras disease, a rare chronic inflammatory disorder most commonly presenting with asymmetric swelling in the head and neck region, is helpful in avoiding unnecessary diagnostic tests and starting prompt treatment, only a few reports emphasized radiological findings in detail. Magnetic resonance imaging findings showing the infiltrative nature of the disease and diffuse loss of fat tissue even in nonpalpable normally appearing regions of the head and neck in a young man with Kimuras disease are presented in this report.     

Magnetic resonance imaging of active sacroiliitis: Do we really need gadolinium?

Introduction

Magnetic resonance imaging (MRI) of active inflammatory changes of the sacroiliac joint (SIJ) in spondyloarthritis (SpA) is performed with short tau inversion recovery (STIR) sequences and fat-saturated T1-weighted fast spin-echo (FSE) sequences after administration of gadolinium-based contrast medium (T1/Gd). The aim of the present study was to compare these two pulse sequences in terms of diagnosis, diagnostic confidence, and quantification of inflammatory changes.

Materials and methods

The study included 105 patients with suspected SpA; 72 patients developed clinical SpA over time. All patients were examined with STIR and T1/Gd and each of the two sequences was analyzed separately in conjunction with unenhanced T1 FSE images. For quantitative estimation of inflammatory changes, each sacroiliac joint (SIJ) was divided into 4 quadrants (and severity per quadrant was assigned a score of 0-4, resulting in a maximum sum score of 16 per SIJ). Diagnostic confidence was assessed on a visual analogue scale ranging from 0 to 10.

Results

Active sacroiliitis was diagnosed in 46 patients and ruled out in 34 using STIR, whereas findings were inconclusive in 25 patients. The corresponding numbers for T1/Gd were 47, 44, and 14. Diagnostic confidence was significantly lower for STIR (7.3 ± 2.6) compared with T1/Gd (8.7 ± 1.9) (p < 0.001).The sum scores were 2.5 (±3.3) for STIR and 2.2 (±3.2) for T1/Gd for the right SIJ and 2.2 (±2.9) (STIR) and 1.9 (±3.1) (T1/Gd) for the left SIJ. Agreement was high with intraclass correlation coefficient (ICC) values of 0.86 for the right SIJ and 0.90 for the left SIJ and positive correlation (r = 0.62 right, 0.60 left).

Summary

STIR sequences alone are sufficient for establishing a reliable diagnosis and quantify the amount of inflammation in active sacroiliitis. A contrast-enhanced study is dispensable in patients with established disease or in the setting of clinical follow-up studies. However, a contrast-enhanced MR sequence is beneficial to ensure maximum diagnostic confidence when patients with early sacroiliitis are examined.     

Magnetic resonance imaging in patients with nipple discharge: should we recommend it?

Objectives  

Comparing the sensitivity of Contrast-Enhanced Magnetic Resonance Imaging (CEMRI), mammography and ultrasonography in patients with nipple discharge (ND).     

Magnetic resonance imaging for extramammary Paget’s disease: radiological and pathological correlations

Extramammary Paget’s disease (EMPD) is a rare cutaneous neoplasm that is thought to represent intraepithelial adenocarcinoma developing in an area rich in apocrine glands. Magnetic resonance imaging (MRI) findings for this disease are not well established. We report three cases of pathologically confirmed EMPD in which MRI was performed before surgery. The lesions were widespread in the epidermis and the dermis. Lesions were sharply well enhanced on gadolinium-enhanced T1-weighted imaging and appeared hyperintense on diffusion-weighted imaging in all cases. Areas with enhancement in depth corresponded well with the pathological lesion. In addition, different malignant legions were found on the same images from MRI in two cases, indicating potential associations with other malignancies. We describe the MRI findings and their pathological correlation. MRI could be useful for preoperative evaluation of disease spread and detection of associated malignancies.     

Does diffusion weighted imaging have a prognostic value in differentiating gynecological diseases?

IntroductionApparent diffusion coefficient (ADC) values are effective in the diagnosis of different gynecological lesions.MethodsA retrospective evaluation was made of 12 patients with uterine cervix carcinoma and 151 patients with uterine lesions, comprising endometrial cancer, endometrial polyps, carcinosarcoma, submucous myoma, adenomyosis, endometrial hyperplasia, gestational trophoblastic neoplasm (GTN), and leiomyomas. As a control group, 20 healthy volunteers with normal endometrium and normal cervix were also evaluated. In three series, one-shot, spin echo, echo planar, b = 1000 s/mm² value and diffusion-weighted imaging (DWI) were applied to all subjects and ADC values were obtained.ResultsThe mean ADC values of Group 1 (Endometrial carcinoma) were lower than those of all the other groups (P < 0.001) and the mean ADC value of group 6 (GTN) was higher than that all other groups (P < 0.001). A statistically significant difference was found between the groups in terms of the lesion-myometrium ADC ratios (P < 0.001).ConclusionThere are few studies in literature related to ADC measurements in GTN. The ADC values of GTN were found to be significantly higher than the other uterine lesions. These results will aid in the design of future studies and might be used to guide management of patients with GTN.Implications for practiceDiffusion-weighted MRI seems to be a promising imaging technique in differentiating different uterine lesions.     

The effect of gadoxetic acid enhancement on lesion detection and characterisation using T₂ weighted imaging and diffusion weighted imaging of the liver

Objectives

To evaluate the effect of gadoxetic acid enhancement on the detection and characterisation of focal hepatic lesions on T₂ weighted and diffusion weighted (DW) images.

Methods

A total of 63 consecutive patients underwent T₂ weighted and DW imaging before and after gadoxetic acid enhancement. Two blinded readers independently identified all of the focal lesions using a five-point confidence scale and characterised each lesion using a three-point scale: 1, non-solid; 2, indeterminate; and 3, solid. For both T₂ weighted and DW imaging, the accuracies for detecting focal lesions were compared using the free-response receiver operating characteristic analysis; the accuracies for lesion characterisation were compared using the McNemar test between non-enhanced and gadoxetic acid-enhanced image sets. For hepatic lesions ≥1 cm, the lesion-to-liver contrast-to-noise ratio (CNR) and the apparent diffusion coefficient (ADC) were compared in the non-enhanced and enhanced image sets using the generalised estimating equations.

Results

For both T₂ weighted and DW images, the accuracies for detecting focal lesions (p≥0.52) and those for lesion characterisation (p≥0.63) did not differ significantly between the non-enhanced and enhanced image sets. The lesion-to-liver CNR was significantly higher on enhanced DW images than on non-enhanced DW images (p=0.02), although the difference was not significant for T₂ weighted imaging (p=0.65). The mean ADC values of lesions did not differ significantly on enhanced and non-enhanced DW imaging (p=0.75).

Conclusion

The acquisition of T₂ weighted and DW images after administration of gadoxetic acid has no significant effect on the detection or characterisation of focal hepatic lesions, although it improves the lesion-to-liver CNR on DW images.Various contrast agents have been developed and utilised for MRI of the liver in order to facilitate the detection and characterisation of focal hepatic lesions. Gadoxetic acid (gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid, Primovist^®; Bayer Schering Pharma, Berlin, Germany) is a recently developed, liver-specific contrast agent. As it has combined extracellular and hepatocyte-specific properties, gadoxetic acid can provide functional information regarding the cellular composition of focal hepatic lesions on hepatobiliary phase imaging as well as haemodynamic information on dynamic MRI following bolus injection. These properties of gadoxetic acid have been reported to improve the accuracy of liver MRI for lesion detection and characterisation [1-7].By contrast, these advantages of gadoxetic acid-enhanced liver MRI are obtained with increased examination time, as delayed scanning approximately 20 min after contrast administration is necessary for optimal hepatobiliary phase imaging [4,5,7-9]. Among the pulse sequences commonly acquired for clinical liver MRI, T₂ weighted and diffusion weighted (DW) imaging are frequently performed using a respiratory-triggered method in order to improve image quality [10-12], thus a lengthy acquisition time is required. To shorten the examination time for gadoxetic acid-enhanced MRI, it has been proposed to perform respiratory-triggered T₂ weighted and DW imaging during the interval between dynamic T₁ weighted imaging and the hepatobiliary phase imaging [7,13,14]. However, this modification in the MRI protocol is only feasible if the administration of gadoxetic acid does not degrade the image quality and provides comparable image quality and accuracy to non-enhanced imaging.Although previous studies have demonstrated that gadolinium-enhanced T₂ weighted images improve the conspicuity of focal hepatic lesions compared with unenhanced T₂ weighted images [15,16], these studies used non-specific extracellular contrast agents. Considering the different properties of extracellular contrast agents and gadoxetic acid, these results might not be easily applied to gadoxetic acid-enhanced MRI.Therefore, the purpose of our study was to evaluate the effect of gadoxetic acid on lesion detection and characterisation using T₂ weighted and DW imaging.     

Magnetic resonance imaging of lymphatic vessels without image subtraction: a practicable imaging method for routine clinical practice?

OBJECTIVE: To assess the feasibility of a time-efficient, high-resolution magnetic resonance lymphangiography (HR MRL) protocol without image subtraction for the detection of lymphatic vessels in patients with primary and secondary lymphedema. METHODS: Three consecutive patients with lymphedema of the lower extremities (2 primary bilateral, 1 secondary unilateral) underwent HR MRL without image subtraction. An amount of 9 mL of gadodiamide and 1 mL of mepivacaine hydrochloride 1% were subdivided into 5 portions and injected intracutaneously into the dorsal aspect of each foot outside the scanner before image acquisition. Magnetic resonance imaging was performed with a 1.5-T system equipped with high-performance gradients. For HR MRL, a 3-dimensional, spoiled gradient-echo sequence (Volumetric Interpolated Breath-hold Examination) was used. The extent and distribution of the lymphedema was evaluated using a heavily T2-weighted, 3-dimensional turbo-spin echo sequence. RESULTS: The HR MRL bilaterally detected the inguinal lymph nodes and the lymphatic vessels in the lower and upper leg in the 2 patients with primary lymphedema. In the patient with left-sided secondary lymphedema, the inguinal lymph nodes and the lymphatic vessels in the lower and upper leg were depicted on the right side. The diameter of the displayed lymphatic vessels varied between 1 and 5 mm. Three-dimensional, maximum-intensity projection images of different angles of view provided detailed outlining of the lymphatic vessels and differentiation from veins, which showed a lower signal intensity. CONCLUSION: The HR MRL without image subtraction is safe, technically feasible, and has the potential to become a diagnostic imaging tool in daily clinical practice because of its time efficiency.     

Magnetic resonance fistulography for the demonstration of anovaginal fistula: an alternative imaging technique?

Anovaginal fistulae (AVF) are frequently seen in patients with inflammatory bowel disease, especially in Crohn disease with active colonic inflammation. Herein, we report a 21-year-old woman with Crohn disease suffering from vaginal discharge and anal pain. Although clinical presentation was very suggestive of AVF, physical examination and colonoscopy were inconclusive. We used an alternative technique and performed magnetic resonance fistulography by applying rectal contrast for the demonstration of AVF.     

Magnetic resonance imaging of acute “wiiitis” of the upper extremity

We present the first reported case of acute “wiiitis”, documented clinically and by imaging, of the upper extremity, caused by prolonged participation in a physically interactive virtual video-game. Unenhanced magnetic resonance imaging (MRI) demonstrated marked T2-weighted signal abnormality within several muscles of the shoulder and upper arm, without evidence of macroscopic partial- or full-thickness tearing of the muscle or of intramuscular hematoma.     

Diffusion-weighted magnetic resonance imaging in Marchiafava–Bignami disease: follow-up studies

Marchiafava–Bignami disease (MBD), an acute toxic demyelination of the corpus callosum in alcoholics, is associated with poor evolution in the majority of patients. We report here the early and late diffusion magnetic resonance imaging (MRI) and apparent diffusion coefficient (ADC) studies of two patients suffering from MBD with favourable outcome. Diffusion and anatomical MRI changes were parallel to the clinical evolution, suggesting that MRI studies can be helpful for diagnosis and follow-up. Unlike in stroke, restricted diffusion on ADC maps does not seem to be a sign of irreversibility.     

Clinical applications of susceptibility weighted MR imaging of the brain – a pictorial review

Introduction Susceptibility-weighted imaging (SWI) is a novel magnetic resonance (MR) technique that exploits the magnetic susceptibility differences of various tissues, such as blood, iron and calcification. This pictorial review covers many clinical conditions illustrating its usefulness. Methods SWI consists of using both magnitude and phase images from a high-resolution, three-dimensional fully velocity-compensated gradient echo sequence. Phase mask is created from the MR phase images, and multiplying these with the magnitude images increase the conspicuity of the smaller veins and other sources of susceptibility effects, which is depicted using minimal intensity projection (minIP). Results The phase images are useful in differentiating between diamagnetic and paramagnetic susceptibility effects of calcium and blood, respectively. This unique MR sequence will help in detecting occult low flow vascular lesions, calcification and cerebral microbleed in various pathologic conditions and aids in characterizing tumors and degenerative diseases of the brain. This sequence also can be used to visualize normal brain structures with conspicuity. Conclusion Susceptibility-weighted imaging is useful in differentiating and characterizing diverse brain pathologies.     

Magnetic resonance imaging features of nasopharyngeal carcinoma and nasopharyngeal non-Hodgkin's lymphoma: Are there differences?

Purpose

To describe differences in the primary tumour and distribution of cervical lymphadenopathy for cases of nasopharyngeal carcinoma (NPC) and nasopharyngeal non-Hodgkin's lymphoma (NPNHL) using magnetic resonance (MR) imaging.

Materials and methods

MR images of patients with NPC (n = 272) and NPNHL (n = 118) were independently reviewed by two experienced radiologists.

Results

NPC had a higher incidence of tumour invasion associated with the levator and tensor muscles of the velum palatine, the longus colli and medial pterygoid muscles, the base of the pterygoid process, the clivus, the base and greater wing of the sphenoid bone, the petrous apex, the foramen lacerum, the foramen ovale, the hypoglossal canal, and intracranial infiltration. In contrast, NPNHL had a higher incidence of tumour invasion associated with the hypopharynx, the palatine and lingual tonsils, as well as the ethmoid and maxillary sinuses. NPNHL also had a higher incidence of extensive and irregular bilateral lymphadenopathy, and lymphadenopathy in the parotid.

Conclusions

NPC more often involved an unsymmetrical tumour with a propensity to invade both widely and deeply into muscle tissue, the fat space, the neural foramen, and the skull base bone. In contrast, NPNHL tended to be a symmetrical and diffuse tumour with a propensity to spread laterally through the fat space and along the mucosa to the tonsils of the oropharynx and hypopharynx. These differences facilitate a differentiation of these diseases using MR images, and enhance our understanding of the biological behavior of these malignant tumours of the nasopharynx.     

Atypical hemangioma and malignant lesions of spine: Can diffusion weighted Magnetic Resonance Imaging help to differentiate?

Objective

The aim of the work was directed to evaluate the value of diffusion weighted Magnetic Resonance Imaging in diagnosis, characterization and differentiation of atypical hemangioma and malignant lesions of spine.

Materials and methods

This study included three groups: group (A) 8 (33%) patients with metastatic bony lesions of spine, group (B) 6 (25%) patients with atypical hemangioma and group (C) 10 (42%) patients with typical hemangioma.All patients were presented with different degrees of back pain. MRI was done for all patients (including T1, T2, T2 fat suppression and DWI with IV contrast administration when needed). Complementary non contrast CT was also done.

Results

Atypical hemangioma and malignant lesions were low in T1 and high in T2 WI. Restricted diffusion and low ADC values were seen in metastasis compared with atypical hemangioma. Complementary CT revealed the lytic nature of malignant lesions while in hemangiomas, it showed their characteristic striated appearance.

Conclusion

Diffusion weighted Magnetic Resonance Imaging is a useful tool in diagnosis, characterization and differentiation of atypical hemangioma and metastasis of spine.     

Characterization of soft tissue masses: can quantitative diffusion weighted imaging reliably distinguish cysts from solid masses?

Objective

To investigate the accuracy of quantitative diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) mapping for characterizing soft tissue masses (STMs) as cysts or solid masses.

Materials and methods

This IRB-approved retrospective study included 36 subjects with 37 STMs imaged by conventional MRI (T1-weighted, T2-weighted, contrast-enhanced T1-weighted sequences) and DWI (b-values 50, 400, 800 s/mm²) with ADC mapping. STMs were defined as non-solid cysts by histology or clinical follow-up, and as solid by histology. For each STM, ADC values (range, mean) were recorded by two observers. Differences between ADC values in cysts and solid STMs were compared using Wilcoxon rank-sum and receiver-operating characteristic (ROC) analysis.

Results

There were higher minimum (1.65 vs 0.68, p?=?0.003) and mean (2.31 vs 1.45, p?=?0.005) ADC values in cysts than solid STMs respectively. Areas under the ROC for minimum and mean ADC values were 0.82 and 0.81 respectively. Using threshold ADC values of 1.8 (minimum) or 2.5 (mean) yielded a sensitivity of 60 % and 80 % respectively, and a specificity of 100 % for classifying a STM as a cyst; for tumors with high fluid–signal intensity, the performance of these threshold values was maintained.

Conclusion

Diffusion-weighted imaging with ADC mapping provides a non-contrast MRI alternative for the characterization of STMs as cysts or solid masses. Threshold ADC values exist that provide 100 % specificity for differentiating cysts and solid STMs, even for tumors of high fluid–signal intensity on T2-weighted images.