Readout-Segmented Echo-Planar Imaging in Diffusion-Weighted MR Imaging in Breast Cancer: Comparison with Single-Shot Echo-Planar Imaging in Image Quality

Objective

The purpose of this study was to compare the image quality of standard single-shot echo-planar imaging (ss-EPI) and that of readout-segmented EPI (rs-EPI) in patients with breast cancer.

Materials and Methods

Seventy-one patients with 74 breast cancers underwent both ss-EPI and rs-EPI. For qualitative comparison of image quality, three readers independently assessed the two sets of diffusion-weighted (DW) images. To evaluate geometric distortion, a comparison was made between lesion lengths derived from contrast enhanced MR (CE-MR) images and those obtained from the corresponding DW images. For assessment of image parameters, signal-to-noise ratio (SNR), lesion contrast, and contrast-to-noise ratio (CNR) were calculated.

Results

The rs-EPI was superior to ss-EPI in most criteria regarding the qualitative image quality. Anatomical structure distinction, delineation of the lesion, ghosting artifact, and overall image quality were significantly better in rs-EPI. Regarding the geometric distortion, lesion length on ss-EPI was significantly different from that of CE-MR, whereas there were no significant differences between CE-MR and rs-EPI. The rs-EPI was superior to ss-EPI in SNR and CNR.

Conclusion

Readout-segmented EPI is superior to ss-EPI in the aspect of image quality in DW MR imaging of the breast.     

Image quality associated with the use of an MR-compatible incubator in neonatal neuroimaging

Objectives

MRI in the neonate poses significant challenges associated with patient transport and monitoring, and the potential for diminished image quality owing to patient motion. The objective of this study was to evaluate the usefulness of a dedicated MR-compatible incubator with integrated radiofrequency coils in improving image quality of MRI studies of the brain acquired in term and preterm neonates using standard MRI equipment.

Methods

Subjective and objective analyses of image quality of neonatal brain MR examinations were performed before and after the introduction of an MR-compatible incubator. For all studies, the signal-to-noise ratio (SNR) was calculated, image quality was graded (1–3) and each was assessed for image artefact (e.g. motion). Student''s t-test and the Mann–Whitney U-test were used to compare mean SNR values.

Results

39 patients were included [mean gestational age 39 weeks (range 30–42 weeks); mean postnatal age 13 days (range 1–56 days); mean weight 3.5 kg (range 1.4–4.5 kg)]. Following the introduction of the MR-compatible incubator, diagnostic quality scans increased from 50 to 89% and motion artefact decreased from 73 to 44% of studies. SNR did not increase initially, but, when using MR sequences and parameters specifically tailored for neonatal brain imaging, SNR increased from 70 to 213 (p=0.001).

Conclusion

Use of an MR-compatible incubator in neonatal neuroimaging provides a safe environment for MRI of the neonate and also facilitates patient monitoring and transport. When specifically tailored MR protocols are used, this results in improved image quality.MRI of the brain is an important clinical tool for the evaluation of neonates with encephalopathy, suspected brain injury or developmental brain anomalies. Specific MR techniques may also provide information on myelination, metabolism and functional capabilities of the neonatal brain [1-3].Neuroimaging in the neonate presents a number of challenges. Transporting the critically ill neonate to the MRI unit presents significant practical problems. These infants require a carefully controlled microenvironment with a need for thermoregulation and constant haemodynamic monitoring and may need ventilatory support [4]. Handling the infant immediately prior to image acquisition can cause distress, and resultant movement may produce non-diagnostic images due to motion artefact. Sedation of neonates and infants can be performed but is not without risk, and a sedated neonate requires continuous monitoring during the examination with MR-compatible pulse oximetry and electrocardiogram [5,6].MR-compatible neonatal incubators have been developed to provide a safe and efficient method of transporting neonates to the MR suite and to allow monitoring of the baby during the examination. Stabilisation of the neonatal head within the incubator and close attention to swaddling technique are necessary to reduce patient movement during image acquisition, thereby reducing the need for sedation. Many of these incubators are equipped with an integrated radiofrequency (RF) coil, specifically tailored to the size of the neonate, which should improve image quality by increasing the signal-to-noise ratio (SNR). Previous studies have shown promising results with regard to patient safety [7,8]. Currently, there is little information on how image quality from an integrated incubator–coil unit compares with standard MR equipment [8]. Maximising image quality can be achieved by using a closely fitting RF coil (a dedicated neonatal head coil or a knee coil) and by modifying MR sequences which need to be specifically tailored to the neonatal brain because of its higher water content [5].The aim of our study was to compare the imaging performance of an MR-compatible incubator with integrated RF coils with standard MRI equipment in both term and preterm neonates.     

The Image Quality and Radiation Dose of 100-kVp versus 120-kVp ECG-Gated 16-Slice CT Coronary Angiography

Objective

This study was conducted to assess the feasibility of performing 100-kVp electrocardiogram (ECG)-gated coronary CT angiography, as compared to 120-kVp ECG-gated coronary CT angiography.

Materials and Methods

We retrospectively evaluated one hundred eighty five gender- and body mass index-matched 16-slice coronary CT sets of data, which were obtained using either 100 kVp and 620 effective mAs or 120 kVp and 500 effective mAs. The density measurements (image noise, vessel density, signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]) and the estimated radiation dose were calculated. As a preference test, two image readers were independently asked to choose one image from each pair of images. The results of both protocols were compared using the paired t-test or the Wilcoxon signed rank test.

Results

The 100-kVp images showed significantly more noise and a significantly higher vessel density than did the 120-kVp images. There were no significant differences in the SNR and CNR. The estimated reduction of the radiation dose for the 100-kVp protocol was 24%; 7.8 ± 0.4 mSV for 100-kVp and 10.1 ± 1.0 mSV for 120-kVp (p < 0.001). The readers preferred the 100-kVp images for reading (reader 1, p = 0.01; reader 2, p = 0.06), with their preferences being stronger when the subject''s body mass index was less than 25.

Conclusion

Reducing the tube kilovoltage from 120 to 100 kVp allows a significant reduction of the radiation dose without a significant change in the SNR and the CNR.     

Comparison of a 28-channel receive array coil and quadrature volume coil for morphologic imaging and T2 mapping of knee cartilage at 7T

Purpose:

To compare a new birdcage‐transmit, 28‐channel receive array (28‐Ch) coil and a quadrature volume coil for 7T morphologic MRI and T2 mapping of knee cartilage.

Materials and Methods:

The right knees of 10 healthy subjects were imaged on a 7T whole body magnetic resonance (MR) scanner using both coils. 3D fast low‐angle shot (3D‐FLASH) and multiecho spin‐echo (MESE) sequences were implemented. Cartilage signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), thickness, and T2 values were assessed.

Results:

SNR/CNR was 17%–400% greater for the 28‐Ch compared to the quadrature coil (P ≤ 0.005). Bland–Altman plots show mean differences between measurements of tibial/femoral cartilage thickness and T2 values obtained with each coil to be small (?0.002 ± 0.009 cm / 0.003 ± 0.011 cm) and large (?6.8 ± 6.7 msec/?8.2 ± 9.7 msec), respectively. For the 28‐Ch coil, when parallel imaging with acceleration factors (AF) 2, 3, and 4 was performed SNR retained was: 62%–69%, 51%–55%, and 39%–45%.

Conclusion:

A 28‐Ch knee coil provides increased SNR/CNR for 7T cartilage morphologic imaging and T2 mapping. Coils should be switched with caution during clinical studies because T2 values may differ. The greater SNR of the 28‐Ch coil could be used to perform parallel imaging with AF2 and obtain similar SNR as the quadrature coil. J. Magn. Reson. Imaging 2012;441‐448. © 2011 Wiley Periodicals, Inc.

     

Screening for atherosclerotic plaques in the abdominal aorta in high-risk patients with multicontrast-weighted MRI: a prospective study at 3.0 and 1.5 tesla

Objective

This prospective study compares MRI of atherosclerotic plaque in the abdominal aorta at 3 T with that at 1.5 T in patients suffering from hereditary hyperlipidaemia, a major risk factor for atherosclerosis.

Methods

MRI of the abdominal aorta at 1.5 and 3 T was performed in 21 patients (mean age 58 years). The study protocol consisted of proton density (PD), T₁, T₂ and fat-saturated T₂ weighted black blood images of the abdominal aorta in corresponding orientation. Two independent radiologists performed image rating. First, image quality was rated on a five-point scale. Second, atherosclerotic plaques were scored according to the modified American Heart Association (AHA) classification and analysed for field strength-related differences. Weighted κ statistics were calculated to assess interobserver agreement.

Results

Interobserver agreement was substantial for nearly all categories. MRI at 3 T offered superior image quality in all contrast weightings, most significantly in T₁ and T₂ weighted techniques. Plaque burden in the study collective was unexpectedly moderate. The majority of plaques were classified as AHA III lesions; no lesions were classified above AHA V. There was no significant influence of the field strength regarding the AHA classification.

Conclusion

Abdominal aortal plaque screening is basically feasible at both field strengths, whereas the image quality is rated superior at 3 T. However, the role of the method in clinical practice remains uncertain, since substantial findings in the high-risk collective were scarce.Atherosclerosis is a systemic disease of the vessel wall that mainly occurs in medium-sized and large arteries; its thrombotic or thromboembolic complications are the main cause of mortality and morbidity in industrialised countries [1,2]. It is characterised by a thickening of the vessel wall, especially the intima, and is histologically composed of a lipid core with an overlying fibrous cap. The main plaque components are fibrous elements (e.g. connective tissue, collagen, proteoglycans), lipids (e.g. cholesterol, phospholipids), smooth muscle cells and inflammatory cells (e.g. macrophages, T lymphocytes). The composition of the atherosclerotic plaque determines its vulnerability [3-6]. The so-called “vulnerable plaque” consists of a large lipid core and a thin fibrous cap, although the characteristics of the vulnerable plaques vary depending on the arterial region (i.e. coronaries, carotids, aorta) [6-8]. Rupture of atherosclerotic plaques as a result of an endothelial lesion is the most frequent cause of the unpredictable onset of acute thromboembolic vascular events such as myocardial infarction, ischaemic stroke or sudden cardiac death [9,10]. Therefore, it is necessary to characterise plaque components and determine them at an early stage to prevent cardiovascular events. Several invasive and non-invasive imaging modalities are used to study atherosclerotic vessel lesions: conventional (B-mode) ultrasound, intravascular ultrasound (IVUS), conventional angiography, CT, angioscopy and MRI [5,10]. Most of them identify luminal diameter or stenosis, wall thickness and plaque volume, but are not able to determine plaque components [5,11]. Several recent studies showed that in vivo and ex vivo MRI as a non-invasive method can characterise the composition of atherosclerotic plaques such as fibrous tissue, lipid core, calcification, haemorrhage and thrombus [5,10,12-18]. The aim of this characterisation is the determination of the risk of plaque rupture.Most of the previous publications regarding plaque imaging in the human aorta are of studies performed at 1.5 T. Newer publications show the advantages of high field strength, such as faster imaging with parallel imaging techniques and higher signal-to-noise ratio (SNR) [19,20].The purpose of this study was to compare in vivo multimodality MR plaque imaging of the human aorta at 1.5 T and 3 T in a patient collective at high risk for atherosclerosis, in which atherosclerotic wall alterations can be expected. The evaluation focused on image quality and on the analysis of atherosclerotic plaque components according to the American Heart Association (AHA) classification [3,21].In the context of the prospective study, plaque imaging was always performed in addition to whole-body MR angiography (WBMRA) and is therefore part of a whole-body screening approach.     

Signal-to-noise ratio increase in carotid atheroma MRI: a comparison of 1.5 and 3 T

Objectives

This study reports quantitative comparisons of signal-to-noise ratio (SNR) at 1.5 and 3 T from images of carotid atheroma obtained using a multicontrast, cardiac-gated, blood-suppressed fast spin echo protocol.

Methods

18 subjects, with carotid atherosclerosis (>30% stenosis) confirmed on ultrasound, were imaged on both 1.5 and 3 T systems using phased-array coils with matched hardware specifications. T₁ weighted (T₁W), T₂ weighted (T₂W) and proton density-weighted (PDW) images were acquired with identical scan times. Multiple slices were prescribed to encompass both the carotid bifurcation and the plaque. Image quality was quantified using the SNR and contrast-to-noise ratio (CNR). A phantom experiment was also performed to validate the SNR method and confirm the size of the improvement in SNR. Comparisons of the SNR values from the vessel wall with muscle and plaque/lumen CNR measurements were performed at a patient level. To account for the multiple comparisons a Bonferroni correction was applied.

Results

One subject was excluded from the protocol owing to image quality and protocol failure. The mean improvement in SNR in plaque was 1.9, 2.1 and 2.1 in T₁W, T₂W and PDW images, respectively. All plaque SNR improvements were statistically significant at the p<0.05 level. The phantom experiment reported an improvement in SNR of 2.4 for PDW images.

Conclusions

Significant gains in SNR can be obtained for carotid atheroma imaging at 3 T compared with 1.5 T. There was also a trend towards increased CNR. However, this was not significant after the application of the Bonferroni correction.Carotid MRI has been in use since the mid-1990s for detecting atherosclerosis [1], with advances being driven by a greater understanding of the pathophysiology of plaque development and progression [2]. This has in turn led to a desire to be able to distinguish characteristics of carotid atheroma (such as a large lipid-rich necrotic core or a thin fibrous cap) that put an individual at a significantly greater risk of a future stroke [3]. MRI has been repeatedly validated against the gold standard of histology for the characterisation of carotid atheroma and measurement of plaque components [1,2,4,5]. The capacity for MRI to demonstrate plaque characteristics has been applied to assess the long-term pathogenesis of atherosclerosis and to monitor the effects of therapeutic interventions [6-9].The current limiting factors for multicontrast MRI in atheroma are image resolution and scan time, but the advent of higher field strengths has provided the opportunity to advance the quality of carotid imaging. The requirement for high-resolution imaging at small fields of view places high demands on the hardware being used, and current protocols typically use signal averaging to improve signal-to-noise ratio (SNR). In theory, SNR should increase linearly with field strength; thus, a 1.5 vs 3 T comparison experiment should produce an approximate doubling of the SNR [10]. This expected increase in SNR could be used either to improve spatial resolution or to reduce the number of averages, and hence reduce the scan time in future protocols.Initial studies have indicated the benefit of 3 T MRI of the carotid artery wall. One of the early studies, in 2005, used a double inversion recovery (DIR) prepared turbo spin echo (TSE) sequence to image a phantom and healthy volunteers [11]. The phantom experiments demonstrated an SNR increase of a factor of 2.5 for 3 T over 1.5 T, compared with 2.1 in vivo. A separate image with a larger field of view (FOV; 24×12 cm as opposed to 12×12 cm) but the same bandwidth/pixel size was used to define the background regions of interest (ROI) for the SNR calculation. The superlinear increase in the phantom was ascribed to the differential noise contribution of the small coil elements at the different field strengths. In addition to this, the lower SNR gain in vivo was attributed to the differences in T₁ and T₂ at the higher field strength, as well as the need to use a lower refocusing flip angle at 3 T (160°) in two of the subjects owing to specific absorption rate (SAR) limitations.A study published in 2006 performed multicontrast fast spin echo (FSE) imaging with DIR preparation and fat suppression without cardiac gating [12]. A cohort of five healthy volunteers and two atheroma-affected subjects were imaged at both field strengths, and SNR and contrast-to-noise ratio (CNR) values increased by 1.5–1.8 times at 3 T. Noise levels were determined from four ROIs drawn in an artefact-free background area in a rectangular FOV (16×12 cm), and the wall/luminal signal intensities were corrected for the mean noise contribution.A 2007 study using a small cohort (five healthy volunteers, five with atherosclerosis) produced comparable results [13], albeit with different coils (eight-element at 3 T and four-element at 1.5 T) and slightly different pixel sizes used at the two field strengths. A two-fold increase in SNR for the vessel wall (in sections unaffected by plaque) was reported after adjustment for the larger voxel size used at 1.5 T. However, differences in SNR enhancement between the different contrast weightings were not described.A single case report considering multicontrast imaging in a patient with moderate carotid stenosis using 1.5 and 3 T systems from different manufacturers found a significant improvement in SNR across T₁ weighted (T₁W), T₂ weighted (T₂W) and proton density weighted (PDW) images at 3 T, varying from a 64% to 83% increase [14].While the majority of these studies confirm the expected increase in SNR with field strength, they are based upon small sample sizes (mainly normal volunteers) and varying numbers of sequences, and they utilise a range of SNR measurement methodologies, as well as differences in coil design/manufacture and MRI system manufacturers at the two field strengths.In comparison with the previous studies, the current work provides a substantially more detailed and standardised comparative analysis of SNR at 1.5 and 3.0 T for the widely used multicontrast imaging using, as far as possible, identical pulse sequences, coil designs and MRI systems. Unlike the previous studies, rather than using normal volunteers, a larger cohort of patients with confirmed carotid atheroma of varying degrees of severity was used, as would be seen in clinical practice.     

The Clinical Feasibility of Using Non-Breath-Hold Real-Time MR-Echo Imaging for the Evaluation of Mediastinal and Chest Wall Tumor Invasion

Objective

We wanted to determine the clinical feasibility of using non-breath-hold real-time MR-echo imaging for the evaluation of mediastinal and chest wall tumor invasion.

Materials and Methods

MR-echo imaging was prospectively applied to 45 structures in 22 patients who had non-small cell lung cancer when the tumor invasion was indeterminate on CT. The static MR imaging alone, and the static MR imaging combined with MR-echo examinations were analyzed. The surgical and pathological findings were compared with using the Wilcoxon-signed rank test and McNemar''s test.

Results

The accuracy, sensitivity and specificity of the combined MR-echo examination and static MR imaging for determining the presence of invasion were 84%, 83% and 85%, respectively, for the first reading session and they were 87%, 83% and 87%, respectively, for the second reading session (there was substantial interobserver agreement, k = 0.74). For the static MR imaging alone, these values were 62%, 83% and 59%, respectively, for the first reader and they were 69%, 67% and 74%, respectively, for the second reader (there was moderate interobserver agreement, k = 0.49). The diagnostic confidence for tumor invasion was also higher for the combined MR-echo examination and static MR imaging than that for the static MR imaging alone (p < 0.05).

Conclusion

The combined reading of a non-breath-hold real-time MR-echo examination and static MR imaging provides higher specificity and diagnostic confidence than those for the static MR imaging reading alone to determine the presence of mediastinal or chest wall tumor invasion when this was indeterminate on CT scanning.     

MR Imaging Findings of Clonorchiasis

Objective

The purpose of this study was to evaluate the MR spectrum and MR cholangiographic imaging findings of clonorchiasis.

Materials and Methods

We reviewed 26 patients with confirmed clonorchiasis by either stool tests (n=24) or surgery (n=2). MR imaging was performed on a 1.5 T system (GE Medical Systems, Milwaukee, WI) with a torso coil. Axial T1- and T2-weighted, gadolinium-enhanced dynamic images and MR cholangiography were obtained. Image analyses were used to identify abnormalities of the intrahepatic and extrahepatic bile ducts and the presence of hepatobiliary malignancy. All MR examinations were reviewed by the consensus of two abdominal radiologists.

Results

Intrahepatic bile duct abnormalities were seen in 23 (89%) of the 26 patients. The most common finding was mild dilatation of the intrahepatic bile duct which was found in 21 (81%). "Too many intrahepatic ducts" were found in 16(62%), wall enhancement and thickening in 21 (81%) and filling defects and ductal stricture in the intrahepatic bile duct in 6 (24%) and 3 (12%) patients, respectively. Extrahepatic ductal dilation was found in 5 (19%) and 9 (35%) revealed hepatobiliary malignancy.

Conclusion

MR imaging revealed various findings of clonorchiasis, including dilatation, wall enhancement, stricture of the intrahepatic ducts and filling defect within the intrahepatic bile duct.     

MRI study of atherosclerotic plaque progression using ultrasmall superparamagnetic iron oxide in Watanabe heritable hyperlipidemic rabbits

Objective:

The purpose of this study was to evaluate plaque progression by using MRI with ultrasmall superparamagnetic iron oxide (USPIO) and by histopathological studies.

Methods:

We divided 12 Watanabe heritable hyperlipidemic (WHHL) rabbits into 4 groups based on their age (3, 9, 14 and 26 months) and injected them intravenously with 0.8 mmol (Fe) kg⁻¹ of USPIO (size, 32 nm; concentration, 15 mg dl⁻¹). On the fifth post-injection day, they were again given an intravenous injection with 40 μmol kg⁻¹ of the same USPIO, and MR angiography (MRA) was performed. The signal-to-noise ratio (SNR) in regions of interest in the wall of the upper abdominal aorta was calculated on coronal images. Specimens from the same level of the aorta were subjected to iron staining and RAM-11 immunostaining and used for histopathological study. For statistical analysis of the MRA and histopathological findings, we used analysis of variance [Tukey''s honest significant difference (HSD) test].

Results:

In 9-month-old rabbits, the SNR was significantly lower than in rabbits of the other ages (p < 0.01), and the area of RAM-11 (DAKO Corporation, Glostrup, Denmark) and iron uptake in the aortic wall was significantly larger (RAM-11, p < 0.01; iron, p < 0.05). These areas were the smallest in 3-month-old rabbits.

Conclusion:

Histopathologically, the number of macrophages was the greatest in 9-month-old rabbits. Our findings indicate that the SNR on MRI scans reflects the number of macrophages in the aortic wall of WHHL rabbits.

Advances in knowledge:

USPIO-enhanced MRI visualized the accumulation of macrophages in early atherosclerotic plaques of WHHL rabbits in the course of natural progression.     

MRI with intraoral orthodontic appliance—a comparative in vitro and in vivo study of image artefacts at 1.5?T

Objectives:

We investigated artefacts caused from orthodontic appliances at 1.5-T MRI of the head and neck region and whether the image quality can be improved utilizing the artefact-minimizing sequence WARP.

Methods:

In vitro tests were performed by phantom measurements of different orthodontic devices applying different types of MR sequences [echoplanar imaging (EPI), turbo spin echo (TSE) and TSE-WARP, gradient echo (GRE)]. Two independent readers determined after calibration the level of artefacts. Subsequently, the interobserver agreement was calculated. The measurement of artefacts was based on the American Society for Testing Materials Standard F 2119-07. For in vivo imaging, one test person was scanned with an inserted multibracket appliance. The level of artefacts for 27 target regions was evaluated.

Results:

In vitro: ceramic brackets and ferromagnetic steel brackets produced artefact radii up to 1.12 and 7.40 cm, respectively. WARP reduced these artefacts by an average of 32.7%. The Bland–Altman-Plot indicated that maximum measurement differences of 3 mm have to be expected with two calibrated observers. In vivo: the EPI sequence for brain imaging was not analysable. The TSE sequence of the brain did not demonstrate artefacts except for the nasal cavity. Conversely, the TSE sequence of the cervical spine revealed severe artefacts in the midface region. The GRE sequence appeared to be more susceptible to artefacts than did the TSE sequence.

Conclusions:

In vitro measurements allow an estimation of the in vivo artefact size. Orthodontic appliances may often remain intraorally when performing MRI. WARP showed a more significant effect in vitro than in vivo.     

Coronary Microembolization with Normal Epicardial Coronary Arteries and No Visible Infarcts on Nitrobluetetrazolium Chloride-Stained Specimens: Evaluation with Cardiac Magnetic Resonance Imaging in a Swine Model

Objective

To assess magnetic resonance imaging (MRI) features of coronary microembolization in a swine model induced by small-sized microemboli, which may cause microinfarcts invisible to the naked eye.

Materials and Methods

Eleven pigs underwent intracoronary injection of small-sized microspheres (42 µm) and catheter coronary angiography was obtained before and after microembolization. Cardiac MRI and measurement of cardiac troponin T (cTnT) were performed at baseline, 6 hours, and 1 week after microembolization. Postmortem evaluation was performed after completion of the imaging studies.

Results

Coronary angiography pre- and post-microembolization revealed normal epicardial coronary arteries. Systolic wall thickening of the microembolized regions decreased significantly from 42.6 ± 2.0% at baseline to 20.3 ± 2.3% at 6 hours and 31.5 ± 2.1% at 1 week after coronary microembolization (p < 0.001 for both). First-pass perfusion defect was visualized at 6 hours but the extent was largely decreased at 1 week. Delayed contrast enhancement MRI (DE-MRI) demonstrated hyperenhancement within the target area at 6 hours but not at 1 week. The microinfarcts on gross specimen stained with nitrobluetetrazolium chloride were invisible to the naked eye and only detectable microscopically. Increased cTnT was observed at 6 hours and 1 week after microembolization.

Conclusion

Coronary microembolization induced by a certain load of small-sized microemboli may result in microinfarcts invisible to the naked eye with normal epicardial coronary arteries. MRI features of myocardial impairment secondary to such microembolization include the decline in left ventricular function and myocardial perfusion at cine and first-pass perfusion imaging, and transient hyperenhancement at DE-MRI.     

Ultrashort echo time (UTE) MRI for the assessment of caries lesions

Objective:

Direct in vivo MRI of dental hard tissues by applying ultrashort echo time (UTE) MRI techniques has recently been reported. The objective of the presented study is to clinically evaluate the applicability of UTE MRI for the identification of caries lesions.

Methods:

40 randomly selected patients (mean age 41 ± 15 years) were enrolled in this study. 39 patients underwent a conventional clinical assessment, dental bitewing X-ray and a dental MRI investigation comprising a conventional turbo-spin echo (TSE) and a dedicated UTE scan. One patient had to be excluded owing to claustrophobia. In four patients, the clinical treatment of the lesions was documented by intraoral pictures, and the resulting volume of the cavity after excavation was documented by dental imprints and compared with the MRI findings.

Results:

In total, 161 lesions were identified. 157 (97%) were visible in the UTE images, 27 (17%) in the conventional TSE images and 137 (85%) in the X-ray images. In total, 14 teeth could not be analysed by MR owing to artefacts caused by dental fillings. All lesions appear significantly larger in the UTE images as compared with the X-ray and TSE images. In situ measurements confirm the accuracy of the lesion dimensions as observed in the UTE images.

Conclusion:

The presented data provide evidence that UTE MR imaging can be applied for the identification of caries lesions. Although the current data suggest an even higher sensitivity of UTE MRI, some limitations must be expected from dental fillings.     

Effects of Dual-Energy CT with Non-Linear Blending on Abdominal CT Angiography

Objective

To determine whether non-linear blending technique for arterial-phase dual-energy abdominal CT angiography (CTA) could improve image quality compared to the linear blending technique and conventional 120 kVp imaging.

Materials and Methods

This study included 118 patients who had accepted dual-energy abdominal CTA in the arterial phase. They were assigned to Sn140/80 kVp protocol (protocol A, n = 40) if body mass index (BMI) < 25 or Sn140/100 kVp protocol (protocol B, n = 41) if BMI ≥ 25. Non-linear blending images and linear blending images with a weighting factor of 0.5 in each protocol were generated and compared with the conventional 120 kVp images (protocol C, n = 37). The abdominal vascular enhancements, image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and radiation dose were assessed. Statistical analysis was performed using one-way analysis of variance test, independent t test, Mann-Whitney U test, and Kruskal-Wallis test.

Results

Mean vascular attenuation, CNR, SNR and subjective image quality score for the non-linear blending images in each protocol were all higher compared to the corresponding linear blending images and 120 kVp images (p values ranging from < 0.001 to 0.007) except for when compared to non-linear blending images for protocol B and 120 kVp images in CNR and SNR. No significant differences were found in image noise among the three kinds of images and the same kind of images in different protocols, but the lowest radiation dose was shown in protocol A.

Conclusion

Non-linear blending technique of dual-energy CT can improve the image quality of arterial-phase abdominal CTA, especially with the Sn140/80 kVp scanning.     

The T2-Shortening Effect of Gadolinium and the Optimal Conditions for Maximizing the CNR for Evaluating the Biliary System: a Phantom Study

Objective

Clear depiction of the common bile duct is important when evaluating neonatal cholestasis in order to differentiate biliary atresia from other diseases. During MR cholangiopancreatography, the T2-shortening effect of gadolinium can increase the contrast-to-noise ratio (CNR) of the bile duct and enhance its depiction. The purpose of this study was to confirm, by performing a phantom study, the T2-shortening effect of gadolinium, to evaluate the effect of different gadolinium chelates with different gadolinium concentrations and different magnetic field strengths for investigating the optimal combination of these conditions, and for identifying the maximum CNR for the evaluation of the biliary system.

Materials and Methods

MR imaging using a T2-weighted single-shot fast spin echo sequence and T2 relaxometry was performed with a sponge phantom in a syringe tube. Two kinds of contrast agents (Gd-DTPA and Gd-EOB-DTPA) with different gadolinium concentrations were evaluated with 1.5T and 3T scanners. The signal intensities, the CNRs and the T2 relaxation time were analyzed.

Results

The signal intensities significantly decreased as the gadolinium concentrations increased (p < 0.001) with both contrast agents. These signal intensities were higher on a 3T (p < 0.001) scanner. The CNRs were higher on a 1.5T (p < 0.001) scanner and they showed no significant change with different gadolinium concentrations. The T2 relaxation time also showed a negative correlation with the gadolinium concentrations (p < 0.001) and the CNRs showed decrease more with Gd-EOB-DTPA (versus Gd-DTPA; p < 0.001) on a 3T scanner (versus 1.5T; p < 0.001).

Conclusion

A T2-shortening effect of gadolinium exhibits a negative correlation with the gadolinium concentration for both the signal intensities and the T2 relaxation time. A higher CNR can be obtained with Gd-DTPA on a 1.5T MRI scanner.     

The Significance of Perfusion Defect at Myocardial Perfusion MR Imaging in a Cat Model of Acute Reperfused Myocardial Infarction

Objective

To determine whether the size of a perfusion defect seen at myocardial perfusion MR imaging represents the extent of irreversibly damaged myocardium in acute reperfused myocardial infarction.

Materials and Methods

In nine cats, reperfused myocardial infarction was induced by occlusion of the left anterior descending coronary artery for 90 minutes and subsequent reperfusion for 90 minutes. At single-slice myocardial perfusion MR imaging at the midventricular level using a turbo-FLASH sequence, 60 short-axis images were sequentially obtained with every heart beat after bolus injection of gadomer-17. The size of the perfusion defect was measured and compared with both the corresponding unstained area seen at triphenyl tetrazolium chloride (TTC) staining and the hyperenhanced area seen at gadophrin-2-enhanced MR imaging performed in the same cat six hours after myocardial perfusion MR imaging.

Results

The sizes of perfusion defects seen at gadomer-17-enhanced perfusion MR imaging, unstained areas at TTC staining, and hyperenhanced areas at gadophrin-2-enhanced MR imaging were 20.4 ± 4.3%, 29.0 ± 9.7%, and 30.7 ± 10.6% of the left ventricular myocardium, respectively. The perfusion defects seen at myocardial perfusion MR imaging were significantly smaller than the unstained areas at TTC staining and hyperenhanced areas at gadophrin-2-enhanced MR imaging (p < .01). The sizes of both the perfusion defect at myocardial perfusion MR imaging and the hyperenhanced area at gadophrin-2-enhanced MR imaging correlated well with the sizes of unstained areas at TTC staining (r = .64, p = .062 and r = .70, p = .035, respectively).

Conclusion

In this cat model, the perfusion defect revealed by myocardial perfusion MR imaging underestimated the true size of acute reperfused myocardial infarction. The defect may represent a more severely damaged area of infarction and probably has prognostic significance.     

MRI of the wrist at 7 tesla using an eight‐channel array coil combined with parallel imaging: Preliminary results

Purpose:

To determine the feasibility of performing MRI of the wrist at 7 Tesla (T) with parallel imaging and to evaluate how acceleration factors (AF) affect signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), and image quality.

Materials and Methods:

This study had institutional review board approval. A four‐transmit eight‐receive channel array coil was constructed in‐house. Nine healthy subjects were scanned on a 7T whole‐body MR scanner. Coronal and axial images of cartilage and trabecular bone micro‐architecture (3D‐Fast Low Angle Shot (FLASH) with and without fat suppression, repetition time/echo time = 20 ms/4.5 ms, flip angle = 10°, 0.169–0.195 × 0.169–0.195 mm, 0.5–1 mm slice thickness) were obtained with AF 1, 2, 3, 4. T1‐weighted fast spin‐echo (FSE), proton density‐weighted FSE, and multiple‐echo data image combination (MEDIC) sequences were also performed. SNR and CNR were measured. Three musculoskeletal radiologists rated image quality. Linear correlation analysis and paired t‐tests were performed.

Results:

At higher AF, SNR and CNR decreased linearly for cartilage, muscle, and trabecular bone (r < ?0.98). At AF 4, reductions in SNR/CNR were:52%/60% (cartilage), 72%/63% (muscle), 45%/50% (trabecular bone). Radiologists scored images with AF 1 and 2 as near‐excellent, AF 3 as good‐to‐excellent (P = 0.075), and AF 4 as average‐to‐good (P = 0.11).

Conclusion:

It is feasible to perform high resolution 7T MRI of the wrist with parallel imaging. SNR and CNR decrease with higher AF, but image quality remains above‐average. J. Magn. Reson. Imaging 2010;31:740–746. © 2010 Wiley‐Liss, Inc.

     

Grading Anterior Cruciate Ligament Graft Injury after Ligament Reconstruction Surgery: Diagnostic Efficacy of Oblique Coronal MR Imaging of the Knee

Objective

The purpose of this study was to evaluate the diagnostic efficacy of using additional oblique coronal MRI of the knee for grading anterior cruciate ligament (ACL) graft injury after ligament reconstruction surgery.

Materials and Methods

We retrospectively reviewed 51 consecutive MR knee examinations of 48 patients who underwent both ACL reconstruction and follow-up arthroscopy. The MR examinations included the orthogonal axial, sagittal, coronal images and the oblique coronal T2-weighted images, which were oriented in parallel with the course of the femoral intercondylar roof. Two radiologists independently evaluated the status of the ACL grafts with using the routine knee MRI and then with adding the oblique coronal imaging. The severity of ACL graft injury was graded using a 3-point system from MR images as intact, partial tear or complete tear, and the results were compared with the arthroscopic results. Weighted kappa statistics were used to analyze the diagnostic accuracies of the knee MRI with and without the additional oblique coronal imaging. For each evaluation, the observers reported a confidence level for grading the ACL graft injuries in the two imaging groups.

Results

The weighted kappa values according to the routine knee MRI were 0.555 (reader 1) and 0.515 (reader 2). The inclusion of additional oblique coronal imaging increased the weighted kappa values to 0.666 (reader 1) and 0.611 (reader 2). The mean confidence levels by each reader were significantly higher (p < 0.01, paired t-test) with the additional oblique coronal imaging than by using the routine knee MRI alone.

Conclusion

The additional use of oblique coronal MRI of the knee improves both the diagnostic accuracy and confidence for grading ACL graft injury.     

Brain MRI Findings of Carbon Disulfide Poisoning

Objective

To evaluate the findings of brain MRI in patients with carbon disulfide poisoning.

Materials and Methods

Ninety-one patients who had suffered carbon disulfide poisoning [male:female=87:4; age, 32-74 (mean 53.3) years] were included in this study. To determine the extent of white matter hyperintensity (Grade 0-V) and lacunar infarction, T2-weighted MR imaging of the brain was performed.

Results

T2-weighted images depicted white matter hyperintensity in 70 patients (76.9%) and lacunar infarcts in 27 (29.7%).

Conclusion

In these patients, the prevalent findings at T2-weighted MR imaging of the brain were white matter hyperintensity and lacunar infarcts. Disturbance of the cardiovascular system by carbon disulfide might account for these results.     

Qualitative and Quantitative Assessment of Isotropic Ankle Magnetic Resonance Imaging: Three-Dimensional Isotropic Intermediate-Weighted Turbo Spin Echo versus Three-Dimensional Isotropic Fast Field Echo Sequences

Objective

To compare the image quality of volume isotropic turbo spin echo acquisition (VISTA) imaging method with that of the three-dimensional (3D) isotropic fast field echo (FFE) imaging method applied for ankle joint imaging.

Materials and Methods

MR imaging of the ankles of 10 healthy volunteers was performed with VISTA and 3D FFE sequences by using a 3.0 T machine. Two radiologists retrospectively assessed the tissue contrast between fluid and cartilage (F-C), and fluid and the Achilles tendon (F-T) with use of a 4-point scale. For a quantitative analysis, signal-to-noise ratio (SNR) was obtained by imaging phantom, and the contrast ratios (CRs) were calculated between F-T and F-C. Statistical analyses for differences in grades of tissue contrast and CRs were performed.

Results

VISTA had significantly superior grades in tissue contrast of F-T (p = 0.001). Results of 3D FFE had superior grades in tissue contrast of F-C, but these result were not statistically significant (p = 0.157). VISTA had significantly superior CRs in F-T (p = 0.002), and 3D FFE had superior CRs in F-C (p = 0.003). The SNR of VISTA was higher than that of 3D FFE (49.24 vs. 15.94).

Conclusion

VISTA demonstrates superior tissue contrast between fluid and the Achiles tendon in terms of quantitative and qualitative analysis, while 3D FFE shows superior tissue contrast between fluid and cartilage in terms of quantitative analysis.     

In Vivo MR Imaging of Magnetically Labeled Mesenchymal Stem Cells in a Rat Model of Renal Ischemia

Objective

This study was designed to evaluate in vivo MR imaging for the depiction of intraarterially injected superparamagnetic iron oxide (SPIO)-labeled mesenchymal stem cells (MSCs) in an experimental rat model of renal ischemia.

Materials and Methods

Left renal ischemia was induced in 12 male Sprague-Dawley rats by use of the catheter lodging method. In vivo MR signal intensity variations depicted on T2*-weighted sequences were evaluated in both the left and right kidneys prior to injection (n = 2), two hours (n = 4), 15 hours (n = 2), 30 hours (n = 2) and 72 hours (n = 2) after injection of SPIO-labeled MSCs in both kidneys. Signal intensity variations were correlated with the number of Prussian blue stain-positive cells as visualized in histological specimens.

Results

In an in vivo study, it was determined that there was a significant difference in signal intensity variation for both the left and right cortex (40.8 ± 4.12 and 26.4 ± 7.92, respectively) and for both the left and right medulla (23.2 ± 3.32 and 15.2 ± 3.31, respectively) until two hours after injection (p < 0.05). In addition, signal intensity variation in the left renal cortex was well correlated with the number of Prussian blue stain-positive cells per high power field (r = 0.98, p < 0.05).

Conclusion

Intraarterial injected SPIO-labeled MSCs in an experimental rat model of renal ischemia can be detected with the use of in vivo MR imaging immediately after injection.