Malignant lymphoma of the gingiva: MR evaluation.

PURPOSEOur purpose was to document the MR imaging findings of malignant lymphoma of the gingiva.METHODSFive patients with histologically proved malignant lymphoma of the gingiva were studied by MR imaging. The MR images were analyzed for tumor size, extent, and signal characteristics, bone involvement, and associated cervical lymph node enlargement.RESULTSClinical examination tended to underestimate the size of lymphomatous lesions. The signal intensity of the lesions was isointense to hyperintense relative to muscle on noncontrast T1-weighted images and showed variable contrast enhancement patterns. On T2-weighted images, signal intensity was isointense to hypointense relative to the oral mucosa. In one case, the mass extended to the submandibular space; in the remaining cases, the masses were limited to the gingiva and the adjacent bone. MR imaging revealed that gingival lymphomatous masses were broad-based along the mandible or maxilla and eroded through the cortex into the marrow space, but the cortex was still recognizable. No nodal involvement was noted in any of the patients with malignant lymphoma.CONCLUSIONThe signal characteristics of gingival lymphoma overlap those of other tumors. The cortex separating marrow involvement from the broad-based gingival mass generally appears to be permeated with small erosions but is still recognizable.     

Metallic residues as a source of artifacts in magnetic resonance imaging of the temporomandibular joint

OBJECTIVES: To establish the source of metallic artifacts on postoperative MRI of the temporomandibular joint after arthroplasty. METHODS: An experiment was carried out to evaluate MR artifacts which were thought to have been caused by minute metallic particles deposited at surgery. Four types of cutting instruments were used to cut an extracted tooth: a diamond bur attached to a dental air turbine handpiece, a steel bur and bone bur attached to a dental micromotor handpiece and a bone file. The tooth fragments were collected in plastic centrifuge tubes in water. These samples were evaluated with six MR sequences. RESULTS: MR artifacts were clearly demonstrated in samples using the bone bur and the bone file but not the diamond and steel burs. CONCLUSIONS: The artifacts seen on postoperative MRI were derived from minute metal particles from the bone bur or file used for condylar arthroplasty. Metal artifacts should be considered when interpreting postoperative MR images.     

钯银合金对磁共振成像影响的初步研究

目的: 探讨口腔修复用钯银合金对磁共振成像的影响.材料和方法:在临床随机选取中切牙至第二磨牙的钯银合金桩核4个,金属全冠2个,烤瓷全冠1个.放置于受检者右侧腹部,采用临床常用序列(SSFSE;FRFSE;GRE; DWI)扫描.然后,选择2位口腔中有多个钯银合金固定修复体的志愿者,采用颅脑磁共振常用序列(T1Flair;FSE;GRE;DWI)和参数分别在1.5T和3.0T的磁场中扫描.结果:钯银合金在1.5T磁场中行腹部和颅脑磁共振检查时无明显伪影形成,对磁共振成像无影响.在3.0T磁场中在牙齿周围有轻微伪影出现,对脑部、上下颌骨均无影响.结论:①钯银合金固定修复体在磁共振检查时没有热效应和投射效应,对患者和仪器是安全的.装有钯银合金固定修复体的患者可以做磁共振检查.②钯银合金固定修复体在做MRI检查时在低场强的磁场中没有显著的伪影.在高场强的磁场中,有轻微伪影,但只局限于牙齿,不影响周边组织结构及器官的成像.③建议给装有钯银合金固定修复体的患者做磁共振检查时尽量使用低磁场,并且最好不要用GRE序列.     

磨牙桩冠修复的临床效果分析

目的观察汞合金桩核与铸造金属桩核在磨牙桩冠修复中的临床疗效。方法选择我院2005～2010年经完善根管治疗后的69颗磨牙,进行桩冠修复。69颗磨牙分为两组:一组为牙体缺损不低于龈缘者,采用汞合金桩核,共39颗;另一组牙体缺损位于龈缘下方者,采用铸造金属桩核,共30颗。全部病例随访3年后进行疗效分析。结果桩冠修复3年后,汞合金桩核组成功37颗,失败2例(颗)均为冠脱落,铸造金属桩核组成功29颗,失败1例(颗),根折所致。结论用汞合金桩核和铸造金属桩核修复缺损磨牙,两者均能达到良好的临床疗效。     

MR of the cerebral operculum: topographic identification and measurement of interopercular distances in healthy infants and children.

PURPOSETo evaluate the role of axial, coronal, and sagittal MR in identification of surface landmarks of the cerebral operculum and to determine the reference values of interopercular distances of each hemisphere in healthy infants and children on MR images.METHODSTwo hundred fourteen cerebral opercula of 35 healthy infants and 72 healthy children were retrospectively evaluated from 107 routine MR brain examinations. The surface landmarks of the operculum and interopercular distances of each hemisphere, which were subjectively divided into anterior interopercular distance (anterior sylvian width) and posterior interopercular distance (posterior sylvian width), were recorded from axial, coronal, and sagittal MR images, respectively. The mean value of anterior interopercular distance of each hemisphere was obtained by averaging two linear measurements of the anterior sylvian width from lateral, sagittal, and axial planes of the same side. Likewise, the posterior interopercular distance of each side of the brain was obtained from averaging of two measurements on lateral, sagittal, and coronal planes.RESULTSThe landmarks of the operculum were best identified by sagittal MR, followed by axial and coronal images. The average values of left anterior interopercular distance, right anterior interopercular distance, left posterior interopercular distance, and right posterior interopercular distance in infants were 1.9 +/- 1.3, 1.6 +/- 1.1, 0.4 +/- 0.7, and 0.2 +/- 0.4 mm, and in children, 0.9 +/- 1.3, 1.0 +/- 1.4, 0.03 +/- 0.23, and 0.01 +/- 0.07 mm, respectively. Infants showed significantly wider interopercular distances than children. Left anterior interopercular distance was significantly wider than right in infants, but not in children. Male children displayed a more significant increase in anterior interopercular distance than did female children. There was no statistic difference in measurements of anterior interopercular distance and posterior interopercular distance between female and male infants.CONCLUSIONSThe operculum should be evaluated with MR in three planes. Infants may show conspicuous sylvian fissures that should not exceed 4.5 mm (mean + 2 SD) anteriorly on axial and sagittal planes and 1.8 mm posteriorly on sagittal and coronal planes. Healthy children who have fully developed opercula should have an anterior interopercular distance of no more than 3.5 mm and a posterior interopercular distance of 0.5 mm.     

Diagnostic accuracy of cone-beam CT in the assessment of mandibular invasion of lower gingival carcinoma: Comparison with conventional panoramic radiography

Purpose

To evaluate the diagnostic accuracy of cone-beam CT in assessing mandibular invasion by lower gingival carcinoma and compare it with that of panoramic radiography.

Patients and methods

Fifty patients with squamous cell carcinoma of the lower gingiva who were examined by both panoramic radiography and cone-beam CT before surgery were included in this study. Five radiologists used a 6-point rating scale to independently evaluate cone-beam CT and panoramic images for the presence or absence of alveolar bone and mandibular canal involvement by tumor. Using the histopathogical findings as the gold standard, we calculated and compared the area under the receiver operating characteristic curve (Az value) and the sensitivity and specificity of the two imaging modalities.

Results

In evaluations of both alveolar bone and mandibular canal involvement, the mean Az value for cone-beam CT (0.918 and 0.977, respectively) was significantly higher than that for panoramic radiography (0.793 and 0.872, respectively). The mean sensitivity for cone-beam CT (89% and 99%, respectively) was significantly higher than that for panoramic radiography (73% and 56%, respectively). There was no significant difference in the mean specificity. While cone-beam CT could provide high-resolution three-dimensional images, the image quality around the alveolar crest was often hampered by severe dental artifacts and image noise, resulting in difficulties in detecting subtle alveolar invasion.

Conclusion

Cone-beam CT was significantly superior to panoramic radiography in evaluating mandibular invasion by lower gingival carcinoma. Its diagnostic value in detecting subtle alveolar invasion, however, may be limited by severe dental artifacts and image noise.     

Pseudothrombosis in the portal venous system: a potential pitfall with gadolinium-enhanced dynamic gradient-recalled echo imaging of the liver

Gadolinium-enhanced dynamic magnetic resonance (MR) images in 90 patients were reviewed to assess the artifacts mimicking portal venous thrombosis. The incidence of definite signal-intensity decrease mimicking pathologic condition was higher (P < 0.01) in the right (8%) and left (9%) portal vein branches and portal trunk (6%) than in the splenic (0%) or superior mesenteric (1%) vein with equilibrium-phase images. Radiologists should remember that dynamic MR images occasionally show signal-intensity decrease mimicking portal venous thrombosis due to flow artifact.     

MR volumetric analysis of the human entorhinal,perirhinal, and temporopolar cortices.

PURPOSEOur purpose was to investigate the normal volumes of the human entorhinal, perirhinal, and temporopolar cortices on MR imaging studies using a customized program.METHODSWe designed a protocol in which the volumes of the entorhinal, perirhinal, and temporopolar cortices were determined from coronal MR images using anatomic landmarks defined on the basis of cytoarchitectonic analyses of 49 autopsy cases. MR volumetry of these cortical areas was performed in 52 healthy volunteers.RESULTSThe overall mean volumes were 1768 +/- 328 mm3/1558 +/- 341 mm3 (right/left) for the entorhinal cortex, 2512 +/- 672 mm3/2572 +/- 666 mm3 for the perirhinal cortex, and 2960 +/- 623 mm3/3091 +/- 636 mm3 for the temporopolar cortex. The right entorhinal cortex was 12% larger than the left. The volume of the temporopolar cortex was reduced bilaterally by 13% in the older age group compared with younger subjects, while the volumes of the entorhinal and perirhinal cortices were unaffected by age. There were no differences between men and women in the volumes of any of the three cortices.CONCLUSIONOur method provides a tool by which to measure volumes of the entorhinal, perirhinal, and temporopolar cortices on coronal MR images.     

High signal intensity in the dural sinuses on 3D-TOF MR angiography at 3.0 T

PurposeThe objective of this study was to examine the frequency of high signal intensity in the dural sinuses of normal subjects upon magnetic resonance (MR) angiography using 3.0-T scanners.MethodsA total of 748 consecutive healthy subjects underwent three-dimensional time-of-flight MR angiography at 3.0 T. Sixteen subjects were excluded. MR angiographic source images were retrospectively reviewed for the presence of high signal intensity in the inferior petrosal sinus, pterygoid sinus, or sigmoid sinus.ResultsOf the 732 examinations, 10 (1.3%) showed high signal intensity in the dural sinuses (left inferior petrosal sinus, n=4; left pterygoid sinus, n=3; left sigmoid sinus, n=6). High signal intensity in the dural sinuses was observed only on the left side. The minimum diameter of the left brachiocephalic vein was significantly smaller in subjects with high signal intensity than in the control group.ConclusionIn our study with healthy subjects at 3.0 T, the frequency of high signal intensity in the dural sinuses is as low as 1.3%. Retrograde flow due to physiological stenosis of the left brachiocephalic vein may be one of the causes of this phenomenon.     

Essential hypertension and neurovascular compression at the ventrolateral medulla oblongata: MR evaluation.

PURPOSETo investigate, using MR imaging, neurovascular compression at the ventrolateral medulla oblongata in patients with essential hypertension.METHODSThirty-two patients with essential hypertension (57.6 +/- 7 years of age), 6 patients with secondary hypertension (56.7 +/- 10.3 years of age), and 18 control subjects (50.5 +/- 11 years of age) were evaluated. Transaxial three-dimensional fast low angle shot images were obtained (38/6/1 [repetition time/echo time/excitations]). The center of a 40-mm-thick slab (16 partitions) was placed at the pontomedullary junction. We evaluated the relationships between the upper ventrolateral medulla and the vertebral arteries and branches identified by their flow-related hyperintensities in each group.RESULTSIn the essential hypertension group, 29 (90.6%) of 32 cases showed neurovascular compression. Of those, 22 demonstrated neurovascular compression on the left side, 3 on both sides, and 4 on the right side. In the control group, 4 cases of 18 showed neurovascular compression. In the secondary hypertension group, 1 of 6 cases showed neurovascular compression. The rates of observed neurovascular compression between controls and essential hypertension group were statistically significant.CONCLUSIONWe found a close correlation between essential hypertension and neurovascular compression at the ventrolateral medulla oblongata on the left side. MR with a 3-D fast low-angle shot sequence has acceptable spatial resolution and depicts blood vessels simultaneously by flow-related phenomena.     

Functional MR to localize sustained visual attention activation in patients with attention deficit hyperactivity disorder: a pilot study.

PURPOSETo evaluate brain control activation in patients with attention deficit hyperactivity disorder (ADHD) and to provide an initial comparison between activated regions in ADHD subjects and those previously localized in an unaffected population.METHODSTen patients with ADHD underwent imaging with a functional blood oxygen level-dependent MR technique during sustained visual vigilance. Pixel activation was inspected visually and statistical group analysis was performed.RESULTSActivation was seen over the bilateral middle frontal gyri, the superior parietal lobules, and the inferior parietal lobules. The predominant activity occurred in the right middle frontal gyrus. Application of an additional statistical constraint revealed significant activity in the right inferior and left superior parietal lobules.CONCLUSIONADHD patients effectively tolerated the necessary MR imaging constraints despite their difficulty with confinement and immobility. Single-section functional MR imaging revealed activation in brain regions known to be involved in the maintenance of the attention in healthy subjects responding to auditory, tactile, or visual stimulation; additional areas of activity that were identified may represent true abnormal regions in the affected population or artifacts.     

A comparison of functional MR activation patterns during silent and audible language tasks.

PURPOSETo compare word generation tasks performed silently and aloud as paradigms for functional MR.METHODSImages were obtained at 1.5 T, with echoplanar acquisition in nine subjects performing word generation aloud or silently. Functional images created from the echoplanar images by means of cross-correlation techniques were superimposed on anatomic reference images. The location of activation from the two tasks was tabulated; the number of activated pixels in each region from the two tasks was compared.RESULTSBoth silent and aloud word generation produced activation in the inferior frontal lobes, sensorimotor cortex regions, supplementary motor areas, and anterior cingulate gyri, predominantly in the dominant hemisphere. Significantly more activated pixels and fewer artifacts were detected with silent word generation than with word generation aloud.CONCLUSIONWord generation silently or aloud produce activation in the brain. Greater activation can be detected in the left frontal lobe with silent word generation, although the subject''s performance of the task cannot be monitored independently during silent word generation.     

口腔内金属材料和磁共振检查伪影

检测口腔内常用金属材料在磁共振检查时否为影和伪影的严重程度;并比较不同检查序列对伪影的影响。材料与方法：对２２种２５件口腔内常用金属材料做了磁共振成像测试,磁共振仪磁场强度为１．５Ｔ,所用序列是梯度回波,部分材料加做自旋回波和快速自旋回波。     

MR changes in the calcarine area resulting from retinal degeneration.

PURPOSETo study MR images for atrophic changes in the calcarine area resulting from retinal degeneration.METHODSMR images from nine patients with retinal degeneration confirmed by ophthalmologic examination and from 30 healthy volunteers were reviewed. The causes of retinal degeneration were hereditary pigmentary degeneration of the retina (four patients), high myopia (two patients), and chorioretinal atrophy (three patients); all patients had visual disturbances and visual field abnormalities. To estimate the morphological changes of the calcarine area, the widths of the right and left calcarine fissures were measured on T1-weighted sagittal images and compared with images from age-matched control subjects.RESULTSThe calcarine fissures were significantly dilated in the patients with retinal degeneration. The anterior and middle points, which represent the peripheral visual field center, were more dilated than the posterior point.CONCLUSIONThe MR findings suggested calcarine atrophy related to retinal degeneration. Transneuronal degenerative changes may occur in the calcarine area after retinal degeneration.     

Sagittal MR of multiple sclerosis in the spinal cord: fast versus conventional spin-echo imaging.

PURPOSEWe compared conventional spin-echo (CSE) with fast spin-echo (FSE) dual-echo MR images to determine which of these sequences was better able to depict spinal cord abnormalities in patients with multiple sclerosis (MS).METHODSCSE and FSE dual-echo MR images were obtained in 37 patients with MS and in six healthy control subjects, all of whom were examined on a 1.0-T MR unit with a phased-array coil and cardiac triggering. Two blinded interpreters graded the MR studies, first separately and then by consensus. Images were scored for presence of artifacts, number of focal lesions, and presence of a diffuse increase in signal intensity.RESULTSNo abnormalities were seen in the volunteers. The CSE sequences were significantly less hindered by MR imaging artifacts than were the FSE sequences. Interobserver agreement was slightly higher for the CSE than the FSE sequences. After reaching a consensus, the observers found that both CSE and FSE techniques enabled detection of approximately the same number of focal lesions; however, in three patients, small single lesions seen on the CSE images were missed on the FSE images. Also, depiction of a diffuse increase in signal intensity was better on the CSE images. As a result, more patients had abnormal findings on the CSE sequences than on the FSE sequences (35 versus 31).CONCLUSIONCardiac-triggered dual-echo FSE sequences are almost as good as CSE sequences for depicting spinal MS lesions. Therefore, in cases of established spinal MS, FSE techniques may be as effective as CSE techniques. Because sensitivity for subtle abnormalities is lower with FSE imaging, CSE remains the preferred technique for patients with suspected MS of the spinal cord.     

Comparison of spin-echo MR pulse sequences for imaging of the brain.

PURPOSETo determine the value of the gradient- and spin-echo (GRASE) technique as compared with the fast spin-echo and conventional spin-echo techniques in MR imaging of the brain.METHODSSixty-six patients with ischemic and neoplastic brain lesions were examined with T2-weighted spin-echo, fast spin-echo, and GRASE sequences. Three independent observers evaluated the contrast characteristics of anatomic and pathologic structures and of artifacts. Quantitative image analysis included region-of-interest measurements of anatomic structures and lesions.RESULTSThe contrast of anatomic structures was superior in images obtained with conventional and fast spin-echo techniques as compared with those obtained with the GRASE technique. Extended lesions, such as tumors and territorial infarcts, were identified equally with all techniques. For delineation of small ischemic lesions, GRASE was slightly inferior to fast and conventional spin-echo sequences. Flow artifacts were considerably reduced with fast spin-echo and GRASE sequences. Chemical-shift artifacts were significantly reduced, but ringing artifacts were more pronounced with GRASE.CONCLUSIONFast spin-echo remains the standard technique in MR imaging of the brain. However, GRASE might be useful in special cases, such as with uncooperative patients whose conventional or fast spin-echo images show severe motion artifacts.     

Magnetic susceptibility artifacts on high-resolution MR of the temporal bone.

PURPOSETo determine whether signal variations and subtle anatomic deformities observed in high-resolution MR studies of temporal bones were caused by the large susceptibility differences at air-fluid interfaces near the round and oval window.METHODSA systematic study of healthy subjects and plastic phantoms was conducted. The phantom consisted of a series of cylindrical holes of various small sizes within a solid block of plastic. These holes were partially filled with water and then covered with a reservoir of gelatin to simulate the otic capsule air-water interfaces. On a 1.5-T system, T2-weighted fast spin-echo images and three-dimensional Fourier transform gradient acquisition in steady state images were obtained using dedicated phased-array radio frequency coils. The directions of the frequency and in-plane phase-encoding gradients were swapped, and the receiver bandwidth was changed to demonstrate the dependence of the artifacts on these parameters.RESULTSThe phantom images confirmed and characterized artifacts consistent with magnetic susceptibility differences at the air-water interfaces. There is a combination of signal loss, misregistration in the frequency-encoding direction, and high signal foci related to the air-water interfaces. Furthermore, the artifacts were worse with narrower receiver bandwidth. Similar consistent artifact patterns were seen near the oval and round windows in studies of healthy subjects.CONCLUSIONSIn high-resolution MR imaging there are significant deformities in the display of the normal anatomy because of magnetic susceptibility.     

Effect of low back posture on the morphology of the spinal canal

Objective. To define the possible mechanism of posture-dependent symptoms of spinal stenosis by measuring the effect of low back posture on morphologic changes of the intervertebral discs and spinal canal in healthy young people. Design.Twenty healthy young volunteers underwent magnetic resonance imaging while supine with their spine in neutral, flexed, extended, and right and left rotational positions. The axial MR images at the middle of the intervertebral discs of L3–4 and L4–5 were analyzed to measure the difference in the size and shape of the intervertebral discs and spinal canal in each posture. Results.  Extension or rotation decreased the sagittal diameters and cross-sectional areas of the dural sac and spinal canal and increased the thickness of the ligamentum flavum, whereas flexion had the opposite effects. The gap between the convex posterior disc margin and the anterior margin of the facet joint on each side, represented as the subarticular sagittal diameter, increased with flexion and decreased with extension or rotation. The direction of rotation did not result in asymmetry of the subarticular sagittal diameter, but right rotation caused thickening of the right ligamentum flavum, and vice versa. The shape and dimensions of the disc did not change significantly according to the positions of the low back. Conclusions.With extension or rotation, the thickness of the ligamentum flavum increased and the posterior margin of the intervertebral disc was approximated to the facet joint without any change in shape and size of the disc. These phenomena result in a decrease in the size of the spinal canal and dural sac in extension or rotation postures in young healthy people without disc degeneration, and may explain the posture-dependent symptom of spinal stenosis. Received: 18 October 1999 Revision requested: 9 November 1999 Revision received: 13 December 1999 Accepted: 17 January 2000     

Motion artifacts on coronary CT angiography images in patients with a pericardial effusion

BackgroundPatients with a pericardial effusion can have a pendulum-like movement of the heart. No reports associate the presence of pericardial fluid with coronary CT angiography (CTA) images that are degraded by motion artifact.ObjectiveWe tested the hypothesis that patients with pericardial effusion have coronary CTA images compromised by motion artifacts, even when other known causes of motion artifact in coronary imaging are minimized.MethodsAmong the prospectively electrocardiogram-gated single heart beat 320-detector row coronary CTA studies performed from September 2009 to May 2013, 13 consecutive studies acquired with a heart rate <60 beats/min that indicate a pericardial effusion formed an effusion cohort. A control cohort included 13 studies with no pericardial fluid performed by the same CT scanner; these were pair-matched to the effusion cohort for heart rate, sex, age, and body mass index. All studies were free of arrhythmia and respiratory motion. Motion artifact was separately assessed (3-point scale) at 8 coronary segments by 2 cardiovascular imaging teams.ResultsThe mean pericardial effusion volume for the effusion cohort was 129 ± 57 mL (range, 39–222 mL). Intra-observer/interobserver reproducibility of the motion artifact scores were good (κ = 0.636–0.791). Motion artifacts were more frequently observed in the effusion cohort for the left circumflex (no, mild, severe artifact, 54%, 46%, 0% vs 81%, 19%, 0%, respectively, for effusion vs control; P = .039) and right coronary arteries (no, mild, severe artifact = 41%, 44% 15% vs 79%, 21%, 0%, respectively, for effusion vs control; P < .001), especially for the middle or distal segments. Larger effusion volumes were associated with more severe motion artifacts.ConclusionPatients with pericardial effusion have coronary CTA images compromised by cardiac motion artifacts, particularly in the left circumflex and right coronary arteries.     

Artifact reduction from metallic dental materials in T1‐weighted spin‐echo imaging at 3.0 tesla

Purpose:

To investigate and propose a method of artifact reduction arising from metallic dental materials by applying a slice‐encoding for metal artifact correction (SEMAC) technique on T1‐weighted spin‐echo (SE) imaging at 3 Tesla.

Materials and Methods:

The view angle tilting (VAT) technique was adapted to conventional T1‐weighted spin‐echo (SE) sequence to correct the in‐plane distortion, and the SEMAC technique was used for correcting the remaining through‐plane distortions. Fourier transform based B0 field simulations were performed to estimate the amount of field perturbation and a scout imaging method was developed which guide in selecting the number of slice‐encodings needed in SEMAC sequences. Phantoms of six different dental materials with various shapes and sizes that are used in practice (amalgam; titanium implant; gold and Ni‐Cr crowns; Ni‐Ti and stainless steel orthodontic wires) were imaged. In vivo images of two subjects were also acquired. The amounts of artifact reduction were quantified in phantom studies.

Results:

Compared with conventional SE imaging in phantom studies, in‐plane artifacts were reduced by up to 43% in the VAT SE images and 80% in the SEMAC images. Through‐plane artifacts were reduced by up to 65% in SEMAC images. In vivo SEMAC images also showed reduced artifacts.

Conclusion:

The SEMAC technique can mitigate artifact caused by metallic dental materials for T1w‐SE imaging. J. Magn. Reson. Imaging 2013;37:471–478. © 2012 Wiley Periodicals, Inc.