Fat suppression in MR imaging: techniques and pitfalls

A paradoxical signal intensity increase in fatty livers using opposed-phase gradient echo imaging with fat-suppression pulses

With the increase in obese and overweight children, nonalcoholic fatty liver disease has become more prevalent in the pediatric population. Appreciating subtleties of magnetic resonance (MR) signal intensity behavior from fatty livers under different imaging conditions thus becomes important to pediatric radiologists. We report an initially confusing signal behavior-increased signal from fatty livers when fat-suppression pulses are applied in an opposed-phase gradient echo imaging sequence-and seek to explain the physical mechanisms for this paradoxical signal intensity behavior. Abdominal MR imaging at 3 T with a 3-D volumetric interpolated breath-hold (VIBE) sequence in the opposed-phase condition (TR/TE 3.3/1.3 ms) was performed in five obese boys (14+/-2 years of age, body mass index >95th percentile for age and sex) with spectroscopically confirmed fatty livers. Two VIBE acquisitions were performed, one with and one without the use of chemical shift selective (CHESS) pulse fat suppression. The ratios of fat-suppressed over non-fat-suppressed signal intensities were assessed in regions-of-interest (ROIs) in five tissues: subcutaneous fat, liver, vertebral marrow, muscle and spleen. The boys had spectroscopically estimated hepatic fat levels between 17% and 48%. CHESS pulse fat suppression decreased subcutaneous fat signals dramatically, by more than 85% within regions of optimal fat suppression. Fatty liver signals, in contrast, were elevated by an average of 87% with CHESS pulse fat suppression. Vertebral marrow signal was also significantly elevated with CHESS pulse fat suppression, while spleen and muscle signals demonstrated only small signal increases on the order of 10%. We demonstrated that CHESS pulse fat suppression actually increases the signal intensity from fatty livers in opposed-phase gradient echo imaging conditions. The increase can be attributed to suppression of one partner of the opposed-phase pair that normally contributes to the destructive interference between water and fat. The result is a paradoxical increase in signal from fatty liver that will depend on both fat content and the relative longitudinal relaxation times of fat methylene protons and water.

Mature and immature ovarian teratomas: CT, US and MR imaging characteristics

Ovarian teratomas (OTs) are the most common germ cell neoplasm. They include mature cystic teratomas, monodermal teratomas (neural tumors, struma ovarii, carcinoid tumors) and immature teratomas. Teratomas are the most common benign ovarian neoplasms in women less than 45 years old. OTs are usually characterized by ultrasound (US) and magnetic resonance (MR) whereas they are usually an incidental finding on CT. The purpose of this paper is to review the most common types of teratomas and to describe CT, US and MR imaging features of the various types of mature and immature OTs.

Diffusion-weighted whole-body imaging with background body signal suppression (DWIBS): features and potential applications in oncology

Diffusion-weighted magnetic resonance imaging (DWI) provides functional information and can be used for the detection and characterization of pathologic processes, including malignant tumors. The recently introduced concept of “diffusion-weighted whole-body imaging with background body signal suppression” (DWIBS) now allows acquisition of volumetric diffusion-weighted images of the entire body. This new concept has unique features different from conventional DWI and may play an important role in whole-body oncological imaging. This review describes and illustrates the basics of DWI, the features of DWIBS, and its potential applications in oncology.

Diffusion-weighted whole-body imaging with background body signal suppression (DWIBS): features and potential applications in oncology

Diffusion-weighted magnetic resonance imaging (DWI) provides functional information and can be used for the detection and characterization of pathologic processes, including malignant tumors. The recently introduced concept of "diffusion-weighted whole-body imaging with background body signal suppression" (DWIBS) now allows acquisition of volumetric diffusion-weighted images of the entire body. This new concept has unique features different from conventional DWI and may play an important role in whole-body oncological imaging. This review describes and illustrates the basics of DWI, the features of DWIBS, and its potential applications in oncology.

The value of chemical fat-saturation pulse added to T1-weighted spin-echo sequence in evaluating gadolinium-enhancing brain lesions in multiple sclerosis

PURPOSE

This study was undertaken to assess the value of a chemical (spectral) fat-saturation (fat-sat) pulse added to a T1-weighted spin-echo sequence after intravenous administration of paramagnetic contrast agent in detecting enhancing lesions in multiple sclerosis.

MATERIALS AND METHODS

Twenty patients with relapsing-remitting multiple sclerosis underwent a brain 1.0-Tesla magnetic resonance (MR) scan with T1-weighted spin-echo sequences (24 contiguous para-axial slices with a thickness of 5 mm, pixel size 0.96 mm(2), number of excitations 2, flip angle 90 degrees ) 5 min after intravenous injection of 0.1 mmol/kg of gadodiamide with and without fat-sat, acquired with randomised order of priority. Two readers counted by consensus the number of enhancing lesions and assigned a conspicuity score (low conspicuity=1; high conspicuity=2) to each enhancing lesion during a randomised reading without any visual comparison between the two corresponding images (with and without fat-sat) of the same patient. McNemar and Wilcoxon matched-pair signed-rank tests were used.

RESULTS

Seventy-two enhancing lesions without fat-sat and 94 with fat-sat were detected; 22 lesions were visible only with fat-sat, whereas no lesion was detected only without fat-sat (p<0.0001). The conspicuity score was 1.17+/-0.38 (mean+/-standard deviation) and 1.57+/-0.44, respectively (p<0.0001).

CONCLUSIONS

A fat-sat pulse added to a T1-weighted spin-echo sequence increases significantly the number and conspicuity of contrast-enhancing lesions in patients with relapsing-remitting multiple sclerosis.

Quantitative and semiquantitative evaluation of erythropoietin-induced bone marrow signal changes in lumbar spine MRI in patients with tumor anemia

BACKGROUND

The topic of this article is the quantitative and semiquantitative assessment of bone marrow signal alteration in magnetic resonance imaging (MRI) of the lumbar spine in patients with tumor anemia during therapy with epoietin beta or placebo.

PATIENTS AND METHODS

We examined 32 patients with head or neck cancer (16 epoietin beta, 16 placebo) during radiotherapy in a double-blind multicenter trial. During radiotherapy, the patients underwent epoietin beta therapy for 7-9 weeks. Lumbar spine measurements using T1-w SE, OPP and Turbo- STIR were taken prior to the first epoietin beta or placebo therapy, after the acquired hemoglobin level had been reached, and after the final radiotherapy. The semiquantitative assessment was made blinded by 2 independent radiologists.

RESULTS

We found significant differences between both groups. The first MRI showed normal marrow signals. The second MRI revealed a quantified decrease in bone marrow signal in T1-w SE (p < 0.018) and an increase in OPP (p < 0.01) and Turbo-TIR (p < 0.048) sequences. At the third MR imaging, quantified relative marrow signals returned to baseline level in all sequences. Semiquantitative assessment confirmed these results.

CONCLUSION

In both analyses, lumbar spine MRI demonstrates significant bone marrow changes in T1-w SE, OPP and Turbo-STIR sequences during epoietin beta therapy.

3.0 Tesla imaging of the musculoskeletal system

High-field MRI at 3.0T is rapidly gaining clinical acceptance and experiencing more widespread use. The superiority of high-field imaging has clearly been demonstrated for neurological imaging. The impact of 3.0T imaging of the musculoskeletal system has been less dramatic due to complex optimization issues. Areas under consideration include coil technology, protocol modification, artifact reduction, and patient safety. In this article we review these issues and describe our experience with 3.0T musculoskeletal MRI. Fundamentally, an increased signal-to-noise ratio (SNR) is responsible for improved imaging at higher field strength. Increased SNR allows more headroom to adjust parameters that affect image resolution and examination time. It has been established that T1 relaxation time increases at 3.0T, while T2 time decreases. Consequently, scanner parameters require adjustment for optimization of images. Chemical shift and magnetic susceptibility artifacts are more pronounced and require special techniques to minimize the effect on image quality. Spectral fat saturation techniques can take advantage of the increased chemical shift. The specific absorption rate (SAR) and acoustic noise thresholds must be kept in mind at these higher fields. We additionally present some of the clinical issues we have experienced at 3.0T. A decision must be made as to whether to trade higher resolution for reduced scanning time. In general, we believe that routine imaging at 3.0T increases diagnostic confidence, especially for evaluations of cartilaginous and ligamentous structures.

Methods and applications of diffusion imaging of vertebral bone marrow

Diffusion-weighted imaging (DWI) is an MRI technique that is sensitive to random water movements at spatial scales far below typical MRI voxel dimensions. DWI is a valuable tool for the diagnoses of diseases that involve alterations in water mobility. In the spine, DWI has proven to be a highly useful method for the differential diagnosis of benign and malignant compression fractures. In these pathologies, the microscopic structure of bone marrow is altered in a very different ways, leading to different water mobility, which can be depicted by DWI. Most of the pulse sequences developed for MRI can be adapted for DWI. However, these DWI-adapted sequences are frequently affected by artifacts, mostly caused by physiological motion. Therefore, the introduction of additional correction techniques, or even the development of new sequences is necessary. The first part of this article describes the principles of DWI and the sequences used for DWI of the spine: spin echo (SE), turbo spin echo (TSE), single-shot echo planar imaging (EPI), and steady-state free precession (SSFP) sequences. In the second part, clinical applications of DWI of the spinal bone marrow are extensively discussed.

Interleaved water and fat imaging and applications to lipid quantitation using the gradient reversal technique

PURPOSE

To implement and evaluate the gradient reversal-based chemical shift imaging technique to obtain qualitative and quantitative spatially-registered fat and water images with high imaging efficiency at very high field.

MATERIALS AND METHODS

A multiecho gradient reversal-based sequence allowing interleaved water-fat imaging during a single acquisition and quantitation of fat/water content is presented. The sequence was optimized and implemented at 11.7T. The quantitation was verified with water-fat phantoms and applied to lipid measurement in an in vivo mouse model.

RESULTS

Results from phantoms, in vivo lipid measurement in mouse liver and hind limb muscle, and ex vivo rat knee imaging experiments demonstrated the robustness and high selectivity of this technique for interleaved and quantitative water and fat imaging at very high field.

CONCLUSION

The proposed MRI technique permits interleaved water and fat imaging, with which spectrally well-separated water and fat images at the identical slice locations could be obtained in a single acquisition without increasing scan time. The technique could be used for in vivo quantitative mapping of lipid content and applied to investigations using small animal experiment models.

Artifacts and pitfalls in MR imaging of the pelvis

Artifacts are intimately intertwined with MRI. For the practicing radiologist, effective supervision, troubleshooting, and interpretation of diagnostic MR studies require a solid knowledge of the pertinent artifacts. This article seeks to familiarize the reader with commonly encountered artifacts and pitfalls in pelvic imaging, the mechanism behind their generation, and methods of minimizing their negative impact or maximizing their diagnostic yield. It also serves as an exciting tool to learn many aspects of basic and advanced MR physics. Artifacts are categorized into patient- and sequence-related artifacts. Various manifestations of motion and vascular artifacts, susceptibility, altered tissue contrast, blurring, chemical shift artifact, volume averaging, and gadolinium (Gd) pseudolayering are explained, along with their proposed remedies.

Fat saturation technique and gadolinium in MRI of lumbar spinal degenerative disease

We evaluated the potential of MR sequences with Fat Saturation and gadolinium in patients with degenerative disease of the lumbar spine and low back pain, by studying both anterior and posterior elements of the lumbar spine. We examined 3323 patients (age range 15-78 years) presenting low back pain. We used T2-weighted sequences with Fat Saturation and in some selected cases (1063 patients, 32%) administered gadolinium using T1-weighted sequences with Fat Saturation. In particular we used gadolinium in the following cases: 1) presence of hyperintense areas on T2 weighted images with Fat Saturation in the osteo-articular and muscular-ligamentous structures of the lumbar spine; 2) Clinical-radiological discrepancy in patients without disc-root conflict and clinical suspicion of posterior vertebral compartment syndrome. We found degenerative-inflammatory changes in osteo-articular, ligamentous and muscular structures in 1063 patients: osteochondrosis, "aseptic discitis", facet joint effusion and synovitis, osteoarthritis, synovial cysts, spondylolysis, degenerative-inflammatory changes of the posterior ligaments (flava, interspinous and supraspinous ligaments) and posterior perispinal muscles. To improve diagnostic accuracy and allow correct therapeutic guidance, MR examination in patients with low back pain must evaluate both anterior and posterior elements of the lumbar spine. Our study indicates that T2 sequences with Fat Saturation and, in selected cases, gadolinium administration, better visualize or disclose degenerative-inflammatory changes in the lumbar spine, showing the active-inflammatory phase and extension of these processes which may not be depicted during a standard MR examination.

Imaging of muscle disorders in children

Muscle inflammation is a relatively common pathological process in childhood. The diagnosis of the underlying cause relies on an appreciation of the pattern of clinical features, as well as the results of biochemical, histological and radiological investigations. Often the clinical and biochemical features are non-specific and insensitive. Consequently, the radiological abnormalities are very important in establishing a diagnosis and an understanding of the imaging features of muscle inflammatory disorders in childhood is needed. Some of the imaging protocols needed to investigate a variety of muscle and soft-tissue inflammatory conditions in childhood are reviewed in this article. Those features that are helpful in narrowing the differential diagnosis are indicated and a logical approach to the investigation of affected children is provided. The value of MR imaging is highlighted.

MR imaging of therapy-induced changes of bone marrow

MR imaging of bone marrow infiltration by hematologic malignancies provides non-invasive assays of bone marrow cellularity and vascularity to supplement the information provided by bone marrow biopsies. This article will review the MR imaging findings of bone marrow infiltration by hematologic malignancies with special focus on treatment effects. MR imaging findings of the bone marrow after radiation therapy and chemotherapy will be described. In addition, changes in bone marrow microcirculation and metabolism after anti-angiogenesis treatment will be reviewed. Finally, new specific imaging techniques for the depiction of regulatory events that control blood vessel growth and cell proliferation will be discussed. Future developments are directed to yield comprehensive information about bone marrow structure, function and microenvironment.

Lipoma of the cerebellopontine angle

Lipomas of the cerebellopontine angle (CPA) are unusual tumors that typically present with hearing loss, tinnitus, dizziness, and occasionally facial neuropathies. We describe the case of a healthy 42-year-old woman who presented with left-sided hearing loss and facial synkinesis. T1-weighted magnetic resonance imaging revealed an enhancing lesion of the left CPA with no signal on fat suppression sequences. Despite conservative therapy, the patient developed progressive hemifacial spasm, and a suboccipital craniotomy approach was used to debulk the tumor, which encased cranial nerves V, VII, VIII, IX, X, and XI. Surgical histopathology demonstrated mature adipocytes, consistent with lipoma. Two years after surgery, the patient remains free of facial nerve symptoms. Cerebellopontine angle lipomas are rare lesions of the skull base and are reliably diagnosed with T1-weighted and fat suppression magnetic resonance sequences, which we recommend in the routine radiologic workup of CPA tumors. Accurate preoperative diagnosis is crucial because most CPA lipomas should be managed conservatively. Partial surgical resection is indicated only to alleviate intractable cranial neuropathies or relieve brainstem compression.

Fat-containing lesions of the liver: radiologic-pathologic correlation

Fat-containing tumors of the liver are a heterogeneous group of tumors with characteristic histologic features, variable biologic profiles, and variable imaging findings. Benign liver lesions that contain fat include focal or geographic fatty change (steatosis), pseudolesions due to postoperative packing material (omentum), adenoma, focal nodular hyperplasia, lipoma, angiomyolipoma, cystic teratoma, hepatic adrenal rest tumor, pseudolipoma of the Glisson capsule, and xanthomatous lesions in Langerhans cell histiocytosis. Malignant liver lesions that can contain fat include hepatocellular carcinoma, primary and metastatic liposarcoma, and hepatic metastases. Identification of fat within a liver lesion can be critical in characterization of the lesion. The imaging characteristics of a lesion coupled with the pattern of intratumoral fatty change are helpful in narrowing the differential diagnosis. Although the presence of fat can be demonstrated with computed tomography or ultrasound, magnetic resonance imaging is the most specific imaging technique for demonstration of both microscopic and macroscopic fat.

Renal angiomyolipoma with minimal fat: differentiation from other neoplasms at double-echo chemical shift FLASH MR imaging

PURPOSE

To prospectively evaluate the diagnostic performance of double-echo gradient-echo (GRE) chemical shift magnetic resonance (MR) imaging in the differentiation of angiomyolipoma (AML) with minimal fat from other renal neoplasms, with pathologic examination or follow-up data serving as the reference standard.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Double-echo GRE chemical shift MR imaging was performed in 55 patients (29 men and 26 women; mean age, 49 years +/- 14 [standard deviation]) with 55 renal tumors, including 37 (67%) pathologically proved tumors (23 renal cell carcinomas, nine AMLs, two oncocytomas, two lymphomas, and one reninoma) and 18 (33%) clinically diagnosed tumors (17 AMLs and one indeterminate malignancy). All tumors showed no intratumoral fat and had homogeneous enhancement and a prolonged or gradual enhancement pattern on biphasic helical computed tomographic scans. Signal intensity was measured in the renal tumor and spleen on in-phase and opposed-phase images. The signal intensity index and tumor-to-spleen ratio in AMLs and non-AMLs were calculated and compared with the Student t test. Receiver operating characteristic (ROC) analysis was performed to evaluate the diagnostic accuracy of the signal intensity index and tumor-to-spleen ratio and to extract the optimal cut-off values in the differentiation of AMLs and non-AMLs.

RESULTS

The signal intensity index and tumor-to-spleen ratio were different between AMLs (42% +/- 11 and -43% +/- 17, respectively) and non-AMLs (5% +/- 14 and -4% +/- 16, respectively) (P < .001). The area under the ROC curve was 0.975 for the signal intensity index and 0.952 for the tumor-to-spleen ratio. For differentiation of AMLs from non-AMLs, sensitivity and specificity were (a) 96% and 93%, respectively, with a signal intensity index of 25% and (b) 88% and 97%, respectively, with a tumor-to-spleen ratio of -32%.

CONCLUSION

Double-echo GRE chemical shift MR imaging can be used to differentiate AML with minimal fat from other renal neoplasms.

CT and MR imaging of extrahepatic fatty masses of the abdomen and pelvis: techniques, diagnosis, differential diagnosis, and pitfalls

The differential diagnosis of extrahepatic abdominopelvic masses is wide. Demonstration of fat within a lesion at noninvasive imaging is an important clue for narrowing the differential diagnosis. Macroscopic fat is readily identified with both computed tomography (CT) and magnetic resonance (MR) imaging. Demonstration of microscopic fat is more difficult and may require special techniques. Identification of fat with CT is based on x-ray resorption and therefore on the attenuation (typically less than -20 HU). Several MR imaging techniques have been developed for fat suppression. Two of the most widely available are spectroscopic fat saturation and chemical shift (in-phase/opposed-phase) imaging. Entities with predominantly macroscopic fat include myelolipoma, angiomyolipoma, teratoma, liposarcoma, lipoma, epiploic appendagitis, omental infarction, and mesenteric panniculitis. Lesions with predominantly microscopic fat include adrenal adenoma and some teratomas. Other fat-containing entities involve the mesentery and bowel wall; these include fibrofatty mesenteric proliferation and submucosal fat deposition.

Coronal oblique turbo STIR imaging of the sacrum and sacroiliac joints at routine MR imaging of the lumbar spine

The objective of the study was to evaluate the clinical impact of coronal oblique imaging of the lumbrosacral junction and the sacrum at initial presentation for MR imaging of the lumbar spine in patients presenting with low back pain or sciatic pain. Two hundred and sixty consecutive patients attending for MRI of the lumbar spine underwent simultaneous coronal oblique turbo short tau inversion recovery (STIR; TR 2500, TE 40, TI 150, echo train length 7, number of scan acquisitions 2) imaging of the sacrum and the sacroiliac joints with a field of view of 30-cm and 3-mm slices (acquisition time 3 min and 20 s). Images were reviewed by two experienced radiologists to determine the cause of back pain, with and without images of the sacrum and sacroiliac joints. The added value of the additional sequence was assessed. Correlation was made with surgery, response to nerve root injection or clinical follow-up at 3 months. Subgroup analysis was performed to determine if patient stratification according to sex or symptoms would be useful. In total, in 19 of 260 patients (7.3%), abnormalities were identified at coronal STIR imaging. In 7 of 260 patients (2.7%), pathology was identified in the sacrum thought to account for back pain, altering the diagnosis made on the standard sequences. These diagnoses were sacroiliitis (n=2), sacral stress fracture (n=1), degenerative sacroiliac joints (n=1), degenerative accessory articulation between the lumbar spine and the sacrum (n=1), Tarlov cyst of nerve root (n=1) and retroverted uterus causing sciatic pain (n=1). Patient stratification according to sex or the presence or absence of sciatic symptoms was not useful in predicting the added benefit of the additional sequence. Routine coronal STIR imaging of the sacrum as part of lumbar spine MRI improves assessment of patients presenting with low back pain or sciatica in only a small number of patients.

[Out of phase magnetic resonance imaging and liver applications]

The increasing indications for MRI evaluation of diseases of the abdomen, especially liver tumors, has promoted the development of sequences allowing further histological characterization. Out of phase sequences provide suppression of lipids and water signal at the cellular level. Available on all MR imagers, it is the most sensitive sequence to depict small amounts of lipids in the liver. Best applications of this sequence include liver steatosis, tumoral characterization with regards to lipid content (adenoma, hepatocellular carcinoma...) and depiction of tumors in abnormal liver. Performed without contrast injection, and using fast imaging acquisition, we believe that out of phase imaging should be performed for magnetic resonance imaging of the liver.

Efficacy of spectral presaturation of inversion recovery in evaluating delayed myocardial enhancement

OBJECTIVE

Delayed myocardial enhancement is caused by a variety of cardiovascular diseases. The extent of the enhanced area has been examined by the inversion recovery (IR) method, whereby at the inversion time (TI), normal myocardium shows a low signal intensity. In this sequence, as pericardial fat shows a very high intensity, a delayed enhancement just below the pericardium may be indistinct. To improve the accuracy of delayed myocardial enhancement, we employed the spectral presaturation of inversion recovery (SPIR) method.

MATERIALS AND METHODS

Thirty-five patients with symptoms of cardiovascular disease aged between 36 and 80 years old (mean age, 62 years old) were investigated. Thirty were men and five were women. Inversion recovery and SPIR images were obtained 25 min after initial administration of a gadolinium-based contrast material. Each TI, when the signal intensity of the normal myocardium was null, was determined by images obtained at serial different TIs. A radiologist and a cardiologist examined each image by a consensus reading. The extent of myocardial enhancement was described as none, subendocardial, transmural and a random pattern in each case. Images were ranked over three levels and were based on whether myocardial enhancement could be easily detected or whether the contour of the myocardium was visualized precisely. Student's t-test was conducted to compare the quality of two sequences in all patients and in 22 patients who showed delayed myocardial enhancement.

RESULTS

The imaging quality in evaluating delayed myocardial enhancement in all patients was superior with IR compared with SPIR, although it was not statistically significant. The imaging quality in the patients with delayed myocardial enhancement was similar between SPIR and IR. SPIR was superior to the IR sequence in two of the four patients who exhibited transmural enhancement.

CONCLUSION

SPIR exhibited equivalent image quality to IR in evaluating delayed myocardial enhancement. As it has the potential advantage in patients with rich adipose tissue surrounding the myocardium, it can be an alternative sequence to evaluate myocardial viability.

Aspectos técnicos da ressonância magnética de mama com meio de contraste: revisão da literatura

Com a difusão do uso de meios de contraste, avanços na tecnologia das bobinas de superfície e desenvolvimento de protocolos rápidos de aquisição de imagens, a ressonância magnética (RM) de mama com meio de contraste tem-se mostrado importante modalidade na detecção, diagnóstico e estadiamento do câncer de mama. Apesar desses avanços, existem alguns pontos não consensuais no que diz respeito aos aspectos técnicos e critérios de interpretação de imagem da RM contrastada de mama. Neste artigo fazemos revisão bibliográfica dos parâmetros de interpretação de imagens e aspectos técnicos da RM de mama, incluindo considerações sobre a "performance" do equipamento, bobinas de radiofreqüência dedicadas, modo de utilização de contraste paramagnético, técnicas de supressão de gordura, planos de aquisição, seqüências de pulso e fontes de artefato.

Short tau inversion recovery and proton density-weighted fat suppressed sequences for the evaluation of osteoarthritis of the knee with a 1.0 T dedicated extremity MRI: development of a time-efficient sequence protocol

Aim of this study was to develop a time-efficient sequence protocol for a 1.0 T dedicated MR system to be used for whole-organ scoring of osteoarthritis (OA). Thirty-four knees were examined using a protocol that included fat suppressed fast spin echo proton density weighted sequences (PDFS) in three planes plus a coronal STIR sequence. Two radiologists scored each knee by consensus for five OA features. In separate sessions, all knees were scored using three different combinations of sequences: (1) all four sequences (reference protocol, 16 min 31 s scanning time), (2) three PDFS sequences without STIR ("No STIR", 12 min 25 s scanning time) and (3) sagittal and axial PDFS sequences plus a coronal STIR sequence ("No PDFS", 11 min 49 s scanning time). Agreement of the readings using both subsets of sequences compared to the reference protocol was evaluated using weighted kappa statistics. kappa-coefficients showed good or excellent agreement for both sequence subsets in comparison to the reference protocol for all assessed features. kappa-coefficients for No PDFS/No STIR: bone marrow abnormalities (0.74/0.67), subarticular cysts (0.84/0.63), marginal osteophytes (0.77/0.71), menisci (0.75/0.79), tibial cartilage (0.71/0.78). Optimization of sequence protocols consisting of three sequences results in time savings and cost efficiency in imaging of knee OA without loss of information over a more time consuming protocol.

Novel rapid fat suppression strategy with spectrally selective pulses

Short repetition time gradient echo sequences are gaining popularity in clinical applications such as dynamic contrast enhancement imaging, cardiac imaging, and MR angiography. Performing fat suppression in these sequences is usually time consuming and often somewhat ineffective, due to the relatively short T(1) and long T(2) of fat. A novel rapid fat suppression strategy using spectrally selective pulses is introduced and compared with clinically popular sequences such as fat presaturated fast field echo (FFE) and turbo field echo (TFE) and binomial water-selective spatial-spectral excitation (SSE, or SPSP excitation) FFE. The new strategy combines fat presaturation with low-order binomial water-selective SSE pulses in a TFE sequence. This enables the use of a long echo train length to decrease exam time, but without creation of excess fat signal contamination of the resultant images. The fat nullification is also more reliable as fat signals in central k-space data are suppressed twice. An implementation of this strategy is compared with traditional methods in both phantom and human studies, confirming that the new technique provides strong fat suppression with few artifacts despite the short scan duration.

Imaging for neuro-ophthalmic and orbital disease

PURPOSE

To provide an update on imaging of the brain and orbit for ophthalmologists.

DESIGN

Literature review.

METHODS

A systematic English-language medline search and summary of recent literature on imaging of brain and orbit was performed.

RESULTS

Computed tomography and magnetic resonance (MR) scanning are the mainstays for the evaluation of most disorders involving the brain and orbit. Computed tomography angiography and magnetic resonance angiography are relatively newer applications that are useful for the evaluation of arterial and venous disorders. Special sequences such as fat suppression and fluid attenuation inversion recovery are useful techniques for specific ophthalmic indications. Diffusion weighted imaging and perfusion-weighted imaging are improving the evaluation of acute stroke. Functional MRI, positron emission tomography scanning and single photon emission computed tomography may provide useful information regarding brain or tumor metabolism. Magnetic resonance spectroscopy has expanded our knowledge of brain function. Newer imaging studies have improved our diagnostic abilities on many fronts, including new sequences, new applications of imaging studies, and functional imaging of brain.

CONCLUSION

New imaging techniques for brain and orbit have an increased potential for improving diagnostic yield. Accurate and timely communication with the neuroradiologist can optimize the prescription and interpretation of imaging in ophthalmology.

MR evaluation of arrhythmogenic right ventricular cardiomyopathy in pediatric patients

OBJECTIVE

The aim of our study was to correlate the findings of three MR imaging sequences with the clinical findings of possible arrhythmogenic right ventricular cardiomyopathy in pediatric patients.

MATERIALS AND METHODS

Twenty-six consecutive pediatric patients underwent MR imaging with ECG-gated non-breath-hold spin-echo T1-weighted non-fat-suppressed and fat-suppressed sequences. The MR images were evaluated for thinning or fat signal in the right ventricular wall and for enlargement or increased trabeculation of the right ventricle or right ventricular outflow tract. Cine MR imaging was used to assess wall motion abnormalities. Cardiac biopsy was performed in 17 patients. Biopsy results and other clinical findings suggesting arrhythmogenic right ventricular cardiomyopathy were tabulated.

RESULTS

Two MR imaging studies were of poor quality as a result of arrhythmias, and one study was incomplete. In the 23 remaining patients, there were (mean +/- SD) 1.5 +/- 1.0 and 0.8 +/- 1.0 findings of possible arrhythmogenic right ventricular cardiomyopathy in the non-fat-suppressed and the fat-suppressed sequences, respectively. Fat-compatible signal in the myocardium was detected in 16 (70%) of 23 non-fat-suppressed studies and in five (22%) of 23 fat-suppressed studies (p = 0.003). The non-fat-suppressed sequence had a higher sensitivity (75% vs 43%) and a lower specificity (38% vs 75%) for fatty infiltration than did the fat-suppressed sequence when correlated with the biopsies. The linear correlation between all MR findings and all clinical diagnostic criteria, including biopsy, was better for the combination of cine and both T1 sequences (r = 0.58) than for the non-fat-suppressed (r = 0.53) or fat-suppressed (r = 0.46) T1 sequences alone.

CONCLUSION

MR imaging showed moderate correlation with the clinical criteria in the diagnosis of arrhythmogenic right ventricular cardiomyopathy.

O valor da ressonância magnética na detecção de nódulos hepáticos utilizando-se diversas técnicas ponderadas em T2: existe consenso?

Desde o início da década de 80 a ressonância magnética vem sendo utilizada para o estudo do abdome e principalmente na detecção de nódulos hepáticos. As imagens ponderadas em T2 são as que trouxeram maior benefício quando comparadas à tomografia computadorizada com contraste. Inúmeras técnicas e seqüências de ressonância magnética ponderadas em T2 surgiram desde então, na tentativa de aumentar a eficácia diagnóstica, com menores tempos de exame. Neste sentido, foram publicados inúmeros trabalhos demonstrando a utilidade de seqüências rápidas e ultra-rápidas, com e sem supressão de gordura, em apnéia, com sincronizador respiratório e com bobinas de sinergia, entre outros avanços tecnológicos. No entanto, não há um consenso sobre qual a técnica mais apropriada e sensível para a detecção de lesões hepáticas focais. Neste artigo fazemos uma revisão bibliográfica e análise crítica das diversas técnicas de imagens ponderadas em T2, no que diz respeito às suas sensibilidades na detecção de nódulos hepáticos.

Comparison of contrast-enhanced magnetization transfer imaging and contrast-enhanced fat saturation T1-weighted imaging in nasopharyngeal carcinoma

OBJECTIVE

The objective of this study was to evaluate the efficacy of contrast-enhanced magnetization transfer (CEMT) imaging in the study of nasopharyngeal carcinoma (NPC).

METHODS

The contrast-to-noise ratio (CNR) of CEMT images was compared with the CNR of contrast-enhanced fat-saturation (CEFS) T1-weighted images in locoregional tumors and adenopathies of 50 patients with pathologically proven NPC.

RESULTS

The CEMT images showed higher CNRs than CEFS images of local nasopharyngeal regions. The mean CNRs of the precontrast T1-weighted, CEFS, and CEMT images were 4.9, 15.4, and 21.2, respectively. There was a statistically significant difference (p < 0.01) in the CNRs of CEFS and CEMT images. In considering images of nodal metastasis, the mean values in these three groups were 0.7, 16.8, and 19.7, respectively, with the difference (p < 0.05) between CEFS and CEMT being statistically significant.

CONCLUSIONS

The CEMT image with a larger CNR is superior to the CEFS image in detecting locoregional NPC. CEMT can be useful in imaging patients with possible small tumors and local recurrences.

Water excitation as an alternative to fat saturation in MR imaging: preliminary results in musculoskeletal imaging

PURPOSE

To compare fat suppression methods by using spectrally selective fat saturation and section-selective water excitation in standard magnetic resonance (MR) imaging sequences used in day-to-day musculoskeletal practice.

MATERIALS AND METHODS

Eighty-three patients underwent MR examination with a 1.5-T system. The two methods were compared by using three common sequences: T1-weighted spin-echo (SE) imaging performed after contrast material injection (n = 24), intermediate-weighted fast SE (n = 36) imaging, and T2-weighted fast SE (n = 36) imaging. Acquisition times of the sequences and signal-to-noise and contrast-to-noise ratios of bone, muscle, fat, and water for the two methods were compared quantitatively. Images were then qualitatively reviewed by two radiologists who were blinded to the type of fat suppression used. Image quality was scored according to four criteria (homogeneity of fat suppression, susceptibility and foldover artifacts, conspicuousness of lesion, and overall image quality) by using a five-point scale (0, bad; 1, poor; 2, fair; 3, good; and 4, excellent). A paired Student t test was used to compare the quantitative data, and a nonparametric paired-data Wilcoxon signed rank test was used for qualitative analysis.

RESULTS

Water excitation allowed a substantial decrease in acquisition time (by up to 50%) for T1-weighted sequences. Quantitative measurements revealed a greater signal-to-noise ratio (P <.01) with water excitation for all three sequences, whereas the contrast-to-noise ratio was greater with water excitation only in intermediate-weighted sequences (P <.01). Qualitatively, water excitation proved statistically better than or equal to fat saturation for all criteria in all imaging sequences (P <.05). Mean scores of overall image quality ranged between 2.5 and 3.0 for fat saturation and 3.4 and 3.7 for water excitation, respectively (P <.05).

CONCLUSION

Section-selective water excitation is faster than conventional fat saturation and produces images of better quality.

Characterization of hematopoietic bone marrow in male professional cyclists by magnetic resonance imaging of the lumbar spine

PURPOSE

To prospectively evaluate hematopoietic bone marrow of male professional cyclists in relation to performance data and laboratory data, and in comparison to age-matched healthy volunteers.

MATERIALS AND METHODS

Twenty male cyclists and 44 volunteers (27 males and 17 females) were prospectively studied by magnetic resonance imaging (MRI) at high-field strength. A sagittal T1-weighted (T1-w) spin-echo (SE) sequence, a gradient-echo (GE) sequence with an echo time (TE) for out-of-phase (OOP) imaging, and a turbo inversion-recovery sequence with short inversion time (TIRM) for fat suppression was used. The averaged bone marrow signal intensity (SI) of three adjacent vertebrae was related to the signal of an adjacent nondegenerative disk.

RESULTS

The cyclists revealed a significantly different SI as compared to male volunteers in the OOP (0.34 +/- 0.14 vs. 0.28 +/- 0.09, P < 0.05) and T1-w sequences (1.62 +/- 0.19 vs. 1.77 +/- 0.30, P < 0.05). Only in TIRM was there a significant difference compared to female volunteers (0.36 +/- 0.08 vs. 0.44 +/- 0.04, P < 0.01). MRI data of cyclists did not correlate to hemoglobin, erythrocyte, or reticulocyte counts; ferritin, relative heart volume, relative maximal power (rPmax; W/kg bw), or relative maximal oxygen consumption (VO(2)max). A borderline linear correlation was found for hematocrit (OOP: r = 0.42, P = 0.06; TIRM: r = 0.44, P = 0.06).

CONCLUSION

Bone marrow hyperplasia is observed in male professional cyclists in the axial skeleton. The MR findings are probably independent of mechanically induced marrow edema. A multifactorial cause must be considered, as single laboratory and performance data did not appear to contribute significantly to these results.

Feasibility of MR imaging-guided breast lumpectomy for malignant tumors in a 0.5-T open-configuration MR imaging system

RATIONALE AND OBJECTIVES

The authors performed this study to develop the technology for and evaluate the utility of a 0.5-T vertical open-configuration magnetic resonance (MR) imaging system for imaging-guided breast lumpectomy of malignant tumors.

MATERIALS AND METHODS

Twenty women with breast cancer underwent MR imaging-guided lumpectomy in a 0.5-T vertical open-configuration MR system. During lumpectomy, pre- and postresection images were acquired with and without contrast material. Images were used both for tumor localization and to monitor resection. If residual enhancement was observed, additional resection was performed in an effort to secure negative pathologic margins.

RESULTS

The procedure evolved over time with technology innovations and improvements. Specifically, instruments were acquired that were compatible with MR imaging breast procedures, the echo time with the Dixon technique was modified to optimize image quality, contrast material injection was timed for maximum lesion enhancement, breath-hold image acquisition was instituted, and the biopsy cavity was filled with saline and the incision closed before image acquisition.

CONCLUSION

All breast lesions were identified despite limited spatial resolution and fat-suppression techniques. The evolved techniques facilitated intraoperative margin evaluation and prompted additional surgical margin resection in five patients, sparing four from an additional surgical procedure. Intraoperative MR imaging has the potential to improve the complete pathologic excision of invasive breast cancer.

Patterns of gadopentetate-enhanced MR imaging of radiocarpal joints of healthy subjects

OBJECTIVE

The aim of our study was to evaluate prospectively the grades and patterns of gadopentetate-enhanced MR imaging in the radiocarpal joints of healthy subjects after IV contrast administration.

SUBJECTS AND METHODS

The study included 18 healthy subjects (nine men, nine women; age range, 24-34 years; mean age, 30.8 years). We obtained coronal T1-weighted spin-echo images with fat suppression before and after IV administration of gadopentetate dimeglumine and additional axial T1-weighted spin-echo images after contrast administration. Patterns of signal-intensity enhancement in and around the radiocarpal joints were evaluated qualitatively and quantitatively.

RESULTS

In eight (44.4%) of 18 healthy subjects, enhancement of the radiocarpal joints was seen and exclusively located in the region of the prestyloid recess. Enhancement patterns were bandlike in three (16.7%) of 18 healthy subjects, homogeneous in another three (16.7%) of 18, and nodular in two (11.1%) of 18.

CONCLUSION

After IV administration of gadopentetate, signal-intensity enhancement in the radiocarpal joint is frequently seen in healthy subjects and is not predictive of inflammatory joint disease. If contrast enhancement is present, three distinct patterns are usually revealed, all invariably located in the region of the prestyloid recess.

Need for background suppression in contrast-enhanced peripheral magnetic resonance angiography

To determine if background suppression is beneficial for peripheral magnetic resonance angiography (pMRA), nonsubtracted, subtracted, and fat-saturated contrast-enhanced (CE) pMRA were compared in 10 patients with peripheral arterial disease. Signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs), as well as venous enhancement and subjective interpretability, were determined in a station-by-station fashion for each technique. In three patients X-ray angiography was available as a standard of reference. SNRs and CNRs were significantly higher for fat-saturated vs. the other two techniques (P = 0.005). Subjective interpretability was best for subtracted data sets in the lower-leg station. In the iliac station, fat-saturated data sets were considered to have significantly lower interpretability than subtracted data sets. Venous enhancement occurred significantly more often in the lower-leg station with the fat-saturated technique. The value of subtraction depends on the hardware one has available and is a useful tool if dedicated surface coils are used. Background suppression by means of magnitude subtraction leads to the best lower-leg image interpretability. Care must be taken to avoid venous enhancement in the lower-leg station when using fat saturation.

Imaging of osteomyelitis in children

Imaging approach to osteomyelitis in children should aim toward a timely and accurate diagnosis in view of the need for prompt therapy to prevent sequelae. One must take advantage of the specific value of each imaging modality and adopt a strategy that works best for a given child in a given institution.

An appraisal of magnetic resonance imaging of the wrist in rheumatoid arthritis

OBJECTIVES

To evaluate the role of magnetic resonance imaging (MRI) in the diagnosis, staging, and follow-up of the rheumatoid wrist.

METHODS

A Medline search was performed to identify all publications from the years 1985 to 1999 concerning MRI of the wrist in patients with rheumatoid arthritis (RA). Additional papers were retrieved by scanning the references to the Medline-listed articles. Details of the MRI technique, as well as clinical data, were analyzed and compared.

RESULTS

A total of 55 papers were identified. There were considerable variations in imaging sequence, section type, and slice thickness. Erosions and synovitis were the conditions that mostly profited from the adoption of MRI. Although the visualization of erosions was better detailed with MRI than with conventional radiography, erosions were only rarely related to clinical and laboratory parameters. Another advantage was that synovitis imaging, which can be enhanced by contrast agents, was amenable to quantitation. The extent of the synovial surface and the rate of contrast enhancement in a series of consecutive, rapidly acquired images were the most common measures.

CONCLUSIONS

MRI of the rheumatoid wrist is a useful technique to ascertain the criteria for diagnosis and progression of RA, and to monitor the effects of treatment. Implementation of a standardized protocol could further increase its value.