Post-contrast T1-weighted Sequences Research Articles

Magnetic resonance imaging anatomy of the rabbit brain at 3T.

BackgroundRabbits are widely accepted as an animal model in neuroscience research. They also represent very popular pet animals, and, in selected clinical cases with neurological signs, magnetic resonance imaging (MRI) may be indicated for imaging the rabbit brain. Literature on the normal MRI anatomy of the rabbit brain and associated structures as well as related reference values is sparse. Therefore, it was the purpose of this study to generate an MRI atlas of the normal rabbit brain including the pituitary gland, the cranial nerves and major vessels by the use of a 3 T magnet.ResultsBased on transverse, dorsal and sagittal T2-weighted (T2w) and pre- and post-contrast 3D T1-weighted (T1w) sequences, 60 intracranial structures were identified and labeled. Typical features of a lissencephalic brain type were described. In the 5 investigated rabbits, on T1w images a crescent-shaped hyperintense area caudodorsally in the pituitary gland most likely corresponded to a part of the neurohypophysis. The optic, trigeminal, and in part, the facial, vestibulocochlear and trochlear nerves were identified. Mild contrast enhancement of the trigeminal nerve was present in all rabbits. Absolute and relative size of the pituitary gland, midline area of the cranial and caudal cranial fossa and height of the tel- and diencephalon, 3rd and 4th ventricles were also determined.ConclusionsThese data established normal MRI appearance and measurements of the rabbit brain. Results provide reference for research studies in rabbits and, in rare instances, clinical cases in veterinary medicine.Electronic supplementary materialThe online version of this article (doi:10.1186/s13028-015-0139-6) contains supplementary material, which is available to authorized users.

De Novo Assessment of Pediatric Musculoskeletal Soft Tissue Tumors: Beyond Anatomic Imaging.

MRI plays a central role in the assessment of pediatric musculoskeletal soft tissue tumors. Although these neoplasms may initially be evaluated on other modalities, such as sonography, MRI is essential for accurately determining the extent of disease. Traditionally, MRI has been performed with sequences that provide excellent anatomic detail, with T1-weighted, fluid-sensitive, and static postcontrast T1-weighted sequences. However, with the introduction of noncontrast sequences such as diffusion-weighted imaging and magnetic resonance spectroscopy to the arsenal of available MRI techniques, functional and metabolic features of a neoplasm can now be examined noninvasively. These more recent MRI methods offer information for lesion characterization, the assessment of treatment response, and the distinction of postoperative scar from recurrence. Dynamic contrast-enhanced perfusion imaging is another useful functional technique that can be acquired before conventional static postcontrast imaging, without requiring additional contrast material. This review presents recent advances in MRI methodology that enable a comprehensive clinical assessment of musculoskeletal tumors in the pediatric population. The roles and challenges of combining anatomic, functional, and metabolic MRI sequences will be discussed as they relate to newly discovered soft tissue tumors in children.

Nonenhancing Leptomeningeal Metastases: Imaging Characteristics and Potential Causative Factors.

The diagnosis of leptomeningeal metastasis (LM) has increased in frequency, as new therapies have lengthened the survival of patients with cancer. Early diagnosis and intervention help improve quality of life and prevent further neurological deterioration in LM. The detection of LM is often established by magnetic resonance imaging examinations, cerebrospinal fluid analysis, or both. We present a series of cases where LM was identified on fluid-attenuated inversion recovery or T2-weighted image but was nonenhancing on the traditionally more sensitive postcontrast T1-weighted sequences. Nonenhancing LM is unusual and not yet fully understood but should be considered in the appropriate clinical context and may become more common with increased utilization of antiangiogenic therapies.

MR appearance of parathyroid adenomas at 3 T in patients with primary hyperparathyroidism: what radiologists need to know for pre-operative localization.

To identify frequent MRI features of parathyroid adenomas (PTAs) in patients with primary hyperparathyroidism (PHPT) using a fast protocol with a 3 T magnet. Thirty-eight patients with PHPT underwent a 3 T-MR. All patients had positive US and Tc-99 sestamibi, for a total number of 46 PTAs. T2-weighted IDEAL-FSE and T1 IDEAL-sequences, before and after contrast, were performed. Five features of PTAs were recognised: hyperintensity, homogeneous or "marbled" appearance and elongated morphology on T2-sequences; cleavage plane from thyroid gland on T2-outphase; rapid enhancement in post-contrast T1. Image quality for T2-weighted IDEAL FSE and usefulness for IDEAL post-contrast T1-weighted and T2-outphase sequences were also graded. PTAs were hyperintense in T2-sequences in 44/46 (95.7%), "marbled" in 30/46 (65.2%) and elongated in 38/46 (82.6%) patients. Cleavage plane was observed in 36/46 (78.3%), and rapid enhancement in 20/46 (43.5%) patients. T2-sequences showed both excellent fat suppression and image quality (average scores of 3.2 and 3.1). T2-outphase images demonstrated to be quite useful (score 2.8), whereas, post-contrast T1 images showed a lower degree of utility (score 2.4). A fast protocol with 3.0-T MRI, recognising most common features of PTAs, may be used as a second-line method in the preoperative detection of PTAs. 3 T MRI protocol based on T2-weighted IDEAL FSE sequences was used. T2-hyperintensity and elongated morphology are common features of PTAs. 3 T MRI could be used in the preoperative detection of PTAs.

Diagnostic value of 3D fluid attenuated inversion recovery sequence in multiple sclerosis.

Magnetic resonance imaging (MRI) is an indispensable tool in the diagnostic work-up of multiple sclerosis (MS). To date, guidelines suggest MRI protocols containing axial dual-echo, unenhanced and post-contrast T1-weighted sequences. Especially the usage of dual-echo sequences has markedly improved the ability of MRI to detect cortical and infratentorial lesions. Newer 3D FLAIR sequences are supposed to provide even more positive imaging features such as improved detection of white matter lesions and a better resolution due to smaller slice thickness. To evaluate the diagnostic impact of 3D FLAIR sequences in comparison to conventional T2 and PD sequences. Examinations of 20 MS patients (10 women, 10 men) were reviewed retrospectively. All patients received MRI standard protocol containing PD and T2 sequences and a mid-sagittal T2 sequence. Additionally an isotropic 3D FLAIR sequence was performed. Whole-brain lesion load and number of lesions in juxtacortical, infratentorial, and midcallosal localizations were assessed by two observers independently and compared. Whole lesion load and the count of detectable lesions at the 3D FLAIR sequence were significantly higher in the juxtacortical and infratentorial regions compared to the PD/T2 sequence. Detection rate of midcallosal lesions did not differ significantly in sagittal T2 and 3D FLAIR sequence. 3D FLAIR sequences can improve the detection of brain lesions in patients with MS and are even more sensitive in depicting lesions in cortical and infratentorial locations than current dual-echo sequences. The sequence can replace both PD/T2 sequences and mid-sagittal T2 sequences of the corpus callosum.

Neurovascular study of the trigeminal nerve at 3 t MRI.

This study aimed to show a novel visualization method to investigate neurovascular compression of the trigeminal nerve (TN) using a volume-rendering fusion imaging technique of 3D fast imaging employing steady-state acquisition (3D FIESTA) and coregistered 3D time of flight MR angiography (3D TOF MRA) sequences, which we called "neurovascular study of the trigeminal nerve". We prospectively studied 30 patients with unilateral trigeminal neuralgia (TN) and 50 subjects without symptoms of TN (control group), on a 3 Tesla scanner. All patients were assessed using 3D FIESTA and 3D TOF MRA sequences centered on the pons, as well as a standard brain protocol including axial T1, T2, FLAIR and GRE sequences to exclude other pathologies that could cause TN. Post-contrast T1-weighted sequences were also performed. All cases showing arterial imprinting on the trigeminal nerve (n = 11) were identified on the ipsilateral side of the pain. No significant relationship was found between the presence of an artery in contact with the trigeminal nerve and TN. Eight cases were found showing arterial contact on the ipsilateral side of the pain and five cases of arterial contact on the contralateral side. The fusion imaging technique of 3D FIESTA and 3D TOF MRA sequences, combining the high anatomical detail provided by the 3D FIESTA sequence with the 3D TOF MRA sequence and its capacity to depict arterial structures, results in a tool that enables quick and efficient visualization and assessment of the relationship between the trigeminal nerve and the neighboring vascular structures.

Differentiation of Leptomeningeal and Vascular Enhancement on Post-contrast FLAIR MRI Sequence: Role in Early Detection of Infectious Meningitis.

To qualitatively and quantitatively differentiate leptomeningeal and vascular enhancement on Post-contrast Fluid Attenuated Inversion Recovery (PCFLAIR) sequence compared to post-contrast T1-weighted (PCT1W) sequence with fat suppression (FS) and evaluate its role in early detection of infectious meningitis. Thirty-one patients with diagnosis of meningitis were evaluated with pre and post-contrast FLAIR and T1-weighted sequences with fat suppression (FS). Qualitative assessment was done by two observers for presence, absence or equivocal status of leptomeningeal enhancement. Further, quantitative estimation of single pixel signal intensities (SPSI) for meningeal and vascular enhancement was undertaken. A statistical comparison was performed using Kappa coefficient and t-test. The overall qualitative accuracy was 90.3% for PCFLAIR compared to 54.8% for PCT1W with FS sequence. PCFLAIR was found to be 100% accurate in the detection of tubercular and pyogenic meningitis and 70% accurate in the detection of viral meningitis while PCT1W with FS sequence showed the corresponding accuracy to be 76.2% and 0% respectively. Both observers rated PCFLAIR images better than PCT1W with FS at detecting meningitis (p<0.05). The quantitative assessment revealed that the SPSI difference between the average meningeal and vascular enhancement on PCFLAIR was significantly greater than that on PCT1W with FS sequence (t= 6.31, p<0.01). PCFLAIR sequence has insignificant component of vascular enhancement compared to meningeal enhancement. This makes meningeal inflammation easily discernable and aids in early detection of infectious meningitis.

Influence of field strength, coil type and image resolution on assessment of synovitis by unenhanced MRI – a comparison with contrast-enhanced MRI

To explore if the reliability of synovitis assessment by unenhanced MRI is influenced by different MRI field-strengths, coil types and image resolutions in RA patients. Forty-one RA patients and 12 healthy controls underwent hand MRI (wrist and 2(nd)--5(th) metacarpophalangeal joints) at 4 different field-strengths (0.23 T/0.6 T/1.5 T/3.0 T) on the same day. Seven protocols using a STIR sequence with different field-strengths, coils (flex coils/dedicated phased-array extremity coils) and resolution were applied and scored blindly for synovitis (OMERACT-RAMRIS method). A 1.5 T post-contrast T1-weighted sequence was used as gold standard reference. Fair-good agreement (ICC=0.38--0.72) between the standard reference and the different STIR protocols (best agreement with extremity coil and small voxel size at 1.5 T). The accuracy for presence/absence of synovitis was very high per person (0.80--1.0), and moderate-high per joint (0.63--0.85), whereas exact agreements on scores were moderate (0.50--0.66). The intrareader agreement (15 patients and 3 controls) on presence/absence of synovitis was very high (0.87--1.0). Unenhanced MRI using STIR sequence is only moderately reliable for assessing hand synovitis in RA, when contrast-enhanced MRI is considered the gold standard reference. Contrast injection, field strength and coil type influence synovitis assessment, and should be considered before performing MRI in clinical trials and practice. • STIR is only moderately reliable for synovitis assessment, compared with post-contrast-T1-w. • Contrast injection, field strength, and coil type influence synovitis assessment. • Contrast injection is recommended for reliable and reproducible hand synovitis assessment.

Abbreviated protocol for breast MRI: Are multiple sequences needed for cancer detection?

ObjectiveTo evaluate the ability of an abbreviated breast magnetic resonance imaging (MRI) protocol, consisting of a precontrast T1 weighted (T1W) image and single early post-contrast T1W image, to detect breast carcinoma. Materials and methodsA HIPAA compliant Institutional Review Board approved review of 100 consecutive breast MRI examinations in patients with biopsy proven unicentric breast carcinoma. 79% were invasive carcinomas and 21% were ductal carcinoma in situ. Four experienced breast radiologists, blinded to carcinoma location, history and prior examinations, assessed the abbreviated protocol evaluating only the first post-contrast T1W image, post-processed subtracted first post-contrast and subtraction maximum intensity projection images. Detection and localization of tumor were compared to the standard full diagnostic examination consisting of 13 pre-contrast, post-contrast and post-processed sequences. ResultsAll 100 cancers were visualized on initial reading of the abbreviated protocol by at least one reader. The mean sensitivity for each sequence was 96% for the first post-contrast sequence, 96% for the first post-contrast subtraction sequence and 93% for the subtraction MIP sequence. Within each sequence, there was no significant difference between the sensitivities among the 4 readers (p=0.471, p=0.656, p=0.139). Mean interpretation time was 44s (range 11–167s). The abbreviated imaging protocol could be performed in approximately 10–15min, compared to 30–40min for the standard protocol. ConclusionAn abbreviated breast MRI protocol allows detection of breast carcinoma. One pre and post-contrast T1W sequence may be adequate for detecting breast carcinoma. These results support the possibility of refining breast MRI screening protocols.

Hyperperfusion of multiple sclerosis plaques characterized by 3D FSE arterial spin labelling.

Multiple sclerosis (MS) is a common inflammatory demyelinating disorder of central nervous system, and the disease burder could be well evaluated by conventional magnetic resonance imaging (MRI), including T2-weighted, fluid-attenuatd inversion recovery, and postcontrast T1-weighted sequences. We investigated the perfusion state of MS plaques using brain perfusion imaging in a 12-year-old boy with MS.

Non-invasive imaging of vascular inflammation.

In large-vessel vasculitides, inflammatory infiltrates may cause thickening of the involved arterial vessel wall leading to progressive stenosis and occlusion. Dilatation, aneurysm formation, and thrombosis may also ensue. Activated macrophages and T lymphocytes are fundamental elements in vascular inflammation. The amount and density of the inflammatory infiltrate is directly linked to local disease activity. Additionally, patients with autoimmune disorders have an increased cardiovascular (CV) risk compared with age-matched healthy individuals as a consequence of accelerated atherosclerosis. Molecular imaging techniques targeting activated macrophages, neovascularization, or increased cellular metabolic activity can represent effective means of non-invasive detection of vascular inflammation. In the present review, novel non-invasive imaging tools that have been successfully tested in humans will be presented. These include contrast-enhanced ultrasonography, which allows detection of neovessels within the wall of inflamed arteries; contrast-enhanced CV magnetic resonance that can detect increased thickness of the arterial wall, usually associated with edema, or mural enhancement using T2 and post-contrast T1-weighted sequences, respectively; and positron emission tomography associated with radio-tracers such as [18F]-fluorodeoxyglucose and the new [11C]-PK11195 in combination with computed tomography angiography to detect activated macrophages within the vessel wall. Imaging techniques are useful in the diagnostic work-up of large- and medium-vessel vasculitides, to monitor disease activity and the response to treatments. Finally, molecular imaging targets can provide new clues about the pathogenesis and evolution of immune-mediated disorders involving arterial vessels.

Imaging intracranial vessel wall pathology with magnetic resonance imaging: current prospects and future directions.

To date, the probable cause of ischemic stroke is often inferred from the size and location of the infarct, in combination with an evaluation of the heart and the presence of extracranial arterial occlusion or high-grade stenosis.1 Currently used conventional lumenography-based methods such as digital subtraction angiography, computed tomography angiography, and magnetic resonance (MR) angiography are used to determine the presence of such an acute occlusion or high-grade arterial stenosis. From extracranial studies, it is known that luminal narrowing may be absent in patients with severe atherosclerosis owing to arterial remodeling.2–4 Therefore, these methods do not provide information about the underlying pathological processes, which most often involve the vessel wall.5 Vessel wall changes such as vessel wall thickening, enhancement, or the presence of vulnerable atherosclerotic plaques without luminal stenosis are therefore often missed but might be of importance for a better understanding of ischemic stroke.6 Furthermore, intracranial atherosclerosis is an important cause of ischemic stroke7 and often involves the vessel wall. Patients with intracranial atherosclerosis have high recurrent stroke rates,8 and increasingly more attention is being directed to the assessment of the intracranial vessel wall, necessitating an imaging technique directly assessing the intracranial vessel wall. MR imaging (MRI) seems the most promising technique to reliably image intracranial vessel wall pathologies because of its superior soft tissue contrast. Recent advances in MRI9 have made it possible to obtain information about these abnormalities within the intracranial vessel wall, which provides an imaging tool to investigate the role of intracranial vessel wall abnormalities in the diagnosis of stroke. In this review, we discuss the current status of intracranial vessel wall MRI and its potential to identify different intracranial vessel wall pathologies. First, we present the state-of-the-art MRI methods to visualize the intracranial vessel wall …

Radiographic Patterns of Orbital Involvement in IgG4-Related Disease

Immunoglobin G4 (IgG4)-related disease is a systemic condition characterized by lymphoplasmacytic infiltrates that can involve the orbit. The purpose of this study was to identify the various patterns of orbital IgG4-related disease on imaging. Retrospective review of radiologic examinations including CT, MRI, and positron emission tomography was performed in patients with proven cases of IgG4-related disease. A total of 9 patients with orbital IgG4-related disease were identified, including 9 with CT, 4 with MRI, and 4 with 18-fluorodeoxyglucose positron emission tomography. Patterns of involvement included lacrimal gland enlargement, lacrimal sac involvement, extraocular muscle thickening, preseptal involvement, orbital fat involvement, and cranial nerve involvement, many of which occurred simultaneously. Associated demineralization of the orbital wall was evident on CT in 2 cases. On T2-weighted MRI, the lesions appeared as hypointense in 2 cases, heterogeneously hypointense to isointense in 1 case, and hyperintense in 1 case. Diffuse enhancement was present in all 3 cases in which postcontrast T1-weighted sequences were available. The lesions were hypermetabolic on positron emission tomography in 3 of 4 cases. There was definite extraorbital involvement by IgG4-related disease in 3 of the 9 patients and suspected involvement in another 3 of the 9 patients. IgG4-related disease displays a wide variety of imaging manifestations in the orbit. Extraorbital disease is often present and can help suggest the diagnosis.

Technical innovation in dynamic contrast-enhanced magnetic resonance imaging of musculoskeletal tumors: an MR angiographic sequence using a sparse k-space sampling strategy

We demonstrate the clinical use of an MR angiography sequence performed with sparse k-space sampling (MRA), as a method for dynamic contrast-enhanced (DCE)-MRI, and apply it to the assessment of sarcomas for treatment response. Three subjects with sarcomas (2 with osteosarcoma, 1 with high-grade soft tissue sarcomas) underwent MRI after neoadjuvant therapy/prior to surgery, with conventional MRI (T1-weighted, fluid-sensitive, static post-contrast T1-weighted sequences) and DCE-MRI (MRA, time resolution = 7-10 s, TR/TE 2.4/0.9 ms, FOV 40 cm(2)). Images were reviewed by two observers in consensus who recorded image quality (1 = diagnostic, no significant artifacts, 2 = diagnostic, <25 % artifacts, 3 = nondiagnostic) and contrast enhancement characteristics by static MRI (presence/absence of contrast enhancement, percentage of enhancement) and DCE-MRI (presence/absence of arterial enhancement with time-intensity curves). Results were compared with histological response (defined as <5 % viable tumor [soft tissue sarcoma] or <10 % [bone sarcoma] following resection). Diagnostic quality for all conventional and DCE-MRI sequences was rated as 1. In 2 of the 3 sarcomas, there was good histological response (≤5 % viable tumor); in 1 there was poor response (50 % viable tumor). By static post-contrast T1-weighted sequences, there was enhancement in all sarcomas, regardless of response (up to >75 % with good response, >75 % with poor response). DCE-MRI findings were concordant with histological response (arterial enhancement with poor response, no arterial enhancement with good response). Unlike conventional DCE-MRI sequences, an MRA sequence with sparse k-space sampling is easily integrated into a routine musculoskeletal tumor MRI protocol, with high diagnostic quality. In this preliminary work, tumor enhancement characteristics by DCE-MRI were used to assess treatment response.

Magnetic Resonance Techniques in Multiple Sclerosis

Magnetic resonance imaging (MRI) is sensitive to focal multiple sclerosis (MS) lesions. For this reason, conventional MRI measures of the burden of disease derived from dual-echo, fluid-attenuated inversion recovery and postcontrast T1-weighted sequences are regularly used to monitor disease course in patients with confirmed MS and have been included in the diagnostic workup of patients in whom MS is suspected. Other quantitative magnetic resonance (MR)-based techniques with a higher pathological specificity (including magnetization transfer-MRI, diffusion tensor-MRI, and proton MR spectroscopy) have been extensively applied to measure disease burden within focal visible lesions and in the normal-appearing white matter and gray matter of MS patients at different stages of the disease. These methods, combined with functional imaging techniques, are progressively improving our understanding of the factors associated with MS evolution. More recently, the application of new imaging modalities capable of measuring pathological processes related to the disease that have been neglected in the past (eg, iron deposition and perfusion abnormalities) and the advent of high- and ultrahigh-field magnets have provided further insight into the pathobiological features of MS. After a brief summary of the main results obtained from the established and emerging MR methods, this review discusses the steps needed before the latter become suitable for widespread use in the MS research community.

EFFECT OF DELAYED ACQUISITION TIMES ON GADOLINIUM‐ENHANCED MAGNETIC RESONANCE IMAGING OF THE PRESUMABLY NORMAL CANINE BRAIN

A delay in imaging following intravenous contrast medium administration has been recommended to reduce misdiagnoses. However, the normal variation of contrast enhancement in dogs following a delay has not been characterized. Contrast-enhanced MR imaging of 22 dogs was assessed, in terms of identification of normal anatomic structures, to investigate the variation associated with 10-min delay between contrast medium administration and imaging. All dogs had a normal brain MR imaging study and unremarkable cerebrospinal fluid. Specific regions of interest were assessed both objectively, using computer software, and subjectively using three observers. Mean contrast enhancement > 10% was seen in the pituitary gland, choroid plexus, meninges, temporal muscle, trigeminal nerve, and the trigeminal nerve root. Structures with an active blood-brain barrier had minimal contrast enhancement (< 6%). Enhancing structures had significantly more contrast enhancement at t = 1 min vs. t = 10 min, except in temporal muscle, the trigeminal nerve and the trigeminal nerve root. Interobserver agreement was moderate to good in favor of the initial postcontrast T1-weighted (T1w) sequence. The observers found either no difference or poor agreement in identification of the nonvascular structures. Intraobserver agreement was very good with all vascular structures and most nonvascular structures. A degree of meningeal enhancement was a consistent finding. The initial acquisition had higher enhancement characteristics and observer agreement for some structures; however, contrast-to-noise was comparable in the delayed phase or not significantly different. We provide baseline references and suggest that the initial T1w postcontrast sequence is preferable but not essential should a delayed postcontrast T1w sequence be performed.

Computed Tomography and Magnetic Resonance Appearance of Sporadic Meningioangiomatosis Correlated With Pathological Findings

Meningioangiomatosis (MA) is a rare benign localized lesion of leptomeninges and underlying cerebral cortex. Preoperative diagnosis is difficult and challenging because of its diverse clinical, pathological, and imaging features. We retrospectively analyzed 7 cases of MA to explore their imaging features and correlate with pathological findings. Imaging studies including computed tomography (CT) and magnetic resonance imaging (MRI) were retrospectively reviewed in 7 patients with surgically and pathologically verified intracranial MA (not associated with neurofibromatosis). Computed tomography studies were performed in axial plane without iodinated contrast-material administration; magnetic resonance studies consisted of axial T1-weighted, T2-weighted, Fluid attenuated Inversion Recovery (FLAIR), and postcontrast T1-weighted sequences and coronal or sagittal precontrast and postcontrast T1-weighted sequences. Computed tomography showed focal extensively calcified lesions in 3 cases, lesions with patchy calcification in 2 cases, and no apparent calcification in 2 cases. Magnetic resonance imaging demonstrated predominantly hypointensity on T1-weighted images and hyperintensity on T2-weighted images. Six of 7 cases exhibited gyriform hyperintensity on FLAIR sequences, which correlated with proliferating microvessels with perivascular cuffs of spindle-cell proliferation within the cortex on histopathological analysis. After contrast-material administration, all but 1 showed heterogeneous enhancement. The nonenhancing lesion on MRI was completely calcified on CT. Gyriform hyperintensity on FLAIR sequence is the main MRI feature of MA, which correlates with proliferating microvessels with perivascular cuffs of spindle-cell proliferation within the cortex on pathological analysis. Plain CT scan is essential to demonstrate the extent of calcification of these lesions.

MR Imaging of the Midfoot and Forefoot

AbstractMR imaging is the diagnostic modality of choice for the evaluation of traumatic, inflammatory and neoplastic processes affecting the midfoot and forefoot soft tissue structures including muscles, ligaments, and tendons. MR imaging is also valuable in the diagnosis of occult bony trauma, stress reaction or fractures, and osteomyelitis. Exquisite contrast resolution, noninvasiveness, and multiplanar capabilities are unique features that make MR imaging a powerful diagnostic technique. The authors employ a basic protocol using T1‐weighted, fast spin echo proton density with and without frequency‐selective fat saturation, and fast spin echo T2‐weighted sequences as well as short‐tau inversion recovery (STIR) imaging. Additional imaging following intravenous gadolinium administration is indicated when osteomyelitis and neoplastic processes are suspected. Post‐contrast fat‐suppressed T1‐weighted sequences are necessary if intravenous or intra‐articular gadolinium is utilized.

MRI appearance of perianal carcinoma in Crohn's disease

Detection of carcinoma in perianal Crohn's disease can be difficult. The purpose of this study was to describe the MRI appearance of anorectal cancer in patients with perianal Crohn's disease. A total of six patients with anorectal carcinoma (four mucinous adenocarcinoma, two squamous) in Crohn's disease were retrospectively reviewed. Axial T2 and dynamic postcontrast fat-suppressed T1-weighted gradient echo sequences were performed, and findings were compared with 18 noncancer patients with perianal fistulae in Crohn's disease. MRI characteristics of carcinoma were irregular inner wall contours and delayed mild enhancement of internal tissue. The combined features of an irregular internal wall and delayed enhancing tissue were seen exclusively in cancer patients. The four cases of mucinous adenocarcinoma all displayed a pattern of lobulated fluid-filled cavities with delayed internal tissue enhancement. This pattern was not seen in any of the control cases. The presence of a double-layered enhancement pattern was seen in both cases of squamous carcinoma and in only one of four cases of mucinous adenocarcinoma and one of 18 noncancer cases. The pattern of contrast enhancement is valuable in the MRI diagnosis of carcinoma in perianal Crohn's disease.

MAGNETIC RESONANCE IMAGING CHARACTERISTICS OF PERIPHERAL NERVE SHEATH TUMORS OF THE CANINE BRACHIAL PLEXUS IN 18 DOGS

Magnetic resonance imaging (MRI) examinations from 18 dogs with a histologically confirmed peripheral nerve sheath tumor (PNST) of the brachial plexus were assessed retrospectively. Almost half (8/18) had a diffuse thickening of the brachial plexus nerve(s), six of which extended into the vertebral canal. The other 10/18 dogs had a nodule or mass in the axilla (1.2-338 cm3). Seven of those 10 masses also had diffuse nerve sheath thickening, three of which extended into the vertebral canal. The majority of tumors were hyperintense to muscle on T2-weighted images and isointense on T1-weighted images. Eight of 18 PNSTs had only minimal to mild contrast enhancement and many (13/18) enhanced heterogeneously following gadolinium DTPA administration. Transverse plane images with a large enough field of view (FOV) to include both axillae and the vertebral canal were essential, allowing in-slice comparison to detect lesions by asymmetry of structures. Higher resolution, smaller FOV, multiplanar examination of the cervicothoracic spine was important for appreciating nerve root and foraminal involvement. Short tau inversion recovery, T2-weighted, pre and postcontrast T1-weighted pulse sequences were all useful. Contrast enhancement was critical to detecting subtle diffuse nerve sheath involvement or small isointense nodules, and for accurately identifying the full extent of disease. Some canine brachial plexus tumors can be challenging to detect, requiring a rigorous multiplanar multi-pulse sequence MRI examination.