Head and neck: initial clinical experience with fast spin-echo MR imaging.

Fast spin-echo (FSE) is a new magnetic resonance (MR) imaging pulse sequence that employs echo trains of 180 degrees radio-frequency pulses to generate multiple refocused echoes during a single repetition-time interval. Phase encoding is reordered with the lowest spatial frequency views obtained in the echoes nearest the desired effective echo time. These techniques were used to examine 30 patients with pathologic conditions of the head and neck. The images were compared with closely matched conventional T2-weighted spin-echo (SE) images obtained during the same examination. Three unblinded readers evaluated 15 sets of both images for lesion conspicuity, motion artifact, diagnostic information, number of lesions seen, image quality, and sharpness of lesion borders. In all categories, FSE images were judged better than or equal to SE images, and in most cases FSE images were obtained in one-fourth to one-half the imaging time. In no case were lesions depicted on conventional T2-weighted SE images missed on FSE images; in fact, more lesions were seen on FSE images than on conventional T2-weighted SE images.

Extracranial head and neck: PET imaging with 2-[F-18]fluoro-2-deoxy-D-glucose and MR imaging correlation.

The aim of this study was to define and quantitate the normal anatomy of the extracranial head and neck with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET). This information was used to study 12 patients with primary squamous cell carcinomas. In all cases, the lymphoid tissue of the Waldeyer ring and the palatine and lingual tonsils could be differentiated from the airway, striated muscle, osseous structures, and salivary glands. Striated muscle had markedly less activity than lymphoid or salivary gland tissue. In the 12 patients with primary tumors, FDG PET depicted the tumor as an area of increased activity significantly higher than that of normal tissue. In one instance, FDG PET allowed detection of a tumor not seen at magnetic resonance (MR) imaging or computed tomography. Of the 34 lymph nodes positive for carcinoma, 24 were positive according to MR size criteria and 25 were detected with FDG PET. FDG PET allowed detection of three nonenlarged metastatic nodes that were negative at MR imaging.

Computed tomography versus standard radiography in the assessment of fractures of the mandible.

Twenty-nine fractures of the mandible were studied by standard radiographs and axial computed tomographic scans (hard copy). Independent reviewers analyzed each study in a blinded, non-paired fashion. When radiographic diagnostic sensitivities were compared on the basis of known surgical findings, the plain films were found to have a higher diagnostic sensitivity (89%) than the hard copy computed tomograms (64%). This difference occurred primarily with images of nondisplaced fractures in posterior portions of the mandible, and is likely the result of tomographic orientation and volume averaging. Though computed tomography has emerged as the standard diagnostic test in evaluating intracranial and maxillofacial trauma, this study demonstrates that computed tomographic scanning alone is inadequate in excluding nondisplaced fractures of the posterior mandible.

Fat-suppression failure artifacts simulating pathology on frequency-selective fat-suppression MR images of the head and neck.

PURPOSE: To describe fat-suppression failure artifacts and to caution against their misinterpretation. METHOD: Magnetic-susceptibility artifacts were studied in a phantom model and the results were compared to MR images obtained in clinical cases. FINDINGS: Artifacts manifested themselves as regions of focal fat-suppression failure and appeared as bright signals without geometric distortions at magnetic-susceptibility interfaces along the static field (z) direction. The location and extent of these artifacts were independent of either frequency or phase-encoding direction and are different from those observed in gradient-echo images. CONCLUSIONS: In representative clinical MR exams, these artifacts were identified in the high nasopharynx and low orbit and should not be misinterpreted as pathology.

MR imaging-guided interstitial Nd:YAG laser phototherapy: dosimetry study of acute tissue damage in an in vivo model.

A dosimetry study of acute tissue damage induced by interstitial application of the neodymium-yttrium-aluminum-garnet (Nd:YAG) laser was performed with magnetic resonance (MR) imaging. The MR appearance of the lesion was correlated with gross and histopathologic findings. Seventy-six lesions were induced in rabbit muscle with laser power outputs of 5-20 W and exposure times of 20-600 seconds. MR imaging was performed immediately after laser exposure. T2-weighted spin-echo images clearly showed the acute thermal injuries caused by laser energy deposition and correlated best with histopathologic findings. These images showed three distinct layers, corresponding to central ablation, coagulative necrosis, and interstitial edema, respectively, in the pathologic findings. Lesion diameters measured on MR images showed a linear correlation with those in gross sections. Lesion volume increased not only with increasing total energy delivered but with increasing power output for a fixed total energy delivered. MR imaging is an accurate modality for dosimetry studies of laser-induced acute lesions.

Nonneoplastic enhancing lesions mimicking intracanalicular acoustic neuroma on gadolinium-enhanced MR images.

The authors describe five patients with nonneoplastic lesions of the facial and/or vestibulocochlear nerves that demonstrated focal enhancement within the internal auditory canal on magnetic resonance (MR) images. MR and surgical findings for four patients with unilateral sensorineural hearing loss and one with Ramsay Hunt syndrome were reviewed. Three patients with hearing loss underwent surgical exploration and decompression of the internal auditory canal. The MR findings in all four patients with hearing loss were similar: Focal enhancement of the internal auditory canal was depicted on postcontrast T1-weighted images. Nonneoplastic lesions of the seventh and eighth cranial nerves may show focal enhancement on MR images, which mimics the appearance of a small intracanalicular neuroma. This potential for misdiagnosis may have important therapeutic implications.

Meckel cave lesions: percutaneous fine-needle-aspiration biopsy cytology.

The authors describe the novel combination of two traditional methods to facilitate diagnosis of Meckel cave lesions, which may otherwise require craniotomy to obtain adequate tissue samples. Fine-needle-aspiration biopsy cytology was performed on tissue obtained with a percutaneous approach via the foramen ovale with use of fluoroscopic guidance and intravenous analgesia during an outpatient procedure. This new application of fine-needle-aspiration biopsy cytology results in decreased patient morbidity and significant cost reduction.

Magnetic resonance imaging of the tongue and oropharynx.

In general, MRI produces superior soft tissue detail in evaluating the tongue and oropharynx than does CT. MRI is therefore considered the study of choice in this area. Lack of artifact from dental amalgam and beam hardening artifact from the mandible on MRI also eliminates two major shortcomings of CT in the examination of this area. Finally, the ability of MRI to obtain direct coronal and sagittal scan planes is a distinct advantage in recognizing intrinsic tongue musculature and assessing tumor volume and spread for treatment planning.