Diffusion-weighted imaging of the head and neck in healthy subjects: reproducibility of ADC values in different MRI systems and repeat sessions.

BACKGROUND AND PURPOSE: DWI is typically performed with EPI sequences in single-center studies. The purpose of this study was to determine the reproducibility of ADC values in the head and neck region in healthy subjects. In addition, the reproducibility of ADC values in different tissues was assessed to identify the most suitable reference tissue. MATERIALS AND METHODS: We prospectively studied 7 healthy subjects, with EPI and TSE sequences, on 5 MR imaging systems at 3 time points in 2 institutions. ADC maps of EPI (with 2 b-values and 6 b-values) and TSE sequences were compared. Mean ADC values for different tissues (submandibular gland, sternocleidomastoid muscle, spinal cord, subdigastric lymph node, and tonsil) were used to evaluate intra- and intersubject, intersystem, and intersequence variability by using a linear mixed model. RESULTS: On 97% of images, a region of interest could be placed on the spinal cord, compared with 87% in the tonsil. ADC values derived from EPI-DWI with 2 b-values and calculated EPI-DWI with 2 b-values extracted from EPI-DWI with 6 b-values did not differ significantly. The standard error of ADC measurement was the smallest for the tonsil and spinal cord (standard error of measurement = 151.2 × 10(-6) mm/s(2) and 190.1 × 10(-6) mm/s(2), respectively). The intersystem difference for mean ADC values and the influence of the MR imaging system on ADC values among the subjects were statistically significant (P < .001). The mean difference among examinations was negligible (ie, <10 × 10(-6) mm/s(2)). CONCLUSIONS: In this study, the spinal cord was the most appropriate reference tissue and EPI-DWI with 6 b-values was the most reproducible sequence. ADC values were more precise if subjects were measured on the same MR imaging system and with the same sequence. ADC values differed significantly between MR imaging systems and sequences.

Spinal imaging and intervention: 1998.

Imaging of the lumbar spine is the most common application of magnetic resonance (MR) imaging in many radiologic practices. MR imaging has replaced computed tomography (CT) and CT myelography as the primary mode of spinal imaging and has relegated myelography to a secondary role in the evaluation of lumbar spinal disorders. At the same time, however, it has become evident that the correlation between gross anatomic findings as depicted on MR images and the clinical signs and symptoms detected by the clinician may be lacking. Defining the precise anatomic source of patients' complaints on the basis of imaging studies must be approached judiciously because a significant proportion of the population has disc disease as depicted on imaging studies, yet many have no clinical findings.

Characters discriminating two seed husking mechanisms in finches (Fringillidae: Carduelinae) and estrildids (Passeridae: Estrildinae).

Finches have two major types of seed husking, each with two phases: crushing and seed husk disposal. Recent observations show that both Spice Finches and Greenfinches husk seeds by a crushing mechanism, but the Greenfinch, Carduelis chloris, applies mediolateral movements of the lower mandible, especially during seek husk disposal, while such movements are not-found in the Spice Finch, Lonchura punctulata. A detailed comparison of the anatomies of their jaw apparatuses elucidates that numerous discriminating characters form an integrated complex that parallels the difference in seed husking. These focus on 1) a more flattened shape of the articular facets in the quadratomandibular articulation and a lack of the postorbital ligament, resulting in decoupling of the quadratomandibular joint facets, and release of the pseudotemporal muscle from jaw elevation only and 2) adductor mandibulae and pterygoid muscles with an increased medial component in the Greenfinch. Muscles built heavier in the Greenfinch than the Spice Finch, especially mediolaterally oriented muscles, are in concurrence with muscle asymmetries found in crossbills (Loxia sp.), a finch-species employing unilateral mandibular rotation. These two groups of differences are conditions to transform a dorsoventrally oriented into an improved, mediolaterally oriented husking design. These features, though in concert with many others, are proposed as they key innovations that released the increase of crushing forces by extending forces from jaw muscles and improvement of the disposal of the crushed shell by left-right lower mandible manipulation. Such an improved husking capacity may have opened the vast food-array of hard-shelled, dicotyledon seeds, allowing extensive trophic radiation. J. Morphol 232:1-33, 1997. © 1997 Wiley-Liss, Inc.