Retrospectively gated cardiac cine imaging with temporal and spatial acceleration.

Parallel imaging methods are routinely used to accelerate the image acquisition process in cardiac cine imaging. The addition of a temporal acceleration method, whereby k-space is sampled differently for different time frames, has been shown in prior work to improve image quality as compared to parallel imaging by itself. However, such temporal acceleration strategies prove difficult to combine with retrospectively gated cine imaging. The only currently published method to feature such combination, by Hansen et al. [Magn Reson Med 55 (2006) 85-91] tends to be associated with prohibitively long reconstruction times. The goal of the present work was to develop a retrospectively gated cardiac cine method that features both parallel imaging and temporal acceleration, capable of achieving significant acceleration factors on commonly available hardware and associated with reconstruction times short enough for practical use in a clinical context. Seven cardiac patients and a healthy volunteer were recruited and imaged, with acceleration factors of 3.5 or 4.5, using an eight-channel product cardiac array on a 1.5-T system. The prescribed FOV value proved slightly too small in three patients, and one of the patients had a bigemini condition. Despite these additional challenges, good-quality results were obtained for all slices and all patients, with a reconstruction time of 0.98±0.07 s per frame, or about 20 s for a 20-frame slice, using a single processor on a single PC. As compared to using parallel imaging by itself, the addition of a temporal acceleration strategy provided much resistance to artifacts.

The role of various immersion liquids at digital dermoscopy in structural analysis.

BACKGROUND: Dermoscopy is a useful method that allows dermal and epidermal structures to be easily analysed non-invasively. AIM: In this study, immersion oil, which is widely used in dermoscopy, and ultrasound gel, which is less preferred, are evaluated comparatively in terms of displaying structural parameters and number of air bubbles in the image. METHODS: A total of 71 nevomelanocytic or non-melanocytic pigmented lesions were taken up for this study. Structural characteristics of the obtained images were assessed by an experienced observer who scored the images in terms of color, pigment network, globule, vascular structure, number of air bubbles and other pigmentation parameters. RESULTS: In the images obtained through immersion oil or ultrasound gel from all of the lesions, no statistical difference was found between the average values of air bubbles and in the evaluation of structural components (t=1.09, P=0.2). In the identification of pigment network in melanocytic lesions, immersion oil was observed to be more appropriate than ultrasound gel (t=0.01, P=0.02). CONCLUSIONS: Ultrasound gel may be preferred in the assessment of mucosa and nail bed lesions. Ultrasound gel is a good alternative compared to immersion oil in pigmented skin lesions as it is cheap and easily removable.

A method for quantifying artefacts in mapping methods illustrated by application to headbanging.

Maps of disease rates (and other quantities) often must contend with variance associated with variable population sizes and low incidence within spatial units. These characteristics can lead to substantial statistical noise that can mask underlying spatial variation. As Gelman and Price illustrated, most conventional mapping methods fail to address this problem, and in fact can introduce statistical artefacts; mapped quantities can show spatial patterns even when there are no spatial patterns in the underlying parameter of interest. Kafadar evaluated the performance of the headbanging algorithm for spatial smoothing (Tukey and Tukey, Hansen) for eliminating small scale variation and preserving edge structure. Here we perform a simulation study to investigate the artefacts of maps smoothed by unweighted and weighted headbanging. We find substantial artefacts that depend on the spatial structure of the statistical variation (for example, the spatial pattern of sample sizes) and on the details of the spatial distribution of geographic units. The methods used here could readily be adapted to study other spatial smoothers; we choose headbanging because (i) it is an important method used in practice, and (ii) its heavily computational nature is naturally studied using simulation (in contrast to the analytical methods used by Gelman and Price).

It takes a confounded face to pop out of a crowd.

It is widely reported that a picture of an angry face seems to figuratively pop out of an array of happy faces, although all of these reports are based on a single experiment by Hansen and Hansen. Pop out, when it occurs, indicates that an observer has located the target by means of a preattentive, parallel search. Hansen and Hansen concluded that it was the affect displayed by the face which caused it to pop out from its surrounding distracters. However, Hansen and Hansen's angry faces contained extraneous dark areas which were introduced when they transformed Ekman and Friesen's photographs of angry and happy faces into black-on-white sketches. When the original artifact-free gray-scaled versions of angry and happy faces were used no evidence for pop out was found. All target faces were found during a serial, self-terminating search regardless of their expression. The angry face in Hansen and Hansen's experiments may have popped out from a crowd of happy faces because of a contrast artifact inadvertently introduced when they created their stimuli.

Molecules internalized by clathrin-independent endocytosis are delivered to endosomes containing transferrin receptors.

We have previously demonstrated that the preendosomal compartment in addition to clathrin-coated vesicles, comprises distinct nonclathrin coated endocytic vesicles mediating clathrin-independent endocytosis (Hansen, S. H., K. Sandvig, and B. van Deurs. 1991. J. Cell Biol. 113:731-741). Using K+ depletion in HEp-2 cells to block clathrin-dependent but not clathrin-independent endocytosis, we have now traced the intracellular routing of these nonclathrin coated vesicles to see whether molecules internalized by clathrin-independent endocytosis are delivered to a unique compartment or whether they reach the same early and late endosomes as encountered by molecules internalized with high efficiency through clathrin-coated pits and vesicles. We find that Con A-gold internalized by clathrin-independent endocytosis is delivered to endosomes containing transferrin receptors. After incubation of K(+)-depleted cells with Con A-gold for 15 min, approximately 75% of Con A-gold in endosomes is colocalized with transferrin receptors. Endosomes containing only Con A-gold may be accounted for either by depletion of existing endosomes for transferrin receptors or by de novo generation of endosomes. Cationized gold and BSA-gold internalized in K(+)-depleted cells are also delivered to endosomes containing transferrin receptors. h-lamp-1-enriched compartments are only reached occasionally within 30 min in K(+)-depleted as well as in control cells. Thus, preendosomal vesicles generated by clathrin-independent endocytosis do not fuse to any marked degree with late endocytic compartments. These data show that in HEp-2 cells, molecules endocytosed without clathrin are delivered to the same endosomes as reached by transferrin receptors internalized through clathrin-coated pits.