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At least 163 records · Page 9Linked to original sources

PubMed2006

A new way for multidimensional medical data management: volume of interest (VOI)-based retrieval of medical images with visual and functional features.

The advances in digital medical imaging and storage in integrated databases are resulting in growing demands for efficient image retrieval and management. Content-based image retrieval (CBIR) refers to the retrieval of images from a database, using the visual features derived from the information in the image, and has become an attractive approach to managing large medical image archives. In conventional CBIR systems for medical images, images are often segmented into regions which are used to derive two-dimensional visual features for region-based queries. Although such approach has the advantage of including only relevant regions in the formulation of a query, medical images that are inherently multidimensional can potentially benefit from the multidimensional feature extraction which could open up new opportunities in visual feature extraction and retrieval. In this study, we present a volume of interest (VOI) based content-based retrieval of four-dimensional (three spatial and one temporal) dynamic PET images. By segmenting the images into VOIs consisting of functionally similar voxels (e.g., a tumor structure), multidimensional visual and functional features were extracted and used as region-based query features. A prototype VOI-based functional image retrieval system (VOI-FIRS) has been designed to demonstrate the proposed multidimensional feature extraction and retrieval. Experimental results show that the proposed system allows for the retrieval of related images that constitute similar visual and functional VOI features, and can find potential applications in medical data management, such as to aid in education, diagnosis, and statistical analysis.

Algorithms↗

PubMed2005

Medical image retrieval based on plaque appearance and image registration.

The increasing amount of medical images produced and stored daily in hospitals needs a datrabase management system that organizes them in a meaningful way, without the necessity of time-consuming textual annotations for each image. One of the basic ways to organize medical images in taxonomies consists of clustering them depending of plaque appearance (for example, intravascular ultrasound images). Although lately, there has been a lot of research in the field of Content-Based Image Retrieval systems, mostly these systems are designed for dealing a wide range of images but not medical images. Medical image retrieval by content is still an emerging field, and few works are presented in spite of the obvious applications and the complexity of the images demanding research studies. In this chapter, we overview the work on medical image retrieval and present a general framework of medical image retrieval based on plaque appearance. We stress on two basic features of medical image retrieval based on plaque appearance: plaque medical images contain complex information requiring not only local and global descriptors but also context determined by image features and their spatial relations. Additionally, given that most objects in medical images usually have high intra- and inter-patient shape variance, retrieval based on plaque should be invariant to a family of transformations predetermined by the application domain. To illustrate the medical image retrieval based on plaque appearance, we consider a specific image modality: intravascular ultrasound images and present extensive results on the retrieval performance.

Humans↗

PubMed1999

Medial temporal lobe activation during episodic encoding and retrieval: a PET study.

Recent neuroimaging studies have obtained evidence of activation in the medial temporal lobe (MTL) during episodic encoding and retrieval. On the basis of a meta-analysis of MTL activations in studies that used positron emission tomography (PET), Lepage et al. (Hippocampus 1998;8:313-322) suggested that episodic encoding tends to involve the anterior MTL, whereas episodic retrieval tends to involve the posterior MTL. In a meta-analysis of studies that used PET and functional magnetic resonance imaging, Schacter and Wagner (Hippocampus 1999;9:7-24) reported weaker evidence for such a rostrocaudal distribution of encoding and retrieval activations. However, these meta-analyses were based largely on studies that examined encoding or retrieval separately. Here, we report a direct, within-subjects comparison of MTL activation during episodic encoding and retrieval by using PET. Results indicated that both encoding and retrieval were associated with blood flow increases in similar MTL regions with little indication that encoding and retrieval are preferentially associated with activity in the anterior versus the posterior MTL. Direct comparisons revealed greater blood flow increases in posterior MTL during encoding than retrieval.

Adult↗

PubMed2000

Conjunction analysis of cortical activations common to encoding and retrieval.

The notion of overlap between encoding and retrieval processes is central in cognitive theories of episodic memory, but to date most functional neuroimaging studies have emphasized differences between these processes. In the present study, overlap between encoding and retrieval processes was investigated by analyzing data from a positron emission tomography (PET) study of encoding and retrieval of different kinds of event information. Using a conjunction analysis, we specifically aimed at identifying overlap in activation patterns for encoding and retrieval of three classes of event information: item, temporal, and spatial. It was found that both encoding and retrieval of spatial information activated posterior parietal areas bilaterally. In addition, item encoding and retrieval were associated with increased activity in the right temporal pole, and temporal encoding and retrieval with left inferior frontal and left inferior temporal regions. These findings suggest that when specific episodic information is retrieved from memory, regions involved in encoding of the same information are engaged.

Brain Mapping↗

PubMed2004

Recollective qualities modulate hippocampal activation during autobiographical memory retrieval.

Recent neuroimaging studies report preferential hippocampal engagement during autobiographical memory (AM) retrieval. Although the basis of this preferential activation remains unclear, it may be related to the temporal specificity, recency, or recollective qualities of AMs, such as detail, emotionality, and personal significance. Typically, however, these variables are confounded, and thus we sought to investigate the contributions of each to hippocampal activation during AM retrieval. We conducted an event-related functional magnetic resonance imaging (fMRI) study in which participants retrieved temporally specific AMs and general, repeated AMs, and rated each for level of detail, emotion, or personal significance. These ratings, as well as the recency of AMs, were used in parametric modulation analyses to identify brain regions that correlated positively with ratings, independent of recency, and vice versa. Retrieval of AMs activated a number of regions, including the hippocampus. No differences in hippocampal activation were evident between specific and general AM retrieval, suggesting that temporal specificity, on its own, is not a key modulator of hippocampal activation. Activation of the left hippocampus during specific AM retrieval did vary with the level of detail, personal significance, and at a subthreshold level, emotionality, when the effect of recency was covaried out. Further, during general AM retrieval, all three recollective qualities modulated activity in the right hippocampus. Although the recency of specific AMs modulated hippocampal activation bilaterally, this effect dissipated in the left hippocampus when detail or emotionality was included as a covariate, and was no longer present in either hippocampus when personal significance was taken into account. Our results suggest that recollective qualities are important predictors of hippocampal engagement during AM retrieval independent of factors such as recency. These findings are consistent with theories of hippocampal function that emphasize its role in the recollection of multifaceted autobiographical experiences.

Adult↗

PubMed1998

Neural correlates of memory retrieval during recognition memory and cued recall.

Regional brain activity, measured by H215O PET, was investigated during recognition memory and word-stem cued recall of words in order to compare the neural correlates of two components of memory retrieval-effort and success-as a function of task. For each task there was a baseline and two retrieval conditions. In one retrieval condition (zero density), none of the test items corresponded to words encoded in a preceding study phase. Differences in activity between this condition and the baseline were employed to characterize the neural correlates of retrieval effort in each task. In the other retrieval condition (high density), 80% of the test items had been studied previously. Differences in brain activity between this condition and the zero-density condition were taken to represent the neural correlates of successful retrieval. The principal findings concern the right anterior prefrontal cortex, a region demonstrated previously to be active during episodic retrieval. Relative to baseline, this region showed no evidence of activation in the zero-density condition of the recognition task, but did show enhanced activity in the equivalent condition of the cued-recall task. In contrast, relative to the zero-density condition, the high-density condition was associated with increased right prefrontal activity during recognition, but reduced activity during cued recall. It is proposed that the right prefrontal cortex supports cognitive processes that operate on information retrieved in response to a test item and that these processes contribute to the evaluation of whether the information represents an appropriate prior episode.

Adult↗

PubMed2000

Dissociable temporal lobe activations during emotional episodic memory retrieval.

The richness of human recollective experience is, in part, related to evocation of previously experienced emotions. An extensive functional neuroimaging literature has provided a description of brain regions involved in retrieving emotionally neutral episodic memories. Whether similar or distinct systems are involved in retrieving emotional memories is unresolved. This question motivated the present functional neuroimaging study, using 0-15 positron emission tomography (PET), where we compared patterns of brain activation associated with retrieving previously studied emotional and neutral pictorial material. By varying task requirements and item density we characterized two distinct neural response patterns during emotional memory retrieval. First, we identified an anterior temporal pole activation that reflected the psychological set associated with emotional memory retrieval. Second, we identified a left amygdala response sensitive to actual retrieval of emotional items. These data suggest distinct functional roles for temporal lobe regions during emotional memory retrieval involving context-related tonic anterior temporal pole activation and a phasic item-related amygdala response. We conclude that brain regions involved in episodic memory retrieval reflect not only physical attributes of stimulus material, for example, their verbal or visual qualities, but also their affective significance.

Amygdala↗

PubMed2002

Retrieval of relational information: a role for the left inferior prefrontal cortex.

Neuroimaging studies have implicated different areas of prefrontal cortex and medial temporal lobe structures (MTL) in episodic retrieval tasks. However, the role of specific regions in particular aspects of episodic memory is still unclear. In this experiment we studied changes in regional cerebral blood flow (rCBF) associated with relational and nonrelational retrieval of studied pairs of words. For relational retrieval, a list of either studied or rearranged pairs was presented and subjects (n = 8) were asked to indicate whether pairs had appeared on the study list. Under the nonrelational retrieval condition they indicated whether one or both words of the pair had appeared on the study list. As compared to the baseline condition (looking at a cross-mark), increased rCBF was observed in the left inferior prefrontal cortex (LIPFC) for both studied pairs and rearranged pairs under the relational retrieval condition. Under the nonrelational condition, an increase was observed in right inferior frontal gyrus. The MTL showed a trend for increased rCBF in the rearranged-pair condition. This increase was probably associated with the encoding that accompanies retrieval of novel stimuli. Results suggest that the lateralized activation of prefrontal cortex observed in episodic memory tasks may be related to the degree of relational processing involved. The LIPFC appears to be associated with relational retrieval and the right prefrontal cortex with nonrelational retrieval.

Adolescent↗

PubMed2004

Retrieving "nonretrievable" inferior vena caval Greenfield filters: a therapeutic option for filter malpositioning.

Filter malpositioning is a possible complication of inferior vena caval (IVC) filter insertion that may result in inadequate protection from pulmonary embolism. For nonretrievable filters, this is traditionally managed with either observation or additional filter placement. The purpose of this study is determine the incidence of filter malpositioning after bedside insertion under duplex ultrasound (DUS) or intravascular ultrasound (IVUS) guidance, and to report techniques for retrieving and repositioning IVC filters previously considered nonretrievable. All IVC filter insertions performed under DUS or IVUS guidance over an 8-year period were identified. Data regarding insertion technique, device used, and technical success were retrospectively collected. Cases of IVC filter malpositioning were determined and form the basis of this study. Technical details for IVC filter retrieval and repositioning are described. Of 486 patients undergoing DUS (n = 435) or IVUS (n = 51) guided IVC filter insertion, 12 patients (2.4%) had inadequate positioning as determined by postoperative radiography. Two of these patients had no further filter manipulation, three had a second filter placed under fluoroscopic guidance, and the most recent five had filters retrieved and repositioned under fluoroscopic guidance. Of those patients undergoing retrieval and repositioning, all five had Greenfield filters, which are not traditionally regarded as retrievable. All attempted retrievals or replacements were technically successful without additional filter-related complications. Bedside IVC filter insertion under DUS or IVUS guidance has a low incidence of filter misplacement. Although not traditionally regarded as retrievable, Greenfield filters can be safely retrieved and repositioned using advanced endovascular techniques in the event of malpositioning.

Adolescent↗

PubMed2005

Co-activation of the amygdala, hippocampus and inferior frontal gyrus during autobiographical memory retrieval.

Functional MRI was used to investigate the role of medial temporal lobe and inferior frontal lobe regions in autobiographical recall. Prior to scanning, participants generated cue words for 50 autobiographical memories and rated their phenomenological properties using our autobiographical memory questionnaire (AMQ). During scanning, the cue words were presented and participants pressed a button when they retrieved the associated memory. The autobiographical retrieval task was interleaved in an event-related design with a semantic retrieval task (category generation). Region-of-interest analyses showed greater activation of the amygdala, hippocampus, and right inferior frontal gyrus during autobiographical retrieval relative to semantic retrieval. In addition, the left inferior frontal gyrus showed a more prolonged duration of activation in the semantic retrieval condition. A targeted correlational analysis revealed pronounced functional connectivity among the amygdala, hippocampus, and right inferior frontal gyrus during autobiographical retrieval but not during semantic retrieval. These results support theories of autobiographical memory that hypothesize co-activation of frontotemporal areas during recollection of episodes from the personal past.

Adolescent↗

PubMed2005

Brain regions associated with successful and unsuccessful retrieval of verbal episodic memory as revealed by divided attention.

Which brain regions are implicated when words are retrieved under divided attention, and what does this tell us about attentional and memory processes needed for retrieval? To address these questions we used fMRI to examine brain regions associated with auditory recognition performed under full and divided attention (DA). We asked young adults to encode words presented auditorily under full attention (FA), and following this, asked them to recognize studied words while in the scanner. Attention was divided at retrieval by asking participants to perform either an animacy task to words, or odd-digit identification task to numbers presented visually, concurrently with the recognition task. Retrieval was disrupted significantly by the word-, but not number-based concurrent task. A corresponding decrease in brain activity was observed in right hippocampus, bilateral parietal cortex, and left precuneus, thus demonstrating, for the first time, involvement of these regions in recognition under DA at retrieval. Increases in activation of left prefrontal cortex (PFC), associated with phonological processing, were observed in the word- compared to number-based DA condition. Results suggest that the medial temporal lobe (MTL) and neo-cortical components of retrieval, believed to form the basis of episodic memory traces, are disrupted when phonological processing regions in left PFC are engaged simultaneously by another task. Results also support a component-process model of retrieval which posits that MTL-mediated retrieval does not compete for general cognitive resources but does compete for specific structural representations.

Acoustic Stimulation↗

PubMed2006

Differential activation of ventrolateral prefrontal cortex during working memory retrieval.

Brain imaging studies have suggested a predominant involvement of prefrontal areas during retrieval of information from working memory (WM). This study used event-related functional magnetic resonance imaging to assess the gradual recruitment of brain areas during verbal WM-retrieval with a parametrically varied modified version of the Sternberg Item Recognition Paradigm. In particular, we were interested in activation differences during retrieval of negative and positive probes. Fifteen subjects performed a WM-task which required the retrieval of a probe letter from a set of a maximum of three letters. The analysis of the retrieval period regardless of probe type revealed bilateral VLPFC activation during retrieval from a single remembered item. These initially activated regions showed a gradual activation increase of left VLPFC (BA 47) and anterior PFC (BA 10) as well as and bilateral DLPFC (BA 9) with increasing retrieval demand, i.e. during retrieval of two and three previously remembered letters. The comparison of negative and positive probes (non-targets versus targets) revealed greater activity in VLPFC (BA 47) in response to negative than to positive probes. These findings demonstrate that ventral areas of prefrontal cortex seem to be differentially engaged during the discrimination of a non-target from a previously manipulated set.

Adult↗

PubMed2004

Differences of cerebral activation between superior and inferior learners during motor sequence encoding and retrieval.

Cerebral activation during memory encoding and retrieval might depend on subjects' learning capacity, either by corresponding to better performance in superior learners or by reflecting increased effort in inferior learners. To investigate these alternative hypotheses, the study compared cerebral activation during encoding and retrieval of a motor sequence in groups of subjects with superior and inferior learning performances. Ten healthy subjects underwent functional magnetic resonance imaging (fMRI) while performing a motor sequence encoding paradigm (i.e. finger tapping sequence) and a retrieval paradigm (i.e. reproduction of the learned sequence). Subjects were divided into superior and inferior learners according to the correctness of sequence reproduction during retrieval. During encoding, there was strong bilateral activation in the middle frontal gyrus, the supplementary motor area (SMA), the lateral parietal lobe and the cerebellum. During retrieval, again strong activation was found in identical areas of the prefrontal cortex, the parietal lobe and the cerebellum. During encoding, inferior learners showed more left-sided activations in the left middle frontal and inferior parietal gyri. Superior learners showed increased activation in the corresponding right-sided brain areas during encoding as well as during retrieval. Differences of cerebral activations in the prefrontal and parietal cortex during encoding and retrieval were found to be related to retrieval performance, i.e. success and effort. Further intervention studies are needed to assess whether these interindividual differences are the cause or the consequence of differences in memory performance.

Achievement↗

PubMed2005

Effects of memory consolidation on human hippocampal activity during retrieval.

Day-to-day memories undergo transformation from short-term to long-term storage, a process called memory consolidation. Animal studies showed that memory consolidation requires protein synthesis and the growth of new hippocampal synapses within 24 h. To test for effects of memory consolidation in the human, we examined brain activation during the retrieval of information at 10 min and at 24 h following learning using functional magnetic resonance imaging (fMRI), an indirect measure of synaptic activity. Learning instructions were adjusted to yield a comparable retrieval quantity and retrieval quality at 10 min and 24 h after learning. The left hippocampal formation exhibited enhanced activity during the retrieval at the 24 h lag compared to the retrieval at the 10 min lag. Moreover, the activity in the left anterior hippocampal formation showed stronger correlations with retrieval quantity and retrieval quality at the 24 h lag than at the 10 min lag. This suggests that the relation between left anterior hippocampal activity and retrieval success became closer as consolidation progressed. These fMRI results in the human hippocampal formation may correspond to the neurobiological results in the animal hippocampal formation of a strengthening and growth of synaptic connections within 24 h.

Adult↗

PubMed2003

Postoperative pain, complications, and satisfaction rates in patients who undergo surgical sperm retrieval.

OBJECTIVE: To determine patients' experiences with surgical sperm retrieval and its common complications. DESIGN: A questionnaire based survey using visual analogue scales (VAS) and closed questions to analyze complication, pain, and satisfaction rates. SETTING: Tertiary care university hospital. PATIENT(S): One hundred consecutive males undergoing surgical sperm retrieval by percutaneous epididymal sperm aspiration (PESA) or testicular sperm extraction (TESE). INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): We surveyed for pain perception complication rates and satisfaction scores. RESULT(S): Of the 85 patients who replied, 21 underwent retrieval for nonobstructive causes, 37 following failed reversal of vasectomy, and 27 for other obstructive causes. Retrieval was successful in 100% of obstructive causes and in 61% for nonobstructive azoospermia. Epididymal retrieval was successful in 23 patients, 30 patients underwent TESE after failed PESA, and 23 had TESE only. There were significant increases in pain perception scores and reported complications with TESE over PESA (31 vs. 16; and 21 out of 63 vs. 2 out of 22, respectively), but no difference in satisfaction rate. The cause of azoospermia did not affect pain perception or satisfaction in TESE. Complication rates were increased in larger testes (3 out of 22 vs. 24 out of 63). Unsuccessful sperm retrieval did not significantly affect patients' pain perception or satisfaction. Surgical sperm retrieval was rated as significantly less painful than both vasectomy and reversal (21% vs. 42% vs. 57%, respectively) and was associated with significantly fewer days absent from work (3.0 vs. 8.5). CONCLUSION(S): Surgical sperm retrieval by PESA or TESE is a safe procedure with only minor complications that is tolerated well by patients.

Adult↗

PubMed1997

Avoidance of oocyte retrieval on the weekend through the use of scheduled ovarian hyperstimulation for in vitro fertilization and embryo transfer.

OBJECTIVE: To avoid oocyte retrieval for IVF-ET during the weekend, the scheduled method of ovarian hyperstimulation, in which oocyte retrieval is planned in advance for Monday through Wednesday, was evaluated. DESIGN: A retrospective study. SETTING: The IVF-ET unit of the Department of Obstetrics and Gynecology at Tokushima University Hospital. PATIENT(S): One hundred seventy-eight cycles in patients undergoing ovarian hyperstimulation for IVF-ET were stimulated according to the scheduled method of ovarian hyperstimulation (scheduled group). One hundred seventy-one cycles in patients of similar age and with comparable causes of infertility were stimulated according to the conventional method of ovarian hyperstimulation for IVF-ET (conventional group). INTERVENTION(S): In the scheduled method, under GnRH-a, the day of oocyte retrieval was determined in advance for IVF-ET. Ovarian stimulation with FSH and hMG was started 12 days before oocyte retrieval. MAIN OUTCOME MEASURE(S): The cancellation and clinical pregnancy rates (PRs), the days of oocyte retrieval, and other clinical parameters were evaluated in the two groups. RESULT(S): The cancellation rates in the scheduled and conventional groups were 9.6% and 4.7%, respectively. In about 75% of cycles in the scheduled group, oocyte retrieval was conducted on the scheduled day. When oocyte retrieval was scheduled for Monday through Wednesday, overtime work on the weekend could be avoided in 91% of the cycles without cancellation. The clinical PR was comparable between the two groups. CONCLUSION(S): The scheduled method of ovarian hyperstimulation for IVF-ET was useful for avoiding oocyte retrieval on the weekend.

Adult↗

PubMed2005

Colon polyp retrieval after cold snaring.

BACKGROUND: The removal of small colon polyps by cold snare transection without electrocautery effectively eliminates polyps, and anecdotal reports indicate a low risk of bleeding and perforation. Concerns about using cold snaring have centered on the risk of immediate bleeding and the difficulty in retrieving the polyp. The objective was to determine the retrieval rates of polyps after cold snaring after two different methods of resection and retrieval. METHODS: Consecutive polyps were identified by a single colonoscopist who chose the technique of polypectomy (hot snare, cold snare, or cold forceps). If cold snaring was chosen, an independent observer assigned the polyp to method A (cold resection of polyp without tenting and then suction of the transected polyp into a trap) or method B (ensnare the polyp, pull it into the colonoscope channel, and then transect it while suctioning). The size and the approximate location of all polyps were recorded and all collected specimens were sent separately for histologic examination. Results Of 519 consecutively encountered polyps, 400 were removed by cold snare: 197 were assigned to method A and 203 to method B. The mean size of polyps that were cold snared was 3.5 mm. The mean time to remove and to retrieve polyps with method A was 14.5 seconds (n = 58) and with method B was 18.1 seconds (n = 60) ( p = 0.03). There were no complications from cold snaring. The rate of successful retrieval with method A was 100% (197 of 197 polyps) and with method B was 98% (199 of 203 polyps) ( p = 0.04). CONCLUSIONS: Cold snare removal of colon polyps is associated with a high polyp retrieval rate. Each of two methods of polyp retrieval was effective. Snare transection without tenting of the polyp, followed by suctioning of the specimen off the polyp site, was more efficient, though the difference in efficiency was minimal. Difficulty or failure to retrieve polyps should not be a concern with regard to cold snare polypectomy.

Cold Temperature↗

PubMed1999

Endoscopic techniques for retrieval of proximally migrated biliary stents: the Amsterdam experience.

BACKGROUND: Endoscopic retrieval of proximally migrated biliary plastic stents may be technically challenging and sometimes unsuccessful. Despite the widespread use of such stents, there are few reports on the technique for retrieval of migrated stents. METHODS: We reviewed the records of patients who were found to have proximally migrated biliary stents during the last 3 years at a tertiary referral center. Our study analyzed the various techniques used for endoscopic retrieval and evaluated the factors influencing the choice of a particular technique. RESULTS: Endoscopic retrieval of a proximally migrated stent was attempted in 41 patients and was successful in 37 (90%). The retrieval techniques included Dormia basket, balloon, balloon and basket, basket and ball tip catheter, forceps, and Soehendra stent retriever. The Dormia basket technique was successful in the majority of cases. CONCLUSION: Proximally migrated biliary stents can be successfully removed endoscopically in most cases. The choice of a retrieval technique is dependent on several factors including biliary ductal dilatation, depth of stent migration, distal stent impaction and biliary stricture distal to the migrated stent. The placement of an additional stent alongside an irretrievable stent is a satisfactory alternative to retrieval.

Catheterization↗