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At least 307 records · Page 17Linked to original sources
PubMed2005

Dehiscence of the superior and/or posterior semicircular canal: delineation on T2-weighted axial three-dimensional turbo spin-echo images, maximum intensity projections and volume-rendered images.

The purpose of this study was to compare the ability of T2-weighted three-dimensional turbo spin-echo (TSE) images, maximum intensity projections and three-dimensional volume-rendered images for delineation of semicircular canal dehiscence. In 26 patients with dehiscence of the superior and/or posterior semicircular canal and 26 control patients, TSE images were obtained with two different resolutions and maximum intensity projection (MIP) and 3D volume-rendered images reconstructed. All images were evaluated by two radiologists in consensus regarding the visualization of anatomical structures and dehiscence of the semicircular canals. Computed tomography was used to confirm or exclude dehiscence. Dehiscence of the semicircular canals was delineated on axial MR images and on 3D volume-rendered images, but not on MIP images. The number of false positive cases was reduced from 3 to 0 with an increase in matrix, rendering results similar to those obtained with CT. Dehiscence of the semicircular canals can be assessed on high resolution MR images. Volume-rendered 3D images allow for immediate perception of the location of defects in semicircular canal dehiscence. These images may facilitate understanding of the extent and location of the defects.

Adolescent↗
PubMed1994

Intraoral computed radiography using the Fuji computed radiography imaging plate. Correlation between image quality and reading condition.

The quality of images obtained by a new method of intraoral computed radiography using three types of imaging plates and a drum scanner designed exclusively for use with an imaging plate was investigated. The aperture size for reading of radiographic data from the imaging plate and for film recording was 50, 100, or 150 microns 2. The results indicated that high resolution type imaging plate for mammography produced the best image quality. For each imaging plate, it was also found that the image quality improved as the aperture size was decreased. However, the high resolution type IP even at the aperture size of 100 microns 2 showed diagnostic accuracy as high as the image processing of conventional periapical radiographs. This finding suggests that this new imaging system using an imaging plate at the reading and recording aperture size 100 microns 2 has promise for use in intraoral radiography.

Evaluation Studies as Topic↗
PubMed2004

Ventilation imaging of the lung: comparison of hyperpolarized helium-3 MR imaging with Xe-133 scintigraphy.

RATIONALE AND OBJECTIVES: To compare hyperpolarized helium-3 (HHe) magnetic resonance imaging (MRI) of the lung with standard Xe-133 lung ventilation scintigraphy. MATERIALS AND METHODS: We performed a retrospective review of 15 subjects who underwent HHe MRI and Xe-133 lung ventilation imaging. Coronal MRI sections were acquired after a single inhalation of HHe gas, and standard posterior planar lung ventilation scintigraphy was performed during continuous breathing of Xe-133 gas. The first breath scintigram of each patient was compared with a composite MR image composed of the sum of the individual MR images and with the individual helium-3 MR images. Ventilation defects on the two imaging modalities were compared for size, conspicuity, and concordance in presence and location. Assessment was done separately for each of four lung quadrants. RESULTS: Comparing the composite HHe MR images with Xe-133 scintigraphy, ventilation defect size, conspicuity and concordance were the same in 67% (40/60), 63% (38/60), and 62% (37/60) quadrants, respectively. Comparing the individual HHe MR image sections with the Xe-133 ventilation scan, there was concordance between the ventilation defects in 27% (16/60) of quadrants. More defects were identified on the individual HHe MR images in 62% (37/60) of quadrants. CONCLUSION: There was good agreement between composite HHe MR image and first breath Xe-133 scintigraphic images, supporting the widely held assumption that HHe MRI likely depicts first breath lung ventilation.

Adolescent↗
PubMed2006

Real-time 3-dimensional echocardiographic imaging of congenital heart disease using matrix-array technology: freehand real-time scanning adds instant morphologic details not well delineated by conventional 2-dimensional imaging.

OBJECTIVE: We sought to investigate whether real-time (RT) 3-dimensional echocardiography (RT3D) using matrix-array technology could resolve a specific morphologic detail that could not be well resolved during conventional 2-dimensional (2D)/Doppler echocardiographic imaging of congenital heart disease. BACKGROUND: Although 2D echocardiography is currently the primary imaging modality of congenital heart disease, there are still some anatomic details that cannot be well delineated by that modality. METHODS: In all, 70 patients underwent RT3D examination using matrix-array transducer. Applying the standard sweeping technique as for 2D imaging, freehand RT imaging was used for immediate feedback. The 2D examinations of the last 23 consecutive patients were used to validate the additional value of RT3D by 3 examiners blinded to the findings of RT3D. RESULTS: The adequacy of 2D imaging to resolve the morphologic detail in question ranged from 30% to 70%, whereas RT3D imaging was considered successful in delineating the morphologic detail in 80% to 100% of patients instantly. The image resolution was superior or equivalent to that obtained by 2D imaging. Heart valves, septal defects, and volumetric valvular and vascular color flow morphologies were well delineated by RT3D. CONCLUSION: Matrix-array RT3D is a significant breakthrough technology that allowed instant visualization of cardiac anatomic details that could not be well delineated by 2D imaging. Further improvements of some technical limitations should make RT3D matrix-array cardiac imaging a significant modality in the field of echocardiographic imaging of congenital cardiac anomalies.

Adolescent↗
PubMed2000

[Examination of the image quality from digital fluoroscopy equipment with 1k- and 2k-image matrix].

PURPOSE: The image quality of 1k- and 2k-radiographs from digital fluoroscopy equipments (Sireskop SX and Polystar SX--Siemens) are characterized by comparison with each other to evaluate the relevance of this technique in clinical routine. MATERIAL AND METHODS: We examined fabricated and evaluated images with 1k- and 2k-image matrix from several high and low contrast phantoms and from skeleton phantoms. On the one hand, the digital image values can be used directly for the evaluation, on the other hand the comparing evaluation by experienced radiologists resulted from a visual consideration in a blind study. RESULTS: The quality difference of the 1k- and 2k-images depends mainly on the distance of the investigated sector of the object to the image intensifier and on the scattering of the radiation in the object positioned between the investigated sector and the image intensifier. The nearer the investigated object is located to the intensifier and the smaller the radiation is scattered in the object, the more the image quality of a radiograph with a 2k-matrix is increasing in comparison to an image with 1k-matrix. The higher the tube voltage, the smaller are the differences. CONCLUSION: The image quality enhancement because of the more sensitive sampling of the Saticon target in the 2k-matrix is limited by the opening of the iris positioned in the light distributor. Therefore the image quality differences of medical 1k- and 2k-radiographs in many cases are small.

Bone and Bones↗
PubMed2004

Toward development of imaging modalities for islets after transplantation: insights from the National Institutes of Health Workshop on Beta Cell Imaging.

BACKGROUND: Pancreatic islet transplantation can provide insulin independence and near normal glucose control in selected patients with type 1 diabetes mellitus. However, in most cases, achieving insulin independence necessitates the use of at least two donor pancreases per recipient and the rate of insulin independence may decline after transplantation. To better understand the fate of transplanted islets and the relationship between transplanted islet mass, graft function, and overall glucose homeostasis, an accurate and reproducible method of imaging islets in vivo is needed. METHODS: Recent advances in noninvasive imaging techniques such as magnetic resonance imaging, positron emission tomography, and other imaging modalities show great promise as potential tools to monitor islet number, mass, and function in the clinical setting. A recent international workshop, "Imaging the Pancreatic Beta Cell," sponsored by the National Institute of Biomedical Imaging and Bioengineering, the National Institute of Diabetes and Digestive and Kidney Diseases, and the Juvenile Diabetes Research Foundation International focused on these emerging efforts to develop novel ways of imaging pancreatic beta cells in vivo. RESULTS: Potential clinically applicable techniques include the use of directed magnetic resonance contrast agents such as lanthanides (Ln(3+)) and manganese (Mn(2+)) or magnetic resonance imaging probes such as superparamagnetic iron oxide nanoparticles. Potential techniques for positron emission tomography imaging include the use of beta cell-specific antibodies, or pharmacologic agents such as glyburide analogs, or d-mannoheptulose. Optical imaging techniques are also being used to evaluate various aspects of beta cell metabolism including intracellular Ca(2+) flux, glucokinase activity, and insulin granular exocytosis. CONCLUSIONS: The consensus among investigators at the imaging workshop was that an accurate and reproducible in vivo measure of functional islet mass is critically needed to further the strides that have been made in both islet transplantation and diabetes research as a whole. Such measures would potentially allow the assessment of islet engraftment and the early recognition of graft loss, leading to greater improvements in islet graft survival and function.

Diagnostic Imaging↗
PubMed2005

An image model and segmentation algorithm for reflectance confocal images of in vivo cervical tissue.

The automatic segmentation of nuclei in confocal reflectance images of cervical tissue is an important goal toward developing less expensive cervical precancer detection methods. Since in vivo confocal reflectance microscopy is an emerging technology for cancer detection, no prior work has been reported on the automatic segmentation of in vivo confocal reflectance images. However, prior work has shown that nuclear size and nuclear-to-cytoplasmic ratio can determine the presence or extent of cervical precancer. Thus, segmenting nuclei in confocal images will aid in cervical precancer detection. Successful segmentation of images of any type can be significantly enhanced by the introduction of accurate image models. To enable a deeper understanding of confocal reflectance microscopy images of cervical tissue, and to supply a basis for parameter selection in a classification algorithm, we have developed a model that accounts for the properties of the imaging system and of the tissues. Using our model in conjunction with a powerful image enhancement tool (anisotropic median-diffusion), appropriate statistical image modeling of spatial interactions (Gaussian Markov random fields), and a Bayesian framework for classification-segmentation, we have developed an effective algorithm for automatically segmenting nuclei in confocal images of cervical tissue. We have applied our algorithm to an extensive set of cervical images and have found that it detects 90% of hand-segmented nuclei with an average of 6 false positives per frame.

Algorithms↗
PubMed2002

Image quality evaluation of flat panel and image intensifier digital magnification in x-ray fluoroscopy.

Interventional devices used in radiology often have dimensions on the order of a pixel, and radiologists resort to image magnification to better visualize such small devices. Traditional image intensifier (II) systems use analog magnification with x-ray exposure inversely proportional to the area of field of view (FOV) so as to maintain light output for the camera. Analog magnification is impossible with flat panel (FP) detectors, and images must be magnified using digital interpolation that does not reduce the pixel partial area effect for small devices. We quantitatively investigated image quality of digital and analog magnification using a clinically relevant task of detecting a partially deployed stent in x-ray fluoroscopy image sequences that were created using realistic detector models. Using the standard exposure strategy for II analog magnification, exposure was increased from a nominal 43.65 nGy (5.0 microR) per frame at 23 cm FOV to 79.9 nGy (9.15 microR) per frame and 117.81 nGy (13.49 microR) per frame at 17 cm and 14 cm FOV, respectively. Contrast sensitivity improved significantly (p<0.1) by 43.5+/-6.5% and 64.1+/-7.3% with the 17 cm and 14 cm FOV, respectively. Exposure for digitally magnified images was varied in an adaptive forced choice experiment so as to match performance with II analog magnification. For digital magnification, bilinear interpolation was used to give magnified stents sizes equivalent to those in the analog magnified images. For equivalent image quality, FP required 34.87+/-2.59, 80.16+/-5.37, and 84.08+/-5.59 nGy per frame at normal, and the two magnification modes, respectively. Hence, FP with digital magnification gives significant (p<0.1) dose savings of 20+/-6% and 27+/-5% at the normal and highest magnification modes, respectively. Digitally magnified II images required exposures of 110.85+/-8.07 and 103.34+/-5.90 nGy per frame for the two magnifications levels, respectively, giving no significant (p>0.1) dose savings. A spatiotemporal human observer model based on signal detection theory successfully predicted the human data and was used to predict other conditions associated with image magnification. Model predictions quantitatively showed that magnification is most useful when signal size is relatively small and that FP digital magnification can improve image quality for the stent deployment task without increasing exposure. In conclusion, the results show that FP digital magnification can be useful and dose efficient as compared to analog magnification.

Humans↗
PubMed2003

Experimental investigation of the dose and image quality characteristics of a digital mammography imaging system.

Our purpose in this study was to investigate the image quality and absorbed dose characteristics of a digital mammography imaging system with a CsI scintillator, and to identify an optimal x-ray tube voltage for imaging simulated masses in an average size breast with 50% glandularity. Images were taken of an ACR accreditation phantom using a LORAD digital mammography system with a Mo target and a Mo filter. In one experiment, exposures were performed at 80 mAs with x-ray tube voltages varying between 24 and 34 kVp. In a second experiment, the x-ray tube voltage was kept constant at 28 kVp and the technique factor was varied between 5 and 500 mAs. The average glandular dose at each x-ray tube voltage was determined from measurements of entrance skin exposure and x-ray beam half-value layer. Image contrast was measured as the fractional digital signal intensity difference for the image of a 4 mm thick acrylic disk. Image noise was obtained from the standard deviation in a uniformly exposed region of interest expressed as a fraction of the background intensity. The measured digital signal intensity was proportional to the mAs and to the kVp5.8. Image contrast was independent of mAs, and dropped by 21% when the x-ray tube voltage increased from 24 to 34 kVp. At a constant x-ray tube voltage, image noise was shown to be approximately proportional to (mAs)(-05), which permits the image contrast to noise ratio (CNR) to be modified by changing the mAs. At 80 mAs, increasing the x-ray tube voltage from 24 to 34 kVp increased the CNR by 78%, and increased the average glandular dose by 285%. At a constant lesion CNR, the lowest average glandular dose value occurred at 27.3 kVp. Increasing or decreasing the x-ray tube voltage by 2.3 kVp from the optimum kVp increased the average glandular dose values by 5%. These results show that imaging simulated masses in a 4.2 cm compressed breast at approximately 27 kVp with a Mo/Mo target/filter results in the lowest average glandular dose.

Equipment Failure Analysis↗
PubMed1997

Improved determination of biplane imaging geometry from two projection images and its application to three-dimensional reconstruction of coronary arterial trees.

A technique has been developed for accurate estimation of three-dimensional (3D) biplane imaging geometry and reconstruction of 3D objects based on two perspective projections acquired at arbitrary orientations, without the need of calibration. The required prior information (i.e., the intrinsic parameters of each single-plane imaging system) for determination of biplane imaging geometry includes (a) the distance between each focal spot and its image plane, SID (the focal-spot to imaging-plane distance); (b) the pixel size, psize (e.g., 0.3 mm/pixel); (c) the distance between the two focal spots ff' or the known 3D distance between two points in the projection images; and (d) for each view, an approximation of the magnification factor, MF (e.g., 1.2), which is the ratio of the SID and the approximate distance of the object to the focal spot. Item (d) is optional but may provide a more accurate estimation if it is available. Given five or more corresponding object points in both views, a constrained nonlinear optimization algorithm is applied to obtain an optimal estimate of the biplane imaging geometry in the form of a rotation matrix R and a translation vector t that characterize the position and orientation of one imaging system relative to the other. With the calculated biplane imaging geometry, 3D spatial information concerning the object can then be reconstructed. The accuracy of this method was evaluated by using a computer-simulated coronary arterial tree and a cube phantom object. Our simulation study showed that a computer-simulated coronary tree can be reconstructed from two views with less than 2 and 8.4 mm root-mean-square (rms) configuration (or relative-position) error and absolute-position error, respectively, even if the input errors in the corresponding 2D points are fairly large (more than two pixels = 0.6 mm). In contrast, input image error of more than one pixel (= 0.3 mm) can yield 3D position errors of 10 cm or more when other existing methods based on linear approaches are employed. For the cube phantom images acquired from a routine biplane system, rms errors in the 3D configuration of the cube and the 3D absolute position were 0.6-0.9 mm and 3.9-5.0 mm, respectively.

Algorithms↗
PubMed2005

The effect of digital image resolution and compression on anterior eye imaging.

AIM: To determine the theoretical and clinical minimum image pixel resolution and maximum compression appropriate for anterior eye image storage. METHODS: Clinical images of the bulbar conjunctiva, palpebral conjunctiva, and corneal staining were taken at the maximum resolution of Nikon:CoolPix990 (2048x1360 pixels), DVC:1312C (1280x811), and JAI:CV-S3200 (767x569) single chip cameras and the JVC:KYF58 (767x569) three chip camera. The images were stored in TIFF format and further copies created with reduced resolution or compressed. The images were then ranked for clarity on a 15 inch monitor (resolution 1280 x 1024) by 20 optometrists and analysed by objective image analysis grading. Theoretical calculation of the resolution necessary to detect the smallest objects of clinical interest was also conducted. RESULTS: Theoretical calculation suggested that the minimum resolution should be > or = 579 horizontal pixels at 25x magnification. Image quality was perceived subjectively as being reduced when the pixel resolution was lower than 767 x 569 (p<0.005) or the image was compressed as a BMP or <50% quality JPEG (p<0.005). Objective image analysis techniques were less susceptible to changes in image quality, particularly when using colour extraction techniques. CONCLUSION: It is appropriate to store anterior eye images at between 1280 x 811 and 767 x 569 pixel resolution and at up to 1:70 JPEG compression.

Conjunctiva↗
PubMed1997

Trends in diagnostic imaging for low back pain: has MR imaging been a substitute or add-on?

PURPOSE: To assess whether magnetic resonance (MR) imaging has replaced other diagnostic imaging modalities in the evaluation of persistent low back pain. MATERIALS AND METHODS: Data on diagnostic imaging use in 2,374 adult patients with persistent low back pain in 1987-1990 were analyzed. Multiple logistic regression was used to estimate the annual adjusted odds of lumbosacral spine radiography, MR imaging, unenhanced computed tomography (CT), or CT myelography use. The national cost of diagnostic imaging for persistent low back pain in 1990 relative to 1987 was estimated. RESULTS: The adjusted odds of performing MR imaging in 1990 relative to 1987 was 3.44 (95% confidence interval, 2.63, 4.51), which reflects an estimated increase from 22 studies per 100 enrollees in 1987 to 75 studies per 100 enrollees in 1990. Use of MR imaging in combination with radiography, unenhanced CT, or CT myelography increased. The additional national cost of diagnostic imaging for persistent low back pain in 1990 relative to 1987 was estimated at $70-$176 million. CONCLUSION: MR imaging was used primarily as an add-on rather than a substitute for other imaging modalities in the evaluation of persistent low back pain. Thus, the volume and cost of diagnostic imaging for persistent low back pain have increased.

Adult↗
PubMed2005

Detection of nuclei in 4D Nomarski DIC microscope images of early Caenorhabditis elegans embryos using local image entropy and object tracking.

BACKGROUND: The ability to detect nuclei in embryos is essential for studying the development of multicellular organisms. A system of automated nuclear detection has already been tested on a set of four-dimensional (4D) Nomarski differential interference contrast (DIC) microscope images of Caenorhabditis elegans embryos. However, the system needed laborious hand-tuning of its parameters every time a new image set was used. It could not detect nuclei in the process of cell division, and could detect nuclei only from the two- to eight-cell stages. RESULTS: We developed a system that automates the detection of nuclei in a set of 4D DIC microscope images of C. elegans embryos. Local image entropy is used to produce regions of the images that have the image texture of the nucleus. From these regions, those that actually detect nuclei are manually selected at the first and last time points of the image set, and an object-tracking algorithm then selects regions that detect nuclei in between the first and last time points. The use of local image entropy makes the system applicable to multiple image sets without the need to change its parameter values. The use of an object-tracking algorithm enables the system to detect nuclei in the process of cell division. The system detected nuclei with high sensitivity and specificity from the one- to 24-cell stages. CONCLUSION: A combination of local image entropy and an object-tracking algorithm enabled highly objective and productive detection of nuclei in a set of 4D DIC microscope images of C. elegans embryos. The system will facilitate genomic and computational analyses of C. elegans embryos.

Algorithms↗
PubMed1996

High-resolution MR imaging of stage I cervical neoplasia with a dedicated transvaginal coil: MR features and correlation of imaging and pathologic findings.

OBJECTIVE: The purposes of this study were to assess the appearance of stage 1 neoplasia of the cervix by high-resolution MR imaging with an enveloping transvaginal receiver coil and to correlate the imaging findings with the pathologic findings. SUBJECTS AND METHODS: Fifteen patients (25-73 years old; mean, 40 years old) with clinical stage I disease were examined with a 37-mm-diameter ring-design solenoid receiver coil placed around the cervix. Axial 2.5-mm contiguous slices were obtained with a field of view of 10-15 cm on a 1.0-T HPQ Vista scanner with T1-weighted (660/20 msec [TR/TE]) and T2- weighted (2500/80 msec) spin-echo sequences and dynamic gradient-echo sequences during injection of gadopentetate dimeglumine (0.1 mmol/kg). Ten patients subsequently underwent Wertheim's hysterectomy, two underwent radiotherapy, two underwent extended cone biopsy for microinvasive disease, and one underwent a punch biopsy. For seven of 10 patients who had a hysterectomy, the widths of the tumor and the residual stroma were measured at eight radial points on the transverse images and at corresponding points on the histologic specimens at 5, 10, 15, 20, and 25 mm from the ectocervix. We then compared the widths of the tumor and the stroma on images and histologic specimens at each of these 40 points. Tumor volumes were calculated from the MR imaging and pathologic data and compared. For the other three patients, detailed MR imaging-pathology correlation was not possible because of multifocal tumor distribution (two patients) and insufficient detailed pathologic data (one patient). RESULTS: Three carcinoma types were recognized. Squamous carcinoma (nine cases) was seen as a centrally expanding intermediate-signal-intensity mass, whereas oat (small)-cell carcinoma (one case) and clear-cell carcinoma (one case) showed a multifocal distribution. For patients who had a radical hysterectomy, we noted good agreement between the widths of the tumor and the stroma determined by MR imaging and histology. Tumor volumes were determined to be 0-28.2 cm3 by MR imaging and 0-18.4 cm3 by pathology. We observed tumor extension into the immediate parametrium in four patients by MR imaging; one of these cases was not confirmed at surgery. Parametrial extension was not underestimated by MR imaging in any case. CONCLUSION: High-resolution imaging of the cervix with a transvaginal coil provides accurate assessment of the intra- and extracervical extents of tumors in clinical stage 1 cervical neoplasia.

Adenocarcinoma, Clear Cell↗
PubMed2000

Test-bolus injection for optimization of arterial phase imaging during contrast-enhanced hepatic MR imaging.

Contrast enhancement during the dynamic MR imaging is important for the detection and characterization of focal liver lesions. The purpose of this study was to determine whether or not a timing examination with a injection of a 1.0-mL bolus of gadopentetate dimeglumine into the antecubital vein followed by rapid dynamic scanning and measurement of signal intensity of the aorta could help to obtain proper arterial-dominant phase images for the characterization of focal hepatic lesions during subsequent multiphase dynamic MR imaging. The imaging delay to acquisition of the first gadolinium-enhanced image for multiphase dynamic MR imaging was set to equal the time to peak aortic enhancement during the test examination. The first contrast-enhanced images of 80 patients with 160 focal liver lesions (hepatocellular carcinoma, n = 79; cavernous hemangioma, n = 51; metastatic tumor, n = 30) were then retrospectively reviewed. Peak aortic enhancement occurred between 10 and 28 seconds (mean, 16.5 seconds +/- 3.1) after starting the infusion of contrast material in 80 patients during the test-examination. Depending on the findings of intrahepatic vascular enhancement on the full-scale dynamic images, hepatic arterial phase (n = 11, 14%) or sinusoid phase (n = 65, 81%) imaging was obtained during the first gadolinium-enhanced acquisition in 76 (95%) of 80 patients. Three different lesions were well characterized and easily distinguished from each other (p < .0001) on the first-phase images depending on their enhancement pattern. In the majority of patients, timing examination with test-bolus injection was helpful in obtaining qualified images for the characterization of various focal lesions.

Adult↗
PubMed2001

Detection of intracranial hemorrhage: comparison between gradient-echo images and b(0) images obtained from diffusion-weighted echo-planar sequences.

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging (DWI) is commonly used as the initial and sole imaging examination for the detection of acute cerebral infarction, yet it remains controversial whether MR can detect hyperacute (<24 h) hemorrhage. Hemorrhage is best detected with gradient-echo (GRE) T2*-weighted sequences, because of their magnetic susceptibility effects. DWI uses a spin-echo echo-planar technique (EPI) that is more sensitive than spin-echo T2-weighted imaging to susceptibility effects. Our aim was to determine whether the b(0) image from the DWI-EPI sequence is as sensitive as GRE in detecting hemorrhagic lesions on imaging studies performed to identify acute infarction or hemorrhage. METHODS: All MR studies performed for clinically suspected or radiographically confirmed acute infarction or hemorrhage from 2/1/98 to 8/15/99 were retrospectively interpreted by one neuroradiologist in a blinded fashion. The sensitivity of hemorrhage detection, conspicuity of lesions, and diagnostic certainty were compared between the b(0) EPI and GRE sequences. RESULTS: We found 101 acute infarcts, of which 13 were hemorrhagic, as evidenced by the presence of hypointensity within the infarction on the GRE sequence. This finding served as the reference standard for detection of hemorrhage. Hemorrhage was diagnosed with confidence in only seven cases (54%) on b(0) images; 22 acute hematomas were hypointense on GRE images whereas 19 were hypointense on b(0) images (86%); 17 chronic hematomas were depicted on GRE images and 12 on b(0) scans (63%). Punctate hemorrhages and linear cortical staining were detected on 37 GRE studies but on only four b(0) studies. Hemorrhage was always more conspicuous on the GRE sequences. CONCLUSION: b(0) images from a DWI sequence failed to detect minimally hemorrhagic infarctions and small chronic hemorrhages associated with microangiopathy. GRE scans were more sensitive than b(0) images in the detection of these hemorrhages and should be included in emergency brain MR studies for acute infarction, especially when thrombolytic therapy is contemplated.

Acute Disease↗
PubMed2002

Radiation dose and image quality in diagnostic radiology. Optimization of the dose-image quality relationship with clinical experience from scoliosis radiography, coronary intervention and a flat-panel digital detector.

UNLABELLED: X-rays are known to cause malignancies, skin damage and other side effects and they are thus potentially dangerous. Therefore, it is essential and in fact mandatory to reduce the radiation dose in diagnostic radiology as far as possible. This is also known as the ALARA (as low as reasonably achievable) principle. However, the dose is linked to image quality and the image quality may not be lowered so far that it jeopardizes the diagnostic outcome of a radiographic procedure. The process of reaching this balance between dose and image quality is called optimization. The aim of this thesis was to propose and evaluate methods for optimizing the radiation dose-image quality relationship in diagnostic radiography with a focus on clinical usefulness. The work was performed in three main parts. OPTIMIZATION OF SCOLIOSIS RADIOGRAPHY: In the first part, two recently developed methods for digital scoliosis radiography (digital exposure and pulse fluoroscopy) were evaluated and compared to the standard screen-film method. Radiation dose was measured as kerma area-product (KAP), entrance surface dose (ESD) and effective dose; image quality was assessed with a contrast-detail phantom and through visual grading analysis. Accuracy in angle measurements was also evaluated. The radiation dose for digital exposure was nearly twice as high as the screen-film method at a comparable image quality while the dose for pulsed fluoroscopy was very low but with a considerably lower image quality. The variability in angle measurements was sufficiently low for all methods. Then, the digital exposure protocol was optimized to a considerably lower dose with a slightly lower image quality compared to the baseline. FLAT-PANEL DETECTOR: In the second part, an amorphous-silicon direct digital flat-panel detector was evaluated using a contrast-detail phantom, measuring dose as entrance dose. The flat-panel detector yielded a superior image quality at a lower dose than both storage phosphor plates and screen-film. Equivalent image quality compared to storage phosphor plates was reached at about one-third of the dose. OPTIMIZATION OF PERCUTANEOUS CORONARY INTERVENTION (PCI): In the third part, influence of various settings on radiation dose and image quality in coronary catheterisation and PCI was investigated. Based on these findings, the dose rate for fluoroscopy was reduced to one-third. The dose reduction was evaluated in a clinical series of 154 PCI procedures before and 138 after the optimization. Through this optimization, the total KAP was significantly reduced to two-thirds of the original value. IN SUMMARY: This thesis indicates the possibility of dose reduction in diagnostic radiology through optimization of the radiographic process.

Coronary Angiography↗
PubMed2006

Magnetic resonance imaging image intensity correction with extrapolation and adaptive smoothing.

A significant problem in magnetic resonance imaging (MRI) is the inhomogeneity of the image resulting from a number of factors that are hardware related. The obtained image can be treated as the true image multiplied by a signal modulator, which is usually smooth across the image. A class of MR image intensity correction methods extracts the slowly varying component from the image with low-pass filtering or smoothing to approximate the signal modulator. This usually causes the edge enhancement artifact in the corrected image. A novel method of extrapolating the image in advance is proposed to reduce this effect significantly. Closest point algorithm is implemented to minimize the calculation time for extrapolation. To remove bright spots caused by nonuniform sensitivity profiles, a gradient-weighted smoothing method is discussed in this work. The partial differential equations based model is applied for locally adaptive smoothing. The filtered gradient of the corrupted image is used as the weight for smoothing. Phantom and clinical data collected on various MRI systems are used for evaluation of our method. These experimental results show that the proposed method solves the edge enhancement and bright spots problem effectively and robustly.

Algorithms↗