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N Papanikolaou

Publications and source records attributed to N Papanikolaou.

At least 19 recordsLinked to original sources
PubMed2006

Dark lumen MR colonography: can high spatial resolution VIBE imaging improve the detection of colorectal masses?

PURPOSE: To assess whether the detection of colorectal lesions can be improved using high spatial resolution VIBE imaging. MATERIALS AND METHODS: 48 patients underwent same-day dark lumen MR colonography (MRC) and conventional colonoscopy (CC) as the standard for the detection of colorectal masses. MRC was performed using contrast-enhanced standard and high spatial resolution T1-weighted 3D VIBE sequences. The findings and the image quality of the standard and high spatial resolution VIBE sequences were compared qualitatively and quantitatively. The findings of both sequences regarding colorectal lesions were compared to those of a subsequently performed colonoscopy. RESULTS: The high spatial resolution VIBE sequence significantly improved the quantitative image quality (CNR 54.0 vs. 36.8). However, high spatial resolution VIBE imaging did not detect more colorectal lesions than the standard VIBE sequence. In addition, none of the sequences employed was able to detect lesions with a diameter of less than 5 mm (CC 40 lesions). However, 13 colorectal lesions with a diameter of greater than 5 mm were detected by both sequences (CC 15). CONCLUSION: High spatial resolution VIBE imaging did not improve the detection of colorectal masses and MRC fails to detect colorectal lesions with a diameter of less than 5 mm.

Adult↗
PubMed2006

Experimental determination of the effect of detector size on profile measurements in narrow photon beams.

The aim of this work is to investigate experimentally the detector size effect on narrow beam profile measurements. Polymer gel and magnetic resonance imaging dosimetry was used for this purpose. Profile measurements (Pm(s)) of a 5 mm diameter 6 MV stereotactic beam were performed using polymer gels. Eight measurements of the profile of this narrow beam were performed using correspondingly eight different detector sizes. This was achieved using high spatial resolution (0.25 mm) two-dimensional measurements and eight different signal integration volumes A X A X slice thickness, simulating detectors of different size. "A" ranged from 0.25 to 7.5 mm, representing the detector size. The gel-derived profiles exhibited increased penumbra width with increasing detector size, for sizes >0.5 mm. By extrapolating the gel-derived profiles to zero detector size, the true profile (Pt) of the studied beam was derived. The same polymer gel data were also used to simulate a small-volume ion chamber profile measurement of the same beam, in terms of volume averaging. The comparison between these results and actual corresponding small-volume chamber profile measurements performed in this study, reveal that the penumbra broadening caused by both volume averaging and electron transport alterations (present in actual ion chamber profile measurements) is a lot more intense than that resulted by volume averaging effects alone (present in gel-derived profiles simulating ion chamber profile measurements). Therefore, not only the detector size, but also its composition and tissue equivalency is proved to be an important factor for correct narrow beam profile measurements. Additionally, the convolution kernels related to each detector size and to the air ion chamber were calculated using the corresponding profile measurements (Pm(s)), the gel-derived true profile (Pt), and convolution theory. The response kernels of any desired detector can be derived, allowing the elimination of the errors associated with narrow beam profile measurements.

Fourier Analysis↗
PubMed2005

Monte Carlo simulations of ferromagnetism in p-Cd1-xMnxTe quantum wells.

Monte Carlo simulations, in which the Schrödinger equation is solved at each Monte Carlo sweep, are employed to assess the influence of magnetization fluctuations, short-range antiferromagnetic interactions, disorder, magnetic polaron formation, and spin-Peierls instability on the carrier-mediated Ising ferromagnetism in two-dimensional electronic systems. The determined critical temperature and hysteresis are affected in a nontrivial way by the antiferromagnetic interactions. The findings explain striking experimental results for modulation-doped p-Cd1-xMnxTe quantum wells.

Journal Article↗
PubMed2005

Bipolar electrocoagulation vs conventional monopolar hot biopsy forceps in the endoscopic treatment of diminutive rectal adenomas.

OBJECTIVE: To assess whether a cold biopsy from a diminutive rectal adenoma followed by destruction with bipolar (gold probe) electrocoagulation using large probes and high power setting would be a safe and efficient alternative to conventional monopolar hot biopsy forceps (MHBF). PATIENTS AND METHODS: Eligible patients were those undergoing colonoscopy, fulfilling the criteria of additional clearing colonoscopy and having at least one suspected rectal adenoma < or = 5 mm. At the time of endoscopy patients were randomized to receive treatment for their diminutive rectal adenomas either with cold biopsy followed by repeated gold probe electrocoagulation (Group A) using a 10 Fr catheter with setting 8 (40 W) for 1 second or with MHBF (Group B). These patients were followed up with a colonoscopy at 2-4 months. RESULTS: A total number of 24 (15 males, 9 females; mean age 56 years) patients were included in group A and 26 (14 males, 12 females; mean age 58 years) in group B. A total number of 38 and 37 diminutive rectal adenomas was detected in patients of Group A and Group B, respectively. At follow up colonoscopy residual adenoma tissue was found in 2 (5.2%) adenomas of 38 in Group A and in 4 (10.8%) of 37 in Group B (P > 0.3). No complications related to colonoscopy or endoscopic treatments in both groups occurred. CONCLUSIONS: Our data suggest that the use of cold biopsy followed by bipolar electrocoagulation using large probes and high power setting for destroying diminutive rectal adenoma seems to be equally effective and safe as MHBF.

Adenoma↗
PubMed2004

Real time high resolution magnetic resonance imaging for the assessment of gastric motility disorders.

BACKGROUND: The aim of this study was to evaluate whether patients with increased or decreased gastric motility can be differentiated from healthy volunteers by means of real time magnetic resonance imaging (MRI). PATIENTS AND METHODS: Ten healthy volunteers, 10 patients with gastroparesis, and 10 patients with functional pylorospasm/peptic pyloric stenosis underwent real time MRI. All patients were examined on two separate days; once prior to therapy and once after adequate therapy. Antral motility was quantified by calculating the gastric motility index. RESULTS: Patients with gastroparesis showed a lower motility index compared with the reference volunteer group while the mean motility index of the patient group with pylorospasm was more than three times higher than that of the reference value of the volunteer group. However, the gastric motility index in the patient group with gastroparesis increased, and in the group with functional pylorospasm/peptic pyloric stenosis it decreased significantly after therapy. CONCLUSION: Real time MRI is a reliable tool for assessment of gastric motion. Furthermore, differences in gastric motility index in patients with increased or decreased gastric motility could be evaluated and quantified. Due to the non-invasive character of MRI, this imaging modality may be an attractive alternative to conventional invasive diagnostic tools for gastric motility disorders and therapeutic monitoring.

Adult↗
PubMed2003

[Magnetosomes as biological model for iron binding: relaxivity determination with MRI].

PURPOSE: In vitro characterization of iron-containing bacterial particles (magnetosomes) as superparamagnetic contrast agents for MRI. MATERIAL AND METHODS: Different concentrations of magnetosomes were examined with a 1.5 T clinical whole-body MR system at 21 degrees C using the transit/receive extremity coil. Both longitudinal and transversal relaxivities (R1 and R2) of the magnetosomes were determined by an inversion recovery snapshot gradient recall echo (IR FLASH) with various inversion times and a multi echo spin echo sequence. Atomic absorption spectrometry (AAS) and electron microscopy were used as reference standard. RESULTS: Longitudinal and transverse relaxivities of the magnetosomes were calculated to be R1 = 7.688 mmol -1 s -1 and R2 = 147.67 mmol -1 s -1, respectively. The corresponding iron concentrations were determined in all dilutions using AAS, while the magnetosomes were morphologically delineated by electron microscopy. CONCLUSION: Magnetosomes represent a new and interesting class of iron-containing contrast agents warranting further evaluation in cellular cultures and animal models. Magnetosomes may be suited for displaying the vector distribution and gene expression of new molecular therapies.

Contrast Media↗
PubMed2003

Detection of malignant bone marrow involvement with dynamic contrast-enhanced magnetic resonance imaging.

BACKGROUND: The purpose of this study was to evaluate the role of dynamic contrast-enhanced magnetic resonance imaging (dMRI) in detecting bone marrow involvement in cancer patients. PATIENTS AND METHODS: We studied 50 consecutive patients with histologically confirmed malignant dissemination to the bone marrow, using dMRI of the lumbosacral spine. Time-signal intensity curves were generated from regions of interest (ROIs) obtained from areas of obvious bone marrow disease (group B). In 16 patients from group B with focal disease, ROIs were also placed on areas with apparently normal bone marrow on static magnetic resonance images (group C). Twenty-two patients with no history of malignancy were used as a control group (group A). Wash-in (WIN) and wash-out (WOUT) rates, time to peak (TTPK), time to maximum slope (TMSP) values and WIN/TMSP ratios were calculated for each patient. Mean values for the three groups were compared statistically. Six patients from group B had follow-up dMRI after chemotherapy: four patients achieved a clinical partial response and two had resistant disease. RESULTS: A significant difference was found between groups A and B for all values. Between groups A and C, in spite of the similar static MRI appearance, all values were significantly different. Between groups B and C, a significant difference was found for WIN, WOUT rates and WIN/TMSP ratio. Follow-up dMRI data analysis correlated well with clinical staging. CONCLUSIONS: dMRI can distinguish normal from malignant bone marrow. It may identify malignant bone marrow infiltration in patients with negative static MRI and serve as both a diagnostic and prognostic tool for patients with bone marrow malignancies.

Adult↗
PubMed2002

Development of contrast-enhanced virtual MR cholangioscopy: a feasibility study.

The purpose of this study was to examine the feasibility of contrast-enhanced virtual MR cholangioscopy (CE VMRC). Intraluminal views of the extrahepatic biliary tree were generated in ten patients undergoing abdominal MRI post mangafodipir trisodium administration employing coronal 2.5-mm 3D fast low-angle shot (FLASH) images (TR 6.8 ms, TE 2.3 ms, matrix 195 x 512) with fat saturation and a commercially available software. Contrast-enhanced VMRC was compared with single-shot turbo spin-echo T2-weighted MR cholangiography (T2 MRC) in terms of ductal visualization and artifact presence, utilizing a five-point grading scale. Four anatomic segments were evaluated: the intra- and extra-pancreatic segment of the common bile duct (CBD), and the cystic duct and the area of hepatic duct bifurcation. Both CE VMRC and T2 MRC depicted 38 of 40 segments. There were no significant differences between CE VMRC and T2 MRC in ranking ductal segments visualization ( p=0.27). The high contrast between intraluminal fluid and extraluminal tissues facilitated the generation of endoscopic views. Contrast-enhanced virtual MR cholangioscopy is a feasible technique providing endoscopic views of the CBD. Initial results show correlation of CE VMRC with projectional MR cholangiography.

Bile Ducts↗
PubMed2002

Biexponential T2 relaxation time analysis of the brain: correlation with magnetization transfer ratio.

RATIONALE AND OBJECTIVES: To measure T2 relaxation times of normal white and gray matter using a novel CPMG sequence and investigate if any correlation exists between magnetization transfer ratio (MTR) and T2 relaxation-related parameters. MATERIALS AND METHODS: Seventeen normal volunteers participated on this study. A single-slice 32-echo sequence was used to calculate the T2 relaxation time of frontal and occipital white matter and cortical gray matter. T2 relaxation analysis included monoexponential and biexponential fitting whereas an F test was used to determine if biexponential fitting was statistically more accurate than monoexponential fitting. Short and long T2 constants were calculated as well as the signal fractions of each pool. MTR calculations were based on a three-dimensional gradient echo (3D FFE) proton density weighted sequence with and without an on-resonance composite prepulse. MTR and T2 relaxation times were calculated and linear regression analysis was applied. RESULTS: Biexponential fitting was more accurate comparing with monoexponential fitting in all WM and GM regions (F > 2.47, P < 0.01). Mean values of short T2 constant for frontal white matter (fWM), occipital white matter (oWM) and gray matter (GM) were 8.10, 9.36, and 22.23 milliseconds, respectively, whereas the mean values of long T2 constant were 85.1, 93.02, and 118.72 milliseconds, respectively. Mean restricted water percentages (RWP)-corresponding to the signal fraction of the protons with short T2-for the fWM, oWM, and GM were 22.01%, 23.36%, and 18.7%. Mean free water percentages (FWP)-corresponding to the signal fraction of the protons with long T2-for the fWM, oWM and GM were 77.99%, 76.64%, and 81.3%. Mean MTR values for fWM, oWM and GM were 68.4%, 68.2%, and 61.3%, respectively. No significant correlation was found in fWM and oWM between MTR and RWP, short and long T2 components while a moderate correlation existed in GM between MTR and RWP (r = 0.57; P = 0.02), MTR and short T2 component (r = -0.69; P = 0.004) and MTR and long T2 component (r = -0.62; P = 0.012). CONCLUSIONS: Two proton pools with different T2 decay characteristics can be separated in normal gray and white matter when using a multiecho sequence with short echo spacing. MTR and T2 relaxation times were significantly correlated in gray matter and the combination of both types of measurements may be helpful in studying myelin related disorders.

Adult↗
PubMed2001

Increased signal intensity on fat-suppressed three-dimensional T1-weighted pulse sequences in patellar tendon: magic angle effect?

OBJECTIVE: To assess the frequency of increased signal intensity in the patellar tendon using three-dimensional T1-weighted MRI pulse sequences. DESIGN AND PATIENTS: Sixty patients were examined with a 1.0 T scanner (15 mT/m gradient strength) using a quadrature coil. Three pulse sequences were applied in the sagittal plane: PD turbo spin echo (PD-TSE), 3D T1-weighted gradient echo with fat suppression (3D-T1-FFE-FS) and 3D T1-weighted echo planar imaging with fat suppression (3D-T1-EPI-FS). The high signal intensity areas were measured in their maximum length. The angle of the patellar tendon relative to the main field position was measured in the same slice. In eight patients with anterior knee pain, and in 11 with no anterior knee pain, a fourth T2-weighted TSE pulse sequence (T2-TSE) was obtained to rule out patellar tendinitis. RESULTS: The correlation of the high signal intensity areas with the relative position of the tendon was found to be significant with the 3D sequences (P = 0.03 for 3D-T1-FFE-FS and P = 0.003 for 3D-T1-EPI-FS). The length of the high signal intensity area in the tendon was 5.4 mm with 3D-T1-FFE-FS, 4.9 mm with 3D-T1-EPI-FS and 3.1 mm with PD-TSE images. No patellar tendinitis was demonstrated on the T2-TSE images. CONCLUSION: The magic angle effect is commonly observed in the 3D based T1-weighted pulse sequences with fat suppression. The presence of the above sign must be recognized by radiologists, so that misdiagnosis of patellar tendinitis is avoided.

Adolescent↗
PubMed2001

MR enteroclysis protocol optimization: comparison between 3D FLASH with fat saturation after intravenous gadolinium injection and true FISP sequences.

The aim of this study was to introduce the true fast imaging with steady-state precession (FISP) sequence for MR enteroclysis and compare it with the already used T1-weighted fast low-angle shot (FLASH) sequence. Twenty-one patients underwent both MR and conventional enteroclysis. The MR enteroclysis examination was performed after administration of an iso-osmotic water solution through a nasojejunal catheter and the following sequences were included: (a) true FISP; and (b) 3D FLASH with fat saturation after intravenous injection of 20 mg Buscopan or 1 mg glucagon and 0.1 mmol/kg gadolinium chelates. The true FISP sequence provided images with significantly fewer motion artifacts, whereas 3D FLASH was less sensitive to susceptibility and chemical shift artifacts. The homogeneity of endoluminal opacification, wall conspicuity, and distention of the small bowel were very good to excellent and the two sequences presented no statistically significant differences here. True FISP provided significantly better overall image quality than did 3D FLASH. The true FISP sequence can provide good anatomic demonstration of the small bowel on T2-like images and could be combined with T1-weighted FLASH images for an integrated protocol of MR enteroclysis.

Adolescent↗
PubMed2001

Prevalence of polyps and diverticulosis of the large bowel in the Cretan population. An autopsy study.

While a number of studies have been performed in the United States, northern Europe, and some other countries on the epidemiology of large bowel polyps and diverticulosis, information from southern Europe and especially Greece is very limited. Our autopsy study sought to determine the prevalence of large bowel polyps and diverticulosis in the population on Crete. Specimens of colon and rectum were obtained during forensic postmortem autopsies and examined for the presence of polypoid lesions and diverticulosis. Data were collected from a total of 502 autopsies (320 men, 182 women; median age 65 years (range 16-93). Polyps were found in 106 cases (21.1%). These were adenomas in 73 cases (14.5%), hyperplastic polyps in 25 (4.9%), and mucosal tags in 8 (1.5%). Diverticulosis of the large bowel was found in 115 (22.9%). The prevalence of adenomas and diverticulosis increased with advanced age. The prevalence of colonic diverticulosis in Crete is slightly lower than that which has been reported in most other studies in economically developed countries. The prevalence of colorectal adenomas in Crete is one of the lowest rates reported in Europe and is compatible to the known low incidence of colorectal cancer in Crete.

Adenoma↗
PubMed2001

Contrast-enhanced magnetic resonance cholangiography versus heavily T2-weighted magnetic resonance cholangiography.

RATIONALE AND OBJECTIVES: To investigate the feasibility of contrast-enhanced magnetic resonance cholangiography (CE-MRC) and compare it with single-shot turbo spin-echo magnetic resonance cholangiography (SSTSE-MRC). METHODS: Fifteen patients with suspected metastatic liver disease (n = 10) or biliary tree abnormalities (n = 5) underwent a magnetic resonance imaging (1.5-T system) examination before and after mangafodipir administration. Contrast-enhanced MRC with a three-dimensional fast low-angle shot sequence after mangafodipir trisodium administration was compared with SSTSE-MRC. Four anatomic segments were evaluated: the intrapancreatic and extrapancreatic common bile duct segments, the cystic duct, and the area of hepatic bifurcation. Contrast-enhanced MRC and SSTSE-MRC were separately analyzed on a 5-point grading scale in terms of ductal segment visualization and lumen narrowing or dilatation. RESULTS: There was no difference (P = 0.375) in segment visualization between CE-MRC and SSTSE-MRC; 56 of the 60 segments were visualized by both techniques. In the evaluation of ductal narrowing or dilatation, nonsignificant differences (P = 0.500) were observed. Contrast-enhanced MRC was not influenced by fluid superimposition and provided additional information from background tissues. CONCLUSIONS: Contract-enhanced MRC is a feasible technique showing anatomic correlation with SSTSE-MRC, and it can in addition provide functional information. Contrast-enhanced MRC may be used in selected patients when traditional SSTSE-MRC is inconclusive.

Bile Ducts↗
PubMed2001

MR enteroclysis imaging of Crohn disease.

Magnetic resonance (MR) enteroclysis imaging is emerging as a technique for evaluation of the small bowel in patients with Crohn disease. Administration of 1.5-2 L of isosmotic water solution through a nasojejunal catheter ensures distention of the bowel and facilitates identification of wall abnormalities. True fast imaging with steady-state precession (FISP), half-Fourier acquisition single-shot turbo spin-echo (HASTE), and postgadolinium T1-weighted three-dimensional fast low-angle shot sequences can be employed in a comprehensive and integrated MR enteroclysis examination protocol to overcome specific disadvantages of each of the sequences involved. Superficial abnormalities that are ideally delineated with conventional enteroclysis are not consistently depicted with MR enteroclysis. The characteristic transmural abnormalities of Crohn disease such as bowel wall thickening, linear ulcers, and cobblestoning are accurately shown with MR enteroclysis imaging, especially with the true FISP sequence. MR enteroclysis is comparable to conventional enteroclysis in the detection of the number and extent of involved small bowel segments and in the disclosure of luminal narrowing or prestenotic intestinal dilatation. The clinical utility of MR enteroclysis in Crohn disease has not been fully established. At present, the method may be used for follow-up studies of known disease, estimation of disease activity, and determination of the extramucosal extent and spread of the disease process.

Artifacts↗
PubMed2001

Neutropenia induced by paraquat poisoning.

Paraquat is a synthetic, nonselective, contact herbicide, which causes injury to tissues following contact. When ingested in sufficient amounts, paraquat has life-threatening effects on the gastrointestinal tract, lungs, kidney, liver, heart and other organs. This is a case report of a 15-year-old girl from an agricultural area who was admitted to hospital for treatment. She presented with discomfort, nausea and vomiting. She had drunk a small wine glass full of paraquat. After 18 days in the hospital, the girl developed neutropenia. This is the first reported case of paraquat poisoning-induced neutropenia.

Adolescent↗
PubMed2000

Complex band structure and tunneling through ferromagnet /Insulator /Ferromagnet junctions

We investigate the importance of metal-induced gap states for the tunneling of metal electrons through epitaxial insulator films. By introducing an imaginary part kappa to the wave vector in order to describe the decay of the wave function in the insulator, we obtain the complex band structure in the gap region. The spectrum of the decay parameters kappa is calculated for the semiconductors Si, Ge, GaAs, and ZnSe. In most cases, for large enough film thicknesses the tunneling is dominated by states of normal incidence on the interface. Possible exceptions are considered. Based on our conclusions, we discuss the spin-dependent tunneling in Fe/semiconductor/Fe (001) junctions.

Journal Article↗
PubMed2000

Blueberry juice used per os in upper abdominal MR imaging: composition and initial clinical data.

The aim of this study was to evaluate the use of a commercially available blueberry juice (BJ) both as a positive and negative oral contrast agent and to present the exact contents of paramagnetic ions. The concentration of Mn and Fe were determined in tinned myrtilles in syrup (atomic absorption). Nine healthy volunteers and 12 patients (age range 20-65 years) were examined using a 1-T MR scanner before and after per os administration of 430 ml of BJ. A qualitative analysis of signal alterations in the stomach, duodenum, and proximal small intestine was performed. In addition, a quantitative analysis was assessed in terms of signal-to-noise ratio calculation. The mean concentration (x +/- SD) of the ions found in the content of the three cans were 3.3 +/- 0.4 microg/g for iron and 20.6 +/- 2.6 microg/g for manganese. Based on the qualitative evaluation, signal alteration on T1-weighted images after administration of BJ was statistically significant in the stomach and duodenum, but not in the proximal small bowel. Signal alteration on T2-weighted images was not statistically significant in any part of the gastrointestinal tract. The quantitative analysis of the T1- and T2 shortening showed that BJ is efficient with only T1-weighted sequences, and this applied to the stomach, duodenum, and proximal small bowl. Blueberry juice can be used as an oral contrast agent in upper abdominal MR for T1-weighted imaging.

Administration, Oral↗