Texture-based and diffusion-weighted discrimination of parotid gland lesions on MR images at 3.0 Tesla.

The purpose of this study was to evaluate whether texture-based analysis of standard MRI sequences and diffusion-weighted imaging can help in the discrimination of parotid gland masses. The MR images of 38 patients with a biopsy- or surgery-proven parotid gland mass were retrospectively analyzed. All patients were examined on the same 3.0 Tesla MR unit, with one standard protocol. The ADC (apparent diffusion coefficient) values of the tumors were measured with three regions of interest (ROIs) covering the entire tumor. Texture-based analysis was performed with the texture analysis software MaZda (version 4.7), with ROI measurements covering the entire tumor in three slices. COC (co-occurrence matrix), RUN (run-length matrix), GRA (gradient), ARM (auto-regressive model), and WAV (wavelet transform) features were calculated for all ROIs. Three subsets of 10 texture features each were used for a linear discriminant analysis (LDA) in combination with k nearest neighbor classification (k-NN). Using histology as a standard of reference, benign tumors, including subtypes, and malignant tumors were compared with regard to ADC and texture-based values, with a one-way analysis of variance with post-hoc t-tests. Significant differences were found in the mean ADC values between Warthin tumors and pleomorphic adenomas, as well as between Warthin tumors and benign lesions. Contrast-enhanced T1-weighted images contained the most relevant textural information for the discrimination between benign and malignant parotid masses, and also for the discrimination between pleomorphic adenomas and Warthin tumors. STIR images contained the least relevant texture features, particularly for the discrimination between pleomorphic adenomas and Warthin tumors. Texture analysis proved to differentiate benign from malignant lesions, as well as pleomorphic adenomas from Warthin tumors, based on standard T(1w) sequences (without and with contrast). Of all benign parotid masses, Warthin tumors had significantly lower ADC values than the other entities.

Time-efficient CT colonography interpretation using an advanced image-gallery-based, computer-aided "first-reader" workflow for the detection of colorectal adenomas.

OBJECTIVES: To assess the performance of an advanced "first-reader" workflow for computer-aided detection (CAD) of colorectal adenomas ≥ 6 mm at computed tomographic colonography (CTC) in a low-prevalence cohort. METHODS: A total of 616 colonoscopy-validated CTC patient-datasets were retrospectively reviewed by a radiologist using a "first-reader" CAD workflow. CAD detections were presented as galleries of six automatically generated two-dimensional (2D) and three-dimensional (3D) images together with interactive 3D target views and 2D multiplanar views of the complete dataset. Each patient-dataset was interpreted by initially using CAD image-galleries followed by a fast 2D review to address unprompted colonic areas. Per-patient, per-polyp, and per-adenoma sensitivities were calculated for lesions ≥ 6 mm. Statistical testing employed Fisher's exact and McNemar tests. RESULTS: In 91/616 patients, 131 polyps (92 adenomas, 39 non-adenomas) ≥ 6 mm and two cancers were identified by reference standard. Using the CAD gallery-based first-reader workflow, the radiologist detected all adenomas ≥ 10 mm (34/34) and cancers. Per-patient and polyp sensitivities for lesions ≥ 6 mm were 84.3 % (75/89), and 83.2 % (109/131), respectively, with 89.1 % (57/64) and 85.9 % (79/92) for adenomas. Overall specificity was 95.6 % (504/527). Mean interpretation time was 3.1 min per patient. CONCLUSIONS: A CAD algorithm, applied in an image-gallery-based first-reader workflow, can substantially decrease reading times while enabling accurate detection of colorectal adenomas in a low-prevalence population. KEY POINTS: Computer-aided detection (CAD) is increasingly used to help interpret CT colonography (CTC). An image-gallery first-reader CAD-workflow is feasible for detection of colorectal adenomas ≥ 6 mm. Image-gallery first-reader CAD yields per-patient sensitivity of 89.1 % and specificity of 95.6 %. The mean reading time for CTC was 3.1 min, making screening feasible. No large adenoma was missed by the radiologist who reviewed with CAD galleries.

Diffusion tensor MR imaging (DTI) metrics in the cervical spinal cord in asymptomatic HIV-positive patients.

INTRODUCTION: This study was conducted to compare diffusion tensor MR imaging (DTI) metrics of the cervical spinal cord in asymptomatic human immunodeficiency virus (HIV)-positive patients with those measured in healthy volunteers, and to assess whether DTI is a valuable diagnostic tool in the early detection of HIV-associated myelopathy (HIVM). METHODS: MR imaging of the cervical spinal cord was performed in 20 asymptomatic HIV-positive patients and in 20 healthy volunteers on a 3-T MR scanner. Average fractional anisotropy (FA), mean diffusivity (MD), and major (E1) and minor (E2, E3) eigenvalues were calculated within regions of interest (ROIs) at the C2/3 level (central and bilateral anterior, lateral and posterior white matter). RESULTS: Statistical analysis showed significant differences with regard to mean E3 values between patients and controls (p = 0.045; mixed-model analysis of variance (ANOVA) test). Mean FA was lower, and mean MD, mean E1, and mean E2 were higher in each measured ROI in patients compared to controls, but these differences were not statistically significant. CONCLUSION: Asymptomatic HIV-positive patients demonstrate only subtle changes in DTI metrics measured in the cervical spinal cord compared to healthy volunteers that currently do not support using DTI as a diagnostic tool for the early detection of HIVM.

Posterior reversible encephalopathy syndrome: do predisposing risk factors make a difference in MRI appearance?

INTRODUCTION: Posterior reversible encephalopathy syndrome (PRES) is a clinico-neuroradiological entity, characterized by typical neurological deficits, distinctive magnetic resonance imaging (MRI) features, and a usually benign clinical course. Although frequently seen in association with hypertensive conditions, many other predisposing factors, notably cytotoxic and immunosuppressant drugs have been associated with PRES. The aim of this study was to determine differences in the MR appearance of PRES according to various risk factors. METHODS: Thirty consecutive patients with clinical and MRI findings consistent with PRES were included. We identified 24 patients with hypertension-related conditions, including 14 patients with preeclampsia-eclampsia, and six patients without hypertension, in whom PRES was associated with exposition to neurotoxic substances. Lesion distribution, extent of disease, and number of affected brain regions were compared between patients with PRES with and without hypertension, and patients with PRES with and without preeclampsia-eclampsia, respectively. RESULTS: No statistically significant differences in distribution of lesions and extent of disease were observed between patients with PRES with or without hypertension, and patients with or without preeclampsia-eclampsia, respectively. The number of affected brain regions was significantly higher in patients with preeclampsia-eclampsia (p = 0.046), and the basal ganglia region was more frequently involved in these patients (p = 0.066). CONCLUSION: Apart from a significant higher number of involved brain regions and a tendency for basal ganglia involvement in patients with PRES associated with preeclampsia-eclampsia, the MRI appearance of patients with PRES does not seem to be influenced by predisposing risk factors.

What every radiologist should know about idiopathic interstitial pneumonias.

The American Thoracic Society-European Respiratory Society classification of idiopathic interstitial pneumonias (IIPs), published in 2002, defines the morphologic patterns on which clinical-radiologic-pathologic diagnosis of IIPs is based. IIPs include seven entities: idiopathic pulmonary fibrosis, which is characterized by the morphologic pattern of usual interstitial pneumonia (UIP); nonspecific interstitial pneumonia (NSIP); cryptogenic organizing pneumonia (COP); respiratory bronchiolitis-associated interstitial lung disease (RB-ILD); desquamative interstitial pneumonia (DIP); lymphoid interstitial pneumonia (LIP); and acute interstitial pneumonia (AIP). The characteristic computed tomographic findings in UIP are predominantly basal and peripheral reticular opacities with honeycombing and traction bronchiectasis. In NSIP, basal ground-glass opacities tend to predominate over reticular opacities, with traction bronchiectasis only in advanced disease. COP is characterized by patchy peripheral or peribronchovascular consolidation. RB-ILD and DIP are smoking-related diseases characterized by centrilobular nodules and ground-glass opacities. LIP is characterized by ground-glass opacities, often in combination with cystic lesions. AIP manifests as diffuse lung consolidation with ground-glass opacities, which usually progress to fibrosis in patients who survive the acute phase of the disease. Correct diagnosis of IIPs can be achieved only by means of interdisciplinary consensus and stringent correlation of clinical, imaging, and pathologic findings. (c) RSNA, 2007.

Pitfalls in multi-detector row CT colonography: a systematic approach.

Thin-section multi-detector row computed tomographic (CT) colonography is a powerful tool for the detection and classification of colonic lesions. However, each step in the process of a CT colonographic examination carries the potential for misdiagnosis. Suboptimal patient preparation, CT scanning protocol deficiencies, and perception and interpretation errors can lead to false-positive and false-negative findings, adversely affecting the diagnostic performance of CT colonography. These problems and pitfalls can be overcome with a variety of useful techniques and observations. A relatively clean, dry, and well-distended colon can be achieved with careful patient preparation, thereby avoiding the problem of residual stool and fluid. Knowledge of the morphologic and attenuation characteristics of common colonic lesions and artifacts can help identify bulbous haustral folds, impacted diverticula, an inverted appendiceal stump, or mobile polyps, any of which may pose problems for the radiologist. A combined two-dimensional and three-dimensional imaging approach is recommended for each colonic finding. A thorough knowledge of the various pitfalls and pseudolesions that may be encountered at CT colonography, along with use of dedicated problem-solving techniques, will help the radiologist differentiate between definite colonic lesions and pseudolesions.

Demyelinating and infectious diseases of the spinal cord.

Spinal cord diseases generally have distinctive clinical findings that reflect dysfunction of particular sensory or motor tracts. The abnormalities on MR images reflect the pathologic changes that occur in the affected pathways. The complexity and the wide spectrum of diseases affecting the spinal cord require a profound knowledge of neuropathology and exactly tuned imaging strategies. This article describes and illustrates the clinical and imaging characteristics in various demyelinating and infectious conditions of the spinal cord.

Radiation dose management in thoracic CT: an international survey.

PURPOSE: We aimed to examine current practice patterns of international thoracic radiologists regarding radiation dose management in adult thoracic computed tomography (CT) examinations. MATERIALS AND METHODS: An electronic questionnaire was sent to 800 members of five thoracic radiology societies in North America, Europe, Asia, and Latin America addressing radiation dose training and education, standard kVp and mAs settings for thoracic CT, dose reduction practices, clinical scenarios, and demographics. RESULTS: Of the 800 radiologists, 146 responded to our survey. Nearly half (66/146, 45% [95% confidence interval, 37%-53%]) had no formal training in dose reduction, with "self-study of the literature" being the most common form of training (54/146, 37% [29%-45%]). One hundred and seventeen (80% [74%-87%]) had automatic exposure control, and 76 (65% [56%-74%]) used it in all patients. Notably, most respondents (89% [84%-94%]) used a 120 to 125 kVp standard setting, whereas none used 140 kVp. The most common average dose-length-product (DLP) value was 150 to 249 mGy.cm (75/146, 51% [43%-59%]), and 59% (51%-67%) delivered less than 250 mGy.cm in a 70 kg patient. There was a tendency towards higher DLP values with multidetector-row CT. Age, gender, and pregnancy were associated more with dose reduction than weight and clinical indication. CONCLUSION: Efforts for reducing patient radiation dose are highly prevalent among thoracic radiologists. Areas for improvement include reduction of default tube current settings, reduction of anatomical scan coverage, greater use of automatic exposure control, and eventually, reduction of current reference dose values. Our study emphasizes the need for international guidelines to foster greater conformity in dose reduction by thoracic radiologists.

Puumala virus infection: radiologic findings.

A 33-year-old male patient was admitted to our nephrology department with rapidly deteriorating general health, fever, respiratory difficulties, and acute renal failure. Computed tomography of the thorax revealed interstitial edema with thickening of the interlobular septa, peribronchial cuffing, ground-glass opacities, and small pleural and pericardial effusions. Polymerase chain reaction tests verified Puumala virus infection. The patient recovered with supportive treatment. Hantavirus infection should be considered in the differential diagnosis of young patients who present with acute renal failure of an unknown origin and the nonspecific radiologic finding of noncardiogenic interstitial edema, which in combination with typical clinical symptoms and laboratory parameters, can be indicative of this disease.

Diagnostic imaging in Merkel cell carcinoma: lessons to learn from 16 cases with correlation of sonography, CT, MRI and PET.

OBJECTIVE: The authors report imaging findings in a series of 16 patients with MCC, a rare tumour which is often managed primarily by a dermatologist. To our knowledge, no equivalent series of MCC has been described in the nuclear medicine literature. MATERIAL AND METHODS: In this IRB-approved retrospective noncomparative case series 16 patients with biopsy-proven Merkel cell carcinoma were included between January 1999 and October 2007. Twenty-nine whole body PET scans (18F-FDG n=24, 18F-FDOPA n=5) in 16 patients were retrospectively reviewed with regard to tracer uptake in six anatomical sites per patient. For 127/144 of FDG-PET evaluated regions and 68/144 of regions depicted by conventional imaging methods, a valid standard of reference could be obtained. A combined standard of reference was applied, which consisted of histopathology (lymphadenectomy or biopsy) or clinical or radiological follow-up for at least 12 months. RESULTS: the mean FDG uptake over the clinicopatholigical verified FDG avid areas was 4.7 SUV (1.5-9.9 SUV). The region based assessment of diagnostic value, in consideration of the standard of reference, resulted in a sensitivity of 85.7% and a specificity of 96.2% of FDG-PET (n=127) and in a combined sensitivity of 95.5% and a specificity of 89.1% for morphological imaging methods (n=68). Differences between methods did not reach statistical significance (p=1.00, p=0.18). CONCLUSIONS: FDG-PET is a highly useful whole body staging method of comparable value compared to conventional imaging methods with restricted field of view. The lessons learned from case series are discussed.

Comparison of axial, coronal, and primary 3D review in MDCT colonography for the detection of small polyps: a phantom study.

PURPOSE: The purpose of this phantom study is to compare the influence of the reading technique (axial images alone in comparison to 3D endoluminal, coronal, and combined 2D/3D review methods) on the sensitivity and inter-reader variability with MDCT colonography for the detection of small colonic polyps. METHODS: An anthropomorphic pig colon phantom with 75 randomly distributed simulated small polyps of 2-8mm size, was distended with air and scanned in a water phantom using multidetector-row CT with 4mm x 1mm collimation. Three radiologists rated the presence of polyps on a five-point scale. Performance with axial sections alone was compared to the performance with coronal sections, virtual endoscopy (VE), and a combined 2D/3D approach. We calculated sensitivities for polyp detection and used ROC analysis for data evaluation. RESULTS: There was no significant difference between the mean area under the curve (A(z)) for axial images and VE (A(z)=0.934 versus 0.932), whereas coronal images were significantly inferior (A(z)=0.876) to both. The combined 2D/3D approach yielded the best results, with an A(z) of 0.99. Differences in sensitivity between individual readers were significant in axial images (sensitivity, 75-93%, p=0.001) and coronal images (sensitivity, 69-80%, p=0.028), but became non-significant with VE (83-88%, p=0.144) and the combined 2D/3D approach (95-97%, p=0.288). CONCLUSION: Evaluation of axial sections alone leads to significant differences in detection rates between individual observers. A combined 2D/3D evaluation improves sensitivities for polyp detection and reduces inter-individual differences to an insignificant level.

Fungal versus bacterial brain abscesses: is diffusion-weighted MR imaging a useful tool in the differential diagnosis?

INTRODUCTION: The aim of this study was to investigate the appearance of fungal brain abscesses on diffusion-weighted (DW) images, and to evaluate whether the imaging characteristics and apparent diffusion coefficient (ADC) values associated with fungal abscesses were distinct from those of bacterial abscesses. METHODS: We retrospectively reviewed the MR images from nine patients with fungal brain infections, and 17 patients with pyogenic brain abscesses. All patients underwent conventional MR sequences and DW imaging on 1.5-T clinical MR scanners. ADC values of 20 fungal and 20 bacterial brain abscesses were calculated and compared using a random factor analysis of variance. RESULTS: Multiple lesions were present in 6 of 9 patients (67%) with fungal abscesses and in 5 of 17 patients (29%) with bacterial abscesses. On DW images, all but one bacterial brain abscess showed a homogeneous high signal, whereas the appearance of fungal abscesses on DW images was more variable: in five of nine patients with fungal abscesses, the lesions were homogeneously hyperintense, while in the remaining four patients, the lesions were of mixed signal intensity. Mean ADC values were 0.74 x 10(-3) mm(2)/s in the fungal group and 0.486 x 10(-3) mm(2)/s in the bacterial group (P< or =0.05). CONCLUSION: Our results indicate that there is a trend towards higher ADC values in fungal lesions. Additional findings that support fungal rather than bacterial cerebral infection are multiplicity, signal heterogeneity on T2-weighted and DW imaging, and involvement of deep grey-matter nuclei.

Diffusion-weighted MR imaging (DWI) in the evaluation of epidural spinal lesions.

INTRODUCTION: Epidural spinal cord compression is one of the most critical emergency conditions requiring medical attention and requires prompt and adequate treatment. The aim of our study was to assess the role of diffusion-weighted magnetic resonance (MR) imaging (DWI) in the diagnosis and differentiation of epidural spinal lesions. METHODS: Three patients with epidural lymphoma, two with sarcoma and three with epidural metastatic disease were imaged on a 1.5T MRI unit. DWI was performed using navigated, interleaved, multi-shot echo planar imaging (IEPI). Three region of interest (ROI)-measurements were obtained on corresponding apparent diffusion coefficient (ADC) maps, and the mean ADC value was used for further analysis. The cellularity of tumors was determined as the N/C ratio (nucleus/cytoplasma ratio) from histological samples. The ADC values and N/C ratios of lesions were compared using a Kruskal-Wallis test. RESULTS: The mean ADC of the lymphomas was 0.66 x 10(-3) mm2/s, that of the sarcomas was 0.85 x 10(-3) mm2/s and the ADC of the metastatic lesions was 1.05 x 10(-3) mm2/s; however, the differences were not statistically significant. Mean N/C ratios in the lymphoma, sarcomas and metastases were 4:1, 2:1, and 2.6:1, respectively, with a statistically significant difference between the groups (p < 0.025). CONCLUSION: Although not statistically significant due to the small patient sample, our results clearly show a tendency toward decreased diffusivity in neoplastic lesions with higher cellularity. The data from our study suggest that DWI is a feasible and potentially useful technique for the evaluation of epidural lesions that cause spinal cord compression on a per-patient basis.