C. Nolte-Ernsting

Understanding multislice CT urography techniques: many roads lead to Rome

CT urography has emerged as a serious alternative to conventional urography by utilizing the advantages of modern multislice CT techniques for the visualization of the entire upper urinary tract. Several different examination techniques have been developed in multislice CT (MSCT) urography for improving the opacification and distension of the urinary tract. All efforts in performing MSCT urography have to compromise between the best possible image quality and a reasonably low radiation exposure. Initial low-dose examination protocols are already available. Operating modern MSCT urography properly is not difficult, but it presupposes basic knowledge on the variety of current MSCT urography techniques, including such issues as present-day indications, split-bolus injection, compression, saline infusion, low-dose diuretic administration, hybrid scanning, timing of the acquisition delay, examination protocols, postprocessing, image analysis, and radiation exposure. This article is not intended to provide guidelines of how to conduct MSCT urography, but everyone will be able to understand the functionality of several robust operating MSCT urography techniques, which helps making an individual selection for the clinical practice. In the near future, systematic studies are awaited evaluating the morphologic and diagnostic accuracy of MSCT urography regarding diverse urinary tract disorders.

In vivo magnetic resonance imaging of iron oxide-labeled, arterially-injected mesenchymal stem cells in kidneys of rats with acute ischemic kidney injury: detection and monitoring at 3T.

To evaluate MRI for a qualitative and quantitative in vivo tracking of intraaortal injected iron oxide–labeled mesenchymal stem cells (MSC) into rats with acute kidney injury (AKI).

Interventional MR imaging: percutaneous abdominal and skeletal biopsies and drainages of the abdomen

Abstract. Since the introduction of open magnets and short-bore closed magnets, and the availability of fast imaging sequences, MR imaging has become a tool for guidance and control of percutaneous nonvascular and vascular procedures. In general, percutaneous biopsies or drainages require no specific hardware or software modifications. For lesion localization and control of the needle track, simple fast imaging sequences such as fast T1-weighted gradient-echo techniques or fast single-shot T2-weighted spin-echo sequences are sufficient and can be applied depending on the best tissue-to-lesion contrast. Typical scan times range from 1 to 3 s. Different types of biopsy needles are commercially available, allowing sampling of sufficient amounts of tissue. For drainage procedures non-ferromagnetic materials, such as nitinol wires, should be preferred to minimize image distortion by metallic artifacts. Indications for percutaneous biopsies include subdiaphragmatic liver lesions, lesions poorly visible on ultrasound or contrast-enhanced computed tomography, and lesions of the bone marrow characterized by an unspecific bone marrow edema. For percutaneous drainages, subdiaphragmatic lesions appear to be a good indication. With some experience the procedure time is not longer than that under CT or US guidance.

Aneurysmal bone cyst: value of MR imaging and conventional radiography

Abstract. Our objective was to investigate the accuracy and the diagnostic value of different imaging features of primary aneurysmal bone cysts (ABC) in conventional radiographs and MRI. Conventional radiographs and MR images of 34 patients with a suspected aneurysmal bone cyst were reevaluated by six independent radiologists in a blinded fashion. Morphological features, MR signal characteristics, and contrast enhancement patterns were assessed. Diagnoses were correlated with histology. Sensitivity and specificity of the different imaging findings for each imaging technique were calculated. In 24 patients ABC was histologically proven. In 10 cases diagnoses other than ABC were established. Conventional radiography and MRI each demonstrated a sensitivity of 76.4 and 77.8% with a specificity of 55.0 and 66.7%, respectively. With combined use of both imaging modalities sensitivity and specificity increased to 82.6 and 70%, respectively. The ABC was significantly more often seen as circumscribed lesion with bone expansion, lobulation, septa, and pathological cortical bone reaction than those cases with different diagnoses. Septal contrast enhancement proved to be a useful MR imaging finding in suspected ABC. The combined use of conventional radiographs and MRI revealed the highest sensitivity in the diagnosis of ABC in relation to histology. Magnetic resonance imaging provides improved diagnostic specificity and valuable information on soft tissue changes.

Detection of small pulmonary nodules in high-field MR at 3 T: evaluation of different pulse sequences using porcine lung explants

To evaluate two MR imaging sequences for the detection of artificial pulmonary nodules inside porcine lung explants. 67 agarose nodules ranging 3–20xa0mm were injected into ten porcine lungs within a dedicated chest phantom. The signal on T1-weighted images and radiopacity were adjusted by adding 0.125xa0mmol/l Gd-DTPA and 1.5xa0g/l of iodine. A T1-weighted three-dimensional gradient-echo (T1-3D-GRE; TR/TE:3.3/1.1xa0ms, slice:8xa0mm, flip-angle:10°) and a T2-weighted half-Fourier fast-spin echo sequence (T2-HF-FSE; TR/TE:2000/66xa0ms, slice:7xa0mm, flip-angle:90°) were applied in axial orientation using a 3-T system (Intera, Philips Medical Systems, Best, The Netherlands), followed by CT (16×0.5xa0mm) as reference. Nodule sizes and locations were assessed by three blinded observers. In nodules of >10xa0mm, sensitivity was 100% using 3D-GRE-MRI and 94% using the HF-FSE sequence. For nodules 6–10xa0mm, the sensitivity of MRI was lower than with CT (3D-GRE:92%; T2-HF-FSE:83%). In lesions smaller than 5xa0mm, the sensitivity declined to 80% (3D-GRE) and 53% (HF-FSE). Small lesion diameters were overestimated with both sequences, particularly with HF-FSE. This study confirms the feasibility of 3 T-MRI for lung nodule detection. In lesions greater than 5xa0mm, the sensitivity of the 3D-GRE sequence approximated CT (>90%), while sensitivity and PPV with the HF-FSE sequence were slightly inferior.

MRI of degenerative bone marrow lesions in experimental osteoarthritis of canine knee joints

Abstractu2002Objective. The objective of this study was to determine the value of MRI in the detection of degenerative bone marrow abnormalities in an animal osteoarthritis model. Design. In 10 dogs with experimentally induced unilateral osteoarthritis of the knee, MRI was performed using two-dimensional spin-echo (2D-SE) and three-dimensional gradient-echo (3D-GE) imaging. Contrast enhanced T1-weighted 2D-SE sequences were also obtained after injection of gadolinium-DTPA. The results were compared with the gross and histopathologic findings and with radiography. Results. Histopathologic specimens revealed 21 osteosclerotic lesions and 5 intraosseous cysts. On 2D-SE images, 24 of 26 lesions were detected, while 21 of 26 lesions were identified on 2D-GE sequences. Radiography, including conventional tomography, demonstrated 9 of 26 lesions. Regardless of the sequence weighting, all osteosclerotic lesions appeared hypointense on MRI. Signal loss in bone sclerosis resulted primarily from the reduction of intact fat marrow, the increased bone density being of secondary importance. Quantitative signal analysis allowed approximate estimation of the grade of sclerosis. On postcontrast images, sclerotic bone remained hypointense, although significant but non-specific enhancement relative to the normal fat marrow was observed. The extent of contrast enhancement did not correlate with the grade of osteosclerosis. All five cysts were readily diagnosed by MRI. Cysts displayed either central or marginal contrast enhancement within their cavities. Conclusions. MRI provides a sensitive method for the diagnosis of osteoarthritic bone abnormalities, allowing their differentiation from most non-degenerative subarticular lesions.

Evaluation of spatial and temporal resolution for ECG-gated 16-row multidetector CT using a dynamic cardiac phantom

Measurements of spatial and temporal resolution for ECG-gated scanning of a stationary and moving heart phantom with a 16-row MDCT were performed. A resolution phantom with cylindrical holes from 0.4 to 3.0xa0mm diameter was mounted to a cardiac phantom, which simulates the motion of a beating heart. Data acquisition was performed with 16×0.75xa0mm at various heart rates (HR, 60–120xa0bpm), pitches (0.15–0.30) and scanner rotation times (RT, 0.42 and 0.50xa0s). Raw data were reconstructed using a multi-cycle real cone-beam reconstruction algorithm at multiple phases of the RR interval. Multi-planar reformations (MPR) were generated and analyzed. Temporal resolution and cardiac cycles used for image reconstruction were calculated. In 97.2% (243/250) of data obtained with the stationary phantom, the complete row of holes with 0.6xa0mm was visible. These results were independent of heart rate, pitch, scanner rotation time and phase point of reconstruction. For the dynamic phantom, spatial resolution was determined during phases of minimal motion (116/250). In 40.5% (47/116), the resolution was 0.6xa0mm and in 37.1% (43/116) 0.7xa0mm. Temporal resolution varied between 63 and 205xa0ms, using 1.5–4.37 cardiac cycles for image reconstruction.

Multidetector CT urography: experimental analysis of radiation dose reduction in an animal model

The purpose of this study was to evaluate the possibility of reducing X-ray exposure during multidetector CT urography (MDCTU) considering image quality using a porcine model. MDCTU was performed in eight healthy pigs. Scanning was conducted using a gradual reduction of the tube current-time product at 120xa0kV [200–20xa0mAs (eff.) in ten steps]. Three blinded observers independently evaluated the image data for anatomic detail, subjective image quality, and subjective image noise. Overall image quality was compared to milliampere-second settings and radiation dose. Objective noise measurements were assessed. Noise measurements in patients were also performed to verify the comparabilty of the animal model. Adequate image quality allowing for detailed visualization of the upper urinary tract was obtained when the tube current-time product was decreased to 70xa0eff. mAs at 120xa0kV. Image noise did not impair image quality to a relevant degree using these parameters. There was high agreement among the observers (ICCu2009=u20090.95). In the animal experiments, reduced-dose MDCTU produced good image quality. A maximum current-time product reduction to 70xa0eff. mAs at 120xa0kV (CTDIvolu2009=u20095.3xa0mGy) proved to be feasible, thereby offering an advantageous dosage reduction. The study provides a basis for the development of reduced-dose MDCTU protocols in humans.

Evaluation of the influence of acquisition and reconstruction parameters for 16-row multidetector CT on coronary calcium scoring using a stationary and dynamic cardiac phantom

A calcium-scoring phantom with hydroxyapatite-filled cylindrical holes (0.5 to 4xa0mm) was used. High-resolution scans were performed for an accuracy baseline. The phantom was mounted to a moving heart phantom. Non-moving data with the implementation of an ECG-signal were acquired for different pitches (0.2/0.3), heart rates (60/80/95xa0bpm) and collimations (16u2009×u20090.75/16u2009×u20091.5xa0mm). Images were reconstructed with a cone-beam multi-cycle algorithm at a standard thickness/increment of 3xa0mm/1.5xa0mm and the thinnest possible thickness (0.8/0.4 and 2/1). Subsequently, ECG-gated moving calcium-scoring phantom data were acquired. The calcium volume and Agatston score were measured. The temporal resolution and reconstruction cycles were calculated. High-resolution scans determine the calcium volume with a high accuracy (mean overestimation, 0.8%). In the non-moving measurements, the volume underestimation ranged from about 6% (16u2009×u20090.75xa0mm; 0.8/0.4xa0mm) to nearly 25% (16u2009×u20091.5xa0mm; 3/1.5xa0mm). Moving scans showed increased measurement errors depending on the reconstructed RR interval, collimation, pitch, heart rate and gantry rotation time. Also, a correlation with the temporal resolution could be found. The reliability of calcium-scoring results can be improved with the use of a narrower collimation, a lower pitch and the reconstruction of thinner images, resulting in higher patient doses. The choice of the correct cardiac phase within the RR interval is essential to minimize measurement errors.

Cross-sectional imaging patterns of desmoplastic fibroma

Abstract. The aim of this study was to work out the cross-sectional imaging characteristics of desmoplastic fibroma (DF). In 3 patients with histologically proven DF, the imaging characteristics obtained with cross-sectional techniques were reviewed retrospectively. Radiographs and CT scans were available in all patients, and plain and contrast-enhanced MR examinations in 2 patients. Compared with conventional radiographs, CT allowed more accurate assessment of the extent of bone destruction including cortical breakthrough and articular invasion. Intramedullary tumor growth and soft tissue extension was best detected with MRI. Apart from heterogeneity on MR images, DF displayed nonspecific low signal intensity on unenhanced T1-weighted images and an intermediate to high signal intensity including areas of low intensity on T2-weighted images. Desmoplastic fibroma showed a distinct, inhomogeneous gadolinium enhancement. Although cross-sectional imaging features of DF are nonspecific, some MR characteristics, such as inhomogeneous contrast enhancement and the presence of low-intensity regions on T2-weighted images, are helpful in determining the differential diagnosis. Cross-sectional imaging of DF is useful for local staging of the tumor because it provides valuable information about the extent of bone destruction as well as medullary and extraosseous spread.