A. Nömayr

Dose reduction in CT examination of children by an attenuation-based on-line modulation of tube current (CARE Dose)

Abstract. In a controlled patient study we investigated the potential of attenuation-based on-line modulation of the tube current to reduce milliampere values (mAs) in CT examinations of children without loss of image quality. mAs can be reduced for non-circular patient cross sections without an increase in noise if tube current is reduced at those angular positions where the patient diameter and, consequently, attenuation are small. We investigated a technical approach with an attenuation-based on-line control for the tube current realised as a work-in-progress implementation. The CT projection data are analysed in real time to determine optimal mAs values for each projection angle. We evaluated mAs reduction for 100 spiral CT examinations with attenuation-based on-line modulation of the tube current in a group of children. Two radiologists evaluated image quality by visual interpretation in consensus. We compared the mAs values read from the CT scanner with preset mAs of a standard protocol. Four different scan regions were examined in spiral technique (neck, thorax, abdomen, thorax and abdomen). We found the mAs product to be reduced typically by 10–60% depending on patient geometry and anatomical regions. The mean reduction was 22.3% (neck 20%, thorax 23%, abdomen 23%, thorax and abdomen 22%). In general, no deterioration of image quality was observed. There was no correlation between the age and the mean mAs reduction in the different anatomical regions. By classifying the children respectively to their weight, there is a positive trend between increasing weight and mAs reduction. We conclude that mAs in spiral CT examinations of children can be reduced substantially by attenuation-based on-line modulation of the tube current without deterioration of image quality. Attenuation-based on-line modulation of tube current is efficient and practical for reducing dose exposure to children.

Head and neck tumors: imaging recurrent tumor and post-therapeutic changes with CT and MRI.

OBJECTIVE To evaluate criteria for detection of tumor recurrence and post-treatment changes in patients with head and neck malignancies in computed tomography (CT) and magnetic resonance imaging (MRI). METHODS AND MATERIALS Thirty-nine patients with head and neck carcinoma receiving radiochemotherapy were examined before, during and after therapy with MRI. Changes in signal intensity were correlated to histology or clinical course. Three hundred and thirty-one patients with head and neck malignancies were examined with CT after therapy. CT diagnoses were correlated with histology or clinical course. RESULTS Main criteria for recurrent/residual tumor in MRI was infiltrative mass with high signal intensity in T2-weighted images and enhancement after Gd-DTPA in T1-weighted images. Radiation-induced changes led to false positive diagnosis in 46% in the interval up to 3 months after therapy and in 58% in the interval 3-6 months after therapy. The combination of a circumscribed, infiltrative mass with contrast enhancement in CT had a sensitivity of 86% and a specificity of 80%. CONCLUSION CT could accurately demonstrate postoperative changes and tumor recurrence. MRI had advantages in differentiation of tumor and scar, but edema after radiation therapy can spoil diagnosis.

Imaging of head and neck tumors — methods: CT, spiral-CT, multislice-spiral-CT

Spiral-CT is standard for imaging neck tumors. In correspondence with other groups we routinely use spiral-CT with thin slices (3 mm), a pitch of 1.3-1.5 and an overlapping reconstruction increment (2-3 mm). In patients with dental fillings a short additional spiral parallel to the corpus of the mandible reduces artifacts behind the dental arches and improves the diagnostic value of CT. For the assessment of the base of the skull, the orbital floor, the palate and paranasal sinuses an additional examination in the coronal plane is helpful. Secondary coronal reconstructions of axial scans are helpful in the evaluation of the crossing of the midline by small tumors of the tongue base or palate. For an optimal vascular or tissue contrast a sufficient volume of contrast medium and a start delay greater than 70-80 s are necessary. In our opinion the best results can be achieved with a volume of 150 ml, a flow of 2.5 ml/s and a start delay of 80 s. Dynamic enhanced CT is only necessary in some special cases. There is clear indication for dynamic enhanced CT where a glomus tumor is suspected. Additional functional CT imaging during i-phonation and/or Valsalvas maneuver are of great importance to prove vocal cords mobility. Therefore, imaging during i-phonation is an elemental part of every thorough examination of the hypopharynx and larynx region. Multislice-spiral-CT allows almost isotropic imaging of the head and neck region and improves the assessment of tumor spread and lymph node metastases in arbitrary oblique planes. Thin structures (the base of the skull, the orbital floor, the hard palate) as well as the floor of the mouth can be evaluated sufficiently with multiplanar reformations. Usually, additional coronal scanning is not necessary with multislice-spiral-CT. Multislice-spiral-CT is especially advantageous in defining the critical relationships of tumor and lymph node metastases and for functional imaging of the hypopharynx and larynx not only in the transverse plane but also in the coronal plane.

Anatomical accuracy of hybrid SPECT/spiral CT in the lower spine.

AimThe anatomical accuracy of hardware-based registration of skeletal single photon emission computed tomography (SPECT) and X-ray computerized tomography (CT) has as yet not been studied. The aim of this study was to evaluate this variable in the lower spine for a newly introduced hybrid SPECT/spiral-CT camera. MethodsIn 22 patients referred for degenerative joint disease or tumours, whole-body bone scintigraphy including hybrid SPECT/spiral CT of the lower spine was performed. Subsequent analyses were performed on these pairs of images as well as on data sets obtained after using a rigid automated fusion procedure in addition. Two observers independently measured the distances between the visually determined centres of gravity of the CT and SPECT representation of the fourth and fifth lumbar vertebral body in the X-, Y- and Z-directions (X-, Y- and Z-distances). ResultsThe distances determined by the two observers for the two vertebral bodies correlated significantly and were averaged for further analysis. For hybrid SPECT/spiral CT without consecutive automated registration, the mean X-, Y- and Z-distances were 1.6±1.9 mm, 1.7±1.3 mm and 0.9±0.5 mm, respectively. Additional automated registration lowered these values to 1.2±0.9 mm, 1.1±0.7 mm and 0.8±0.4 mm, respectively. The difference for the Y-distance proved statistically significant (P<0.05). Additional automated registration significantly reduced the number of subjects in whom at least one of the distances determined was greater than the SPECT pixel size of 4.6 mm from 14% (n=3) to 0% (P<0.05). ConclusionHardware-based fusion between skeletal SPECT and CT offers a nearly perfect data match in the lower spine. The additional use of a tool for automated rigid registration has the potential to reduce the error of alignment even further and may be useful in patients with reduced compliance leading to movements between the two examinations.

Gamna-Gandy bodies of the spleen detected with MR imaging. A case report

We report a case of a female patient with portal hypertension due to liver cirrhosis. In this case, MR imaging revealed small siderotic nodules of the spleen, called Gamna-Gandy bodies. These lesions are found in patients with portal vein or splenic vein thrombosis, hemolytic anemia, leukemia, or lymphoma, patients receiving blood transfusions, acquired hemochromatosis, or paroxysmal nocturnal hemoglobinuria. There are only few reports in the literature about these siderotic nodules which are not very familiar. MR imaging seems to be the superior imaging method for detection of these lesions. It is important to consider Gamna-Gandy bodies in the differential diagnosis of portal hypertension and the other diseases mentioned above.

Mehrzeilen-Spiral-CT in der Diagnostik von Pankreastumoren

ZusammenfassungZiel unserer Untersuchungen war es, die Möglichkeiten der Mehrzeilen-Detektor-Spiral-CT und ihre Bedeutung für das Staging von Pankreastumoren zu evaluieren. Bei insgesamt 50 Patienten, bei denen der Verdacht auf ein Pankreaskarzinom bestand, wurde im Rahmen der Tumorstagings ein biphasisches hochaufgelöstes Mehrzeilen-Spiral-CT mit einer Schichtkollimation von 4×1 mm, einem Pitch von 3,5–4, 120 ml Kontrastmittel, 50 ml 0,9%NaCl-Bolus, 3,0 ml/s Fluß und einem Startdelay von durchschnittlich 40 s (Pankreasparenchymphase) und 80 s (portalvenöse Phase) durchgeführt. Die Mehrzeilen-Spiral-CT ist in der Lage die gesamte Pankreasloge und auch die angrenzenden Organe mit hoher Ortsauflösung in allen Raumebenen abzubilden. Die nahezu isotrope multiplanare Bildgebung erlaubt die vollständige Erfassung der Tumorausdehnung in allen Raumebenen und eine bessere Abgrenzung der Tumoren gegenüber dem angrenzenden Fettgewebe, den benachbarten Organen (Gefäße, Duodenum, Magen) und einen sichereren Nachweis von peripankreatischen Lymphknoten. Die Mehrzeilen-Spiral-CT und der Einsatz von interaktiven multiplanaren Rekonstruktionen verbessern nachhaltig die Bestimmung der Ausdehnung von Pankreaskarzinomen.SummaryPurpose. Investigation of the capabilities of MSCT and its value for the staging of pancreatic carcinomas. Methods. 50 Patients with suspected pancreatic carcinoma were examined with a biphasic multislice-spiral-CT protocol: slice collimation 4×1 mm, Pitch 3.5–4 mm. After administation of 120 ml contrast medium and 50 ml NaCl with a flow rate of 3.0 ml/s the examination was started with a delay of 40 s (pancreatic phase) and 80 s (portalvenous phase). Results. Multislice spiral CT allows the examination of the whole upper abdomen with nearly isotropic data sets. This is the premise for the optimal assessment of the tumor extent in all planes, excellent demarcation of the tumor against the adjacent vessels and organs and the demarcation of small peripancreatic lymph nodes. Conclusions. Multislice spiral CT and the use of interactive multiplanar reconstructions improve the staging of pancreatic cancer.

[Anatomical accuracy of lesion localization. Retrospective interactive rigid image registration between 18F-FDG-PET and X-ray CT].

UNLABELLED The aim of this study was to evaluate the anatomical accuracy and reproducibility of retrospective interactive rigid image registration (RIR) between routinely archived X-ray computer tomography (CT) and positron emission tomography performed with 18F-deoxyglucose (FDG-PET) in oncological patients. METHODS Two observers registered PET and CT data obtained in 37 patients using a commercially available image fusion tool. RIR was performed separately for the thorax and the abdomen using physiological FDG uptake in several organs as a reference. One observer performed the procedure twice (O1a and O1b), another person once (O2). For 94 malignant lesions, clearly visible in CT and PET, the signed and absolute distances between their representation on PET and CT were measured in X-, Y-, and Z-direction with reference to a coordinate system centered in the CT representation of each lesion (X-, Y-, Z-distances). RESULTS The mean differences of the signed and absolute distances between O1a, O1b, and O2 did not exceed 3 mm in any dimension. The absolute X-, Y-, and Z-distances ranged between 0.57 +/- 0.58 cm for O1a (X-direction) and 1.12 +/- 1.28 cm for O2 (Z-direction). When averaging the absolute distances measured by O1a, O1b, and O2, the percentage of lesions misregistered by less than 1.5 cm was 91% for the X-, 88% for the Y-, and 77% for the Z-direction. The larger error of fusion determined for the remaining lesions was caused by non-rigid body transformations due to differences in breathing, arm position, or bowel movements between the two examinations. Mixed effects analysis of the signed and absolute X-, Y-, and Z-distances disclosed a significantly greater misalignment in the thorax than in the abdomen as well as axially than transaxially. CONCLUSION The anatomical inaccuracy of RIR can be expected to be <1.5 cm for the majority of neoplastic foci. Errors of alignment are bigger in the thorax and in Z-direction, due to non-rigid body transformations caused, e.g., by breathing.

Morphologic and Functional Assessment of Head and Neck Tumors with Multislice CT

Squamous cell carcinoma makes up the most common group of malignant head and neck tumors. As these tumors originate from the mucosal surface, they are accessible for inspection, mirror examination or endoscopy. Endoscopy is the gold standard, facilitating histologic verification, but requiring anesthesia. The aim of imaging modalities like CT and MRI is to accurately assess the infiltration depth into deeper compartments, which can not be directly visualized. Prior to surgery, about 80% of these patients undergo cross-sectional imaging procedures. Multislice spiral CT (MSCT) with the capability of isotropic volume data sets improved the diagnosis and staging of the tumors substantially. Image planes adapted to the specific anatomical demands can be created to optimally display the tumor site and tumor spread along specific pathways. Many patients present advanced stage cancer at the initial consultation. These patients suffer from swallowing and respiratory problems. Thus, it is of great importance to minimize examination time in order to reduce impairments of image quality due to motion artifacts. Despite the excellent soft tissue contrast of MRI, a significant number of examinations are substantially degraded by motion artifacts.

Multislice CT in the Diagnosis of Pancreatic Tumors

Pancreatic carcinoma has a poor prognosis. At 5 years after surgery, less than 10% of the patients are still alive. Clinical symptoms usually do not appear until the advanced stages. Only in 20% of these cases, the tumor is limited to the pancreas (Gebhardt et al. 2000). Even early stages of pancreatic carcinoma with a tumor size of less than 2 cm, also have an extremely poor prognosis. About 40% of early stage pancreatic carcinomas already have lymph node metastases. Perineural invasion is present in 50% of the tumors (Gebhardt et al. 2000). These findings further confirm the poor prognosis. Only complete and successful tumor resection in those patients without lymph node metastases improves prognosis.

Multislice Spiral CT in Preoperative Staging of Rectal Carcinoma

Accurate preoperative staging is important to the success of various treatment modalities for rectal cancer, including surgery and preoperative radiotherapy. Patients with endoscopically proven rectal tumors are examined by computed tomography (CT) for the staging of distant metastases (e.g., liver and lymph nodes along the vessel stem) and for local staging of tumor extension and perirectal lymph nodes.