Pediatric multidetector computed tomography using tube current modulation and a patient image gallery

BACKGROUND

Dose reduction is crucial in pediatric multidetector computed tomography (MDCT).

PURPOSE

To perform pediatric 16-slice MDCT using tube current modulations and to adjust prospectively the tube current using a patient image gallery (IG) providing simulated dose-reduced protocols; and to evaluate and compare the image quality of the IG and the clinical MDCT.

MATERIAL AND METHODS

30 examinations (thorax, n = 15; abdomen, n = 8; pelvis, n = 7) in 20 patients (nine male, age 8.05 +/- 7.33 years, weight 29.8 +/- 24.02 kg) were performed according to an IG on a 16-slice MDCT with additional use of online tube current modulation (CARE Dose). Three radiologists visually assessed image quality from the IG and actual 16-slice MDCT scans. For objective analysis, image noise was determined.

RESULTS

Statistical analysis showed moderate concordance in objective (K = 0.68-0.78) and subjective (K = 0.33-0.64) image assessment between the IG and clinical 16-slice MDCT scans. Depending on the weight group and clinical question, no or only minor dose reductions in the chest, but moderate to considerable reductions in the abdominal/pelvic 16-slice MDCT scans compared to previously used pediatric protocols were achieved. Extra dose reduction was achieved due to additional use of CARE Dose depending on age group and scan region (mean 8.6-23.9%).

CONCLUSION

The IG enabled us to prospectively reduce the tube current and adapt the required image quality to the clinical question. Additional dose reduction was achieved with application of CARE Dose; nevertheless, the images are comparable to the simulated images of the IG.

[Tolerance of magnetic resonance imaging in children and adolescents performed in a 1.5 Tesla MR scanner with an open design]

PURPOSE

To investigate the tolerance of MR examinations in children and adolescents performed in a 1.5 Tesla MR scanner with an expanded bore diameter.

METHOD AND MATERIALS

163 patients, ages 4 to 25, underwent MR examinations in a 1.5 Tesla MR scanner with an open design (MAGNETOM Espree, Siemens, Erlangen, Germany), characterized by a compact length of 125 cm and an expanded 70 cm bore diameter. MR imaging of the brain was carried out in most cases (78.5 %), followed by examinations of the spinal canal (9.8 %), the extremities (9.2 %) and the neck (2.5 %). The patients were divided into four age groups and the success rate, motion artifacts and diagnostic quality of the MR examinations were assessed using a 3-grade scale.

RESULTS

In 119 of 163 patients (73.0 %), MR examination was possible without any motion artifacts. With respect to the different age groups, 41.7 % of the 4 - 7-year-old children, 67.6 % of the 8 - 10-year-old children, 84.1 % of the 11 - 16-year-old children and 95.8 % of the patients older than 17 showed tolerance grade I without motion artifacts and excellent diagnostic image quality. In 39 of 163 children (23.9 %), the MR images showed moderate motion artifacts but had sufficient diagnostic quality. With regard to the different age groups, 52.8 % of the 4 - 7-year-old children, 26.5 % of the 8 - 10-year-old children, 15.9 % of the 11 - 16-year-old children and none of the patients older than 17 showed tolerance grade II with moderate motion artifacts and sufficient diagnostic image quality. In only 4 of 124 children < 10 years old and 1 child > 10 years old, the MR examination was not feasible and had to be repeated under sedation.

CONCLUSION

Pediatric MR imaging using a 1.5 Tesla MR scanner with an open design can be conducted in children and adolescents with excellent acceptance. The failure rate of 3.0 % of cases for pediatric MR imaging is comparable to that of a conventional low-field open MR scanner.

Ureterektopie mit Harnträufeln im Kindesalter — eine diagnostische Herausforderung

Based on the observations in four girls suffering from constant urinary dribbling we analyzed the special features and difficulties in making the diagnosis of an ectopic ureter. In all patients there was marked diagnostic delay. In one symptomatic case the abnormality was not detected before the age of 18 years. Failure to recognize the characteristic signs and symptoms played a crucial role in delaying the diagnosis. Moreover, imaging of ureteral ectopia represents a diagnostic challenge. The ectopic ureters were associated with dysplastic, poorly functioning renal moieties. Common diagnostic imaging procedures, such as ultrasound, intravenous pyelography, or voiding cystourethrography yielded incomplete diagnostic information and often failed to provide a definitive diagnosis. The latter could only be obtained with MR urography. We assessed the diagnostic value of the different examinations and compared our findings with those reported in the literature.

Evaluation of femoral head vascularization in slipped capital femoral epiphysis before and after cannulated screw fixation with use of contrast-enhanced MRI: initial results

In this study we used contrast-enhanced magnetic resonance imaging (MRI) to evaluate the vascularization of the femoral head in children with slipped capital femoral epiphysis (SCFE) before and after cannulated screw fixation. Eleven consecutive children with SCFE, seven boys and four girls, aged 10-15 years were included in the study. There were no preslips; four children had acute, three acute-on-chronic, and four chronic SCFE. The MRI examinations were performed in a 1.5 Tesla MR scanner with use of a coronal STIR sequence, a coronal contrast-enhanced T1-weighted spin-echo sequence, and a sagittal three-dimensional gradient-echo sequence. Morphology, signal intensities, and contrast-enhancement of the femoral head were assessed by two radiologists in consensus. Morphologic distortion of the physis, bone marrow edema within the metaphysis and epiphysis, and joint effusion were the preoperative MRI findings of SCFE in each child. In nine children, the vascularization of the femoral head before and after surgery was normal. In one child, a preoperative avascular zone in the superolateral aspect of the epiphysis revascularized completely after surgery. One child with severe SCFE developed avascular necrosis of the femoral head after open reduction of the slip. We conclude that MRI allows for accurate evaluation of the femoral head vascularization before and after surgery in children with SCFE.

Dosisreduzierte 16-Schicht-Multidetektor-Spiralcomputertomographie bei Säuglingen und Kleinkindern mit bronchoskopischem Verdacht auf vaskulär bedingte Trachealstenosen - erste klinische Ergebnisse

PURPOSE

To evaluate the diagnostic accuracy of contrast-enhanced dose-reduced 16-slice multidetector-row CT (MDCT) in newborns and infants with fiberoptic bronchoscopically suspected vascular-induced tracheal stenosis.

MATERIALS AND METHODS

12 children (4 days to 3 years, 1.2 - 13.5 kg body weight) were examined using i. v. contrast-enhanced 16-slice MDCT (SOMATOM Sensation 16, Forchheim, Germany) without breath-hold and under sedation (11/12). All MDCTs were performed with a dose reduction. The beam collimation was 16 x 0.75 mm, except in the case of one child. MPRs along the tracheal axis in the x-, y- and z-directions and volume-rendering-reconstructions (VRTs) were calculated based on a secondary raw data set in addition to conventional axial slices. 2 radiologists used a three-point grade scale to evaluate the image quality, motion, and contrast media artifacts as well as the usefulness of the 2D- and 3D-reconstructions for determining the diagnosis. Statistical analysis was performed on the basis of a Kappa test.

RESULTS

In all cases the cause of the fiberoptic bronchoscopically suspected tracheal stenosis was revealed: compression due to the brachiocephalic trunk (n = 7), double aortic arch (n = 2), lusorian artery (n = 1), vascular compression of the left main bronchus (n = 2). In 3 patients further thoracic anomalies, such as tracheobronchial (n = 2), and vascular (n = 2) and vertebral (n = 1) anomalies were found. The attenuation in the anomalous vessels was 307 +/- 140 HU. The image noise was 9.8 +/- 1.9 HU. The mean dose reduction was 82.7 +/- 3.2 % compared to a standard adult thoracic CT. All examinations were rated as diagnostically good (median 1, range 1, k = 1). 3D images did not show any stair artifacts (median 2, range 1 - 2, k = 1). The image noise was minor to moderate and hardly any motion artifacts were seen (median 1, range 1 - 2, k = 0.8). Contrast media artifacts were rated zero to minor (median 1.5, range 1 - 2, k = 0.676). MPRs (median 1, range 1, k = 1) and VRTs (median 1, range 1, k = 1) were found to be useful for diagnosis. Subsequent vascular surgery was performed on 8 patients.

CONCLUSION

Contrast-enhanced dose-reduced 16-slice MDCT is effective for demonstrating the cause of fiberoptic bronchoscopically suspected vascular-induced tracheal stenosis even in very small and severely ill children despite the small contrast media amount and free breathing.

[High-resolution T1-weighted MR-lymphography of inguinal lymph nodes after interstitial application of Gadomer-17 in animal experiments]

PURPOSE

To evaluate the microstructural anatomy of inguinal lymph nodes in pigs after interstitial MR-lymphography with the dendritic contrast agent Gadomer-17.

MATERIAL AND METHODS

High-resolution T1-weighted MR-lymphography was performed in inguinal lymph nodes of 10 domestic pigs (39 - 46 kg) after subcutaneous injection of 10 mumol/kg body weight Gadomer-17 in the hind legs of the animals. A 1.5T MR scanner and a ring-shaped surface coil were used. Two different high-resolution gradient-echo sequences with additionally reconstructed maximum-intensity projections were evaluated in a total of 20 lymph nodes. The high-resolution MR-findings were correlated with the histologic sections of the excised inguinal lymph nodes.

RESULTS

Coronal T1-weighted 3D gradient-echo images (TR = 20 msec, TE = 6.1 - 8.3 msec, FA = 20 degrees ) with a slice thickness of 1 mm, a field-of-view of 120 mm and a matrix size of 256 x 256 (reconstructed to 1024 x 1024 voxels) yielding a reconstructed in-plane resolution of 117 x 117 microm (2) were best suited for the high-resolution MR lymphography of inguinal lymph nodes and enabled the differentiation of the hyperintense lymph node sinuses and hypointense lymphoid parenchyma of each lymph node (100 %). Even dilated lymphatic vessels evident in the histologic specimen were best demonstrated on the MIP images.

CONCLUSION

High-resolution interstitial MR lymphography with Gadomer-17 allows the visualization of different tissue compartments of inguinal lymph nodes. This new technique is feasible on a routine 1.5T scanner and may offer potential for the detection of micrometastases in lymph nodes of cancer patients.

[Diagnostic evaluation of chronic inflammatory intestinal diseases in children and adolescents: MRI with true-FISP as new gold standard?]

PURPOSE

To evaluate the impact of magnetic resonance imaging (MRI) with use of True-FISP sequences in the evaluation of inflammatory bowel-wall changes in children and adolescents with Crohn's disease. Furthermore, the diagnostic procedure in children and adolescents with chronic inflammatory bowel disease (IBD) will be discussed in light of the relevant literature.

MATERIAL AND METHODS

Twenty-four children and adolescents aged between 7 and 21 years with suspected or known IBD underwent MRI on a 1.5 T-scanner (Philips ACS-NT, Best, Netherlands). One hour after 1 l of a 2.5 % mannitol solution was given orally, MR imaging was performed using coronal HASTE-M2D, coronal fat-suppressed T2-TSE, axial dynamic T1-weighted GE-sequences before and after i. v.-contrast material injection (0.1 mmol/kg Gd-DTPA) and using a 2D-balanced-FFE-sequence (True-FISP) before and after i. v.-contrast material injection in coronal and axial planes. The MR-images were correlated with endoscopy and the clinical findings. In 14 patients, a recently performed conventional radiographic enteroclysis was available. Each performed MRI sequence was evaluated by three experienced radiologists regarding the sensitivity and specificity of each sequence in the detection of inflammatory bowel wall changes. In addition, the image quality was assessed regarding the different tissue contrasts and the susceptibility to artifacts. The distension of the bowel wall and the patients' acceptance of the MRI examination were recorded.

RESULTS

With a sensitivity in detecting inflammatory small bowel changes of 93.3 % (axial pre-contrast, coronal post-contrast) and 100 % (axial post-contrast, coronal pre-contrast), the True-FISP outnumbers the other performed sequences (T1 = 80 %, HASTE = 13.3 % and T2-TSE = 53.3 %). The difference between True-FISP and contrast-enhanced T1 was not statistically significant, whereas the difference between True-FISP and HASTE and T2-TSE, respectively, was statistically significant. The True-FISP sequences revealed a statistically significant superiority regarding the soft-tissue differentiation in comparison to all other performed MR-sequences. The distension of the bowel wall was good in all patients. The patients' acceptance of the MRI examination was excellent.

CONCLUSION

The described small bowel MRI examination is appropriate for children and adolescents. With the use of True-FISP sequences, it is a convincing method with an outstanding sensitivity in the diagnosis of IBD. Not least because of the lack of radiation exposure, small bowel MRI ought to replace conventional enteroclysis as a gold standard for IBD diagnosis in children and adolescents.

Mehrschicht-Spiral-CT (MSCT) in der Kinderradiologie: Dosisreduktion bei der Untersuchung von Thorax und Abdomen

The advent of multislice spiral CT (MSCT) technique has led to new aspects of dose reduction, especially for the dedicated use of MSCT in children. Optimizing pediatric MSCT protocols according to the clinical problem allows reduction of radiation exposure to a minimum without loss of diagnostic quality. The different parameters that influence the degree of dose reduction, like tube current-time product (mAs), tube voltage (kV), collimation and pitch, are discussed in context with previously published data and our own experience in nearly 200 pediatric CT examinations. In our department, the effective mAs is calculated for a pediatric chest MSCT by multiplication of the body weight in kilogram with a factor of 1 to 1.5 and for a pediatric abdominal MSCT by multiplication with a factor of 2 to 2.5. To calculate the equivalent effective dose for a contrast media-enhanced 80 kV protocol, the effective mAs of the 120 kV protocol can be multiplied by 2.7. A factor less than 2.7 means further dose reduction. Compared to the radiation exposure with a standard adult protocol, the effective dose in a pediatric thoracic MSCT could be reduced by up to 92 % in neonates, 89 % in toddlers and 80 % in school children. In abdominal MSCT, the effective dose could be reduced by up to 90 % in neonates, 89 % in toddlers and 83 % in school children. Using an adequate MSCT technique in children by adjusting the CT scanning parameters to the clinical question and body weight of the examined child enables a significant reduction of radiation exposure in comparison to standard MSCT protocols.

MR urography today

Magnetic resonance (MR) urography is performed by pursuing two different imaging strategies. On the one hand, heavily T2-weighted turbo spin-echo sequences are employed for obtaining unenhanced static-water images of the urinary tract. On the other, the T(1)-weighted MR urographic technique imitates conventional intravenous pyelography and is, therefore, referred to as excretory MR urography. For this reason, a gadolinium contrast agent is injected intravenously and, after its renal excretion, the gadolinium-enhanced urine is imaged with fast T1-weighted gradient-echo sequences. Both MR urographic techniques can be combined for a comprehensive examination of the upper urinary tract. This article reviews the current technical principles, imaging capabilities, and clinical applications of T2- and T1-weighted MR urography in adult and pediatric patients.

[Interstitial T1-weighted MR lymph fistulography with Gadomer-17 in an experimental animal model]

PURPOSE

To visualize and localize fistulas of the thoracic duct with interstitial T 1 -weighted MR lymphography using Gadomer-17.

MATERIALS AND METHODS

In 10 domestic pigs, leaks of the thoracic duct were created surgically or interventional-radiologically. The lymphatic leakage was located within the abdominal portion of the thoracic duct in 5 pigs, within the thoracic portion of the thoracic duct in 3 pigs, and in both, abdominal and thoracic portions of the thoracic duct, in 2 pigs. Subsequently, 10 micro mol/kg KG Gadomer-17 (1.5-1.8 ml) was administered interstitially in both hind legs of the animals. MR lymphography was performed with a 1.5 T MR unit using two different 3D gradient echo sequences before and 10 - 90 minutes after administration of contrast material.

RESULTS

Leaks within the abdominal portion of the thoracic duct were directly visible as opacified fistulas. Indirect signs of active lymphatic fistulas were increasing extravasations of contrast material and free abdominal fluid. The 3D gradient echo sequence with the highest planar resolution (TR = 8,7 - 8,8 ms, TE = 4,2 - 4,3 ms, FA = 40 degrees, matrix size = 327 x 512) was best suited for distinct delineation of the lymphatic system and detailed demonstration of the thoracic duct fistulas. Intrathoracic leaks could not be demonstrated by MR lymphography due to reduced lymphatic flow or extravasated contrast medium at the abdominal puncture site.

CONCLUSION

Interstitial MR lymphography with Gadomer-17 allows sensitive detection and localization of abdominally located leaks of the thoracic duct.

[MR-urography and CT-urography: principles, examination techniques, applications]

MR-urography (MRU) and CT-urography (CTU) provide refined imaging of the upper urinary tract not achievable with conventional intravenous urography (IVU). The traditional MR-urographic technique utilizes unenhanced, heavily T2 -weighted turbo spin-echo sequences for obtaining static fluid images of the urinary tract independent of the excretory renal function. T2 -weighted MR-urograms have proved to be excellent in visualizing the dilated urinary tract, even in non-excreting kidneys. In contrast, T1 -weighted MRU reflects the excretory renal function and displays the urine flow through the upper tract after renal excretion of an intravenously administered gadolinium chelate. The gadolinium-enhanced urine is visualized with fast T1 -weighted 3D-gradient-echo sequences. The combination of gadolinium and low-dose furosemide (5 - 10 mg) is the key for achieving a uniform distribution of gadolinium in the collecting system and for avoiding susceptibility artifacts (T2*-effects) in the urine. T1 -weighted excretory MRU provides impressive urograms of both non-dilated and obstructed collecting systems in patients with normal or moderately impaired renal function. Multislice-CT-urography (MS-CTU) is also an excretory urography like T1 -weighted MRU. Furthermore, MS-CTU can be combined with low-dose furosemide for accelerated passage of excreted contrast material obviating the need for abdominal compression. CT-urography is limited by its radiation burden and the nephrotoxicity of radiographic contrast media. Combining MRU or MS-CTU with conventional MRI or CT offers several applications, e.g., diagnosis of intrinsic and extrinsic tumors. Meanwhile, MRU has replaced IVU in pediatric uroradiology and is also recommended for the assessment of renal transplants. MS-CTU may provide valuable information in chronic urolithiasis, especially if associated with a distorted urinary tract anatomy. Both MRU and MS-CTU will play an important role in modern uroradiology.

[Diagnosis and differential diagnosis of extraskeletal, para-articular chondroma of the knee]

AIM

Extraskeletal chondromas in the region of the knee joint are very rare tumors which may cause diagnostic problems and have concomitant therapeutic consequences.

METHOD

In a case report we present the clinical, radiological and histological features of an a extraskeletal chondroma.

RESULTS

A 47-year-old female patient presented with an infrapatellar, painless tumor of the knee joint. The clinical features were unspecific. On plain X-ray images, calcifications were visabled within Hoffa's fat pad. An important preoperative imaging procedure was MRI, which showed a well defined mass of 2.5 cm in diameter with a hyperintense signal on fat suppressed images. Subsequent operative therapy involved marginal resection of the tumor.

CONCLUSION

The differentiation of this entity especially from myxoid chondrosacroma and synovial chondroamatosis was crucial with respect to an adequate therapy. Further differential diagnoses included heterotopic ossifications, synovial sarcoma, mesenchymoma and soft-tissue osteosarcoma.

MR signal intensity characteristics in Legg-Calvé-Perthes disease. Value of fat-suppressed (STIR) images and contrast-enhanced T1-weighted images

PURPOSE

To evaluate the MR signal intensity characteristics in Legg-Calvé-Perthes disease on fat-suppressed (STIR) images and contrast-enhanced T1-weighted spin-echo images, and to develop criteria for the administration of contrast material.

MATERIAL AND METHODS

Twenty children with Legg-Calvé-Perthes disease underwent conventional radiography and MR imaging of the hip utilizing fat-suppressed (STIR) sequences and T1-weighted spin-echo sequences before and after i.v. contrast administration. The signal intensity characteristics of the femoral head and the proximal femoral metaphysis were assessed retrospectively by two pediatric radiologists.

RESULTS

Evaluation of the MR images revealed six different signal patterns within the femoral head: 1) isointense signal on all images; 2) complete signal void on all images; 3) hyperintense signal on STIR images with; or 4) without contrast enhancement on T1-weighted spin-echo images; 5) isointense signal on STIR images with; or 6) without contrast enhancement on T1-weighted images. Within the metaphysis three different signal patterns were differentiated.

CONCLUSION

Combination of fat-suppressed (STIR) sequences and T1-weighted pre- and post-contrast sequences allows an accurate evaluation of Legg-Calvé-Perthes disease. In patients without signal alterations or complete signal loss on fat-suppressed and T1-weighted spin-echo images, administration of i.v. contrast is not necessary. In case of bone marrow edema on fat-supressed images, contrast-enhanced T1-weighted images are required to identify viable osseous fragments.