CT colonography at low tube potential: using iterative reconstruction to decrease noise.

AIM: To determine the level of iterative reconstruction required to reduce increased image noise associated with low tube potential computed tomography (CT). MATERIALS AND METHODS: Fifty patients underwent CT colonography with a supine scan at 120 kVp and a prone scan at 100 kVp with other scan parameters unchanged. Both scans were reconstructed with filtered back projection (FBP) and increasing levels of adaptive statistical iterative reconstruction (ASiR) at 30%, 60%, and 90%. Mean noise, soft tissue and tagged fluid attenuation, contrast, and contrast-to-noise ratio (CNR) were collected from reconstructions at both 120 and 100 kVp and compared using a generalised linear mixed model. RESULTS: Decreasing tube potential from 120 to 100 kVp significantly increased image noise by 30-34% and tagged fluid attenuation by 120 HU at all ASiR levels (p<0.0001, all measures). Increasing ASiR from 0% (FBP) to 30%, 60%, and 90% resulted in significant decreases in noise and increases in CNR at both tube potentials (p<0.001, all comparisons). Compared to 120 kVp FBP, ASiR greater than 30% at 100 kVp yielded similar or lower image noise. CONCLUSIONS: Iterative reconstruction adequately compensates for increased image noise associated with low tube potential imaging while improving CNR. An ASiR level of approximately 50% at 100 kVp yields similar noise to 120 kVp without ASiR.

Scan length optimization for pulmonary embolism at CT angiography: analysis based on the three-dimensional spatial distribution of 370 emboli in 100 patients.

AIM: To determine the size and three-dimensional spatial distribution of pulmonary emboli (PE) at computed tomography angiography (CTA) to optimize the scan length. MATERIALS AND METHODS: Two experienced radiologists jointly reviewed 100 consecutive, positive PE CTA studies performed in the Emergency Department (53 women; age 61±17 years). All studies were conducted on a 16-detector row CT machine. In each case, the number of emboli was counted and the proximal and distal spatial coordinates of each embolus documented. Coordinates of the main pulmonary artery bifurcation (MPAb) and carina were recorded. For normalization, the thoracic cavity height (H)-from inlet to lowest hemidiaphragm-was measured. The minimal scan lengths for (a) capturing all emboli and (b) rendering a positive diagnosis were determined. RESULTS: Three hundred and seventy (370) emboli were detected. The average number of PE per patient was 3.7 (maximum 12, minimum 1). Their average length was 2.7 cm. Nine patients had saddle emboli (9%), and 71% of emboli were at or below the MPAb. An 18 cm (0.90×H) scan length, centred 4 cm (0.18×H) below the carina, captures all PE in this dataset while reducing z-axis coverage by 29% (34% for normalized data). Moreover, a 14.2 cm (0.78×H) scan length appropriately centred captures at least one embolus in all patients while reducing coverage by 44% (43%). Decreasing scan length to the lesser of 14.2 cm and 0.78×H per patient reduces coverage by 47%. CONCLUSION: Scan length at CTA for PE can be reduced by up to 47% while preserving diagnostic accuracy for PE detection.

Contrast-to-noise ratios of liver lesions using subtraction imaging on multiphase 64-detector row CT.

AIM: To measure contrast-to-noise ratios of liver lesions on conventional enhanced and digitally subtracted multidetector row computed tomography (CT) images. MATERIALS/METHODS: This study was approved by our hospital internal review board (IRB) and all collected data were evaluated in a Health Insurance Portability and Accountability Act (HIPAA)-compliant manner. Subtracted datasets, using pixel-by-pixel subtraction of the post-contrast images from the pre-contrast images, were created from the 64 detector-row CT of patients undergoing three-phase examination of the liver (unenhanced, arterial phase, and portal venous phase). Regions of interest were used to calculate the contrast-to-noise ratios between the lesions and the background liver parenchyma on both the post-contrast and subtracted datasets using the following formula: (Lesion mean (HU) - Liver mean (HU))/standard deviation of mean outside patient (HU). These ratios were compared using a mixed linear statistical model. RESULTS: Contrast-to-noise ratios were calculated for 64 lesions in 50 consecutive patients. Of the 64 lesions, 42 were hypervascular and 22 were hypovascular. Subtracted datasets yielded statistically significant higher contrast-to-noise ratios of hypervascular lesions compared to normal liver parenchyma (p<0.0001). Subtraction did not yield a statistically significant improvement in contrast-to-noise ratios for hypovascular liver lesions (p=0.16). CONCLUSION: Post-processed subtraction CT images generate increased contrast-to-noise ratios for hypervascular liver lesions. As this technique is easy to perform and does not involve additional radiation exposure, it should be considered when evaluating for suspected hypervascular lesions.

Radiofrequency ablation of bony metastatic disease.

Image-guided radiofrequency (RF) ablation is an emerging alternative therapy for treatment of cancer in patients who can not undergo surgical resection. We have performed RF ablation on patients to locally treat and palliate painful osseous metastatic disease for several years. We present an overview of various applications of RF ablation for treating osseous metastatic disease.

Multi-detector CT angiography of the intra-cranial circulation: normal anatomy and pathology with angiographic correlation.

Multidetector computed tomography angiography (MD-CTA) of the intra-cranial circulation shows great potential in the evaluation of intra-cranial vascular disease. Interpreting these studies requires a detailed knowledge of the technique, its advantages and disadvantages, as well as a strong understanding of normal intra-cranial vascular anatomy. The purpose of this review is to describe the technique for MD-CTA, demonstrate normal anatomy, anatomic variants and vascular pathology with an emphasis on aneurysms.

CT of the duodenum: an overlooked segment gets its due.

Abdominal computed tomography (CT) is frequently performed to evaluate gastrointestinal pathologic conditions, and the majority of the gastrointestinal radiology literature has concentrated on the colon, stomach, and distal small bowel. In a description of CT findings of duodenal pathologic conditions, congenital, traumatic, inflammatory, and neoplastic diseases are presented. Congenital duodenal anomalies such as duplications and diverticula are usually asymptomatic, while annular pancreas and malrotation may manifest in the 1st decade of life. CT plays a vital role in the diagnosis of traumatic duodenal injury. Primary inflammatory processes of the duodenum such as ulcers and secondary involvement from pancreatitis can reliably be diagnosed at CT. Infectious diseases of the duodenum are difficult to diagnose, as the findings are not specific. While small bowel malignancies are relatively rare, lipoma, adenoma, and adenocarcinoma, as well as local extension from adjacent malignancies, can be diagnosed at CT. Careful CT technique and attention to the duodenum can result in reliable prospective diagnoses.

State-of-the-art adrenal imaging.

The adrenal gland is a common site of disease, and detection of adrenal masses has increased with the expanding use of cross-sectional imaging. Radiology is playing a critical role in not only the detection of adrenal abnormalities but in characterizing them as benign or malignant. The purpose of the article is to illustrate and describe the appropriate radiologic work-up for diseases affecting the adrenal gland. The work-up of a suspected hyperfunctioning adrenal mass (pheochromocytoma and aldosteronoma) should start with appropriate biochemical screening tests followed by thin-collimation computed tomography (CT). If results of CT are not diagnostic, magnetic resonance (MR) and nuclear medicine imaging examinations should be performed. CT has become the study of choice to differentiate a benign adenoma from a metastasis in the oncology patient. If the attenuation of the adrenal gland is over 10 HU at nonenhanced CT, contrast material-enhanced CT should be performed and washout calculated. Over 50% washout of contrast material on a 10-minute delayed CT scan is diagnostic of an adenoma. For adrenal lesions that are indeterminate at CT in the oncology patient, chemical shift MR imaging or adrenal biopsy should be performed. Certain features can be used by the radiologist to establish a definitive diagnosis for most adrenal masses (including carcinoma, infections, and hemorrhage) based on imaging findings alone.