Patient radiation doses in cardiac computed tomography: comparison of published results with prospective and retrospective acquisition.

Prospective ECG triggering has the potential of reducing radiation exposure while maintaining diagnostic accuracy of cardiac computed tomography (CT). The aim of this study is to review patient radiation doses associated with coronary artery calcium scoring (CACS) and CT coronary angiography (CTCA) and to compare results between prospective and retrospective acquisition schemes. Patient radiation doses from CACS and CTCA were extracted from 67 relevant studies. Mean effective dose for CACS and CTCA with prospective ECG triggering is significantly lower than retrospective acquisition, 0.9±0.4 vs. 3.1±1.4 mSv, p < 0.001, and 3.4±1.4 vs. 11.1±5.4 mSv, p < 0.001, respectively. In both cardiac CT examinations, application of dose modulation techniques result in significantly lower doses in retrospective schemes, however, even with dose modulation, retrospective acquisition is associated with significantly higher doses than prospective acquisition. The number of slices acquired per rotation and the number of X-ray sources of the CT scanner (single or dual source) do not have a significant effect on patient dose.

Adult patient radiation doses from non-cardiac CT examinations: a review of published results.

OBJECTIVES: CT is a valuable tool in diagnostic radiology but it is also associated with higher patient radiation doses compared with planar radiography. The aim of this article is to review patient dose for the most common types of CT examinations reported during the past 19 years. METHODS: Reported dosimetric quantities were compared with the European diagnostic reference levels (DRLs). Effective doses were assessed with respect to the publication year and scanner technology (i.e. single-slice vs multislice). RESULTS: Considerable variation of reported values among studies was attributed to variations in both examination protocol and scanner design. Median weighted CT dose index (CTDI(w)) and dose length product (DLP) are below the proposed DRLs; however, for individual studies the DRLs are exceeded. Median reported effective doses for the most frequent CT examinations were: head, 1.9 mSv (0.3-8.2 mSv); chest, 7.5 mSv (0.3-26.0 mSv); abdomen, 7.9 mSv (1.4-31.2 mSv); and pelvis, 7.6 mSv (2.5-36.5 mSv). CONCLUSION: The introduction of mechanisms for dose reduction resulted in significantly lower patient effective doses for CT examinations of the head, chest and abdomen reported by studies published after 1995. Owing to the limited number of studies reporting patient doses for multislice CT examinations the statistical power to detect differences with single-slice scanners is not yet adequate.

Occupational radiation doses to the extremities and the eyes in interventional radiology and cardiology procedures.

OBJECTIVES: The aim of this study was to determine occupational dose levels in interventional radiology and cardiology procedures. METHODS: The study covered a sample of 25 procedures and monitored occupational dose for all laboratory personnel. Each individual wore eight thermoluminescent dosemeters next to the eyes, wrists, fingers and legs during each procedure. Radiation protection shields used in each procedure were recorded. RESULTS: The highest doses per procedure were recorded for interventionists at the left wrist (average 485 µSv, maximum 5239 µSv) and left finger (average 324 µSv, maximum 2877 µSv), whereas lower doses were recorded for the legs (average 124 µSv, maximum 1959 µSv) and the eyes (average 64 µSv, maximum 1129 µSv). Doses to the assisting nurses during the intervention were considerably lower; the highest doses were recorded at the wrists (average 26 µSv, maximum 41 µSv) and legs (average 18 µSv, maximum 22 µSv), whereas doses to the eyes were minimal (average 4 µSv, maximum 16 µSv). Occupational doses normalised to kerma area product (KAP) ranged from 11.9 to 117.3 µSv/1000 cGy cm² and KAP was poorly correlated to the interventionists' extremity doses. CONCLUSION: Calculation of the dose burden for interventionists considering the actual number of procedures performed annually revealed that dose limits for the extremities and the lenses of the eyes were not exceeded. However, there are cases in which high doses have been recorded and this can lead to exceeding the dose limits when bad practices are followed and the radiation protection tools are not properly used.

Reduction of the estimated radiation dose and associated patient risk with prospective ECG-gated 256-slice CT coronary angiography.

Computed tomography (CT) coronary angiography has been widely used since the introduction of 64-slice scanners and dual-source CT technology, but high radiation doses have been reported. Prospective ECG-gating using a 'step-and-shoot' axial scanning protocol has been shown to reduce radiation exposure effectively while maintaining diagnostic accuracy. 256-slice scanners with 80 mm detector coverage have been currently introduced into practice, but their impact on radiation exposure has not been adequately studied. The aim of this study was to assess radiation doses associated with CT coronary angiography using a 256-slice CT scanner. Radiation doses were estimated for 25 patients scanned with either prospective or retrospective ECG-gating. Image quality was assessed objectively in terms of mean CT attenuation at selected regions of interest on axial coronary images and subjectively by coronary segment quality scoring. It was found that radiation doses associated with prospective ECG-gating were significantly lower than retrospective ECG-gating (3.2 +/- 0.6 mSv versus 13.4 +/- 2.7 mSv). Consequently, the radiogenic fatal cancer risk for the patient is much lower with prospective gating (0.0176% versus 0.0737%). No statistically significant differences in image quality were observed between the two scanning protocols for both objective and subjective quality assessments. Therefore, prospective ECG-gating using a 'step-and-shoot' protocol that covers the cardiac anatomy in two axial acquisitions effectively reduces radiation doses in 256-slice CT coronary angiography without compromising image quality.

Gray-scale and color Doppler ultrasonographic evaluation of reactivated post-traumatic/postoperative chronic osteomyelitis.

OBJECTIVE: We aimed to carry out a systematic assessment of gray-scale and color Doppler ultrasonography (CDUS) findings of reactivated post-traumatic/postoperative chronic osteomyelitis (COM) in adults. MATERIALS AND METHODS: Gray-scale and color Doppler ultrasonography were performed on 40 consecutive patients with a history of long-standing post-traumatic/post-operative chronic osteomyelitis and clinical suggestion of reactivation, in a 32-month-period. All patients had metallic implants: 16 internal fixations, nine external fixations, 11 hip arthroplasties and four knee arthroplasties. The final diagnosis of reactivated COM was based upon biopsy findings, with microbiological and histological examination (n = 27), or a combination of laboratory, clinical and magnetic resonance (MR) findings (n = 13). The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of sonographic signs, including fistulous tracts, periosteal thickening, cortical discontinuity, soft tissue abscess and cellulitis, juxtacortical fluid, distension of the pseudocapsule in arthroplasties, and periosteal vascularity, were estimated. RESULTS: Statistically significant differences between patients with and without reactivated COM were found for fistulous tracts (P < 0.0001), juxtacortical fluid collections (P < 0.001) periosteal thickening (P < 0.01), distension of pseudocapsule (P < 0.05), and periosteal vascularity (P < 0.0001). Low-resistance arterial flow of periosteal vessels presented the highest sensitivity (92%), specificity, and PPV (100%), yielding only two false negative results in two obese patients. Among gray-scale findings, the presence of a fistulous tract yielded the highest specificity and PPV (100%), whereas periosteal thickening was the most sensitive (92%), though not specific, finding (specificity 50%). CONCLUSION: A constellation of gray-scale and CDUS findings can be highly indicative of reactivated bone infection in patients with long-standing chronic post-traumatic/post-operative osteomyelitis.

The role of Doppler Perfusion Index as screening test in the characterization of focal liver lesions.

PURPOSE: Doppler Perfusion Index (DPI) has been used in the detection of overt liver metastatic disease. In the present prospective study we evaluated the use of DPI in the differential diagnosis of liver tumours. MATERIALS AND METHODS: We have included in our study 76 patients with focal hepatic lesion and 39 subjects as control group. All patients were evaluated by Color Doppler Ultrasound, and/or Spiral Computerised Tomography, Magnetic Resonance Imaging and biopsy. The radiologist performed DPI measurements was blind from the final diagnosis of the other methods. RESULTS: DPI measurements in the control group ranged from 0.07 to 0.22 (mean value 0.14), in 42 cases with benign lesions (group A) ranged from 0.05 to 0.53 (mean 0.15) and in 34 cases with malignant lesions (group B) ranged from 0.39 to 0.75 (mean 0.53). There was a statistically significant difference in DPI measurements between the control group and group B. CONCLUSIONS: Our results suggest that the DPI may differentiate malignant from benign focal hepatic lesions and therefore can be used as a screening test in the routine clinical practice.

Radiofrequency ablation of intra-articular osteoid osteoma of the hip.

Diagnosis and treatment of intra-articular osteoid osteoma is challenging. We present 16 patients with intra-articular osteoid osteomas of the hip treated with percutaneous radiofrequency ablation. Eight osteoid osteomas were located in the femoral head, six in the femoral neck, and two in the acetabulum. Three of the 16 patients had had an incorrect previous diagnosis. Percutaneous radiofrequency ablation was a clinical and technical success in all 16 patients. Within the first 24 h after the procedure, pain improved in all patients. Five patients had pain relief within the first 3 days after the procedure, nine patients within the first week and two patients within 2 weeks. Residual or recurrent symptoms were not reported by the last follow-up. At the 12-month follow-up, computed tomography and magnetic resonance imaging showed complete ossification and bone regeneration at the site of the lesion in three patients, partial ossification in six patients and no changes in seven patients. Computed tomography-guided percutaneous radiofrequency ablation is a simple, minimally invasive, safe and effective method for the treatment of most intra-articular osteoid osteomas.

Quality assurance (QA) procedures for software: evaluation of an ADC quality system.

Image viewing and processing software in computed radiography manipulates image contrast in such a way that all relevant image features are rendered to an appropriate degree of visibility, and improves image quality using enhancement algorithms. The purpose of this study was to investigate procedures for the quality assessment of image processing software for computed radiography with the use of existing test objects and to assess the influence that processing introduces on physical image quality characteristics. Measurements of high-contrast resolution, low-contrast resolution, spatial resolution, greyscale (characteristic curve) and geometric distortion were performed 'subjectively' by three independent observers and 'objectively' by the use of criteria based on pixel intensity values. Results show quality assessment is possible without the need for human evaluators, using digital images. It was discovered that the processing software evaluated in this study was able to improve some aspects of image quality, without introducing geometric distortion.

Transcatheter occlusion of a large pulmonary arteriovenous malformation with use of a Cardioseal device.

Large pulmonary arteriovenous malformations (PAVMs) carry a significant risk of neurologic complications and present technical difficulties in transcatheter treatment with use of coils or detachable balloons. A 26-year-old man with a giant PAVM, who had undergone unsuccessful attempted closure with use of a Gianturco-Grifka occlusion device in the past, underwent successful transcatheter embolization with two Cardioseal double umbrella devices designed for occlusion of intracardiac communications. The procedure was technically easy, had no complications, and provided sustained improvement in arterial saturation and exercise tolerance during follow-up. Transcatheter double umbrella device occlusion of large arteriovenous malformations is feasible and should be considered, especially for very large fistulas.

Malignant biliary obstruction: management with percutaneous metallic stent placement.

BACKGROUND/AIMS: To report our experience on palliative management of malignant biliary obstruction with percutaneous placement of metallic stents. METHODOLOGY: During a 3-year period 20 patients with malignant biliary obstruction were treated with percutaneous insertion of metallic biliary endoprostheses. RESULTS: Stent placement was successful in 19 patients, with significant improvement of jaundice in 18 patients. 17 patients have died up to date. In this group survival was 4-324 days (mean: 107 days) and mean stent primary and secondary patency 94.3 and 97.4 days, respectively. Three patients are alive with a follow-up from 20-195 days. Mean secondary patency is 65.3 days (20-134 days). We encountered serious complications in 4 patients (20%). Thirty-day mortality was 15%, while procedural mortality was 10%. Four patients presented 13-120 days (mean: 71.5 days) after the procedure with stent reocclusion (reocclusion rate: 20%). CONCLUSIONS: The procedure is relatively easy and safe to perform, yields excellent palliation of the patient's symptomatology and, therefore, contributes substantially to the maintenance of good quality of life of the patient with malignant biliary obstruction.

Chemotherapy-treated liver metastases mimicking hemangiomas on MR images.

BACKGROUND: To report the observation that chemotherapy-treated liver metastases may mimic the appearance of hemangiomas on T2-weighted and serial postgadolinium gradient-echo magnetic resonance (MR) images. METHODS: T2-weighted and serial postgadolinium spoiled gradient-echo images were prospectively and retrospectively analyzed in six patients. All patients had been treated with chemotherapy for a duration of 2-12 months. Histopathologic evaluation of liver lesions was performed in three patients. RESULTS: Twelve lesions that resembled hemangiomas were identified. Lesions were 0.8-5.5 cm in diameter. All were well defined, oval or lobulated, and demonstrated decreased signal intensity on T1-weighted images and increased signal intensity on T2-weighted images. On immediate postgadolinium images, all lesions demonstrated peripheral nodular enhancement, which coalesced on delayed imaging. Final histopathologic diagnoses were as follows: hepatic metastases from colon cancer (two patients), ovarian cancer (two patients), pancreatic islet cell tumor (one patient), and breast cancer (one patient). CONCLUSIONS: Metastases treated by chemotherapy may mimic the appearance of hemangiomas on a variety of commonly employed MR techniques. In patients undergoing MR imaging for the evaluation of liver metastases, a history of prior chemotherapy administration and duration should be sought to prevent inaccurate staging and inappropriate therapeutic decision making.

Magnetic resonance imaging of the abdominal aorta and iliac vessels using combined 3-D gadolinium-enhanced MRA and gadolinium-enhanced fat-suppressed spoiled gradient echo sequences.

This study evaluates a combined protocol consisting of breath hold immediate post gadolinium 3-D gradient echo MR angiography and blood pool phase gadolinium-enhanced breath hold 2-D fat-suppressed spoiled gradient echo (SGE) sequences in the examination of diseases of the abdominal aorta and iliac vessels. Thirty-two patients with suspected disease of the abdominal aorta, major aortic branches, or iliac vessels underwent MR angiographic study from January 1996 to January 1997. Examinations were performed on a 1.5 T MR imager using 2-D axial SGE, coronal 3-D fast imaging in steady state precession (3-D FISP) following bolus administration of 40 mL of gadolinium, and axial and coronal blood pool phase gadolinium-enhanced fat-suppressed SGE. Post-processed data, including 3-D reconstructions using maximum intensity projection (MIP), targeted MIP, and multiplanar reconstruction (MPR) were evaluated. MR findings in all patients were correlated as follows: surgery (13 patients), angiography (11 patients), contrast enhanced CT (3 patients), non-contrast enhanced CT (1 patient), color doppler US (2 patients), and previous MR study (2 patients). MR findings correlated closely with findings at surgery or other imaging studies in 31 of 32 patients. One patient had renal artery occlusion that was misinterpreted as mild stenosis. The following vascular diseases were present: aneurysm disease [10 patients: aortic aneurysm (8 patients), inflammatory aneurysm (2 patients)], thoracoabdominal aortic dissection (2 patients), arteriovenous fistula (1 patient), stenoses and/or occlusion of the abdominal aorta, major aortic branches and iliac vessels [12 patients: stenoses and/or occlusion of the abdominal aorta with stenoses of the iliac vessels (9 patients), renal artery stenosis (2 patients), occlusion of the abdominal aorta (1 patient)], and occluded artery to pancreatic transplant artery (1 patient). Five patients had normal studies. The 3-D FISP technique accurately defined the luminal contours of vessels, allowing precise depiction of vessel stenosis (i.e., renal artery stenosis or common iliac artery stenosis) and clear demonstration of relationship of aortic branch vessels (i.e., renal arteries) to underlying aortic pathology (i.e., aortic aneurysm or dissection). Blood pool phase gadolinium-enhanced fat-suppressed SGE images were useful in the evaluation of the external surface of vessel walls, and providing accurate measurement of aneurysm diameter and other associated vascular entities (i.e., inflammatory aneurysm, left-sided IVC). Targeted MIP or MPR reconstruction were important for assessing stenoses of medium sized vessels such as renal arteries and branches of the iliac arteries, and for identifying accessory arteries. The combination of immediate post gadolinium 3-D FISP and blood pool phase gadolinium-enhanced fat-suppressed SGE is useful in the evaluation of the abdominal aorta, major aortic branches and iliac vessels. Immediate post gadolinium 3-D FISP images provides diagnostically useful information regarding vessel luminal contour, while blood pool phase gadolinium-enhanced fat-suppressed SGE provides ancillary information on the vessel wall and surrounding tissue.

Magnetic resonance imaging of neuroblastoma using current techniques.

We evaluated the ability of current magnetic resonance (MR) scanning techniques to detect and stage neuroblastoma in children, using surgical and histopathologic correlation. We prospectively and retrospectively reviewed 16 MR examinations from 14 patients with neuroblastoma (13 patients) or ganglioneuroblastoma (1 patient) and compared these to computed tomography (CT) (5 patients) and pathology (all patients). Sequences included: precontrast T1-weighted and T2-weighted images, and gadolinium-enhanced T1-weighted images. The study time for each MR exam was also calculated. Five primary tumors were intrathoracic paraspinous masses, eight were adrenal, and 1 was presacral. Neural foraminal invasion was demonstrated on MR in four of 14 patients. Three of the four patients had undergone CT and neural foraminal invasion was shown in one. Vascular encasement was demonstrated in five of 14 patients on MR images. Three of the five patients had undergone CT and vascular involvement was shown in two. All cases of neural foramina invasion and vascular encasement were proven at surgery. There were no false positive or false negative MR studies of neural foraminal invasion or vascular encasement. Bone marrow invasion was shown in two of 14 patients on MR images which were confirmed by bone marrow aspirate. No false negative cases of bone marrow invasion was shown. In one patient, CT considered one neuroblastoma to be adrenal in location which was correctly shown to be intrathoracic on MR. The mean study time for MR imaging was 49 min. Current MR techniques are accurate at detecting and staging neuroblastoma, and coverage of chest, abdomen, and pelvis can be performed in less than one hour.

Incidental detection of acute myocardial infarction during routine performance of three-dimensional dynamic MR angiographic study with dynamic injection of gadolinium.

We report on the MR appearance of acute myocardial infarction in a 61-year-old man with Ehlers-Danlos syndrome using motion-independent, T2-weighted echo train spin echo and immediate post-gadolinium three-dimensional gradient echo imaging performed as an MRI angiographic study of the aortic arch. The region of acute infarction was of high signal intensity on the T2-weighted images and demonstrated greatly diminished enhancement on the immediate post-gadolinium three-dimensional gradient echo images. MRI findings showed good correlation with autopsy specimens obtained within 24 hours of the MRI study.

Cholangiocarcinoma: spectrum of appearances on MR images using current techniques.

This study describes the spectrum of appearances of cholangiocarcinoma on magnetic resonance (MR) sequences, including gadolinium-enhanced, fat-suppressed spoiled gradient echo images and MR cholangiography. Fifteen patients were included in the study. Histologic diagnosis was established in 11 patients by surgical resection (6 patients), percutaneous biopsy (4 patients), and open liver biopsy (1 patient). The final diagnosis was determined by correlation of the MR findings with cholangiographic studies and laboratory studies in 4 patients. MR studies were performed at 1.5 T, and the following sequences were obtained: T1-weighted spoiled gradient echo (SGE), T1-weighted fat-suppressed spin echo or SGE, T2-weighted fat-suppressed conventional or turbo spin echo, MR cholangiography, and gadolinium-enhanced T1-weighted fat-suppressed SGE images. The following determinations were made: tumor location, tumor extent, ductal dilatation, ductal wall thickness, signal intensity, enhancement pattern, and associated findings. Mass-like neoplasms were peripheral (6 patients), hilar (1 patient), and extrahepatic (2 patients). Circumferential tumors were hilar (2 patients) and extrahepatic (4 patients). All peripheral tumors were multifocal. Mass-like tumors were well-defined, rounded, and ranged from 1 to 14 cm in diameter. Circumferential tumors had less well-defined margins and measured from 3 to 15 mm in thickness. All mass-like tumors were moderately hypointense on T1-weighted images and mildly to moderately hyperintense on T2-weighted images. The circumferential tumors were iso- to moderately hypointense on T1-weighted images and iso- to mildly hyperintense on T2-weighted images. Mass-like tumors were generally well shown on non-contrast and immediate gadolinium-enhanced images, whereas circumferential tumors were poorly seen on non-contrast images and best shown on gadolinium-enhanced T1-weighted fat-suppressed images. The degree of enhancement ranged from minimal to intense on immediate gadolinium-enhanced images, with all tumors becoming more homogeneous in signal intensity on images obtained between 1 and 5 min following contrast administration. Tumor-containing lymph nodes greater than or equal to 1 cm in diameter were demonstrated in 11 out of 15 patients (73.3%). These were best shown on T2-weighted fat-suppressed images and gadolinium-enhanced fat-suppressed SGE images. MR cholangiography demonstrated the level of obstruction and degree of dilatation of the proximal biliary system in 5 out of 6 patients who underwent MR cholangiography. The spectrum of appearances of cholangiocarcinoma is demonstrable on MR images. Mass-like tumors are well shown on both pre- and post-gadolinium sequences. Circumferential tumors may cause minimally increased duct wall thickness and are most clearly shown on gadolinium-enhanced fat-suppressed SGE images obtained 1 to 5 min following gadolinium administration.

Bowel-related abscesses: MR demonstration preliminary results.

The purpose of this study is to describe the appearance of bowel-related abscesses on magnetic resonance (MR) images. Sixteen consecutive patients who had bowel-related abscesses underwent MR examination at 1.5T. MR sequences included T1-weighted fat-suppressed imaging pre- and post-intravenous gadolinium chelate administration (all patients) and breathing-independent single-shot T2-weighted half Fourier turbo (fast) spin echo (6 patients). Patients with pelvic abscesses also underwent sagittal imaging with post-gadolinium T1-weighted images (9 patients) and T2-weighted turbo (fast) spin echo (8 patients). Abscesses were confirmed by open surgery or surgical drainage (6 patients), percutaneous drainage (8 patients), or combined physical examination, fluoroscopic fistulogram, and clinical follow-up (2 patients). Oval-shaped fluid collections were identified in all of the patients, which ranged in diameter from 2 cm to 18 cm, mean: 8 cm. Abscesses were low to intermediate in signal on T1-weighted images, heterogenous and moderately high signal on T2-weighted images, and low signal on post-gadolinium images. A layering effect of lower signal material in the dependent portion of the abscess was noted in abscesses in 6 of 14 patients on T2-weighted images. Post-gadolinium images demonstrated a definable 3- to 7-mm thick abscess wall, which enhanced substantially with contrast. Definition of the wall was best shown on fat-suppressed images post-gadolinium. Substantial enhancement of surrounding periabscess tissues was demonstrated in all cases and was most clearly defined on fat-suppressed images. Image acquisition in two orthogonal planes was of value to demonstrate that fluid collections were oval, and separate from bowel. Image acquisition in the sagittal plane was useful in the evaluation of pelvic abscesses. The results from this preliminary study show that bowel-related abscesses are demonstrable on MR images using gadolinium-enhanced fat-suppressed T1-weighted and turbo (fast) spin-echo T2-weighted sequences. The presence of a thickened, enhancing lesion wall and enhancement of perilesional tissues on T1-weighted fat-suppressed images were observed in all abscesses. A layering effect of low signal intensity material in the dependent portion of the abscess was an important ancillary feature.

Hepatocellular carcinoma in North America: a multiinstitutional study of appearance on T1-weighted, T2-weighted, and serial gadolinium-enhanced gradient-echo images.

OBJECTIVE: The purpose of this study was to define the common appearances of hepatocellular carcinoma (HCC) in patients in North America by analyzing T1-weighted, T2-weighted, and serial gadolinium-enhanced gradient-echo images interpreted by radiologists at multiple institutions in North America. MATERIALS AND METHODS: One hundred thirteen consecutive patients with HCC from eight institutions were included in this retrospective case series. Inclusion criteria included MR imaging examinations performed on 1.5-T MR imagers using T1-weighted breath-hold spoiled gradient-echo images, T2-weighted images, and serial gadolinium-enhanced spoiled gradient-echo images. Diagnosis was established by histology in all patients. Images were analyzed retrospectively for lesion count, lesion diameter as less than or equal to 1.5 cm and greater than 1.5 cm, and signal intensity, by individual experienced radiologists at each institution. RESULTS: We found 354 HCC lesions in the 113 patients. Tumors were solitary in 63 patients, multifocal in 45 patients, and diffuse in five patients. Lesion appearance on combined T1-weighted, T2-weighted, and immediate gadolinium-enhanced spoiled gradient-echo images was as follows: 102 lesions (29%) were hypointense on T1-weighted images, were hyperintense on T2-weighted images, and exhibited diffuse heterogeneous enhancement; 52 lesions (15%) were isointense on both T1- and T2-weighted images and exhibited diffuse homogeneous enhancement (all of these lesions measured < or = 1.5 cm in diameter); 50 lesions (14%) were hypointense on T1-weighted images, were hyperintense on T2-weighted images, and exhibited diffuse homogeneous enhancement; 33 lesions (9%) were hypointense on T1-weighted images, were hyperintense on T2-weighted images, and exhibited predominantly peripheral rim enhancement; and 27 lesions (8%) were hypointense on T1-weighted images, were isointense on T2-weighted images, and exhibited diffuse homogeneous enhancement. The remaining 90 lesions showed less common patterns. The appearance of HCCs greater than 1.5 cm and of HCCs less than or equal to 1.5 cm was significantly different (p = .001). The appearance of histologically proven HCCs is separately described. CONCLUSION: The combination of hypointensity on T1-weighted images, hyperintensity on T2-weighted images, and diffuse heterogeneous enhancement was the most common appearance of HCC on MR images in a multiinstitutional patient population in North America. Small HCCs measuring less than or equal to 1.5 cm were frequently isointense on both T1-weighted and T2-weighted images and may be detected on immediate gadolinium-enhanced images only as diffuse homogeneously enhancing lesions.