Standardized volume rendering for magnetic resonance angiography measurements in the abdominal aorta

Purpose: To compare three methods for standardizing volume rendering technique (VRT) protocols by studying aortic diameter measurements in magnetic resonance angiography (MRA) datasets.

Material and Methods: Datasets from 20 patients previously examined with gadolinium-enhanced MRA and with digital subtraction angiography (DSA) for abdominal aortic aneurysm were retrospectively evaluated by three independent readers. The MRA datasets were viewed using VRT with three different standardized transfer functions: the percentile method (Pc-VRT), the maximum-likelihood method (ML-VRT), and the partial range histogram method (PRH-VRT). The aortic diameters obtained with these three methods were compared with freely chosen VRT parameters (F-VRT) and with maximum intensity projection (MIP) concerning inter-reader variability and agreement with the reference method DSA.

Results: F-VRT parameters and PRH-VRT gave significantly higher diameter values than DSA, whereas Pc-VRT gave significantly lower values than DSA. The highest interobserver variability was found for F-VRT parameters and MIP, and the lowest for Pc-VRT and PRH-VRT. All standardized VRT methods were significantly superior to both MIP and F-VRT in this respect. The agreement with DSA was best for PRH-VRT, which was the only method with a mean error below 1 mm and which also had the narrowest limits of agreement (95% of cases between 2.1 mm below and 3.1 mm above DSA).

Conclusion: All the standardized VRT methods compare favorably with MIP and VRT with freely selected parameters as regards interobserver variability. The partial range histogram method, although systematically overestimating vessel diameters, gives results closest to those of DSA.     

Correlation of femoral artery flow velocity waveform with ipsilateral iliac artery stenoses assessed with magnetic resonance imaging

Background: Magnetic resonance (MR) permits quantitative flow velocity measurements that could be used to detect changes in the curve profile downstream of a high-grade stenosis.

Purpose: To assess whether MR flow measurements can be used to detect iliac artery stenoses.

Material and Methods: Contrast-enhanced magnetic resonance angiography (MRA) and quantitative flow measurements in the lower aorta and proximal femoral arteries were performed in 29 patients with suspected iliac artery stenoses. Stenoses were graded into five degrees: 0%, 1-49%, 50-74%, 75-99%, and 100% diameter reduction. The femoral artery waveforms were evaluated qualitatively by two independent reviewers regarding peak systolic velocity (PSV), aortofemoral difference in time-to-peak (ΔTTP), systolic acceleration (SA), curve-shape index (CSI), and the presence of an early diastolic flow reversal. The correlation between these parameters and the degree of stenosis was assessed.

Results: A significant correlation with degree of stenosis was observed for the qualitative flow waveform evaluations, with a high degree of interobserver agreement (κ = 0.84). A significant correlation was also found between degree of stenosis and PSV, ΔTTP, SA, CSI, and presence of diastolic flow reversal. The flow velocity pattern, however, remained unchanged, both qualitatively and quantitatively, up to a stenosis degree of at least 75%.

Conclusion: Iliac artery stenoses cause femoral artery flow waveform changes that can be detected with MRI, but only at high-grade levels.     

Magnetic resonance elastography of the human brain: a preliminary study

Purpose: To study the application of magnetic resonance elastography (MRE) in the human brain.

Material and Methods: An external force actuator was developed, which produced propagating shear waves in brain tissue. A modified phase-contrast gradient-echo sequence was developed. The propagating shear waves within the brain were directly imaged. The wave images were processed to obtain the elasticity image. Shear waves at 100 Hz, 150 Hz, and 200 Hz were applied.

Results: The propagating shear waves in the brain were visualized on wave images. The elasticity image revealed the difference in tissue elasticity between gray and white matter of the brain.

Conclusion: MRE could be an imaging technique for assessing the elasticity of brain tissue.     

Value of subtraction in fat-saturated three-dimensional contrast-enhanced magnetic resonance angiography of the hemodialysis fistula

Purpose: To evaluate image subtraction in a three-dimensional contrast-enhanced magnetic resonance angiography (3D CE-MRA) using fat suppression for the hemodialysis fistula.

Material and Methods: Fifteen patients suffering from hemodialysis fistula dysfunction were imaged with 3D CE-MRA using fat suppression and digital subtraction angiography (DSA). Non-subtracted and subtracted MRA images using maximum intensity projection (MIP) were constructed and the validity of the MRA interpretations of the degree of vascular stenoses was evaluated using DSA as the standard of reference. Image quality was assessed using qualitative analysis (vessel contrast) and quantitative analysis (contrast-to-noise ratio (CNR) of the vessel versus the background).

Results: In the vessels with stenosis of 50% or greater, the sensitivity and specificity of the non-subtracted MRA were 89.5% and 81.8%, respectively, and of the subtracted MRA 89.5% and 86.4%, respectively. There was no significant difference in the detectability of stenoses between either MRA. The vessel contrast of the anterior interosseous artery and the CNR of the anterior interosseous artery versus the background on the subtracted MRA were significantly superior to those on the non-subtracted MRA. With regard to the radial artery and cephalic vein, there was no significant difference in the vessel contrast and CNR between either MRA.

Conclusion: Both subtracted and non-subtracted MRA techniques are useful in detecting hemodialysis fistula dysfunction.     

Multidetector computed tomography (MDCT) in the diagnosis of pulmonary embolism: interobserver agreement among radiologists with varied levels of experience

Purpose: To assess the interobserver variability of radiologists with varied levels of experience in the interpretation of multidetector computed tomography (MDCT) pulmonary angiographies.

Material and Methods: Review of CT pulmonary angiographies performed on patients included in a diagnostic study evaluating a decision-based algorithm for diagnosing pulmonary embolism (PE). Five radiologists, three board-certified general radiologists and two radiology trainees with 2 years' experience, participated in the study.

Results: According to the consensus reading, PE was present in 91 (31%) and absent in 194 (67%) patients, while in five patients (1.7%) the interpretations were regarded as equivocal. The per-patient agreement on the diagnosis of PE achieved by each of the four readers compared to the consensus reading was very good (κ range 0.85-0.92), but peripheral emboli were missed in four to six patients by three of four observers. The agreement on the most proximal level of PE (per-proximal level) assessed by mean κ value was 0.83 (κ range 0.68-0.91) for the detection of proximal emboli, 0.61 for segmental emboli (κ range 0.40-0.80), and 0.38 for emboli in the subsegmental vessels (κ range 0.0-0.89).

Conclusion: The overall agreement on the diagnosis of PE by MDCT for general radiologists and radiology trainees is very good, and we therefore believe that the initial management of patients with suspected PE could be based on the preliminary assessment performed by on-call radiologists with 2 years of experience.     

Multi-detector computed tomography angiography of the hepatic artery in liver transplant recipients

Purpose: To evaluate the ability of multi-detector row computed tomography angiography (CTA) in detecting hepatic artery complications in the follow-up of liver transplant patients, performing volume-rendering as reconstruction technique.

Material and Methods: The anatomy of hepatic artery was studied in 27 liver transplant recipients with a four-row CT scanner using the following parameters: collimation, 1 mm; slice width, 1 mm; table feed, 6-8 mm/s; spiral reconstruction time, 0.5 s; reconstruction interval, 0.5 mm; mAs, 160; kVp, 120. Before the study, the patients received 1000 ml of water as oral contrast agent to produce negative contrast in the stomach and the small bowel. A non-ionic contrast medium was infused intravenously at a rate of 5 ml/s with a bolus tracking system. Volume-rendering of hepatic artery was performed with the 3D Virtuoso software.

Results: The celiac trunk, the hepatic artery, and the right and left hepatic arteries were successfully displayed in high detail in all patients. Side branches, including small collaterals, and hepatic artery anastomosis could also be readily visualized. Volume-rendered CTA detected six hepatic artery stenoses, two hepatic artery thromboses, and two intrahepatic pseudoaneurysms. In two cases, CT detected hepatic artery stenosis with a diameter reduction of less than 50%, while digital subtraction angiography showed a normal artery.

Conclusion: Volume-rendered multi-detector CTA is a promising non-invasive technique, since it allows images of high quality to be generated with excellent anatomical visualization of the hepatic artery and its complications in liver transplant recipients.     

Assessment of 3D-TOF-MRA at 3.0 Tesla in the characterization of the angioarchitecture of cerebral arteriovenous malformations: a preliminary study

Background: The characterization of brain arteriovenous malformation (AVM) angioarchitecture remains rewarding in planning and predicting therapy. The increased signal-to-noise ratio at higher field strength has been found advantageous in vascular brain pathologies.

Purpose: To evaluate whether 3.0T time-of-flight (TOF) magnetic resonance angiography (MRA) is superior to 1.5T TOF-MRA for the characterization of cerebral AVMs.

Material and Methods: Fifteen patients with AVM underwent TOF-MRA at 3.0T and 1.5T and catheter angiography (DSA), which was used as the gold standard. Blinded readers scored image quality on a four-point scale, nidus size, and number of feeding arteries and draining veins.

Results: Image quality of TOF-MRA at 3.0T was superior to 1.5T but still inferior to DSA. Evaluation of nidus size was equally good at 3.0T and 1.5T for all AVMs. In small AVMs, however, there was a tendency of size overestimation at 3.0T. MRA at 3.0T had increased detection rates for feeding arteries (+21%) and superficial (+13%) and deep draining veins (+33%) over 1.5T MRA.

Conclusion: 3.0T TOF-MRA offers superior characterization of AVM angioarchitecture compared with 1.5T TOF-MRA. The image quality of MRA at both 3.0 and 1.5T is still far from equal to DSA, which remains the gold standard for characterization of AVM.     

Accessory renal artery stenosis and hypertension: are these correlated? Evaluation using multidetector-row computed tomographic angiography

Background: Renal artery stenosis may produce hypertension, and this condition is referred to as renovascular hypertension (RVH).

Purpose: To evaluate, by using multidetector-row spiral computed tomographic angiography (MDCTA), whether a relationship between accessory renal artery stenosis and hypertension may be hypothesized.

Material and Methods: 214 patients (142 males, 72 females; mean age 66 years) who had previously undergone an MDCTA to study the abdominal vasculature were retrospectively studied. Patients with renal artery stenosis (RAS) were excluded from this analysis. The patients were studied by means of a four-detector-row CT, and scans were obtained after intravenous bolus administration of 110-140 ml of a nonionic contrast material with a 3-6 ml/s flow rate. As a second step, by means of statistical analysis, hypertension data were compared with findings of accessory artery stenosis. Two radiologists first independently reviewed the MDCTA images and then, in case of disagreement, in consensus. Interobserver agreement was calculated for all measurements.

Results: The overall number of detected accessory renal arteries was 74 in 56 of the 214 patients. Accessory renal artery stenosis was detected in 21 of the 56 patients. There was a difference in the prevalence of hypertension between patients with (n = 21) and without (n = 35) accessory renal artery stenosis (P = 0.0187). Interobserver agreement was good (kappa value 0.733).

Conclusion: Any statistical association between the presence of accessory renal artery stenosis and hypertension could not be disclosed. However, accessory renal artery stenosis, detected by MDCTA, is an important pathological sign that the radiologist has to assess in the light of its possible association with hypertension.     

Virtual bronchoscopy versus thin section computed tomography in evaluation of moderate and low grade stenoses: receiver operating characteristic curve analysis

Purpose: To evaluate the impact of virtual bronchoscopy, under proper threshold settings, on observer level of confidence in the assessment of bronchial abnormalities producing stenoses ≤75% compared to interpretation of thin section computed tomography (CT) images.

Material and Methods: Sixty-five patients with fiberoptic bronchoscopy positive for tracheobronchial abnormalities were evaluated in a blinded observer study using a commercially available virtual endoscopy software package. The findings of virtual endoscopy were compared with those of fiberoptic bronchoscopy using receiver operating characteristic curves (ROCs) and other statistical tools.

Results: A total of 102 lesions were identified by fiberoptic bronchoscopy, with 44 of these producing bronchial stenoses ≤75%. Concerning the latter lesions, for virtual bronchoscopy the areas under the ROCs were 0.93 and 0.96 for the two observers, respectively, while for thin section CT the corresponding values were 0.86 and 0.88; the differences observed were statistically significant. Contrary to thin section CT, virtual bronchoscopy did not show statistically significant differences from fiberoptic bronchoscopy regarding estimation of degree of stenosis.

Conclusion: Virtual bronchoscopy under proper threshold settings has a statistically significant impact on observer performance where moderate and low-grade bronchial stenoses are concerned and gives an estimate of the degree of stenosis more precisely than thin section CT.     

Automatic image quality quantification and mapping with an edge-preserving mask-filtering algorithm

Background: Imaging modalities in digital radiology produce large amounts of data for which image quality should be determined in order to validate the diagnostic operation.

Purpose: To develop an automatic method for image quality assessment.

Material and Methods: A filtering algorithm using a moving square mask was applied to create a map of filtered local intensity and noise values. Image quality scores were calculated from the filtered image data. The procedure was applied to technical and anthropomorphic (radiosurgery verification phantom [RSVP] head) phantom images obtained with varying radiation dose, field of view (FOV), and image content. The method was also applied to a clinical computed tomography (CT) brain image.

Results: The image quality score (IQs) of the phantom images increased from 0.51 to 0.82 as the radiation dose (CTDI_vol) increased from 9.2 to 74.3 mGy. Correlation of the IQs with the pixel noise was R² = 0.99. The deviation (1 SD) of IQs was 2.8% when the reconstruction FOV was set between 21 and 25 cm. The correlation of IQs with the pixel noise was R² = 0.98 with variable image contents and dose. Automatic tube current modulation applied to the RSVP phantom scan reduced the variation in the calculated image quality score by about 60% compared to the use of a fixed tube current.

Conclusion: The image quality score provides an efficient tool for automatic quantification of image quality. The presented method also produces a 2D image quality map, which can be used for further image analysis.     

Low-field magnetic resonance imaging of the lumbar spine: reliability of qualitative evaluation of disc and muscle parameters

Purpose: To determine the intra- and interobserver reliability in grading disc and muscle parameters using low-field magnetic resonance imaging (MRI).

Material and Methods: MRI scans of 100 subjects representative of the general population were evaluated blindly by two radiologists. Criteria for grading lumbar discs were based on the spinal nomenclature of the Combined Task Force and the literature. Consensus in rating was achieved by evaluating 50 MRI examinations in tandem. The remaining 50 examinations were evaluated independently by the observers to determine interobserver agreement and re-evaluated by one of the observers to determine intra-observer agreement.

Results: Intra- and interobserver agreement was substantial when grading changes in the lumbar discs. Interobserver agreement was fair to moderate in grading the lumbar muscles, whereas intra-observer agreement was almost perfect.

Conclusion: Convincing reliability was found in the evaluation of disc- and muscle-related MRI variables.     

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.     

Measurements before endovascular repair of abdominal aortic aneurysms. MR imaging with MRA vs. angiography and CT

Purpose:
1) To compare measurements obtained with MR imaging (MRI)/contrast-enhanced MR angiography (CE MRA) with measurements obtained with angiography (DSA) and CT, for stent-graft sizing of abdominal aortic aneurysms (AAA). 2) To compare MRA measurements obtained with the two post processing techniques MIP (maximum intensity projection) and VRT (3D volume rendering technique). Material and Methods:
The prospective study included 20 consecutive patients with AAA identified by DSA and CT as suitable for endovascular repair. For the study, MRI/CE MRA was performed. Five measurement variables for stent-graft sizing were chosen. Comparisons were made between MRI/CE MRA, DSA and CT, and between observers. Comparisons were also made between MIP and VRT. Results:
Significantly shorter lengths were obtained with MRA-MIP than with DSA. Three out of six diameter measurements were significantly smaller on MRI/CE MRA than on DSA and CT. No significant differences were found between the observers. One diameter measurement was significantly smaller on MIP than on VRT, while the other measurements showed no significant differences. Conclusion:
The length measurements obtained with MRA-MIP were probably more correct than those with DSA. For more reliable diameter measurements with CE MRA, improvements of the technique, including VRT reconstructions and a standardized determination of the vessel boundaries, are needed.     

Three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) and contrast-enhanced MRA of intracranial aneurysms treated with platinum coils

Background: Contrast-enhanced magnetic resonance angiography (CE-MRA) is less prone to flow-related signal intensity loss than three-dimensional time-of-flight (3D TOF) MRA and may therefore be more sensitive for detection of residual patency in platinum coil-treated intracranial aneurysms.

Purpose: To compare MRA and CE-MRA in the follow-up of intracranial aneurysms treated with platinum coils.

Material and Methods: CE-MRA and 3D TOF MRA (pre- and postcontrast injection) of the intracranial vasculature was performed at 1.5T in 38 patients (47 aneurysms) referred for DSA in the follow-up of coiled intracranial aneurysms.

Results: DSA showed aneurysm patency in 22/47 investigations. Patent aneurysm components were observed with CE-MRA in 18/22 cases, and with 3D TOF MRA in 21/22 cases. There was no significant difference in patent aneurysm component size between CE-MRA and 3D TOF MRA. In addition, CE-MRA showed six, 3D TOF MRA before contrast injection showed seven, and 3D TOF MRA after contrast injection showed eight cases with patent aneurysm components not observed on DSA.

Conclusion: 3D TOF MRA was highly sensitive for detection of patent aneurysm components, and at least as sensitive as CE-MRA. Residual aneurysm patency seems to be better visualized with MRA than with DSA in some cases.     

Computed tomography of the urinary tract: optimalization of low-dose stone protocol in a clinical setting

Purpose: To establish whether information would be lost if slice reconstruction thickness was increased from 3 to 5 mm, and whether this altered how difficult it was to interpret the examinations.

Material and Methods: Twenty-three consecutive patients referred with suspected or known urinary stones were included. All examinations were performed without intravenous contrast media. The original series, with effective mAs 50, were reconstructed with slice thickness 3 and 5 mm, respectively. All demographic and examination data were removed and the series reviewed in PACS by two independent radiologists. Objective findings, i.e. number and size of stones, signs of obstruction, and evaluation of interpretation difficulty, were registered.

Results: Identical findings were registered in 18 of the series of 3 mm (n = 23) and 19 of the series of 5 mm (n = 23). In two series reconstructed with 3 mm slice thickness and in one series with 5 mm slice thickness, the observers disagreed on the presence of urinary stones. Main reasons for interpretation difficulties were given as “lack of intra-abdominal fat” and “many phleboliths in the pelvic region”, but never “disturbing noise”.

Conclusion: To determine the presence and size of urinary stones at low-dose computed tomography, 5 mm reconstruction algorithm seems equal to 3 mm. Patient-related factors influence the interpretation more than image quality.     

Technical optimization of four-channel multidetector-row helical computed tomography for depicting arterial stenosis: a phantom study

Purpose: To determine the effects of detector configuration, as well as vessel orientation, on the depiction accuracy of arterial stenosis using four-channel multidetector-row helical computed tomography (MDCT) angiography in vitro.

Material and Methods: Five acrylic vessel phantoms (3 mm in diameter with 25 or 50% stenosis, or 5 mm with 25, 50, or 75% stenosis) were scanned with a four-channel MDCT scanner at five vessel orientations (0, 30, 45, 60, and 90° to the z-axis) using 4×1.25, 2.5, 3.75, and 5.0-mm detector configurations at beam pitches of 0.75 and 1.5. The percentage of stenosis was calculated by the ratio of the full width at half maximum for stenotic and non-stenotic portions of the phantom, and compared to the actual known values.

Results: A detector configuration of 4×1.25 mm provided good reproducibility, as well as high accuracy for assessing vessel stenosis, while a 4×2.5-mm or wider detector configuration caused underestimations of stenosis. Although the phantoms perpendicular to the z-axis were underestimated, the errors were kept in clinically acceptable ranges using the 4×1.25-mm detector configuration.

Conclusion: Four-channel MDCT accurately discerns stenosis for vessel phantoms of 3 or 5 mm in diameter at any orientation when using a detector configuration of 4×1.25 mm.     

Magnetic resonance enteroclysis in the diagnosis of small-intestinal Crohn's disease: diagnostic accuracy and inter- and intra-observer agreement

Purpose: To evaluate the diagnostic accuracy and inter- and intra-observer agreement of magnetic resonance enteroclysis (MRE) in patients with or without Crohn's disease of the small intestine.

Material and Methods: 60 consecutive patients with or without Crohn's disease examined with MRE were included. Two observers independently reviewed the MRE examinations, searching for 12 pathological signs. The reference standard was ileoscopy or surgery of the terminal ileum performed in 41 patients.

Results: Crohn's disease of the small intestine was found in 24 (40%) patients. MRE findings of increased intestinal wall thickness, intestinal wall enhancement, intestinal wall ulcer, and inflammatory activity of the terminal ileum showed high sensitivity, specificity, and positive and negative predictive values. Intestinal stenosis had sensitivities ranging from 43% to 100%, depending on the cut-off value. Inter- and intra-observer agreement was good or excellent for most pathological signs. However, observer agreement of intestinal wall edema was only fair and moderate.

Conclusion: MRE evaluated Crohn's disease with a high diagnostic accuracy in the terminal ileum. Most MRE variables were evaluated with good or excellent observer agreement, indicating that the method was highly reproducible. Our study supports the notion that MRE is an appropriate method for diagnosing Crohn's disease.     

Split renal function in patients with suspected renal artery stenosis: a comparison between gamma camera renography and two methods of measurement with computed tomography

Purpose: To validate a method for calculating split renal function from computed tomography (CT) compared with gamma camera renography, and to test a new method for the measurement based on a volume-rendering technique.

Material and Methods: Thirty-eight patients, aged 65.7±11.6 (range 37.8-82.1) years, who had undergone both CT angiography and gamma camera renography for a suspected renal artery stenosis were included in this study. Split renal function was calculated from the CT examinations by measuring area and mean attenuation in the image slices of the kidneys, and also by measuring volume and mean attenuation from a 3D reconstruction of the kidneys. Gamma camera renography with ^99mTc-MAG3 with or without captopril enhancement was used as a reference.

Results: The 2D CT method had good correlation with renography (r = 0.93). Mean difference was 4.7±3.6 (0-12) percentage points per kidney. There was also excellent correlation between the two CT methods (r = 1.00).

Conclusion: CT is equivalent to renography in determining split renal function, and the measurement from the CT examination can be made more quickly and equally accurately with a 3D technique.     

Sentinel lymph node biopsy in oral cancer: validation of technique and clinical implications of added oblique planar lymphoscintigraphy and/or tomography

Purpose: To validate lymphatic mapping combined with sentinel lymph node biopsy as a staging procedure, and to evaluate the possible clinical implications of added oblique lymphoscintigraphy and/or tomography and test the intra- and interobserver reproducibility of lymphoscintigraphy.

Material and Methods: Forty patients (17 F and 23 M, aged 32-90) with 24 T1 and 16 T2 squamous cell carcinoma of the oral cavity. Planar lymphoscintigraphy, emission and transmission tomography were performed. Detection and excision of the sentinel nodes were guided by a gamma probe. The sentinel nodes were step-sectioning and stained with hematoxylin and eosin and cytokeratin (CK 1). Histology and follow-up were used as “gold standard”. Tumor location, number of sentinel lymph nodes, metastasis, and recurrences were registered. Two observers evaluated the lymphoscintigraphic images to assess the inter-rater agreement.

Results: Eleven (28%) patients were upstaged. The sentinel lymph node identification rate was 97.5%. Sentinel lymph node biopsy significantly differentiated between patients with or without lymph node metastasis (P = 0.001). Lymphatic mapping revealed 124 hotspots and 144 hot lymph nodes were removed by sentinel lymph node biopsy. Three patients developed a lymph node recurrence close to the primary tumor site during follow-up. Added oblique lymphoscintigraphic images and/or tomography revealed extra hotspots in 15/40 (38%) patients. In 4/40 (10%), extra contralateral hotspots were detected.

Conclusion: Sentinel lymph node biopsy upstaged 28% of the patients. Sentinel lymph nodes close to the primary tumor were difficult to find. Added oblique planar images and/or tomographic images revealed extra clinical relevant hotspots in 38% of patients. Reproducibility proved excellent.     

Pulmonary perfusion in acute pulmonary embolism: agreement of MRI and SPECT for lobar, segmental and subsegmental perfusion defects

Purpose: To assess prospectively the agreement of magnetic resonance (MR) pulmonary perfusion with single-photon emission computed tomography (SPECT) perfusion for perfusion defects down to the subsegmental level in patients with suspected pulmonary embolism (PE).

Material and Methods: In 41 patients with suspected PE, contrast-enhanced MR pulmonary perfusion (3D-FLASH, TR/TE 1.6/0.6 ms) was compared to SPECT perfusion on a per-examination basis as well as at the lobar, segmental, and subsegmental level.

Results: The MRI protocol was completed in all patients, and mean examination time was 3 min 56 s. MR perfusion showed a very high agreement with SPECT (kappa value per examination 0.98, and 0.98, 0.83, and 0.69 for lobar, segmental, and subsegmental perfusion defects, respectively). Of 15 patients with PE, MR perfusion detected 14 cases.

Conclusion: The very high agreement of MR perfusion with SPECT perfusion enables the detection of subtle findings in suspected PE.