Biomedical subjects

P F Hahn

Publications and source records attributed to P F Hahn.

At least 73 records · Page 4Linked to original sources

PubMed1994

Hepatic hemangiomas and malignant tumors: improved differentiation with heavily T2-weighted conventional spin-echo MR imaging.

PURPOSE: To determine whether hemangiomas and malignant tumors can be better differentiated at 1.5-T magnetic resonance imaging with use of more heavily T2-weighted conventional spin-echo sequences. MATERIALS AND METHODS: Eighty-three patients with focal liver lesions (50 malignant tumors, 24 hemangiomas, nine cysts) larger than 1 cm were studied with a 3,000/80, 160 sequence (repetition time msec/echo time [TE] msec). T2 relaxation times and lesion/liver signal intensity ratios at TEs of 80 and 160 msec were measured. Receiver operating characteristic (ROC) analyses of expert readers and quantitative measures were performed. RESULTS: T2 relaxation times demonstrated the best performance in distinguishing hemangiomas from malignant tumors (area under ROC curve = .99 +/- .01). Mean T2 times were 76 msec +/- 11 for malignant tumors, 142 msec +/- 40 for hemangiomas, and 341 msec +/- 38 for cysts. A cutoff T2 value of 112 msec allowed discrimination between hemangiomas and malignant tumors with a 97% accuracy, 100% sensitivity, and 92% specificity. CONCLUSION: Hemangiomas and malignant tumors are better differentiated with use of T2 relaxation times obtained with a more heavily T2-weighted sequence.

Cysts↗

PubMed1994

T2-weighted MR imaging of the upper part of the abdomen: should fat suppression be used routinely?

OBJECTIVE: Fat suppression has shown promise in improving the quality of T2-weighted spin-echo MR images of the upper part of the abdomen. The purpose of this study was to determine whether fat-suppressed images should be routinely used in lieu of conventional images. Accordingly, we prospectively compared the two techniques in a series of patients with both normal and abnormal findings in the upper part of the abdomen. MATERIALS AND METHODS: Conventional and fat-suppressed T2-weighted spin-echo images (3000/80,160 [TR/TE]) were obtained in 45 consecutive patients referred for MR imaging of the upper part of the abdomen. Thirty-three patients had abnormal findings, and 22 of those 33 patients had histologic or follow-up confirmation of the diagnosis (14 with metastasis, one with hepatoma, four with hemangiomas, and three with cysts). Signal intensities (hepatic lesions, liver, spleen) and noise were measured to calculate signal-to-noise ratios and contrast-to-noise ratios. Qualitative comparison (liver, hepatic lesions, porta hepatis, spleen, pancreas, bowel, kidneys, adrenal glands, noise), evaluation of the number of hepatic lesions, and characterization of hepatic lesions were done by independent observers. RESULTS: Compared with conventional images, fat-suppressed images had higher signal-to-noise ratios (lesions, liver, spleen) and contrast-to-noise ratios (lesion-liver and spleen-liver) (p < .005). In qualitative comparison, three of three radiologists preferred fat-suppressed over conventional images for depiction of hepatic lesions and all upper abdominal organs except the liver, for which no clear preference was shown for either technique. Detection rates for hepatic lesions were similar with both types of images (observer 1: 112 lesions on fat-suppressed vs 118 on conventional images, observer 2: 142 vs 135), as was the characterization of hepatic lesions (91% accuracy on fat-suppressed images and 84% accuracy on conventional images, for 22 proved lesions and two observers). CONCLUSION: Fat-suppressed T2-weighted spin-echo MR images were better than non-fat-suppressed images for evaluation of the upper part of the abdomen. These results suggest that fat suppression should be routinely used in T2-weighted MR imaging of the upper part of the abdomen.

Abdomen↗

PubMed1994

A simplified HyperCard data base for patient management in an interventional practice: experience with more than 4000 cases.

OBJECTIVE: Tracking of interventional radiology procedures is essential for patients' care, follow-up, and quality management, as well as for fellowship training and accreditation. Computer data-base systems that require time-consuming data entry are difficult to use in a practice that performs 1500 abdominal interventional procedures each year while concurrently doing diagnostic imaging. We proposed that a data base updated with data from existing sources and furnishing information used daily in patient management could be maintained by the radiologists it serves. MATERIALS AND METHODS: We developed a data base to track abdominal interventional radiology cases by using the HyperCard application program running on Macintosh personal computers. For each procedure, one card is entered into the Current Cases stack, which prints a daily log including new patients, those with management issues, and pending biopsy results. Cards for inactive patients are automatically compressed and transferred to a second stack for permanent archive. The latter can be queried to identify individual patients, to list complications, and for research. RESULTS: In continuous use for 3 years, the system has logged 4322 procedures in 2394 patients. Ninety percent of data entry is by a secretary. The daily log serves as the focus for the case conference at the close of work, when errors are corrected and specific comments entered. Three independent searches for specific types of procedures have failed to identify excluded cases. CONCLUSION: Easy data entry and error correction, together with useful information provided daily by the data base, are features of the system that promote its consistent use.

Database Management Systems↗

PubMed1994

MR imaging of the liver at 1.5 T: value of signal averaging in suppressing motion artifacts.

OBJECTIVE: Prior reports have suggested that signal averaging is not as effective as phase reordering for suppressing motion-related artifacts on T1-weighted spin-echo MR imaging of the liver at high field strengths. We hypothesized that with shorter TEs, signal averaging could be effective, and therefore undertook this study to compare signal averaging with phase reordering at 1.5T. SUBJECTS AND METHODS: Thirty consecutive patients underwent MR imaging of the liver at 1.5 T with two T1-weighted spin-echo pulse sequences. In one sequence we used signal averaging and in the other we used phase reordering as the primary motion suppression techniques. For each patient, the order in which these sequences were performed was randomized; TR (400-500 msec), TE (11-12 msec), and field of view (32-34 cm) remained constant. Images were analyzed quantitatively for liver signal-to-noise ratio (SNR), liver-spleen contrast-to-noise ratio (CNR), and liver-lesion CNR (in 16 patients with focal liver lesions), as well as qualitatively (three observers, blinded to technique) for overall image quality. RESULTS: Signal averaging resulted in images with significantly greater liver SNR, liver-spleen CNR, and liver-lesion CNR than did phase reordering (p = .0001, .002, and .02, respectively). All observers showed a preference for the signal-averaged images. For one observer, this preference was statistically significant; for the others, it was not. CONCLUSION: Signal averaging can be an effective means of suppressing motion-related artifacts on T1-weighted MR images of the liver obtained at 1.5 T.

Artifacts↗

PubMed1994

Echoplanar MR imaging of the liver in patients with focal hepatic lesions: quantitative analysis of images made with various pulse sequences.

OBJECTIVE: We undertook this study to evaluate pulse-sequence performance in terms of liver signal-to-noise ratio (SNR) and lesion-liver contrast-to-noise ratio (CNR) on T1- and T2-weighted echoplanar MR imaging. SUBJECTS AND METHODS: Forty-nine patients referred for MR imaging of the liver were examined at 1.5 T with echoplanar MR imaging using spin-echo, inversion-recovery, and gradient-echo pulse sequences. T2-weighted spin-echo (TE = 25, 50, 100, and 150 msec), T1-weighted inversion-recovery (T1 = 100, 380, 600, and 800 msec), and T2*-weighted gradient-echo (TE = 20 msec) images were acquired after one excitation (TR = infinite), using a 128 x 128 data matrix. T2-weighted spin-echo (TE = 20, 50, 100, and 150 msec) images were also obtained with two excitations (TR = 6 sec), resulting in a 128 x 256 data matrix. Signal intensity measurements were made to calculate liver SNR and lesion-liver CNR. RESULTS: Single-excitation, T2-weighted, spin-echo images at a minimum TE of 25 msec provided the highest liver SNR (p < .05). Single-excitation, T2-weighted, spin-echo images at TEs of 50 and 100 msec, and T1-weighted inversion-recovery images at Tls of 100 and 380 msec provided the highest lesion-liver CNR (p < .05). However, the latter two pulse sequences had considerably inferior liver SNR (p < .05). CONCLUSION: Single-excitation, T2-weighted, spin-echo images provide both superior liver SNR and superior lesion-liver CNR. These results can be used to guide technique selection when echoplanar MR imaging is used to examine the liver.

Echo-Planar Imaging↗

PubMed1993

[The clinical use of echoplanar MR tomography in the detection of focal liver lesions. The results of a quantitative study].

The purpose of the present study was to investigate the clinical application of echoplanar MR imaging compared to conventional MR imaging in the detection of focal liver lesions. A total of three conventional and 12 echoplanar pulse sequences were acquired in 35 patients with focal liver lesions. Motion artifacts were eliminated because of short acquisition times of 32 ms subsequently improving signal-to-noise. A single-shot spin-echo technique with a TE of 26 ms provided the highest liver signal-to-noise ratio (p < 0.05) of all sequences acquired. Contrast-to-noise ratios for a single-shot SE technique with echo times of 50-100 ms were as high as 10-40.

Cysts↗

PubMed1993

Percutaneous management of hilar biliary malignancies with metallic endoprostheses: results, technical problems, and causes of failure.

Malignant obstruction at the biliary hilum is a challenging problem for percutaneous management because of the anatomy of the biliary hilum, which facilitates spread of tumor into multiple biliary radicles. Metallic self-expanding stents were used in 22 patients with hilar malignancies. Sixteen patients had focal common hepatic duct strictures, and six had multisegmental disease. Stents were placed in the biliary system with a single transhepatic approach in 16 patients with common hepatic duct strictures; stent placement in the right and left biliary ducts was performed with a bilateral transhepatic approach in five patients and with a single transhepatic approach in one patient. Metal stent occlusion occurred in six patients (27%) at a mean of 2.5 months after initial insertion. Stent occlusion was due to inspissated debris in two of these patients and to tumor overgrowth in four. The key to successful long-term treatment is to "overstent" to ensure adequate purchase above hilar tumors and insertion in a balanced position. Thus, the prevalence of tumor overgrowth is decreased.

Bile Duct Neoplasms↗

PubMed1993

Gastrostomy conversion to transgastric jejunostomy: technical problems, causes of failure, and proposed solutions in 63 patients.

Sixty-three radiologically guided conversions of gastrostomy to transgastric jejunostomy performed over a 4-year period were reviewed. Conversions succeeded in 31 of 38 surgically placed gastrostomies (82%), in 14 of 18 endoscopically placed gastrostomies (78%), and in seven of seven radiologically placed gastrostomies, for an overall success rate of 83%. Almost all failures (10 of 11 gastrostomies) were primarily the result of unfavorable fundal angulation of the surgical or endoscopic tract; unfavorable angulation was also the most common technical problem encountered in the successful conversions. Of the 52 successful conversions, 23 (44%) necessitated tube replacement: eight for spontaneous proximal migration of the tube, 11 for accidental tube dislodgment, and four for tube blockage. While most gastrostomy to transgastric jejunostomy conversions are simple to perform, in many cases the unfavorable angle of the original transcutaneous tract precludes jejunal intubation and may be a cause for early recoil of a successfully placed jejunal catheter back into the stomach. With early recognition of an unfavorable tract, a fresh transgastric jejunostomy through a new, properly angled puncture may be the preferred approach.

Adolescent↗

PubMed1993

MR angiography of the portal and hepatic venous systems: preliminary experience with echoplanar imaging.

OBJECTIVE: The purpose of this study was to evaluate the ability of echoplanar MR angiography to depict the major hepatic and portal venous structures. SUBJECTS AND METHODS: Echoplanar and conventional MR angiographic examinations were performed in 10 subjects (seven healthy volunteers, three patients with focal hepatic lesions). A gradient-recalled echo (GRE) time-of-flight technique (125/10 [TR/TE], 90 degrees flip angle) was used for echoplanar angiography. Eight complete single-excitation images were acquired at each level in 1.5 sec and then collapsed into a single maximal intensity projection. Conventional time-of-flight MR angiography (34/13, 30 degrees flip angle) also was performed. The vascular anatomy from the right atrium to the splenic vein was imaged (6-mm contiguous levels) in three 10.5-sec breath-holds with echoplanar imaging, as compared with seven 11.5-sec breath-holds with conventional MR angiography. Echoplanar and conventional images were compared quantitatively and qualitatively. RESULTS: Echoplanar imaging was 61% faster than conventional MR angiography. Vessel-to-liver signal-intensity ratios were significantly higher for echoplanar imaging (p < .0001), signal-to-noise ratios were significantly higher for conventional MR angiography (p < .0001), and contrast-to-noise ratios were comparable. Qualitatively, echoplanar imaging and conventional MR angiography provided similar anatomic information about the hepatic and portal veins. CONCLUSION: Angiograms of the hepatic and portal venous systems that are of diagnostic quality can be acquired much more quickly with echoplanar imaging than with conventional MR angiography.

Echo-Planar Imaging↗

PubMed1993

Value of T1 and T2 relaxation times from echoplanar MR imaging in the characterization of focal hepatic lesions.

OBJECTIVE: The purpose of this study was to determine the value of echoplanar imaging in characterizing focal hepatic lesions on the basis of image-derived T1 and T2 relaxation times. SUBJECTS AND METHODS: Forty-six proven hepatic lesions were analyzed: 24 solid (21 metastases, three primary liver tumors) and 22 nonsolid (11 hemangiomas and 11 cysts). Mean lesion size (maximal length) was 4.0 (+/- 3.2) cm, and 16 of 46 lesions were less than 2.0 cm. A commercially available 1.5-T echoplanar-equipped MR scanner was used to obtain fat-suppressed, single-excitation (TR essentially infinite) axial images with a slice thickness of 10 mm. T1-weighted inversion recovery images (TE = 25 msec; TI = 100, 380, 600, or 800 msec) were acquired for 28 of 46 lesions, and T2-weighted spin-echo images (TE = 25, 50, 100, 75 or 150 msec) were acquired for 45 of 46 lesions. For each acquisition (i.e., each different TI or TE), the entire liver was imaged in a single breath-hold of 12 sec or less. RESULTS: The mean T1 was 1004 (+/- 234) msec for solid lesions, 1337 (+/- 216) msec for hemangiomas, and 3143 (+/- 1392) msec for cysts. Although the mean T1 of solid and nonsolid lesions differed (p < .004), overlap precluded the use of T1 as a discriminatory index. Mean T2 times were 80 (+/- 18) msec for solid lesions, 178 (+/- 40) msec for hemangiomas, and 517 (+/- 429) msec for cysts. The mean T2 for hemangiomas is the longest reported to date. A T2 cutoff of 116 msec was 100% accurate for classifying lesions as solid or nonsolid and 93% accurate for characterizing them as benign or malignant. CONCLUSION: Our study suggests that echoplanar-derived T2 times (but not T1 times) are useful for characterizing focal hepatic lesions. An important use may be to characterize small lesions measuring less than 2.0 cm. The main advantages of echoplanar imaging are the absence of motion-induced volume averaging and phase artifacts, the ability to acquire purely T2-weighted images, and the use of multiple data points to calculate relaxation times.

Cysts↗

PubMed1993

CT demonstration of steatotic liver cell adenoma.

A case of lipomatous tumor of the liver in a patient with diffuse liver steatosis is presented. The fatty infiltration of the tumor produced X-ray attenuation clearly visible on CT. Histologic examination of the tumor mass revealed a non-encapsulated tumor composed of hepatocytes with lipid overload.

Adenoma, Liver Cell↗

PubMed1992

An aqueous gastrointestinal contrast agent for use in echo-planar MR imaging.

Four volunteers were imaged with echo-planar imaging before and after ingesting a dilute barium preparation. The contrast material improved bowel visibility by increasing lumen signal intensity, without increasing noise. Long T2 gastrointestinal contrast material can be used in T2-weighted imaging when motion artifacts are suppressed by ultrashort acquisitions.

Administration, Oral↗

PubMed1992

Accumulation of iron oxide particles around liver metastases during MR imaging.

The histologic nature of the bright ring ("peritumoral edema") around some liver metastases on T2-weighted magnetic resonance (MR) images is controversial. In the case reported, particles of the iron oxide contrast agent AMI-25 are retained in the peritumoral zone of a colon cancer metastasis, causing the bright ring to disappear. The location of iron particles in resected specimens could be used systematically to study peritumoral edema.

Adenocarcinoma↗

PubMed1992

Palliation of malignant bile duct obstruction with metallic biliary endoprostheses: technique, results, and complications.

Expandable metallic stents were placed in 34 patients with pathologically proved malignant bile duct obstruction to determine ease of insertion, benefits of a one-stage insertion, and cost-effectiveness relative to conventional plastic stents. Thirty-eight strictures, ranging in length from 1 to 7 cm (mean, 3.2 cm), were present in the 34 patients. Strictures were located in the lower common bile duct (n = 22), middle of the common bile duct (n = 6), and hilar confluence (n = 10). In 13 patients (38%) metallic stents were placed at the time of initial biliary drainage (one-stage procedure), while the remaining patients underwent stent placement within 1-7 days of biliary drainage (two-stage procedure). Biliary obstruction was relieved in 31 of 34 patients (91%). Three patients died within 14 days of stent insertion of unrelated causes, without any change in biliary status. Mean duration of follow-up for all patients was 5.3 months (range, 0.5-14 months). Four episodes of stent occlusion occurred in three patients (12% occlusion rate); each episode was treated successfully. The average length of hospital stay for patients who underwent a one-stage procedure was 13 days (range, 3-33 days) and was 20 days (range, 9-42 days) for patients who underwent a two-stage procedure. The facility of one-step insertion, low occlusion rate, and the many strategies available for treatment of occluded stents make metallic stents an attractive alternative to conventional plastic stents in palliating patients with malignant biliary obstruction.

Adenoma, Bile Duct↗

PubMed1992

Techniques for high-resolution echo-planar MR imaging of the pancreas.

Recent technical advances in echo-planar magnetic resonance (MR) imaging prompted an investigation of these new techniques in pancreatic MR imaging and evaluation of bowel lumen enhancement with an aqueous bowel contrast agent. In 42 subjects (36 healthy, six with pancreatic disease), various T1-weighted inversion-recovery and T2-weighted spin-echo fat-suppressed pulse sequences were assessed with an echo-planar technique implemented with a modified clinical MR imager. Single-excitation imaging (echo time, 26 msec) provided a higher (P less than .05) signal-to-noise ratio than did conventional spin-echo and all other echo-planar techniques. In 13 (72%) of 18 healthy subjects who did not undergo administration of the contrast agent, the entire pancreas was distinguished from adjoining bowel. In all 18 subjects who underwent contrast-enhanced imaging, a significantly greater (P less than .05) intraluminal signal intensity was apparent with all echo-planar pulse sequences and the entire pancreas was identified. In six patients with pancreatic disease, lesions could be identified by their difference in signal intensity.

Barium Sulfate↗

PubMed1992

Acute complicated pancreatitis: redefining the role of interventional radiology.

Computed tomographic (CT) scans in 30 patients who had undergone percutaneous drainage for acute complicated pancreatitis were retrospectively studied to determine the role of percutaneous drainage. Fifty-nine collections were percutaneously drained in these 30 patients. Eighty-one catheters were placed in the 59 collections (average, 1.4 catheters per patient). Patients required an average of three catheter manipulations, seven abdominal CT scans, 5 weeks of catheter drainage, a mean hospital stay of 82 days (range, 42-122 days), and a mean intensive care unit stay of 31 days (range, 1-62 days). Percutaneous intervention was successful in 14 patients, partially successful in four, and unsuccessful in eight. A temporizing effect was seen in four patients. Percutaneous intervention was successful in one of 10 central (pancreas and lesser sac areas) collections and 28 of 49 peripheral collections. Surgical debridement was necessary in 16 patients because of failed or incomplete percutaneous drainage. Complications occurred in five patients, and the mortality rate was 33%. Drainage of central areas should initially be performed by a surgeon, while peripheral collections should be drained percutaneously as they develop.

Acute Disease↗

PubMed1992

Measurement of tissue carcinoembryonic antigen levels from fine-needle biopsy specimens: technique and clinical usefulness.

Levels of tissue carcinoembryonic antigen (CEA) in 54 abdominal fine-needle biopsy specimens from 50 patients were measured to ascertain the use of tissue CEA levels in diagnosis of malignancy. Biopsy was performed in the following sites: liver (n = 34), retroperitoneum (n = 8), adrenal gland (n = 3), pancreas (n = 2), omentum (n = 2), pelvis (n = 2), spleen (n = 2), and stomach (n = 1). Histologic findings proved malignancy in 39 patients and benign disease in 11 patients. In these 11 patients, the mean levels of tissue CEA were lower than the normal level of serum CEA (3 ng/mL). Tissue CEA levels were higher than serum CEA levels in nine patients with colonic carcinoma and in 12 of 16 patients with noncolonic CEA-secreting malignancies. Four patients with noncolonic CEA-secreting malignancies had tissue CEA levels within the normal range (less than 3 ng/mL). Tissue CEA levels were also normal in 13 patients with various non-CEA-secreting tumors. Tissue CEA levels may prove useful in biopsy of necrotic or cystic lesions and assessment of response to ablative therapy for colon metastases.

Adult↗

PubMed1992

Wallstent metallic biliary endoprosthesis: MR imaging characteristics.

Image quality and safety of magnetic resonance (MR) imaging were evaluated in vitro and in eight patients with the most commonly employed metallic biliary endoprosthesis. In vitro, the stent produced no tip deflection at 0.6 or 1.5 T. Trace magnetic susceptibility artifact, similar to artifact from a column of air, paralleled the stent. In patients, image degradation was minimal with conventional pulse sequences. Middle-field-strength spin-echo images revealed minimal artifacts indistinguishable from those produced by pneumobilia.

Biliary Tract↗