Effect of 176Lu background on singles transmission for LSO-based PET cameras.

We explore how the radioactive background from naturally occurring 176Lu affects single photon transmission imaging for lutetium orthosilicate (LSO) scintillator-based PET cameras by estimating the transmission noise equivalent count rate (NECR) including this background. Assuming a typical PET camera geometry (80 cm detector ring diameter), we use a combination of measurement and analytic computation to estimate the counting rates due to transmission, scatter and background events as a function of singles transmission source strength. We then compute a NECR for singles transmission. We find that the presence of radiation from the naturally occurring 176Lu reduces the NECR by 60% or higher for source strengths less than 10 mCi, and that a 25% reduction of the NECR can occur even with a source strength of 40 mCi.

A prospective, randomized, controlled trial of covered expandable metal stents in the palliation of malignant esophageal obstruction at the gastroesophageal junction.

OBJECTIVE: Palliation of malignant esophageal obstruction is an important clinical problem. Expandable metal stents are a major advance in therapy, but many stents become obstructed because of tumor ingrowth. The aim of this study was to compare a new, membrane-covered expandable metal stent to conventional prostheses in a randomized controlled trial. METHODS: Sixty-two patients with malignant inoperable esophageal obstruction at the gastroesophageal junction participated in the study. Patients were randomly assigned to covered or uncovered stents. The principal outcome measure was the need for reintervention because of recurrent dysphagia or migration. Secondary endpoints were relief of dysphagia measured by a dysphagia score (grade 0 = no dysphagia, grade 1 = able to eat solid food, grade 2 = semisolids only, grade 3 = liquids only, grade 4 = complete dysphagia) and the rate of complications and functional status. All patients were observed at monthly intervals until death or for 6 months. RESULTS: One week after stenting the dysphagia score improved significantly in both the uncovered (n = 32, 3 +/- 0.1 to 1 +/- 0.1 [means +/- SEMs], p < 0.001) and covered (n = 30, 3 +/- 0.1 to 1 +/- 0.2 [means +/- SEMs], p < 0.001) stents. Obstructing tumor ingrowth was significantly more likely in the uncovered stent group (9/30) than in the covered group (1/32) (p = 0.005). Significant stent migration occurred in 2/30 patients with uncovered stents, as compared with 4/32 patients in the covered group (p = 0.44). Reinterventions for tumor ingrowth were significantly greater in the uncovered stent group (27%), as compared with 0% in the covered group (p = 0.002). Life table analysis showed similar survival in both groups. CONCLUSION: Membrane-covered stents have significantly better palliation than conventional bare metal stents because of decreased rates of tumor ingrowth that necessitate endoscopic reintervention for dysphagia.

Physical characteristics of the ECAT EXACT3D positron tomograph.

The 'EXACT3D' positron tomograph, which is now in routine clinical research use, was developed with the aim of achieving unprecedented sensitivity, high spatial and temporal resolution and simplicity of design using proven detector technology. It consists of six rings of standard detector blocks (CTI/Siemens EXACT HR+) with 4.39 mm x 4.05 mm x 30 mm elements, giving an axial field of view (FOV) of 23.4 cm. This extended FOV and the absence of interplane septa and retractable transmission rod sources has allowed greatly simplified gantry and detector cassette design. Operation in exclusive 3D mode requires an alternative to the conventional coincidence method for transmission scanning, and a single photon approach using a hydraulically driven 137Cs point source has been implemented. The tomograph has no other moving parts. A single time frame of data without any compression is very large (> 300 Mbyte) and two approaches are employed to overcome this difficulty: (a) adjacent sinograms can be summed automatically into different combinations and (b) listmode (event-by-event) acquisition has been instituted, which is both storage efficient (particularly for acquisition of sparse data sets) and maximizes temporal resolution. The high-speed I/O and computing hardware can maintain a sustained acquisition rate of about 4 million coincidence events per second. A disadvantage of the large axial FOV in 3D is the increased sensitivity to activity outside the coincidence FOV. However, this can be minimized by additional side shielding. The mean spatial resolution is 4.8 +/- 0.2 mm FWHM (transaxial, 1 cm off-axis) and 5.6 +/- 0.5 mm (axial, on-axis). Its absolute efficiency is 5.8% for a line source in air (just spanning the axial FOV) and 10% for a central point source (with thresholds of 350-650 keV). For a uniform 20 cm diameter cylinder, the efficiency is 69 kcps kBq(-1) ml(-1) (after subtraction of a scatter fraction of 42%). Sensitivity relative to the EXACT HR+ (with four rings of blocks) is 2.5 (3D) and 12 (2D) times respectively. The rate of random events in blood flow studies in the brain and body, using 15O-labelled water, can be controlled by limiting the administered dose and inserting additional side shielding.

Mistakes on EUS staging of colorectal carcinoma: error in interpretation or deception from innate pathologic features?

BACKGROUND: Because endoscopic ultrasound (EUS) accuracy for staging gastrointestinal tract tumors is limited by many factors, this study was designed to analyze potential sources of error in the EUS staging of colorectal carcinoma. METHODS: All patients referred for EUS evaluation of colorectal carcinoma were staged prospectively by one ultrasonographer and retrospectively by two others with EUS videotape recordings. Pathologic staging was done independently in a blinded fashion. Deceptive pathologic features were defined for T staging by presence of inflammation extending beyond tumor or microscopic spread without inflammation extending to a level consistent with the next stage, and for N staging by large (> or = 10 mm) benign lymph nodes or small (< 10 mm) malignant lymph nodes. RESULTS: Of 22 patients entered into the study, an inflammatory reaction around microscopic tumor spread thought to actually enhance detection by EUS was present in 57.1% of cases. Nine deceptive pathologic lesions were present in 36.4% (8 of 22) of patients (5 T stage, 4 N stage lesions). Of 40 T and N stage mistakes made by the three physicians, 45% were made in the presence and 55% in the absence of deceptive pathologic lesions. Accuracy increased significantly from the presence to absence of deceptive pathologic lesions, from 53.3% to 83.7% (p = 0.029) for T stage, and 8.3% to 73. 1% for N stage (p = 0.0001). Confidence of T staging correlated significantly with accuracy, increasing from 63.3% when unsure to 88. 2% with staging certainty (p = 0.017), an effect not seen for N staging. CONCLUSIONS: Inflammation and desmoplasia around colorectal carcinoma are often present, but may actually enhance EUS detection of microscopic tumor spread. Deceptive pathologic lesions are present in only one third of patients, but account for almost half (45%) of the errors in T and N staging by EUS. Diagnostic accuracy for EUS was increased with confidence in T stage assessment (but not N stage) and in the absence of deceptive pathologic lesions. Errors in interpretation still accounted for the majority of mistakes (55%) made in EUS staging of colorectal carcinoma.

Injection therapy for variceal bleeding.

The role of injection therapies in the management of esophageal and gastric varices are reviewed. Available radiographic, pharmacologic and alternative endoscopic methods are compared and contrasted with sclerotherapy. Recent studies regarding a combination of endoscopic band ligation and low volume sclerotherapy to achieve best eradication of esophageal varices are reviewed.

Extramucosal stenosis of the esophagus.

Extramucosal lesions of the esophagus compose a small but clinically important group of diagnoses presenting as stenosis. Because of their infrequency, they can present a diagnostic dilemma in patients with dysphagia, odynophagia, or radiologic abnormalities on imaging studies. Definitive management is frequently conservative, consisting of reassurance; definitive surgical management, however, may be necessary.

AIDS-related non-Hodgkin's lymphoma of the pancreas.

Non-Hodgkin's lymphoma is a common complication in patients with human immunodeficiency virus infection that most frequently affects the gastrointestinal tract. We describe the first case report of non-Hodgkin's lymphoma primarily involving the pancreas in a 27-yr-old white man who presented with epigastric pain, weight loss, and jaundice (and was later found to be HIV seropositive). Endoscopic ultrasound and CT scan of the abdomen showed a large mass arising from the body and head of the pancreas obstructing the common bile duct. An attempted ERCP was unsuccessful due to extrinsic compression and distortion of the second part of the duodenum. A percutaneous CT-directed true-cut needle biopsy of the pancreas revealed a small noncleaved B-cell lymphoma. The patient was started on combination chemotherapy. His pancreatic mass, epigastric symptoms, and jaundice resolved completely. This case report illustrates an otherwise rare presentation of isolated pancreatic involvement of non-Hodgkin's lymphoma in a patient with acquired immunodeficiency syndrome. An approach to its diagnosis and management is summarized.

Acute sporadic non-A, non-B, non-C, non-D, non-D, non-E hepatitis.

Patients presenting with clinical and laboratory features consistent with a diagnosis of acute non-A, non-B hepatitis were evaluated for evidence of hepatitis C or hepatitis E infection and for evidence of severe or prolonged disease. Antibody to hepatitis C virus (anti-HCV) was detected in 75 of 108 (69%) patients, antibody to hepatitis E virus (anti-HEV) in three patients (3%), and neither antibody in 31 (29%) patients. One patient had both anti-HCV and anti-HEV. HCV RNA was not detected in sera from any of 20 patients with seronegative (non-ABCDE) hepatitis, but in all 10 patients with anti-HCV who were tested by polymerase chain reaction (PCR). Compared with patients with acute hepatitis C, those with non-ABCDE hepatitis had a lower incidence of parenteral risk factors (6% vs. 70%; P < .001), higher peak serum bilirubin levels (45% vs. 5% with peak levels > 15 mg/dL; P < .001), more prolonged jaundice (25% vs. 0% with peak bilirubin >5 weeks after onset; P < .01), more severe prothrombin time abnormalities (26% vs. 0% with >3 second prolongation; P < .001), more severe hypoalbuminemia (39% vs. 9% with albumin <3 g/dL; P < .01), and more frequent major clinical complications (13% vs. 0% with encephalopathy; P < .01; 10% vs. 0% with death or transplant; P = .024). Patients with acute non-ABCDE hepatitis were less likely to develop chronic hepatitis than those with acute hepatitis C (23% vs. 68%; P < .05). Thus, patients with acute non-ABCDE hepatitis are epidemiologically distinct from those with acute hepatitis C and have a significantly more severe acute illness.

Simultaneous emission and transmission measurements for attenuation correction in whole-body PET.

UNLABELLED: We describe a methodology for measuring and correcting for attenuation in whole-body PET using simultaneous emission and transmission (SET) measurements. METHODS: The main components of the methodology are: (a) sinogram windowing of low activity (< or = 50 MBq) rotating 68Ge/Ga rod sources, (b) segmented attenuation correction (SAC) and (c) maximum likelihood reconstruction using the ordered subsets EM (OS-EM) algorithm. The methods were implemented on a whole-body positron emission tomograph. Quantitative accuracy and the signal-to-noise ratio (SNR) were measured for a thorax-tumor phantom as functions of acquisition time (range: 2-20 min per position). RESULTS: When a typical rod source activity (200 MBq 68Ge/Ga) was used, emission SNR was 60% lower in simultaneous than in separate measurements. The difference was only 14% when the rods contained 45 MBq 68Ge/Ga. The SNR was further improved by SAC in conjunction with OS-EM reconstruction and the relative gain increased with increasing acquisition time. Quantitative estimates of tumor, liver and lung radioactivity agreed with values obtained from a separate high count measurement to within 8%, independent of acquisition time. CONCLUSION: Attenuation correction of whole-body PET images is feasible using SET measurements. There is good quantitative agreement with conventional methods and increased noise is offset by the use of SAC and OS-EM reconstruction.

The design and physical characteristics of a small animal positron emission tomograph.

A small diameter positron emission tomography, designed specifically for small animal studies, was constructed from existing, commercially available, bismuth germanate (BGO) detectors and electronics. The scanner consists of 16 BGO detector blocks arranged to give a tomograph with a diameter of 115 mm and an axial field of view (FOV) of 50 mm. Each block is cut to produce eight (axial) by seven (radial) individual detector elements. The absence of interplane septa enables the acquisition of 3D data sets consisting of 64 sinograms. A 2D data set of 15 sinograms, consisting of eight direct and seven adjacent cross planes, can be extracted from the 3D data set. Images are reconstructed from the 2D sinograms using a conventional filtered backprojection algorithm. Two methods of normalization were investigated, based on either a rotating 68Ge rod source, or a uniform 68Ge plane source, with a uniform cylindrical 18F phantom. Attenuation of the emitted photons was estimated using a rotating 68Ge rod source. The transaxial resolution of the tomograph was measured as 2.3 mm full width at half maximum (FWHM) and 5.6 mm full width at tenth maximum (FWTM) at the centre of the FOV, degrading to 6.6 mm (radial) and 4.4 mm (tangential) FWHM and 10.4 mm (radial) and 14.4 mm (tangential) FWTM at 40.0 mm from the centre of the FOV. The axial slice width was 4.3 mm FWHM, 10.3 mm FWTM at the centre of the transaxial field of view and 4.4 mm FWHM, 10.6 mm FWTM at 20.0 mm from the centre of the FOV. A scatter fraction of 31.0% was measured at 250-850 keV, for an 18F line source centred in a 60 mm diameter, water-filled phantom, reducing to 20.4% and 13.8% as the lower energy discrimination was increased to 380 keV and 450 keV, respectively. The count rate performance was measured using a noise equivalent count rate method, and the linearity of the dead time correction was confirmed over the count rates encountered during routine scanning. In 2D mode, the absolute sensitivity of the tomograph was measured as 9948 counts s-1 MBq-1 at 250-850 keV, 8284 counts s-1 MBq-1 at 380-850 keV and 6280 counts s-1 MBq-1 at 450-850 keV.

Optimizing rod window width in positron emission tomography.

A technique determines the optimal window width for orbiting rod transmission studies in positron emission tomography (PET). Windowing reduces noise in orbiting rod transmission studies. Lines-of-response (LOR) which intersect the rods generate primarily true coincidence events. LOR which pass far from the rods generate random and scatter events. Since the angular position of the orbiting rods is known in real-time, LOR which produce mostly noise are gated off. When optimally determined, the rod window width maximizes the noise equivalent counts (NEC) collected in the transmission study. Transaxial rod projection profiles of trues, randoms, and scatter produce NEC versus window width plots. For the ECAT EXACT line of PET systems and a 20-cm water cylinder, optimal is five LOR wide.

Aspheric rigid gas permeable contact lenses: practitioner discrimination of base curve increments using fluorescein pattern evaluation.

Evaluation of the fluorescein pattern is the main clinical indicator of the fit of a rigid gas permeable (RGP) contact lens to the cornea. Traditionally, manufacturers inventory RGP lenses in 0.05-mm base curve increments. The objective of this study was to test the hypothesis that experienced practitioners are not able to discern base curve/cornea relations of aspheric design lenses correctly to within +/- 0.05 mm. Eleven clinicians with expertise in fitting rigid lenses were asked to interpret fluorescein patterns and lens fittings of the Bausch & Lomb Quantum aspheric RGP lens on five adapted rigid lens wearers. The results showed that the experienced practitioners used in this study were not able to discriminate cornea/base curve relations of Quantum aspheric lenses within +/- 0.05 mm more than 67% of the time (p less than 0.05). There were no patient-to-patient differences based on type of lens fit (interpalpebral or lid attachment) or degree of corneal toricity. Lenses fitted in 0.10-mm base curve steps were judged as being as acceptable as lenses fitted in 0.05 mm steps (p less than 0.05). It was concluded that Quantum aspheric design lenses need only be trial fitted in 0.10-mm base curve steps.

Optical design considerations for contact lens bifocals.

Primary concerns for designing conventional bifocal contact lens optics involve placement of sufficient representation of distance and near optical powers before the pupil and minimizing the presence of secondary images. Geometrical models and lens measurements are used to establish guidelines for predicting bifocal contact lens performance. Proportional optical zone representation, image jump, and power distribution are presented for the most commonly employed bifocal zone configurations. Adequate zone representation and effective lens power are shown to be quite sensitive to variation in pupil size and position. Strategies for optimizing lens performance in view of these effects are discussed.