Nuclear medicine equipment spans a broad family of devices designed to create images from radioactive tracers inside the body or to deliver targeted radiation therapy. At the center of every nuclear medicine department sit two major scanner types: the gamma camera (used for SPECT imaging) and the PET scanner, each detecting radiation in fundamentally different ways. But the equipment list extends well beyond scanners, reaching into cyclotrons that manufacture short-lived isotopes, generators that supply tracers on demand, dose calibrators that measure radioactivity before injection, automated synthesis modules shielded behind lead and tungsten, and handheld probes that guide surgeons in the operating room. Understanding how these pieces fit together clarifies both what nuclear medicine can do today and where the technology is headed.
The Gamma Camera and SPECT
The workhorse of conventional nuclear medicine imaging is the gamma camera, almost universally called the Anger camera after Hal Anger, who developed the design in the late 1950s. It uses a large flat crystal of sodium iodide coupled to an array of light-sensitive tubes that convert incoming gamma rays into electrical signals, which are then mapped into an image. This basic architecture has dominated single-photon emission computed tomography (SPECT) for decades, though alternatives using solid-state detector materials like cadmium zinc telluride (CZT) have entered clinical use, particularly for cardiac imaging.1PubMed Central. SPECT detectors: the Anger Camera and beyond
What sits between the patient and the detector crystal matters enormously. A collimator, essentially a slab of lead riddled with tiny holes or a cone-shaped aperture, determines which gamma rays reach the crystal. Traditional parallel-hole collimators offer relatively low sensitivity and resolution below one centimeter, which is adequate for many clinical tasks but limiting for fine detail.2PubMed Central. Review of SPECT collimator selection, optimization, and fabrication for clinical and preclinical imaging Pinhole and multi-pinhole collimators improve the trade-off between sensitivity and resolution, a development that has been especially important in small-animal research imaging, where sub-millimeter detail is needed.3PubMed Central. Advances in pinhole and multi-pinhole collimators for single photon emission computed tomography imaging Swapping collimators on the same camera changes its imaging characteristics dramatically, so departments typically keep several types on hand and choose based on the clinical question.
PET Scanners and Coincidence Detection
Positron emission tomography works on a completely different detection principle. Instead of collimating single gamma rays, a PET scanner surrounds the patient with a ring of detectors and waits for pairs of photons flying in opposite directions, produced when a positron from the tracer collides with an electron. By recording which two detectors fire at nearly the same instant, the system traces a line through the body and figures out where the annihilation event happened, no physical collimator required.4PubMed Central. Detectors in positron emission tomography This electronic collimation gives PET an inherent sensitivity advantage over SPECT and produces images with higher spatial resolution in most clinical settings.
A major leap in PET performance came with time-of-flight (TOF) technology, which measures the tiny difference in arrival times of the two photons. That time gap tells the scanner approximately where along the line the event occurred, narrowing down the source and boosting image quality. Modern TOF PET systems have improved the trade-off between lesion contrast and image noise, meaning scans can be done faster, with less injected tracer, or with sharper pictures of small tumors.5PubMed Central. Update on time-of-flight PET imaging
The detectors themselves have undergone a generational shift. Older PET scanners relied on bulky photomultiplier tubes to convert scintillation light into electrical signals. Over the past decade, these have been widely replaced by silicon photomultipliers (SiPMs), compact solid-state devices that are faster, more sensitive, and compatible with magnetic fields, which matters for hybrid PET/MRI systems.6Nuclear Medicine and Molecular Imaging. Digital PET Systems The move to SiPMs is often described as the transition from analog to digital PET.
Hybrid Imaging Systems
A PET or SPECT image shows where a tracer concentrates but gives limited anatomical detail. The patient’s bones, organs, and soft tissues are largely invisible. Combining a nuclear medicine scanner with an anatomical imaging modality solves this, and hybrid systems are now standard in most imaging departments.
PET/CT
PET/CT, introduced commercially in the early 2000s, pairs a PET ring with a CT scanner in the same gantry. The CT component provides two things: a detailed anatomical map for pinpointing tracer uptake, and attenuation correction data that compensates for the way body tissues absorb some of the photons before they reach the detectors.7PubMed. Eliminating CT radiation for clinical PET examination using deep learning Early work on combined PET/CT demonstrated that CT-based attenuation correction could be used to produce accurately registered anatomical localization of structures seen in the PET image.8PubMed. Attenuation correction for a combined 3D PET/CT scanner PET/CT is now the default platform for oncologic PET imaging worldwide.
PET/MRI
Combining PET with MRI is technically harder. Classic PET electronics fail in even a weak magnetic field, and PET signal processing can disturb the high-frequency signals MRI depends on.9PubMed. PET/MRI: challenges, solutions and perspectives The switch to SiPM-based detectors was a key enabler, since silicon photomultipliers are insensitive to magnetic fields. Early simultaneous PET/MRI prototypes showed that the MRI system caused less than a ten percent reduction in detected radioactive decay events, and MR image quality was largely preserved with the PET hardware inside the magnet.10PubMed Central. Simultaneous in vivo positron emission tomography and magnetic resonance imaging PET/MRI has found a clinical niche in neuroimaging, pediatric oncology, and pelvic cancers, where MRI’s superior soft-tissue contrast adds diagnostic value beyond what CT provides. It also reduces the patient’s exposure to ionizing radiation from the anatomical scan, since MRI uses no X-rays.
Total-Body PET
Conventional PET scanners have an axial field of view of roughly 20 to 30 centimeters, meaning they image one bed position at a time and the table moves stepwise to cover the full torso. Total-body PET scanners break this limitation with detector arrays stretching nearly two meters. The first such system, the uEXPLORER, has an axial field of view of 194 centimeters, enough to cover the entire adult body in a single acquisition for more than 99 percent of the population.11PubMed Central. First Human Imaging Studies with the EXPLORER Total-Body PET Scanner
The sensitivity gain is dramatic. Because detectors surround the entire body at once, the system captures far more of the emitted photon pairs. Performance testing showed a sensitivity of 174 thousand counts per second per megabecquerel and spatial resolution of three millimeters or better near the center of the field of view.12PubMed Central. Performance Evaluation of the uEXPLORER Total-Body PET/CT Scanner Based on NEMA NU 2-2018 with Additional Tests to Characterize PET Scanners with a Long Axial Field of View In practical terms, this means scans that previously required 20 minutes can be done in under a minute, or the injected tracer dose can be slashed while maintaining image quality. Total-body PET also enables dynamic imaging of tracer movement through all organs simultaneously, something impossible when the scanner can see only a slice of the body at a time.
Producing Radioactive Tracers
Most of the equipment described above is useless without a supply of short-lived radioactive tracers, and producing those tracers requires its own specialized hardware.
Medical Cyclotrons
PET tracers like fluorine-18 (the isotope behind FDG, the most widely used PET tracer) are made in medical cyclotrons, compact particle accelerators that bombard a target material with protons to create the desired isotope. A typical medical cyclotron accelerates protons to about 10 to 18 million electron volts. Because fluorine-18 has a half-life of under two hours, PET centers either operate their own cyclotron or rely on regional radiopharmacies that deliver doses by ground transport each morning.13PubMed. Analysis of induced radionuclides in replacement parts and liquid wastes in a medical cyclotron solely used for production of 18F for [18F]FDG The cyclotron vault requires heavy concrete and steel shielding, and replacement parts become radioactive over time and must be managed as waste.
Generators
SPECT imaging relies heavily on technetium-99m, which has a six-hour half-life and is obtained not from a cyclotron but from a benchtop generator. The standard technetium generator is a column of alumina onto which molybdenum-99, the parent isotope, has been adsorbed. Passing sterile saline through the column extracts (or “elutes”) technetium-99m in a form ready to label radiopharmaceuticals.14Journal of Nuclear Medicine Technology. Simple Elution Aid for Multiple, Fractionated, and Partial Elution of 99mTc Generators are delivered weekly and can be eluted once or twice daily, making technetium-99m available on demand even in hospitals without a cyclotron. The three most commonly used separation methods are chromatography, sublimation, and solvent extraction, with chromatographic generators dominating clinical practice.15The International Journal of Applied Radiation and Isotopes. Technetium-99m generators—The available options
Automated Synthesis Modules
After the isotope is produced, it must be chemically attached to the right molecule to create a radiopharmaceutical. For PET tracers, this happens inside automated radiosynthesis modules, enclosed systems that handle highly radioactive starting material without exposing staff. These modules sit inside hot cells, lead-lined cabinets with thick shielded glass windows and remote manipulators. One self-shielded modular system demonstrated that surface dose rates stayed below 20 microsieverts per hour even when handling cesium-137, with shielding reducing exposure by a factor of roughly 900 or more.16PubMed. A novel, self-shielded modular radiosynthesis system for fully automated preparation of PET and therapeutic radiopharmaceuticals
Dose Calibrators and Activity Measurement
Before any radiopharmaceutical is injected, its radioactivity must be measured to confirm the patient receives the correct dose. This is the job of the dose calibrator, a pressurized ionization chamber paired with an electrometer that displays a reading directly in activity units. With proper calibration against national standards, these devices can measure activity with an uncertainty on the order of about one percent.17PubMed Central. An update on “dose calibrator” settings for nuclides used in nuclear medicine The calibration factor, often called a “dial setting,” must be set correctly for each specific isotope.
In practice, accuracy can fall short of that ideal. A comparison of four different calibrators across multiple isotopes and measurement geometries found deviations from reference values reaching up to about 30 percent for some isotope and geometry combinations.18PubMed. A comparison of four radionuclide dose calibrators using various radionuclides and measurement geometries clinically used in nuclear medicine Errors of that size could affect both image quantification and therapeutic dosing, which is why regulatory guidelines require routine constancy checks, linearity testing, and geometry-specific validation. As nuclear medicine moves toward more personalized dosing for radionuclide therapies, accurate activity measurement has become a higher-stakes concern than it was in the purely diagnostic era.19PubMed. Accuracy, reproducibility, and uncertainty analysis of thyroid-probe-based activity measurements for determination of dose calibrator settings
Theranostic Equipment and Quantitative SPECT/CT
Theranostics, the pairing of a diagnostic imaging agent with a therapeutic radiopharmaceutical targeting the same biological pathway, has pushed equipment requirements in new directions. The most prominent example is the use of lutetium-177-labeled PSMA agents for metastatic prostate cancer. After a therapeutic dose is injected, the same gamma emissions from lutetium-177 can be imaged with a SPECT/CT scanner to estimate how much radiation each tumor and each organ received.
Quantitative SPECT/CT for lutetium-177 dosimetry uses calibrated reconstruction methods so that voxel values correspond to actual tracer concentrations. A study comparing in vivo SPECT measurements to direct sampling of bladder urine found that solid-state SPECT/CT could measure radiotracer concentration to within roughly 20 percent of the true value.20Journal of Nuclear Medicine. Digital Solid-State SPECT/CT Quantitation of Absolute 177Lu Radiotracer Concentration: In Vivo and In Vitro Validation A multicenter evaluation further demonstrated that when imaging protocols are harmonized, different hospitals can achieve consistent quantitative results with lutetium-177, a prerequisite for standardized dosimetry across clinical trials.21PubMed Central. A multicentre and multi-national evaluation of the accuracy of quantitative Lu-177 SPECT/CT imaging performed within the MRTDosimetry project
Timing of the post-treatment scan matters. For tumor dose estimates, scanning beyond 72 hours after injection gave the most accurate results, while healthy tissue doses were best characterized by scanning in the first two days, when tracer clearance from normal organs is still measurable.22PubMed Central. Clinical Radiation Dosimetry in 177Lu-PSMA-617 Therapy Using a Single Posttreatment SPECT/CT Scan: A Novel Methodology to Generate Time- and Tissue-Specific Dose Factors Getting both right often means bringing the patient back for at least two scans at different time points, which adds logistical complexity but gives clinicians the data to adjust future therapy cycles.
Alpha-emitting isotopes like actinium-225 present an additional equipment challenge. Their gamma emissions are fewer and at energies that are harder to image cleanly. Quantitative SPECT/CT of actinium-225 has been demonstrated using high-energy collimators with multiple energy windows, but the technique is still in its early research phase.23PubMed Central. Quantitative SPECT/CT imaging of actinium-225 for targeted alpha therapy of glioblastomas
Intraoperative Gamma Probes
Not all nuclear medicine equipment lives in the imaging suite. Handheld gamma detection probes travel into the operating room, where surgeons use them to locate radiotracer-labeled tissue in real time. The classic application is sentinel lymph node biopsy, but the concept extends to neuroendocrine tumors and other cancers that concentrate specific tracers. In one series, an intraoperative gamma probe localized all somatostatin-receptor-positive lesions of gastrointestinal neuroendocrine tumors, outperforming both surgical palpation and preoperative radiology, which each found fewer than half the lesions.24PubMed. Intraoperative gamma probe detection of neuroendocrine tumors
More recently, portable large-field-of-view gamma cameras have been brought into the operating room alongside the traditional pencil-like probes. These small cameras produce a real-time image of tracer distribution across the surgical field rather than just a point-by-point count rate, giving the surgeon navigational feedback about whether all tracer-avid foci have been resected.25PubMed. Intraoperative Use of a Portable Large Field of View Gamma Camera and Handheld Gamma Detection Probe for Radioguided Localization and Prediction of Complete Surgical Resection of Gastrinoma: Proof of Concept The combination of a point probe for precise localization and a portable camera for overview imaging is a good example of how nuclear medicine equipment is migrating beyond the scanner room.
Artificial Intelligence in Image Reconstruction
Deep learning is reshaping what nuclear medicine scanners can extract from the raw data they collect. Conventional image reconstruction algorithms use mathematical models of the physics of photon detection. Deep-learning methods can supplement or replace parts of that pipeline, either by denoising reconstructed images or by operating directly on the raw projection data. The primary payoff is enabling diagnostic-quality images from lower tracer doses or shorter scan times.26PubMed Central. Deep learning-based image reconstruction and post-processing methods in positron emission tomography for low-dose imaging and resolution enhancement
Several major scanner manufacturers now offer AI-assisted reconstruction as a commercial option. A related application targets the CT component of PET/CT: deep-learning algorithms can generate synthetic CT-like images from the PET data alone, potentially eliminating the CT scan and its associated radiation dose entirely.27PubMed. Eliminating CT radiation for clinical PET examination using deep learning These approaches are still being validated against conventional workflows, but the direction is clear: AI is becoming part of the equipment chain rather than just a post-processing afterthought.
Radiation Safety Monitoring
Working with open radioactive sources every day demands continuous environmental monitoring. Nuclear medicine departments use a combination of personal dosimeters worn by staff, area survey meters that measure ambient dose rates in designated zones, and wipe tests that check for surface contamination. Survey meters are used to classify areas by dose rate and to confirm that radiation levels around hot cells, waste storage, and patient holding areas stay within regulatory limits.28Bangladesh Journal of Nuclear Medicine. Workplace Radiation Monitoring and Analysis: A Single Institution Based Study Portable contamination monitors, thyroid uptake probes, and well counters round out the ancillary measurement devices found in a busy department. None of this hardware produces clinical images, but it is as essential to daily operations as the scanners themselves.
Quality Control and Multicenter Standardization
Every scanner undergoes routine quality control testing. For PET, the NEMA NU 2 standard provides a uniform set of phantom-based tests to characterize sensitivity, spatial resolution, count-rate performance, and image quality. In hybrid PET/MRI systems, MR-based attenuation correction introduces unique challenges: standard clinical attenuation maps can underestimate PET activity by up to roughly a quarter, depending on the system, because MRI does not directly measure tissue density the way CT does. Dedicated phantom protocols reduce that bias substantially, bringing it closer to the single-digit range.29PubMed Central. Quality control for quantitative multicenter whole-body PET/MR studies: A NEMA image quality phantom study with three current PET/MR systems This kind of benchmarking matters most in multicenter clinical trials, where you need to trust that a measurement at one hospital means the same thing as a measurement at another.
Small-animal imaging systems face their own version of these challenges. Micro-PET and micro-SPECT scanners are designed with tighter detector geometries and specialized collimation to resolve structures well below a millimeter, but the fundamental trade-offs between sensitivity, resolution, and field of view remain.30PubMed Central. Instrumentation for molecular imaging in preclinical research: Micro-PET and Micro-SPECT Researchers developing new tracers in mice need quantitative accuracy from these instruments before anything can move toward human trials, so the quality-control pipeline for preclinical systems mirrors the clinical one in rigor, even if the equipment looks very different.