- [Resource Hub](/) - [Blog](/?resource-type=blog-post#library) - Volumetric vs Image-Based Cell Counting for CAR-T QC Blog · 5 min read · CAR-T QC # Volumetric vs Image-Based Cell Counting for CAR-T QC The method explainer: volumetric vs image-based counting for CAR-T QC, and why the CV gap matters at lot release. Key takeaways - Volumetric counting measures each particle's physical volume directly — image-based counting infers count and size from a captured image. - On accuracy, serious instruments run even — a benchtop volumetric analyzer showed no significant difference from a reference volumetric sizer in a peer-reviewed CAR-T QC study, so accuracy will not decide the choice. - Precision is where the methods part — a validated volumetric count holds a CV under 2% against 20 to 30 percent for image-based counts, reading up to 40,000 particles per test instead of imaging a few hundred. - "Accurate enough for release" is settled by precision and provability — not by an accuracy contest between comparable instruments. Volumetric cell counting measures each particle's physical volume directly. Image-based cell counting infers count and size from a captured brightfield or fluorescence image. For CAR-T QC, the two methods reach comparable accuracy, so the choice turns on precision and on whether you can prove the count. That choice reflects a larger shift. In GMP cell-therapy manufacturing, the cell count and viability go on the certificate of analysis, so a count can function as a release-grade measurement rather than housekeeping. As [what makes a cell count audit-ready](/resources/gmp-cell-therapy-qc-counting-audit-ready/) lays out, an audit-ready count clears two bars: it has to be accurate, and it has to be one you can prove. Accuracy is the table-stakes bar. The harder half, the one most method comparisons skip, is how volumetric and image-based counting differ once accuracy is settled. ## What is the difference between volumetric and image-based cell counting? Volumetric counting sizes and counts each particle by measuring its physical volume as it passes through a sensing zone, so a cell's size is a direct physical reading. Image-based counting captures a picture of a small sample chamber and uses software to find objects, then infers count and size from what the optics resolve. The two methods differ in what they depend on. A volumetric reading comes from the particle's actual displacement, not from focus, staining, or how cleanly an algorithm separates two touching cells in an image. An image-based reading depends on image quality and the software's object-calling. That is why it can drift when cells are small, translucent, clumped, or mixed with debris. ## Which is more accurate for CAR-T QC, volumetric or image-based? Comparable. A benchtop volumetric analyzer, the Moxi GO II, showed no significant difference from a reference volumetric sizer for both count and size in a peer-reviewed Penn Medicine CAR-T QC study (Pajarillo et al., Cytotherapy 2024). Between serious instruments, accuracy is not the differentiator . It is the price of entry. So accuracy will not decide this. What you can prove about the count is the tiebreaker. The more useful question is which method holds a steady number, read after read, on the samples that are hardest to count. ## Why does counting precision (CV) matter more than accuracy on cell-therapy samples? Precision is reproducibility: read the same lot twice, and how close are the two numbers. Reported as a coefficient of variation (CV), it is where the two methods separate. A validated volumetric count holds a CV under 2%. Image-based counts commonly run a CV of 20 to 30 percent on the same class of sample. That gap widens exactly where cell-therapy samples are toughest to count. Autologous CAR-T lots are often small, the cells can be close in size to debris, and concentrations can run low. Those are the conditions that push an image-based count around. When a lot is size-of-one and the number lands on a certificate of analysis, a wide CV becomes a question you have to answer: why did two reads of the same lot disagree? A tight CV keeps that question from ever reaching your auditor. ## How many particles does a volumetric count actually measure? Up to 40,000 particles per test, in 10 to 15 seconds, each sized by its own physical volume. An image-based counter typically resolves a few hundred particles in the imaged area. That roughly hundred-fold difference in sample size drives the precision gap. A number built from tens of thousands of direct measurements is steadier than one extrapolated from a few hundred imaged objects. Reading more particles also means a rare or off-size population is more likely to be detected than missed in a small field of view. Volumetric instruments report particles, the physically correct unit here, since the same measurement counts cells, nuclei, beads, and debris alike. ### How the two methods compare on the dimensions that decide it Dimension Volumetric counting Image-based counting Measurement principle Direct physical volume per particle Count and size inferred from an image Particles per test Up to 40,000 ~100 to 300 Validated count CV Under 2% ~20 to 30% Strongest on Small, translucent, debris-heavy, or low-concentration samples Larger, clean, well-separated cells Reading the table Both methods count accurately. They separate on precision and on the samples they hold up on — which is why the CV row, not the accuracy question, is the one that decides a release-grade count. ## Is a benchtop cell analyzer accurate enough for GMP release? On the evidence, yes. In the Penn Medicine study, a benchtop volumetric analyzer matched a reference volumetric sizer, the method a GMP lab already trusts, with no significant difference in count or size. The accuracy question is settled. But "accurate enough for release" turns on two things accuracy does not cover: precision, so the number holds read to read, and provability, so the number survives an audit. Precision is the volumetric method's edge. Provability is a separate requirement, the other half of an audit-ready count: native 21 CFR Part 11 data integrity, which [what 21 CFR Part 11 requires of a cell counter](/resources/21-cfr-part-11-cell-counter-requirements/) covers in full. A count can be accurate and precise and still fail an audit if the instrument cannot show who changed the data, and when. The instrument gives you a research-use count, viability, and identity record you can prove. Your validated method and quality system own the release decision. ## Where does a benchtop volumetric analyzer stop? The same run also reads viability plus one identity marker, a CD4 or CAR read, at the bench in seconds. In the Penn Medicine study, viability tracked a reference fluorescence analyzer at r²=0.97, with CD4 at r²=0.997 and CAR19 at r²=0.90. That is enough to confirm the cells are alive and are the cells you expect, as a routine in-process or release-adjacent check. It is not a full identity or potency panel. A one- to two-color read does not replace the high-parameter work of a flow cytometry core, and it is not meant to. The benchtop analyzer handles the routine count, viability, and identity confirmation at-line, which frees the core for the panels only it can run. If your primary release assay has to be a full multi-color identity or potency panel, that stays core-facility work, and you will know that quickly. ### Choosing between the methods At release, the number you can stand behind is the one that is both precise and provable. Score any counter against both bars on your own samples, then plan the evaluation against the reference method you already run. [Talk to a Specialist](https://precisioncellsystems.com/request-a-quote/) [The five-requirement evaluation](/resources/audit-ready-cell-counting-gmp-guide/) For research use only. Not for use in diagnostic procedures. On this page - [The method difference](#method-difference) - [Which is more accurate](#which-is-more-accurate) - [Why precision (CV) matters](#why-precision-matters) - [Particles per test](#particles-per-test) - [Accurate enough for release?](#accurate-enough-for-release) - [Where it stops](#where-it-stops) ### Scoping a counter for CAR-T release QC? [Talk to a Specialist](https://precisioncellsystems.com/request-a-quote/) [Back to all resources](/#library) ## Similar resources [Blog](/resources/gmp-cell-therapy-qc-counting-audit-ready/) Moxi GO II 2026 ### GMP Cell-Therapy QC Counting: What Makes a Count Audit-Ready The evergreen guide to what makes a GMP cell-therapy count audit-ready — the hub for the Part 11 and volumetric-vs-image explainers. [Read Blog](/resources/gmp-cell-therapy-qc-counting-audit-ready/) [App Note](https://precisioncellsystems.com/wp-content/uploads/2026/02/Moxi-Applications-Compendium.pdf) Moxi GO II Moxi V Moxi Z 2026 ### Applications Compendium Scientists are concerned with speed, accuracy, and convenience, and those running the lab and industries are concerned with the cost typically associated with high-performing instruments. Our proprietary Coulter Principle-based system delivers on all three accounts, and is therefore a perfect fit for any cell biology benchtop. [Download App Note](https://precisioncellsystems.com/wp-content/uploads/2026/02/Moxi-Applications-Compendium.pdf) [Field Guide](/resources/audit-ready-cell-counting-gmp-guide/) Moxi GO II 2026 ### Audit-Ready Cell Counting for GMP Cell-Therapy QC An educational field guide to the audit-ready framing and the five requirements of a count you can defend. [Read Field Guide](/resources/audit-ready-cell-counting-gmp-guide/) [App Note](/resources/moxi-go-ii-cart-expansion-monitoring/) Moxi GO II 2026 ### CAR-T Expansion Monitoring: Consolidated Cell Characterization Using Moxi GO II Peer-reviewed concordance data showing the Moxi GO II consolidates cell counting, sizing, viability, and 2-color immunophenotyping into a single 15-second, at-bench measurement for CAR-T expansion monitoring — replacing the standard two-instrument core-lab workflow. In a University of Pennsylvania study (Pajarillo et al., Cytotherapy 2024), the Moxi GO II matched gold-standard reference instruments for viability (r² = 0.97), CD4+ T cell identification (r² = 0.997), and CAR19 transduction efficiency (r² = 0.90), eliminating the 3–6 hour turnaround for routine expansion checkpoints. For Research Use Only. [View App Note](/resources/moxi-go-ii-cart-expansion-monitoring/) [Ebook](/resources/your-cell-count-is-a-safeguard/) Moxi GO II Moxi V Moxi Z 2026 ### Your Cell Count is a Safeguard The debris problem: Membrane fragments, aggregates, media residue, and lysed cell debris are present in virtually every biological preparation. How does your counting method distinguish a cell from a piece of debris? [Read Ebook](/resources/your-cell-count-is-a-safeguard/) [App Note](https://precisioncellsystems.com/wp-content/uploads/2026/02/Moxi-Applications-Note-Unlocking-the-Next-Stage-in-CAR-T-Cellular-Analysis.pdf) Moxi GO II 2026 ### Unlocking the Next Stage in CAR-T Cellular Analysis There are a variety of ways to monitor this process in cell culture, the two most prominent being cell counting via imaging-based and coulter-based cell counting methods and higher-level cellular analysis with fluorophore-tagged antibodies and fluorescent reporters via flow cytometry. While each instrument used to achieve these two things has its advantages and disadvantages, few and far between can do both at once. Out of all your options, no other instrument has the power to do both with the speed, precision, and ease that Precision Cell Systems' Moxi Go II can. In this document, we will take you through how you can unlock the next stage in your cellular analysis process for CAR-T with our instruments. [Download App Note](https://precisioncellsystems.com/wp-content/uploads/2026/02/Moxi-Applications-Note-Unlocking-the-Next-Stage-in-CAR-T-Cellular-Analysis.pdf) [Brochure](https://precisioncellsystems.com/wp-content/uploads/2025/12/Moxi_GO_II_Brochure.pdf) Moxi GO II 2025 ### Brochure - Moxi GO II [Download Brochure](https://precisioncellsystems.com/wp-content/uploads/2025/12/Moxi_GO_II_Brochure.pdf) [Tech Note](https://precisioncellsystems.com/wp-content/uploads/2025/09/ORFLO-Single-or-Dual-Color-Viability-Staining-Tech-Tip.pdf) Moxi GO II Moxi V 2025 ### Moxi Single or Dual Color Viability Staining Tech Note [Read Tech Note](https://precisioncellsystems.com/wp-content/uploads/2025/09/ORFLO-Single-or-Dual-Color-Viability-Staining-Tech-Tip.pdf) [Field Guide](/resources/21-cfr-part-11-cell-counter-checklist/) Moxi GO II 2026 ### The 21 CFR Part 11 Cell-Counter Evaluation Checklist A practical one-page scoring tool to evaluate cell counters against 21 CFR Part 11. [Read Field Guide](/resources/21-cfr-part-11-cell-counter-checklist/) [Blog](/resources/21-cfr-part-11-cell-counter-requirements/) Moxi GO II 2026 ### What 21 CFR Part 11 Requires of a Cell Counter The compliance explainer: what 21 CFR Part 11 actually demands of a cell counter — audit trail, e-signature, access control, and a Secure Mode. [Read Blog](/resources/21-cfr-part-11-cell-counter-requirements/) [Blog](/resources/cell-count-is-a-release-assay-cell-therapy/) Moxi GO II 2026 ### In Cell Therapy, Your Cell Count Can Serve as a Release Assay A demand-creation reframe: in GMP cell therapy, the cell count can function as a release assay — and what that shift means for how you count and prove it. [Read Blog](/resources/cell-count-is-a-release-assay-cell-therapy/) [Field Guide](/resources/01-optimization-burden/) Moxi GO II Moxi V 2026 ### The Optimization Burden: Hours Wasted on Viability Protocol Development Every hour spent optimizing viability dye concentrations is an hour not spent on your actual experiments. It's optimized for use - that's the important thing. You don't have to optimize it as a customer. Pre-optimized viability reagents eliminate the titration experiments, the incubation testing, the cell-type-specific protocol development. Why spend time optimizing when validated performance is available from the first use? [Read Field Guide](/resources/01-optimization-burden/)