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Note 3 - Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Notes Tables

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

						Fair Value Measurements Using
						Quoted
						Prices in
						Active
						Markets				Significant
						for				Other				Significant
		Balance at				Identical				Observable				Unobservable
		December				Items				Inputs				Inputs
		31, 2023				(Level 1)				(Level 2)				(Level 3)
Assets
Restricted cash held as a certificate of deposit		$	476			$	476			$	—			$	—
Liabilities
Warrant liability		$	334			$	—			$	—			$	334

Fair Value Measurements Using

Quoted

Prices in

Active

Markets

Significant

for

Other

Significant

Balance at

Identical

Observable

Unobservable

December

Items

Inputs

Inputs

31, 2022

(Level 1)

(Level 2)

(Level 3)

Assets

Restricted cash held as a certificate of deposit

$

484

$

484

$

—

$

—

Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]

		November 2021 Warrants				November 2021 Warrants				July 2020, November 2021 & September 2022 Warrants						July 2020, November 2021 & September 2022 Warrants						May 2023 Warrants
Measurement event		Reporting date				Stockholder approval				Amendment and Issuance						Stockholder Approval						Issuance
Date		December 31, 2021				January 31. 2022				September 9, 2022						November 10, 2022						May 1, 2023
Total Value		9.6 million				7.5 million				5.2 million						1.9 million						1.6 million
Gain		not applicable				2.1 million				not applicable						3.4 million						not applicable
Assumptions:
Exercise price		$	18.55			$	18.55			$	6.30					$	6.30						1.30
Market price		$	13.18			$	10.50			$	6.29					$	2.80					$	0.72			(a)
Volatility			87	%			91	%			79.6			%			79.5			%			80.1			%
Risk-free rate			1.31	%			1.65	%			3.58	-	3.43	%			3.93	-	4.15	%			3.60	-	4.04	%
Dividend yield			0.0	%			0.0	%			0.0			%			0.0			%			0.0			%
Term (years)			6.0				6.0				3.4	-	6.0				3.2	–	5.8				2.1	-	5.1	%

		May 2023 Warrants						December 2023 Warrants				December 2023 Warrants
Measurement event		Stockholder Approval						Issuance				Reporting Date
Date		June 9, 2023						December 21, 2023				December 31, 2023
Total Value		$1.4 million						$0.4 million				$0.3 million
Gain		$0.2 million						not applicable				$56 thousand
Assumptions:
Exercise price		$	1.30					$	0.25			$	0.25
Market price		$	0.68					$	0.23			$	0.20
Volatility			77.6			%			79.3	%			79.3	%
Risk-free rate			3.92	–	4.59	%			3.88	%			3.85	%
Dividend yield			0.0			%			0.0	%			0.0	%
Term (years)			2.0	-	5.0				5.5				5.5

		July 2020 & November 2021 Warrants
Measurement event		Prior to amendment						After amendment
Date		September 9, 2022						September 9, 2022
Total Value		$3.3 million						$5.2 million
Loss		not applicable						$1.9 million
Assumptions:
Exercise price		$	18.55 - 57.75					$	6.30
Market price		$	6.29					$	6.29
Volatility			79.6			%			79.6			%
Risk-free rate			3.43	-	3.58	%			3.43	-	3.58	%
Dividend yield			0.0			%			0.0			%
Term (years)			0.7	–	5.4				3.4	–	6.0

		July 2020, November 2021, September 2022 & November 2022 Warrants
Measurement event		Prior to amendment						After amendment
Date		April 27, 2023						April 27, 2023
Total Value		$0.3 million						$0.5 million
Loss		not applicable						$0.2 million
Assumptions:
Exercise price		$	6.30					$	1.50
Market price		$0.72				(a)		$0.72				(a)
Volatility			80.1			%			80.1			%
Risk-free rate			3.59	-	4.73	%			3.59	–	4.73	%
Dividend yield			0.0			%			0.0			%
Term (years)			1.1	–	5.6				1.1	–	5.6

		May 2023 Warrants
Measurement event		Prior to amendment						After amendment
Date		December 21, 2023						December 21, 2023
Total Value		$56 thousand						$0.2 million
Loss		not applicable						$0.1 million
Assumptions:
Exercise price		$	1.30					$	0.25
Market price		$	0.23					$	0.23
Volatility			79.3			%			79.3			%
Risk-free rate			3.92	–	4.62	%			3.92	–	4.62
Dividend yield			0.0			%			0.0			%
Term (years)			1.5	–	4.5				1.5	–	4.5

		Series B								Series B & C
Measurement event		Prior to amendment				After amendment				Prior to amendment				After amendment
Date		September 9, 2022				September 9, 2022				April 27, 2023				April 27, 2023
Total value (b)		$6.9 million				$12.5 million				$9.6 million				$11.6 million
Deemed dividend		not applicable				$5.7 million				not applicable				$2.0 million
Assumptions:
Exercise price		$	14.00			$	6.30			$	6.30			$	1.30
Market price		$	6.29			$	6.29			$0.72		(a)		$0.72		(a)
Volatility			79.6	%			79.6	%			80.1	%			80.1	%
Risk-free rate			3.64	%			3.64	%			4.91	%			4.91	%
Dividend yield			0.0	%			0.0	%			0.0	%			0.0	%
Term (in years)			1.3				1.3				0.8				0.8

		Series B & C
Measurement event		Prior to amendment				After amendment
Date		December 21, 2023				December 21, 2023
Total value (b)		$1.7 million				$6.8 million
Deemed dividend		not applicable				$5.1 million
Assumptions:
Exercise price		$	1.30			$	0.25
Market price		$	0.23			$	0.23
Volatility			79.3	%			79.3	%
Risk-free rate			5.43	%			5.43	%
Dividend yield			0.0	%			0.0	%
Term (years)			0.3				0.3

		Secured Convertible Notes derivative				Secured Convertible Notes derivative
Measurement event		Issuance				Shareholder approval
Date		April 27, 2023				June 9, 2023
Total value (b)		$0.2 million				$0.2 million
Gain		not applicable				$40 thousand
Assumptions:
Exercise price		$	1.30			$	1.30
Market price		$	0.72	(a)		$	0.75
Volatility			80.1	%			76.9	%
Risk-free rate			4.88	%			5.41	%
Dividend yield			0.0	%			0.0	%
Term (years)			0.8				0.7

X

- Definition

Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique for each separate class of asset and liability measured on recurring and nonrecurring basis.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-SubTopic 10
-Topic 820
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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- Definition

Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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